B&S 130000 series L-Head intake valve issue

[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....

 

[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.

 

[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

 

[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".

 

[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.

 

[mitchstein443]

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!

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..

 

[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

 

[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 engine

 

[cpurvis]

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

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

 

[slomo]

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

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

slomo