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Murray Riding Mower Engine wont turn unless spark plug removed

#1

T

tbone

I have an older 1999 Murray riding lawn mower 14.5 horse Briggs and Stratton IC quiet engine. Over time the mower has gotten harder to crank and have had to use jumper cables to get the engine to turn over fast enough to crank. This is even with a brand new battery. I have replaced the other components (starter solenoid). Interesting enough if I remove the spark plug, the mower engine will turn over freely. I thought it might be a clogged muffler so I removed the muffler. Still wont turn over with spark plug in.

So could this be the starter, even though it appears to still crank? Could it be just a little engine pressure causes the starter to hang? With the spark plug removed, there is little engine pressure.

Any suggestons will be appreciated. A new starter is around $100 so I want to be sure before I go buy one.


#2

K

KennyV

Hello tbone.. and Welcome to this often fun Forum...
If the starter is getting full voltage when attempting to start the engine, there should be no difference between starting with a good battery OR starting with a boost from another battery...Check voltage at the starter While it is attempting to start the engine.

Your starter could be dragging, Is the cable at the starter getting HOT while trying to start? Does it get HOTTER when you jump start? If you have an Inductive Ammeter you can measure the actual current...

If it is dragging you may have a cracked magnet, bad brushes, worn out bushings or a short in the armature... :smile:KennyV


#3

J

jeff

I agree. But there is one other possibility, the engine likely has a compression release. If it is broken, or if the valve adjustment is too wide the release will not operate properly.


#4

BKBrown

BKBrown

Exhaust valve not opening ??????? Excess pressure unless plug is removed ????
Compression release sticking would cause excess pressure.


#5

Jetblast

Jetblast

If the compression release is working, the engine should spin pretty much the same with a spark plug or without. I believe that engine uses the exhaust valve also as a compression release valve, so if your valves aren't adjusted just right, the very small compression release lobe on the cam won't move the valve enough to release pressure for starting. That might be something to check.


#6

T

tbone

KennyV said:
Hello tbone.. and Welcome to this often fun Forum...
If the starter is getting full voltage when attempting to start the engine, there should be no difference between starting with a good battery OR starting with a boost from another battery...Check voltage at the starter While it is attempting to start the engine.

Your starter could be dragging, Is the cable at the starter getting HOT while trying to start? Does it get HOTTER when you jump start? If you have an Inductive Ammeter you can measure the actual current...

If it is dragging you may have a cracked magnet, bad brushes, worn out bushings or a short in the armature... :smile:KennyV
Click to expand...

Yes, the lead wire and starter both get very hot. I have seen the starter actually smoke from time to time. I think I will pull the starter and take to a local repair shop and have them test it. Hopefully that's the issue. i did notice after posting that others have had similar problems some dealing with valve adjustments. Hopefully won't have to go that route.


#7

T

tbone

Jetblast said:
If the compression release is working, the engine should spin pretty much the same with a spark plug or without. I believe that engine uses the exhaust valve also as a compression release valve, so if your valves aren't adjusted just right, the very small compression release lobe on the cam won't move the valve enough to release pressure for starting. That might be something to check.
Click to expand...

Thanks Jetblast. I read some other posts stating similar issues with valve adjustments. Here is a link to the exact briggs and stratton user manuals and parts list. Don't know if you can tell by looking at this if what your suggesting is possible or not. It does appear to be a single cylinder engine.

http://www.briggsandstratton.com/engines/support/?NTT=287707-1272-E1


#8

G

glennsjr

I would do a compression test. Even though they don't give compression figures should still be able to see if it's high causing the problem. When you jump it are you jumping it to the battery or jumping it directly to starter? sounds like maybe a bad ground.


#9

T

tbone

glennsjr said:
I would do a compression test. Even though they don't give compression figures should still be able to see if it's high causing the problem. When you jump it are you jumping it to the battery or jumping it directly to starter? sounds like maybe a bad ground.
Click to expand...

usually jump to battery but have tried to jump directly to starter. Both have the same results. After doing a little more reading, I found some youtube videos showing how to adjust the valves. Looks pretty easy to check so I'll try that as well.


