# Briggs/Stratton L-Head valve timing issue



## kharrisma (Aug 28, 2011)

Hi Folks

I have a 130000 series 5 HP horizontal shaft engine (circa 1993), bolted to an MTD chipper-shredder. It had no compression when I pulled the start rope. Pulled the head, and found both valves stuck in the open position, with evidence of some corrosion around the intake valve. Used penetrating oil and a soft-faced hammer to free up the stuck valves. Put the head back on, tried again; still no compression.

Pulled head again, and this time noticed that the intake valve was not acting right... opens when it should, and _starts_ closing when it should, just past end of intake stroke... but it doesn't close fully; looks closed, but is easily rotated with a thumb until the piston is about an inch down from TDC; _then_ I can no longer spin the valve.

Pulled head again, and removed the valves. Nasty. Cleaned them up thoroughly with a wire wheel, and cleaned the seats with a hand-drill mounted wire wheel. Lapped intake valve, good seating surface across both valve and seat (which is removable, by the way). Noted that the exhaust valve spring appears to be a bit thicker gauge wire than the intake, and it must also be compressed a bit to slide it into the valve adjusting box. However, the intake spring is sitting on the floor of the box, and is easily 3/8" from the top of the box. Put spring and keeper back on intake valve, and once again spun the crank... and it's still doing the "no full seal 'til almost TDC/compression."

The stems are not stiff to move in the guides; if I put the stem into the guide and release it, it falls smoothly down to the seat. The stems are also straight, no detectable bends.

My question is this: should the intake valve spring be taller than it is? Should it have to be compressed a little to slide it into the valve adjusting box like the exhaust valve? Maybe this behavior is due to a weakened and/or partially collapsed intake valve spring?

Maybe it would be a good idea to switch springs, and put the stiffer/taller exhaust spring onto the intake and see if the behavior persists? If not, then it's almost certainly a bad spring, no?

Just curious to see if any of this sounds familiar to anyone here. If I can get decent compression in this thing, it will be worth it to me to go ahead and get a bunch of parts to get it back into service (full gasket set, carb rebuild set, breather/filter cover on valve adjusting box, etc). Don't want to sink much money into this thing if there's something wrong in the crank/cam/con-rod/piston/valve train somewhere. All the small parts are still available, but the bigger parts like pistons are not (not in _any_ size), and others are prohibitively expensive. There IS some scoring in the cylinder (unlined), but I'll have to be happy with honing the cylinder and putting in standard rings. I'd rather go 0.020" over to compensate for wear, but that would require a new piston as well, which I can't get, plus 0.020" is the only other size available besides standard.

Opinions/thoughts/ideas?? I'd also like to avoid pulling the engine off of the chipper (tapered output shaft, and things are relatively rusty) and cracking open the case if it's at all possible to avoid.

Thanks for looking!!


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## paulr44 (Oct 14, 2008)

Scoring in the cylinder...question is how deep? Any score can affect compression. We have some old B&S oversize pistons we'd love to sell, if you post your engine numbers I can take a look at my archive list.

Sounds like you have a pounded valve and seat, resulting in more than complete loss of lash. Not uncommon on dusty-environment and/or poorly maintained flat-heads. If I'm right, you need to cut the seat, and either grind the valve face or replace the valve entirely.

As for the timing, I use the valve-overlap period to check that. At the end of the exhaust stroke, as the piston achieves TDC both valve should be open just a bit. Rocking the engine to and fro at that point the valves should alternate closing fully, and opening a bit.

Unlike the vehicle industry, I've never seen valve spring specs. published in OPE. You'd need a special gauge to measure that anyway, cheaper just to get new springs.


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## kharrisma (Aug 28, 2011)

Hi paulr44,

Scoring is not hideous, but it's not good, either. PO ran the thing with NO air filter in place for God knows how long. At least it had (black) oil in it! Looks like a bit of cylinder wall got 'smeared' a bit, resulting in a slight raised area ahead of an equally slight depression. Wish the damned thing was sleeved! Oh, well... I can 'shave' off the highs and live with the lows. As I said, it's not extensive, just in one small area, the rest is what I'd consider normal wear.

Engine is: B&S 5HP horizontal shaft (mounted to an MTD chipper), 130212-3250-01 (code: 91061910). 

Learned something interesting yesterday: B&S uses something they call "Easy Spin," a means of reducing the compression you have to pull against to start the engine. Intake cam lobe is shaped differently: it holds the intake valve open 0.001" for much of the compression stroke, fully seating only at the last inch-plus of piston travel. I can see this being okay for low RPM conditions like starting... but the wheels fall off of it for me when I try to visualize what's going on when the engine is up to operating range. Maybe that 0.001" becomes less significant at high RPM's, that 'leakage' being factored into the design of the engine, and 'compensated for'? Don't know enough about operating theory to be able to figure that out.

Valves & seats aren't bad (other than the water corrosion on the intake valve face and stem). Cleaned all that up, lapped the seats to get a good, even, smooth matte band on both seat and valve. NOW I have to check to be sure I haven't upset the tappet-valve clearance too much. Then maybe I can see if it fires up at all, and how it runs if it does. If it looks salvageable, I might very well be interested in a set of oversize pistons and rings!

Thanks very much for your reply!


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## Wazza65 (Aug 28, 2021)

paulr44 said:


> Scoring in the cylinder...question is how deep? Any score can affect compression. We have some old B&S oversize pistons we'd love to sell, if you post your engine numbers I can take a look at my archive list.
> 
> Sounds like you have a pounded valve and seat, resulting in more than complete loss of lash. Not uncommon on dusty-environment and/or poorly maintained flat-heads. If I'm right, you need to cut the seat, and either grind the valve face or replace the valve entirely.
> 
> ...


Start with two new valve springs and collets. The bore scoring is of concern. Lift each valve up from there seats about 3/8" and check the wear I'm the valve guides but new springs would be your starting point. You may have a whole series of problems but you have to break it down into steps and start with the most like problem and you definitely have crook springs. Take a good look at the valve inserts in the head they can come lose on some models and a correction is needed.


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