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What was wrong with this mower?
#1
J
jdtm
J
jdtm
I had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
I gave the true problem about a day after the initial post. It is towards the bottom of page 4. A few subsequent posts made it hard to find, so new readers are guessing and not finding any answer. Here it is again right at the beginning so nobody will miss it!
ANSWER
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
I gave the true problem about a day after the initial post. It is towards the bottom of page 4. A few subsequent posts made it hard to find, so new readers are guessing and not finding any answer. Here it is again right at the beginning so nobody will miss it!
ANSWER
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
#2
Scrubcadet10
Scrubcadet10
Timing gears on the cam and crank jump time?
#3
J
jdtm
J
jdtm
No. They are fine. I think that would have lowered the compression reading. 86 PSI is about as high as those engines get with the compression release.Timing gears on the cam and crank jump time?
#4
PTmowerMech
Those have a compression release?
PTmowerMech
No. They are fine. I think that would have lowered the compression reading. 86 PSI is about as high as those engines get with the compression release.
Those have a compression release?
#5
J
jdtm
J
jdtm
Yes. I think just about all of the modern 4-cycle small engines have one. On this engine, it opens the exhaust valve a little.Those have a compression release?
#6
J
jdtm
J
jdtm
To clarify, I do not mean a manual compression release like on a chainsaw but one that is part of the camshaft.Yes. I think just about all of the modern 4-cycle small engines have one. On this engine, it opens the exhaust valve a little.
#7
Scrubcadet10
Scrubcadet10
Yep, L head quantum.Those have a compression release?
#8
Scrubcadet10
Scrubcadet10
HmmmNo. They are fine. I think that would have lowered the compression reading. 86 PSI is about as high as those engines get with the compression release.
#10
PTmowerMech
You say you fixed it. Was an external repair, or did you have to get inside the engine to fix it?
PTmowerMech
I had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
You say you fixed it. Was an external repair, or did you have to get inside the engine to fix it?
#11
S
slomo
S
slomo
A log stuck between the deck and the blade. Or the deck was packed up with clippings.What was the problem?
#12
S
slomo
S
slomo
So another he has fuel, compression, air and spark and it doesn't run.I had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
#13
J
jdtm
J
jdtm
That would be the first place to look since it probably is the most common problem when a mower hits something it should not, and hopefully the crankshaft does not get bent. I would not have started the thread for a ho-hum problem like that. I had mentioned in the initial post that the flywheel key was OK.Usually the fly wheel shears the timing key and rotates a few degrees
#14
J
jdtm
J
jdtm
The engine internals were all OK. There was no damage to the timing gears, piston, valvetrain, crankshaft, or connecting rod.You say you fixed it. Was an external repair, or did you have to get inside the engine to fix it?
#15
J
jdtm
J
jdtm
The recently-sharpened blade tried to split the log for me but did not have enough power behind it to do the job, similar to my experience below, although that was different piece of wood and the mower was OK after I was able to retrieve the blade.A log stuck between the deck and the blade. Or the deck was packed up with clippings.
Attachments
#16
Scrubcadet10
Scrubcadet10
so you had fuel, spark, and compression. that only leaves spark at the correct time?
#17
PTmowerMech
PTmowerMech
Ok, I give. What was it?
#18
J
jdtm
J
jdtm
I will give the answer tonight (assuming nobody guesses correctly before then) in case anyone else wants to venture a guess or ask diagnostic questions before then.Ok, I give. What was it?
#19
J
jdtm
Regarding ignition timing, there was no internal damage, change in the timing gear alignment, or damage to the flywheel key, so ignition timing did not change after the mower met the log.
J
jdtm
HINT: You are drawing more conclusions from the tests I described than they gave.so you had fuel, spark, and compression. that only leaves spark at the correct time?
Regarding ignition timing, there was no internal damage, change in the timing gear alignment, or damage to the flywheel key, so ignition timing did not change after the mower met the log.
#21
PTmowerMech
PTmowerMech
Thinking about the fuel & air flow system, since the timing and everything related has been covered, Maybe something jarred the carb or broke something on the intake. Nothing I can think of along those lines seems plausible.