#10

Jetblast

Jetblast

tbone said:
Thanks Jetblast. I read some other posts stating similar issues with valve adjustments. Here is a link to the exact briggs and stratton user manuals and parts list. Don't know if you can tell by looking at this if what your suggesting is possible or not. It does appear to be a single cylinder engine.

http://www.briggsandstratton.com/engines/support/?NTT=287707-1272-E1
Click to expand...

That looks like a likely suspect, especially if you've never adjusted the valves before. From the illustration I see rockers and valve lash adjustability, so I'd go right to that next since they're probably overdue for adjustment anyway. Best case scenario is you do routine maintenance and fix a big problem in one fell swoop.


#11

T

tbone

Jetblast said:
That looks like a likely suspect, especially if you've never adjusted the valves before. From the illustration I see rockers and valve lash adjustability, so I'd go right to that next since they're probably overdue for adjustment anyway. Best case scenario is you do routine maintenance and fix a big problem in one fell swoop.
Click to expand...

Well good news and bad news. Good news is adjusting the valves did the trick. Bad news is I made about 3 laps around the yard and bam, abrupt engine shut off. Removed the valve cover and I now have a broken rocker arm and bent connecting rod on the intake. So the question is what to do next:

1) Order replacement valve kit and try and fix it.
2) Take it to a repair shop and let them fix it.
3) Buy a replacement engine and install.
4) Buy another riding lawnmower.

So I think it comes down to cost benefit. Let me know what you guys think.


#12

J

jeff

Try jackssmallengine.com for a replacement engine. Otherthan that, take to a shop for repair. You may find that labor and parts to repair may exceed the replacement engine cost.


#13

Jetblast

Jetblast

Holy cow, sorry to hear that. If the rest of the mower is in real good shape I'd probably call a local shop and run the scenario past them for a wild price guesstimate, then repair or replace the engine based upon the feedback you get. If there's a lot of rust on the mower and things are feeling pretty loose and sloppy, a replacement mower might be the better bet in the long run.


#14

T

tbone

Jetblast said:
Holy cow, sorry to hear that. If the rest of the mower is in real good shape I'd probably call a local shop and run the scenario past them for a wild price guesstimate, then repair or replace the engine based upon the feedback you get. If there's a lot of rust on the mower and things are feeling pretty loose and sloppy, a replacement mower might be the better bet in the long run.
Click to expand...

Took a gamble and bought new push rods and a rocker arm. After several tries at getting the valves adjusted, I finally got it to work. Now I read several posts and looked at several videos explaining getting the engine to top dead center and then an additional quarter inch turn. Nothing very clear at all. In short the top valve is the intake, the bottom the exhaust. You adjust the valves on the compression stroke. What is not clear is this at the start of the compression stroke or the end? What I did is turn the engine until the intake opened and closes. At this point I think you are at top dead center. Had a long extension in the spark plug hole and it was at the top. Did'nt move the engine another quarter inch as that starts the exhaust valve to open. I found that you have to kind of play with this until both valves are closed and there is no pressure on the valves with the rocker arms. Adjusted both to .004 and works like a champ now. So $20 bucks hopefully saved me some money for a little while longer.


#15

J

jeff

Good deal, saved a ton!!!


#16

RobertBrown

RobertBrown

tbone said:
Took a gamble and bought new push rods and a rocker arm. After several tries at getting the valves adjusted, I finally got it to work. Now I read several posts and looked at several videos explaining getting the engine to top dead center and then an additional quarter inch turn. Nothing very clear at all. In short the top valve is the intake, the bottom the exhaust. You adjust the valves on the compression stroke. What is not clear is this at the start of the compression stroke or the end? What I did is turn the engine until the intake opened and closes. At this point I think you are at top dead center. Had a long extension in the spark plug hole and it was at the top. Did'nt move the engine another quarter inch as that starts the exhaust valve to open. I found that you have to kind of play with this until both valves are closed and there is no pressure on the valves with the rocker arms. Adjusted both to .004 and works like a champ now. So $20 bucks hopefully saved me some money for a little while longer.
Click to expand...

Great post/great thread tbone!
That's the kind of post that makes this website valuable and worth while. A few pictures would have been excellent, but a great post none the less.
Thanks
RB


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