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B&S 130000 series L-Head intake valve issue

#1

K

kharrisma

Hi Folks,

Have a circa 1991 130212-3250-01 (code 91061910) 5HP horizontal shaft engine (happens to be mounted to a chipper-shredder). Pull start rope: zero compression (based on pull feel - no 'stack up'). Pulled head; both valves stuck open. Freed up exhaust easily, and it cycles and seals well, and 'in time.' Intake, however took a LOT more to free up (penetrating oil, soft-faced hammer, many cycles of open, tap down, open, tap down; evidence of water corrosion) until it was moving easily. Put head back on and tested; still zero compression.

Pulled head again, this time noticed that the intake is opening when it should (few degrees before TDC at end of exhaust stroke), stays open until piston reaches bottom, and as it 'turns the corner' and just begins to head back up, it *seems* to close... but it isn't fully seated; it's easily rotated with twisting thumb pressure atop the valve. It remains easily rotated until the piston is just about an inch from TDC/compression stroke, and only then does it seat sufficiently that it can't be twisted with thumb pressure.

Hmmm. Pulled valve springs/keepers, pulled valves (yucky), and cleaned up with a wire wheel. Cleaned seats with hand-drill mounted wire wheel. Lapped intake valve until valve and seat showed a good sealing band. Went to put spring/keeper back on, and noticed that the exhaust valve spring is not only a thicker gauge wire, but must also be compressed slightly by hand before it can be introduced into the tappet box. The INTAKE valve spring is a lighter gauge, and sitting on the floor of the tappet box, is about 3/8" from the 'ceiling' of the tappet box... sits *much* shorter than the exhaust valve. Seems weak by comparison, too.

Anyway, spun the starter again, and the intake valve is doing the same thing: seemingly opening and closing when it should, but when 'closed' it's not a firm closure, easily rotated until piston is approaching TDC.

Have not yet checked tappet clearances along intake valve travel cycle; I'd like to verify that the spring is normal; if it's supposed to be 'tall' like the exhaust, I'll just order another spring before proceeding any further. Related question: is it a bad idea to just install an exhaust spring on the intake valve to get a tighter seal? Oh... come to think of it, maybe I should put the exhaust spring on the intake and see if that solves my problem!

Anyway, thanks for reading and any input you may share!


#2

Hammermechanicman

Hammermechanicman

That operation of the intake valve is normal. That is what briggs calls easy spin. It acts as a compression release for easier starting. Eliminates the need for a mechanical decompression device. Leave the springs where they are.


#3

K

kharrisma

Thanks Hammermechanic man,

I did run across mention of something like that elsewhere; wasn't sure it was included on this engine. If this is correct, I guess I don't understand how it manages to achieve enough compression to work; if it's pushing out air/fuel charge as the piston is coming up (and not compressing it in the process), how does it manage to start & run? Is it one of those things where it becomes a non-issue when it's actually started & running?


#4

Fish

Fish

Check your clearances...


#5

Hammermechanicman

Hammermechanicman

kharrisma said:
Thanks Hammermechanic man,

I did run across mention of something like that elsewhere; wasn't sure it was included on this engine. If this is correct, I guess I don't understand how it manages to achieve enough compression to work; if it's pushing out air/fuel charge as the piston is coming up (and not compressing it in the process), how does it manage to start & run? Is it one of those things where it becomes a non-issue when it's actually started & running?
Click to expand...

Yes.


#6

B

bertsmobile1

The carburettor is mixing the fuel to the air at the same ratio
So all that is happening is your 500cc engine with a compression ratio of 7:1 ends up being a 100 cc engine with a compression ratio of 4:1
The lower the compression the wider the range of air : fuel ratios that will ignite.
The lower the compression pressure the better spark you get because the resistance between the electrodes drops .
This is why the 4 stroke 150 cc lawnmower starts a whole lot easier than the 25 cc line trimmer motor.
Also why the old side valve engines are easier to start than the equivalent OHV engines.
I have 2 almost identical model L BSA's
Both have the same carbs and the only difference between them is one isa 350 cc OHV @ 7:1 and the other is a 350 cc SV at 5.5: 1
The SV will start if you fart on the kick starter but the OHV requires several strong kicks before it will even attempt to come out to play .
A match in a petrol tank will cause the contents to burn and there you have a compression ratio of 0


#7

K

kharrisma

Hi bertsmobile1,

I am absolutely NOT arguing with you... just trying to understand the 'mechanics' of this thing. Perspective: I was a forklift mechanic for nearly 30 years (electric lifts, unfortunately in this case). I used to HATE working on the propane-fired lifts!