I'm guessing the coil wasn't damaged or moved, since it doesn't touch the flywheel.
Short of the flywheel key being damaged, I can't see anything in or on the engine changing enough to not fire and run (even roughly).
My final answer (without phoning a friend) is something came loose in the carburetor.
I'm guessing the coil wasn't damaged or moved, since it doesn't touch the flywheel.
Short of the flywheel key being damaged, I can't see anything in or on the engine changing enough to not fire and run (even roughly).
My final answer (without phoning a friend) is something came loose in the carburetor.
#22
S
scoyote
S
scoyote
If you have checked all the normal problem boxes and still no start or rough run---aside from a cracked plastic intake manifold--i would guess your bade bolt totally backed off or your blade adaptor has one of those flimsy keys and it stripped or the cast iron has broken away??
#23
J
jdtm
J
jdtm
The blade and blade adapter were OK. However, that is a reasonable guess. The standard flywheel on an engine made for a mower has very little inertia, so without the added intertia from the blade, starting would be difficult. Maybe it would not even start. I am unsure on that.was your issue with the blade or the blade adaptor ?
#24
Scrubcadet10
Scrubcadet10
Here's a hail mary.....
was it out of fuel?
was it out of fuel?
#25
Scrubcadet10
Scrubcadet10
I've attempted to start pushers without a blade, ITS VERY hard, but can be done. expect a few pulls to jerk out of your hand.The blade and blade adapter were OK. However, that is a reasonable guess. The standard flywheel on an engine made for a mower has very little inertia, so without the added intertia from the blade, starting would be difficult. Maybe it would not even start. I am unsure on that.
#26
J
jdtm
HINT: One of my original tests would technically be called an asymmetric test. An asymmetric test will either find if something is OK or bad but not the opposite. For example if you look under your car and see no puddle, you know that you do not have a major coolant leak. However, if there is a puddle, it may have rained recently, or a dog may have visited the area. Or you may be leaking coolant.
J
jdtm
Now you are thinking out of the box, and that will be helpful. But no, the throttle was OK.I dunno.. throttle shaft somehow got wedged shut?
HINT: One of my original tests would technically be called an asymmetric test. An asymmetric test will either find if something is OK or bad but not the opposite. For example if you look under your car and see no puddle, you know that you do not have a major coolant leak. However, if there is a puddle, it may have rained recently, or a dog may have visited the area. Or you may be leaking coolant.
#27
J
jdtm
The plastic intake manifold cracking is another good guess, but it was OK.
J
jdtm
It is unrelated to the issue, but I use this mower as a cheap brush hog sometimes. After going through blade adapters on a routine basis, I made a two-part adapter that allows some motion when there is a hard impact. It is much easier on the internals, and I have never lost another blade adapter or flywheel key since making the change. Everything connecting the blade to the crankshaft was OK.If you have checked all the normal problem boxes and still no start or rough run---aside from a cracked plastic intake manifold--i would guess your bade bolt totally backed off or your blade adaptor has one of those flimsy keys and it stripped or the cast iron has broken away??
The plastic intake manifold cracking is another good guess, but it was OK.
#28
J
jdtm
I was suspicious of the coil thinking an internal connection got damaged with the jarring. However, it was OK.
J
jdtm
I was actually thinking some strange carburetor problem myself when it first happened and I did the initial tests I described. However, I could not come up with a reasonable scenario either, and as it turns out, the carburetor was OK.Thinking about the fuel & air flow system, since the timing and everything related has been covered, Maybe something jarred the carb or broke something on the intake. Nothing I can think of along those lines seems plausible.
I'm guessing the coil wasn't damaged or moved, since it doesn't touch the flywheel.
Short of the flywheel key being damaged, I can't see anything in or on the engine changing enough to not fire and run (even roughly).
My final answer (without phoning a friend) is something came loose in the carburetor.
I was suspicious of the coil thinking an internal connection got damaged with the jarring. However, it was OK.
#29
PTmowerMech
PTmowerMech
@Scrubcadet10 , I'm thinking that if no one had responded, we would've already had the answer by now.
#30
J
jdtm
J
jdtm
Probably not. I was originally thinking that I would give the game about a day. By now, I have explicitly stated that most of the parts were OK. There are not all that many things left to consider.@Scrubcadet10 , I'm thinking that if no one had responded, we would've already had the answer by now.
#31
Scrubcadet10
Scrubcadet10
does this motor have the autochoke feature?
#32
PTmowerMech
Cue the Jeopardy music Alex.
PTmowerMech
does this motor have the autochoke feature?
Cue the Jeopardy music Alex.
#34
Scrubcadet10
Scrubcadet10
I'm beginning to thunk the Flux capacitor went bad.
#36
J
jdtm
J
jdtm
This engine has a date code of 0702. I think flux capacitors are only used on newer models. Besides saying that many things were OK, I mentioned two tests. What does each of those tests *guarantee* to tell you and not tell you about the condition of the engine?I'm beginning to thunk the Flux capacitor went bad.
#37
Scrubcadet10
Scrubcadet10
I give up. I'll wait on the answer.
#38
S
scoyote
S
scoyote
Ok-so you have all the ingredients for success but you don't have it? You have spark--correct valve timing--no fuel delivery problems-no vacuum leaks-blade is tight and not jammed--your air filter is clean--your choke or primer is working fine---but you can't start your mower??? Plus this is apparently related to hitting a chunk of wood? Time for an answer!
#39
J
jdtm
J
jdtm
ANSWER
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
#40
Scrubcadet10
Scrubcadet10
very interesting. good to know.
never trust a spark plug.
never trust a spark plug.
#42
S
slomo
S
slomo
Little air works too.so you had fuel, spark, and compression. that only leaves spark at the correct time?
#43
S
slomo
S
slomo
I try to preach about electrical circuits on here. All need load tested. I would of caught it with the ol' PET-4000. Easy as pie......
#45
J
jdtm
I am curious. Would you describe how it would have caught this problem?
J
jdtm
For everyone's reference, here is the PET-4000 in action:I try to preach about electrical circuits on here. All need load tested. I would of caught it with the ol' PET-4000. Easy as pie......
I am curious. Would you describe how it would have caught this problem?
#46
S
slomo
Grounding a plug to the metal shroud puts a small load on the coil. The PET can tell you a lot more. It will fully stress the coil.
S
slomo
The further you wind out the ground pin the more stress it creates on the coil to produce spark. You wind it out slow till it dies. Take note of the knob position.For everyone's reference, here is the PET-4000 in action:
I am curious. Would you describe how it would have caught this problem?
Grounding a plug to the metal shroud puts a small load on the coil. The PET can tell you a lot more. It will fully stress the coil.
#47
S
slomo
S
slomo
You left out air in post 16, way back. Air, fuel, spark and compression. Just like Betty Crocker.That's fuel.
#48
B
bertsmobile1
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap
So it is a round about way of checking the out put voltage of the coil.
The down side of using one is electricity will follow the path of least resistance so if the insulation on a functioning coil is getting thin then then the coil may develope an internal short rather than jumping the gap so winding it out till the spark is estinguished is very bad for the coil.
Once it has done that then a tracking path is established and the coil will continue to short down that path .
Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .
BAck in the 20's , 30's & 40's then again in the 90's snake oil salesmen sold a high resistance kit called "Spark intensifers " and the latter versions were called Power spark or some trash like that with all of the usual BS about more power, better milage etc etc etc .
The simple 3 point spark tester / magneto tested has been around for over 100 years and are usually made specifically for a particular engine with the large gap set at a safe separation to prevent internal tracking
Because extra voltage is required to jump the gap the induced voltage is retained in the coil winding for longer so they get hotter which in cars & motorcycle with discreet magnetos ( ie not flywheel ones ) can lead to premature failure of the magneto .