So by leaving the intake valve open by 0.001" (according to an explanation of 'easy spin' I found) for most of the compression stroke, B&S is effectively dropping the compression (to that last little bit of piston travel, about 1 inch or so, where the valve is finally tightly sealed), reducing both the trapped volume of air/fuel charge, and compressing it only that little bit? Thus allowing for a wider range of fuel-air mix and therefore easier starting, both by virtue of lower compression resistance to pull, and more tolerance of air:fuel ratio? Makes sense.

Where I lose it is since this works because of the shape of the cam lobe, isn't the same thing happening when the engine is started and running? How does it achieve tull compression with that valve being open a bit until it finally fully seats for that last bit of piston stroke? Same sequence of events, same effect (reduced compression), just higher RPMs. Not understand this.

Other thing that made me blink is: "The lower the compression pressure the better spark you get because the resistance between the electrodes drops." Again, no argument here, just curiosity. Wouldn't the air-gap resistance be *lower* in a higher compression situation due to the greater density of the fuel charge which is being compressed, creating more fuel molecules jammed into the same space than a smaller, lower-compression fuel charge? More particles closer together = better conductor = lower resistance? You seem to be saying exactly the opposite. Most likely I'm missing something or have some basic 'understanding' wrong, but that's what my 'logic-train' is telling me. Or is it the actual pressure of compression that's the issue here, regardless of fuel charge? While I *do* understand electricity very well, spark plugs in a high-compression situation with an explosive fuel charge present isn't something you find in an electric lift truck.

Thanks for your explanation, though! No such thing as useless knowledge. Every bit counts.


#8

Hammermechanicman

Hammermechanicman

Voltage to fire plug goes up as pressire increases.
You can defeat the easy spin feature by opening up the intake lash. This makes the engine harder to start. Will give you a slight increase in low end torque but above about 2000 rpm the easy spin makes negligible difference.


#9

K

kharrisma

Thanks again, hammermechnicman,

Got it. Never thought about it much; quick search produced a nice little graph that shows the relationship between voltage, compression, and fuel-air mixture temperature. Explained a lot. Thanks for that tidbit of knowledge!

Nope, I have no desire to defeat the easy spin feature; I was simply very puzzled by the intake valve behavior, racking my brain for some kind of malfunction, wear or damage that would produce such behavior. Never occurred to me that it wasn't a glitch, it was a feature! Knowing this, I can ignore that aspect of what I see, and go on with seeing if I an get this almost 20 year old engine to run. Much thanks for your help!

I also saw that in order to test the compression of this engine, I need to turn it opposite of the normal operational direction, otherwise the easy spin feature will produce really low readings. Sound accurate?


#10

Hammermechanicman

Hammermechanicman

A better test is what is called a leakdown test. Turning backwards won't give you a true compression reading


#11

K

kharrisma

Well, I guess if compression is a function of valves sealing and rings holding pressure, then a leakdown test is pretty much the same thing as a compression test. Same conclusion (everything tight, good compression), different means of arriving at it (holding pressure). I think. Hate to shell out for a tool I'll probably use only once, though....


#12

Hammermechanicman

Hammermechanicman

A leakdown test is done with the engine crank fixed from turning and the valves closed. It measured the % of leakage paat the rings and valves if they are leaking. The test will tell you the condition of the engine.


#13

B

bertsmobile1

BElieve it or not, at higher speed this does not happen because of actual shape of the cam which at higher speeds allows the valve to close earlier
You have to take the cam out, cut the lobe off and compare it to a standard cam to appreciate how it works
COmputer design is a fantastic thing
And the idea is not new Minerva used it back in the late 1800's when engines had to be cranked by a crank handle


#14

Hammermechanicman

Hammermechanicman

I have a 5hp cam in the barn somewhere. Tomorrow i see if i can find it and take a pic of the cam lobe with the almost impossible to see easy spin "bump".