All of the snake oil jobs did just that so after a while owners started to sue the makers & eventually they got banned every where on the planet except the USA
B
bertsmobile1
Actually that is totally wrongThe further you wind out the ground pin the more stress it creates on the coil to produce spark. You wind it out slow till it dies. Take note of the knob position.
Grounding a plug to the metal shroud puts a small load on the coil. The PET can tell you a lot more. It will fully stress the coil.
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap
So it is a round about way of checking the out put voltage of the coil.
The down side of using one is electricity will follow the path of least resistance so if the insulation on a functioning coil is getting thin then then the coil may develope an internal short rather than jumping the gap so winding it out till the spark is estinguished is very bad for the coil.
Once it has done that then a tracking path is established and the coil will continue to short down that path .
Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .
BAck in the 20's , 30's & 40's then again in the 90's snake oil salesmen sold a high resistance kit called "Spark intensifers " and the latter versions were called Power spark or some trash like that with all of the usual BS about more power, better milage etc etc etc .
The simple 3 point spark tester / magneto tested has been around for over 100 years and are usually made specifically for a particular engine with the large gap set at a safe separation to prevent internal tracking
Because extra voltage is required to jump the gap the induced voltage is retained in the coil winding for longer so they get hotter which in cars & motorcycle with discreet magnetos ( ie not flywheel ones ) can lead to premature failure of the magneto .
All of the snake oil jobs did just that so after a while owners started to sue the makers & eventually they got banned every where on the planet except the USA
#49
Scrubcadet10
Scrubcadet10
I just test them with my briggs tester, it's got about a 1/4" gap to jump.Actually that is totally wrong
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap
So it is a round about way of checking the out put voltage of the coil.
The down side of using one is electricity will follow the path of least resistance so if the insulation on a functioning coil is getting thin then then the coil may develope an internal short rather than jumping the gap so winding it out till the spark is estinguished is very bad for the coil.
Once it has done that then a tracking path is established and the coil will continue to short down that path .
Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .
BAck in the 20's , 30's & 40's then again in the 90's snake oil salesmen sold a high resistance kit called "Spark intensifers " and the latter versions were called Power spark or some trash like that with all of the usual BS about more power, better milage etc etc etc .
The simple 3 point spark tester / magneto tested has been around for over 100 years and are usually made specifically for a particular engine with the large gap set at a safe separation to prevent internal tracking
Because extra voltage is required to jump the gap the induced voltage is retained in the coil winding for longer so they get hotter which in cars & motorcycle with discreet magnetos ( ie not flywheel ones ) can lead to premature failure of the magneto .
All of the snake oil jobs did just that so after a while owners started to sue the makers & eventually they got banned every where on the planet except the USA
#50
J
jdtm
Widening the gap increases the breakdown voltage. Once the spark is started, the voltage drops to nearly 0 even if the gap is made much wider.
J
jdtm
I think "standoff voltage" would be more accurate than stress. From an electrical perspective the idea is that the insulation will be more likely to fail due to the need to withstand greater voltage. From your later comments, you seem to agree.Actually that is totally wrong
You can not add stress in any way shape or form to a magneto coil
Widening the gap just adds resistance to the circuit
The higher the resistance the greater the VOLTAGE required to jump the gap
Widening the gap increases the breakdown voltage. Once the spark is started, the voltage drops to nearly 0 even if the gap is made much wider.
Current has to go somewhere since it is a flow of charged particles, but that is different from voltage. Voltage does not have to go anywhere. It seems perfectly content not jumping out at an unsuspecting person looking at a wall outlet. However, forcing equipment to operate at higher voltages than it was designed to tolerate, such as using a coil/magneto with a wider spark gap will increase the demands on its insulation, which can cause the failure you described.Once a voltage has been induced in a coil, it HAS to go some where so if your super tool prevents it discharging down the spark plug wire , it still has to discharge some where and that will be internally, to the detriment of the magneto coil .
#51
B
bertsmobile1
Thanks for doing that
Some times the brain is a bit too far behind the fingers
I have rebuilt dozens of Lucas mags where the owners fell foul of the "spark intensifiers "
On the propriority testers of this type they are usually just marked "Bad & Good " and the instructions simply tell you to widen the gap during use from the red ( bad ) small gap area into the green ( good ) large gap area while checking the engine rpm
If you get into the green & the revs don't fall off it is good
None that I have seen instruct to widen till the spark fails to occur .
B
bertsmobile1
I stand correctedI think "standoff voltage" would be more accurate than stress. From an electrical perspective the idea is that the insulation will be more likely to fail due to the need to withstand greater voltage. From your later comments, you seem to agree.
Widening the gap increases the breakdown voltage. Once the spark is started, the voltage drops to nearly 0 even if the gap is made much wider.
Current has to go somewhere since it is a flow of charged particles, but that is different from voltage. Voltage does not have to go anywhere. It seems perfectly content not jumping out at an unsuspecting person looking at a wall outlet. However, forcing equipment to operate at higher voltages than it was designed to tolerate, such as using a coil/magneto with a wider spark gap will increase the demands on its insulation, which can cause the failure you described.
Thanks for doing that
Some times the brain is a bit too far behind the fingers
I have rebuilt dozens of Lucas mags where the owners fell foul of the "spark intensifiers "
On the propriority testers of this type they are usually just marked "Bad & Good " and the instructions simply tell you to widen the gap during use from the red ( bad ) small gap area into the green ( good ) large gap area while checking the engine rpm
If you get into the green & the revs don't fall off it is good
None that I have seen instruct to widen till the spark fails to occur .
#52
M
moparjoe
M
moparjoe
Try a different coil.No. They are fine. I think that would have lowered the compression reading. 86 PSI is about as high as those engines get with the compression release.
#54
H
Handy7rick
H
Handy7rick
So where is the solution posted?I had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
#55
RustyAllen
RustyAllen
Second from bottom of page 4.So where is the solution posted?
#58
J
jviews12
J
jviews12
I guess we will never know. I think it is better to publish the solution so that we know after the first reading. Time is precious.
#59
O
ohiodave53
O
ohiodave53
Bert beat me to this and I agree with him on the sheared or partial distorted flywhell key. I had this happen to me before and I believe the key is made of a softer metal than normal keyway stock so that it does shear when an object is struck.
#60
G
Gord Baker
G
Gord Baker
Flywheel key partially sheared.I had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
#62
S
scoyote
S
scoyote
Solution was simple in the end---change out the plug or clean and re-gap---apparently the plug sparked in air but failed in the cylinder. Probably a simple step to add in our troubleshooting rather than tmaking assumptions? Usually when everything seems to check out correct but you're still not getting a result---you have missed something!
#63
doug9694
doug9694
When I first read the problem my 1st thought was try another plug. Maybe I am a little psychic or psycho??
Then thought of other reasons. Conclusion was excessive grass build up. That has the same effect too.
So. If another plug don't work it may be the cleaning that does.
Then thought of other reasons. Conclusion was excessive grass build up. That has the same effect too.
So. If another plug don't work it may be the cleaning that does.
#65
S
scoyote
S
scoyote
You're correct on that Doug---If your blade is stopped up with packed grass engine likely not starting--but it would become noticeable fairly quicklythat the condition would be a problem?
#66
F
first pull
F
first pull
You don't need to do all of that to test spark, just go to harbor freight and get a spark tester for under $5. You don't have to remove the spark plug that way. If I had to guess you may have bent one or both of the push rodsI had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
I gave the true problem about a day after the initial post. It is towards the bottom of page 4. A few subsequent posts made it hard to find, so new readers are guessing and not finding any answer. Here it is again right at the beginning so nobody will miss it!
ANSWER
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
#67
S
scoyote
S
scoyote
If you were following--the plug tested fine in air or as it would with a spark tester which tells you coil is fine but not the whole story---the plug was not firing in the hole!
#68
G
GrumpyCat
G
GrumpyCat
Mid 1990s I had a Kawasaki engine on a John Deere 21" SP that did the same sort of thing. A new NGK spark plug would last 2 years, not 3. Sparked outside the engine but would not run. IIRC it would more likely start cold than restart hot. Once running it stayed running.