#15

F

fixit1ddh

That chipper shredder really does not need easy start. There is enough flywheel effect You will never feel any compression. I have a 1991 MTD chipper shredder. I never felt any compression on the rope till I ground down that intake valve to get rid of the easy start. Now it starts better and it has a ton more torque. Opened the clearance up till easy start was disabled then gave it a few more thousands for when it gets warmed up. That has been over 25 years ago and My old mind does not remember anymore what the numbers were.


#16

mitchstein443

mitchstein443

kharrisma said:
Hi Folks,

Have a circa 1991 130212-3250-01 (code 91061910) 5HP horizontal shaft engine (happens to be mounted to a chipper-shredder). Pull start rope: zero compression (based on pull feel - no 'stack up'). Pulled head; both valves stuck open. Freed up exhaust easily, and it cycles and seals well, and 'in time.' Intake, however took a LOT more to free up (penetrating oil, soft-faced hammer, many cycles of open, tap down, open, tap down; evidence of water corrosion) until it was moving easily. Put head back on and tested; still zero compression.

Pulled head again, this time noticed that the intake is opening when it should (few degrees before TDC at end of exhaust stroke), stays open until piston reaches bottom, and as it 'turns the corner' and just begins to head back up, it *seems* to close... but it isn't fully seated; it's easily rotated with twisting thumb pressure atop the valve. It remains easily rotated until the piston is just about an inch from TDC/compression stroke, and only then does it seat sufficiently that it can't be twisted with thumb pressure.

Hmmm. Pulled valve springs/keepers, pulled valves (yucky), and cleaned up with a wire wheel. Cleaned seats with hand-drill mounted wire wheel. Lapped intake valve until valve and seat showed a good sealing band. Went to put spring/keeper back on, and noticed that the exhaust valve spring is not only a thicker gauge wire, but must also be compressed slightly by hand before it can be introduced into the tappet box. The INTAKE valve spring is a lighter gauge, and sitting on the floor of the tappet box, is about 3/8" from the 'ceiling' of the tappet box... sits *much* shorter than the exhaust valve. Seems weak by comparison, too.

Anyway, spun the starter again, and the intake valve is doing the same thing: seemingly opening and closing when it should, but when 'closed' it's not a firm closure, easily rotated until piston is approaching TDC.

Have not yet checked tappet clearances along intake valve travel cycle; I'd like to verify that the spring is normal; if it's supposed to be 'tall' like the exhaust, I'll just order another spring before proceeding any further. Related question: is it a bad idea to just install an exhaust spring on the intake valve to get a tighter seal? Oh... come to think of it, maybe I should put the exhaust spring on the intake and see if that solves my problem!

Anyway, thanks for reading and any input you may share!
Click to expand...
Ok, the intake valve spring sounds to be weakend. You can try a few things.. but first I'll explain how it happens..

Just like on a car... when the engine is sitting dependingo n the position of the cm shaft one valve may be in the open position, thus, compressing the spring.. over time, the spring becomes used to being compressed and reforms itelf in a weaker/slightly compressed state..

Sometimes, you can fix this spring by heating it up with a torch and letting it naturally cool down.. Sometimes you can shim the spring with a set of washers to compensate for the distance change from being compressed for a long time..

The best way is to spend a couple bucks and replace the spring, while your at it replace the other spring and valves themselves..


#17

S

slomo

If a valve is open at any time on compression stroke, you are obviously losing cylinder pressure. Easy and hard starts, shove that aside. And if you are dumping cylinder pressure when running at normal revs, you are losing torque. I bet this was a Briggs selling feature back in the 50's. Easier for the wife to cut the grass. I'd rather it have full beans all the time.

slomo


#18

Hammermechanicman

Hammermechanicman

This is a pic iof a briggs 5hp cam intake lobe. The prussian blue marks the easy spin bump. It is only a few thousandtha high from the ramp to the transition to the heel. Impossible to see. Lots of folks think these engines have no compression release but it does. If you know what you are doing and cafeful a couple file strokes of a file will add some power to the engine1623939181170.jpg


#19

cpurvis

cpurvis

slomo said:
If a valve is open at any time on compression stroke, you are obviously losing cylinder pressure. Easy and hard starts, shove that aside. And if you are dumping cylinder pressure when running at normal revs, you are losing torque. I bet this was a Briggs selling feature back in the 50's. Easier for the wife to cut the grass. I'd rather it have full beans all the time.

slomo
Click to expand...
Then you'll have to grind your own camshafts because most close the intake slightly after BDC.


#20

S

slomo

cpurvis said:
Then you'll have to grind your own camshafts because most close the intake slightly after BDC.
Click to expand...
If I ever remove a cam, it's getting a date with the grinder wheel.

slomo


#21

VRR.DYNDNS>BIZ

VRR.DYNDNS>BIZ

Hammermechanicman said:
That operation of the intake valve is normal. That is what briggs calls easy spin. It acts as a compression release for easier starting. Eliminates the need for a mechanical decompression device. Leave the springs where they are.
Click to expand...
I second the clearance issue. valve lash is critical and so is the procedure. Buy the manual for your engine, they are resonable.


#22

VRR.DYNDNS>BIZ

VRR.DYNDNS>BIZ

slomo said:
If I ever remove a cam, it's getting a date with the grinder wheel.

slomo
Click to expand...
You will be sorry if you do!!!!!!!!!!!!!!!!!


#23

S

slomo

Kinda doubt it. Chance of me opening one up is pretty slim. Plus I'm "strong like bull". I could pull the stinking rope off the blower housing. Then check myself into the ER. LOL :D

slomo


#24

Hammermechanicman

Hammermechanicman

VRR.DYNDNS>BIZ said:
You will be sorry if you do!!!!!!!!!!!!!!!!!
Click to expand...
Back in the 90's i built engines for guys at the local go cart race track. Most dads just wanted a reliable motor to get their kid through the season. These were all stock class 5hp briggs. There was also the stock appearing class. Only rule was it had to look stock. Stock looking carb and tank and cylinder head. Everything else was run what ya brung. Engine would get billet rod with a popup piston, milled head and then relieved for valves, very high performance cam, stronger valve springs, drilled out carb, ported block, coil and flywheel from a 3.5hp engine, advanced timing. You would be suprised how much power you could get from a 5hp briggs that looked stock. You had to pull the rope like you meant it it. More that a couple broken fingers from these engines. Powerband was around 4k to 8.5k depending on what cam was used. Guys changed oil every race and ran straight SAE40 or SAE50 wt castor based oils. I do miss that smell. You tuned rhe engine temp with ignition timing. You kept advancing the timing till the engine temp got too high then backed off a degree or two. There were probably 50 to 60 different aftermarket cam profiles to choose from.

Wonder how far you can take this one?

Animal Racing Engine

<p>Performance by Design. Briggs & Stratton Racing took the latest approaches in engineering, manufacturing, and testing to design for its dedicated racing engine from the ground up. One of the most popular Briggs racing engines, the Animal engine will help you compete in your next snocross or...
www.briggsandstratton.com www.briggsandstratton.com


#25

S

slomo

Hammermechanicman said:
Back in the 90's i built engines for guys at the local go cart race track. Most dads just wanted a reliable motor to get their kid through the season. These were all stock class 5hp briggs. There was also the stock appearing class. Only rule was it had to look stock. Stock looking carb and tank and cylinder head. Everything else was run what ya brung. Engine would get billet rod with a popup piston, milled head and then relieved for valves, very high performance cam, stronger valve springs, drilled out carb, ported block, coil and flywheel from a 3.5hp engine, advanced timing. You would be suprised how much power you could get from a 5hp briggs that looked stock. You had to pull the rope like you meant it it. More that a couple broken fingers from these engines. Powerband was around 4k to 8.5k depending on what cam was used. Guys changed oil every race and ran straight SAE40 or SAE50 wt castor based oils. I do miss that smell. You tuned rhe engine temp with ignition timing. You kept advancing the timing till the engine temp got too high then backed off a degree or two. There were probably 50 to 60 different aftermarket cam profiles to choose from.

Wonder how far you can take this one?

Animal Racing Engine

<p>Performance by Design. Briggs & Stratton Racing took the latest approaches in engineering, manufacturing, and testing to design for its dedicated racing engine from the ground up. One of the most popular Briggs racing engines, the Animal engine will help you compete in your next snocross or...
www.briggsandstratton.com www.briggsandstratton.com
Click to expand...
WOW, what an ANIMAL. With it's whopping 8.5:1 compression. Look out Big Daddy Don Garlits...... John Force, you'd better pack it in. What is this WW 1?

My old Toyota Corolla 1.8L gas saver at 39mpg has 11:1 compression.

slomo


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