#69
S
SlopeMan2
S
SlopeMan2
enjoyed the read. I have been fooling with lawn mowers, starting with push type reel mowers for 80 years. With help, I built one of the first twisted belt rotary power mowers in our small town, , using a Model N B&S, a wooden deck, and wooden plow handles. While using many mowers over the years, I have never had a spark plug fail due to a hard jar like that. Interesting story, thank youI had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
I gave the true problem about a day after the initial post. It is towards the bottom of page 4. A few subsequent posts made it hard to find, so new readers are guessing and not finding any answer. Here it is again right at the beginning so nobody will miss it!
ANSWER
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
#70
T
TobyU
I will tell you how I would have troubleshooted it though.
I would take that compression tester and put it back in the toolbox and leave it for good because they are a little to no use on small engines I'm not worth the aggravation of walking over to get them. Lol
I also would not have touched the spark plug or even bother checking for spark first.
You describe the mowers running fine and then it hit something and I would not restart but you could pull it normally.
You didn't mention anything about it jerking the rope out of your hand or popping her back firing or being abnormally different to pull other than like a mower that was out of gas so I wouldn't have immediately suspected the flywheel key but I would have kept it in mind.
The first thing I would have done was to go get my car spray because that is the first way I diagnose all mowers now because over 85% of the time it is a few related problem where they're not getting enough.
A quick shot into the carburetor and a few pulls in this case since you've told us the problem, would have ended up giving the same result of a no start so ONLY THEN when I remove the spark plug.
You are completely right about you can't trust 100% I plugged that fires like that but I'll go one step further... Some people don't even use the plug! Some people use one of those dumb little spot testers and put it in line or they check for spark from the spark plug wire to the block or to a screwdriver stuck into the block etc.
This only checks your ignition system on your mower for spot but leaves the barely likely possibility of a flood not working properly or at all!!
So I would have checked for part too but you get pretty good after doing thousands upon thousands of these knowing what a good spark looks like from a weak spark.
If I would have determined it was a good spark but still would not run when I screwed the plug back in my very next step would have been to swap it for a known good plug..
I keep good used plugs just for this reason because as you've proved, a plug can seem okay sitting beside the block but not run in the machine.
I do 100s of these a year and sometimes over 1000.
Even though the overall number of plugs being the problem is very low, I've had two this season that was exactly like you presented this..
Another plug and it was up and running.
The stats I find on bad plugs is about 1 in 450.
Smart, systematic troubleshooting will get you to the root of the problem much faster than what some people do and no need to check flywheel keys etc when you don't rule out something like plug based on bad actual info.
T
TobyU
All true but the theory for a discussion like this is kind of flawed because I don't have the machine right in front of me.I had an issue with a fix that seemed uninituitive enough to me that it might have some value here. Anyone interested in venturing a guess on what was wrong? Let me emphasize that I have fixed the issue, so the thread is more along the lines of entertainment/education vs. helping someone desperate to get something working.
I was cutting very high grass with essentially your basic 21-inch push mower with no self propel. It was powered by a 190 cc B&S L-head engine. While going through the grass, the mower hit a hidden piece of wood and stalled. After that it would not start. There was a bit of an attempt by the mower to run when the recoil was pulled, but it would not stay running no matter how hard I pulled. I took the spark plug out and saw a typical small-engine spark when I held the body of the plug against the head and pulled the recoil. I also did a compression test and measured a respectable 86 PSI reading. I will also mention that the flywheel key was undamaged. What was the problem?
I gave the true problem about a day after the initial post. It is towards the bottom of page 4. A few subsequent posts made it hard to find, so new readers are guessing and not finding any answer. Here it is again right at the beginning so nobody will miss it!
ANSWER
In the first post, I described two test, one for ignition, and one for compression. The ignition test needs to be looked at carefully.
Ignition test procedure: Remove the spark plug, hold the body of the plug against the cylinder head, and pull the recoil.
Ignition test result: There were sparks that were as expected for a small engine.
Ignition test conclusion: NOTHING
If no spark appeared, the test would have indicated that there was a problem in the ignition, so either the armature/coil, the spark plug, the air gap, or very unlikely the magnet on the flywheel was bad.
Seeing sparks only meant that the ignition might be OK. Why? Because the spark plug was firing in air rather than in the cylinder. The voltage needed to fire at atmospheric pressure is less than when the pressure is increased. I changed the spark plug, and the engine started right up and ran normally. Apparently the impact with the log dislodged a deposit in the spark plug which fouled it enough that it would fire in air but not in the cylinder. To confirm what had happened, I cleaned the original plug with a spark plug cleaner and reinstalled it on the engine. The engine again started right up and has been running with this plug for several hours now.
I will tell you how I would have troubleshooted it though.
I would take that compression tester and put it back in the toolbox and leave it for good because they are a little to no use on small engines I'm not worth the aggravation of walking over to get them. Lol
I also would not have touched the spark plug or even bother checking for spark first.
You describe the mowers running fine and then it hit something and I would not restart but you could pull it normally.
You didn't mention anything about it jerking the rope out of your hand or popping her back firing or being abnormally different to pull other than like a mower that was out of gas so I wouldn't have immediately suspected the flywheel key but I would have kept it in mind.
The first thing I would have done was to go get my car spray because that is the first way I diagnose all mowers now because over 85% of the time it is a few related problem where they're not getting enough.
A quick shot into the carburetor and a few pulls in this case since you've told us the problem, would have ended up giving the same result of a no start so ONLY THEN when I remove the spark plug.
You are completely right about you can't trust 100% I plugged that fires like that but I'll go one step further... Some people don't even use the plug! Some people use one of those dumb little spot testers and put it in line or they check for spark from the spark plug wire to the block or to a screwdriver stuck into the block etc.
This only checks your ignition system on your mower for spot but leaves the barely likely possibility of a flood not working properly or at all!!
So I would have checked for part too but you get pretty good after doing thousands upon thousands of these knowing what a good spark looks like from a weak spark.
If I would have determined it was a good spark but still would not run when I screwed the plug back in my very next step would have been to swap it for a known good plug..
I keep good used plugs just for this reason because as you've proved, a plug can seem okay sitting beside the block but not run in the machine.
I do 100s of these a year and sometimes over 1000.
Even though the overall number of plugs being the problem is very low, I've had two this season that was exactly like you presented this..
Another plug and it was up and running.
The stats I find on bad plugs is about 1 in 450.
Smart, systematic troubleshooting will get you to the root of the problem much faster than what some people do and no need to check flywheel keys etc when you don't rule out something like plug based on bad actual info.
#71
T
TobyU
I find plain old champions to last longer.
T
TobyU
NGKs run great.... Until they don't. LolMid 1990s I had a Kawasaki engine on a John Deere 21" SP that did the same sort of thing. A new NGK spark plug would last 2 years, not 3. Sparked outside the engine but would not run. IIRC it would more likely start cold than restart hot. Once running it stayed running.
I find plain old champions to last longer.
#72
mikehouse
mikehouse
Crank shaft badly bent.
#73
G
GrumpyCat
Yes, I agree NGK makes good product. In 10 years with that mower I didn't experiment with other brands of sparkplugs, I should have. Honestly blame the ignition on the Kawasaki not the plug. Yet bought a zero-turn recently specifically with a Kawasaki engine.
G
GrumpyCat
NGK = No Good in Kawasaki.NGKs run great.... Until they don't. Lol
I find plain old champions to last longer.
Yes, I agree NGK makes good product. In 10 years with that mower I didn't experiment with other brands of sparkplugs, I should have. Honestly blame the ignition on the Kawasaki not the plug. Yet bought a zero-turn recently specifically with a Kawasaki engine.
#74
S
SeniorCitizen
S
SeniorCitizen
My experience with champion plugs in a chevy . You may have to walk some .
My experience with NGK plugs in a new 7042 cu. in. Waukesha . If you be lucky you replace the plugs with champion before quitting time the 1st day . If you be un-lucky you replace the NGK with Champion at 2:00 A.M.
My experience with NGK plugs in a new 7042 cu. in. Waukesha . If you be lucky you replace the plugs with champion before quitting time the 1st day . If you be un-lucky you replace the NGK with Champion at 2:00 A.M.
#75
B
bertsmobile1
B
bertsmobile1
Here we go with another Ford vs Chev useless pig headed arguement .
Spark plugs 101
Any genuine brand name spark plug is tested a dozen times during manufacture and another 1/2 dozen at the end of the line before the brand name & grade is painted on the plug
There is no such thing as a best plug or a bad brand of plug .
There is the RIGHT plug for your engine, your elevation & your fuel
Bad out of the box plugs are not bad , the fuel being used is what is bad
Unleaded is conductive at cylinder pressures and E-anything is even worse
Now depending upon a lot of variables, if the engine does not fire on the first full stroke, the fresh fuel condenses on the insulator nose so the second spark runs down the insulator rather than jump the gap
As or brand differences
NGK's have a narrow band of optimal conditions while Champions have a wider band of optimal conditions.
I personally find Champions seem to work better than NGK's in 2 strokes & visa versa for 4 strokes
But I am at the same latitude as LA and almost the same weather
A fellow tech in Melbourne, finds the opposite
Spark plugs 101
Any genuine brand name spark plug is tested a dozen times during manufacture and another 1/2 dozen at the end of the line before the brand name & grade is painted on the plug
There is no such thing as a best plug or a bad brand of plug .
There is the RIGHT plug for your engine, your elevation & your fuel
Bad out of the box plugs are not bad , the fuel being used is what is bad
Unleaded is conductive at cylinder pressures and E-anything is even worse
Now depending upon a lot of variables, if the engine does not fire on the first full stroke, the fresh fuel condenses on the insulator nose so the second spark runs down the insulator rather than jump the gap
As or brand differences
NGK's have a narrow band of optimal conditions while Champions have a wider band of optimal conditions.
I personally find Champions seem to work better than NGK's in 2 strokes & visa versa for 4 strokes
But I am at the same latitude as LA and almost the same weather
A fellow tech in Melbourne, finds the opposite
#76
T
TobyU
As I said, in small push mowers even Hondas, I find NGK to be a little faster to start and maybe run a little smoother BUT they will stop working at any random time. Usually 2-4 years or more but it could be 2 weeks, 2 months etc.
I HATE champions for cars unless it's a Chrysler (since they came with them and seem to like them) but in a mower.... CHAMPION is my plug of choice.
Autolite work fine too despite what some say about their -one experience 18 years ago-....
T
TobyU
I have found the same to be true..so best is relative...Here we go with another Ford vs Chev useless pig headed arguement .
Spark plugs 101
Any genuine brand name spark plug is tested a dozen times during manufacture and another 1/2 dozen at the end of the line before the brand name & grade is painted on the plug
There is no such thing as a best plug or a bad brand of plug .
There is the RIGHT plug for your engine, your elevation & your fuel
Bad out of the box plugs are not bad , the fuel being used is what is bad
Unleaded is conductive at cylinder pressures and E-anything is even worse
Now depending upon a lot of variables, if the engine does not fire on the first full stroke, the fresh fuel condenses on the insulator nose so the second spark runs down the insulator rather than jump the gap
As or brand differences
NGK's have a narrow band of optimal conditions while Champions have a wider band of optimal conditions.
I personally find Champions seem to work better than NGK's in 2 strokes & visa versa for 4 strokes
But I am at the same latitude as LA and almost the same weather
A fellow tech in Melbourne, finds the opposite
As I said, in small push mowers even Hondas, I find NGK to be a little faster to start and maybe run a little smoother BUT they will stop working at any random time. Usually 2-4 years or more but it could be 2 weeks, 2 months etc.
I HATE champions for cars unless it's a Chrysler (since they came with them and seem to like them) but in a mower.... CHAMPION is my plug of choice.
Autolite work fine too despite what some say about their -one experience 18 years ago-....