Briggs and Stratton 20HP V-twin - firing on one cylinder

FordCook

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
First post for me. Hope I'm smart enough to figure this out with a little help from the more experienced forum folks:

Had this L120 John Deere mower since 2005. Have neglected it (sadly) and a few weeks ago it started running very rough (while my son was using it). Next time I started it - it barely ran. I'm fairly mechanical but don't spend much time working on or maintaining my yard machines - sadly. So it seemed to be barely running on one cylinder. When viewed from sitting in the seat - the cylinder on the right appeared to fire and work. The cylinder on the left - not working (head not hot). So I pulled the valve cover and had to pinch myself because one of the valve pushrods was GONE (the steel one) and the aluminum one was bent. I walked away for a few minutes asking myself - what in the world?? So I went back with a good LED headlight on my head and some reading glasses - and discovered the (?) oil return hole and thought... no way... So I got on Youtube and found a couple of guys had the same experience and, indeed, the bent pushrod was disappearing into the crank case. One guy even said he fished it out thru the oil-fill spout. So I picked up a handy telescoping magnet for $2.99 and ---- much to my serious amazement, fished out a bent pushrod thru the oil fill valve.

Then I proceeded to order a new cylinder head along with new pushrods and all the gaskets. Tonight I installed all the goodies and was pretty careful with torque values, etc. I installed two fresh spark plugs too - and put it all together. It started roughly, and ran - smoother than before (because the valves were cooperating I think) - but it still wasn't right. I shut it down and again noticed that the same cylinder was still not firing. I pulled the wire off the plug and the valve cover off and cranked it again. The plug was arcing just fine (I observed a strong spark). And as far as I can tell - the valves appeared to be operating fine (quietly). But that cylinder was not hot and I don't believe it's firing for some reason.

What do you guys recommend? What could be causing this problem? I've got spark. A new head. New pushrods, etc. Apparently I've got gas(?) Thanks for reading and listening to my newbie woes.

Ford Cook
 

bertsmobile1

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
:welcome:

Pull the rocker cover off and check the operation of the valves, make sure you do not have them crossed over so the exhaust opens on the induction stroke.
Double check the valve lash and did you put the lash caps on the ends of the valve stems ?
With the spark plug out and the inlet valve fully open, blow air into the carb you should see & feel it coming out of the plug hole.
Try the same trick with the exhaust valve only this time put the air in the plug hole & check it is coming out the muffler.
 

ILENGINE

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
Remove both spark plugs and both valve covers, and will turning the engine over by hand, observe the valves opening and closing and make sure that they are opening the same distance. I suspect there could be a worn camshaft lobe not allowing the valves to stay open long enough.
 

FordCook

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
Thanks for the helpful replies!!!

I took both valve covers off. Embarrassed to say I did not adjust the rocker clearance on the new head. Not sure about "caps"... It came fully assembled. The clearances were too tight (actually non-existent) - so perhaps the valves weren't fully closing for the compression and fire strokes. I've set them to roughly .005" now. Rocker clearance on the other head checks out fine. I'm waiting for my battery to charge because it had trouble turning the engine over now...

By the way - how would it be possible to mix up the intake/exhaust sequence during re-assembly? I checked and it appears the intake valve opens just after the piston reaches TDC and closes near the bottom of the stroke. Both stay closed on the way up. Then stay closed on the downward power stroke. The exhaust valve opens near the bottom of the power stroke and stays open during the upward exhaust stroke...
 

dfbroxy

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
Did you give the carb a careful cleaning while you had it off?
 

bertsmobile1

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
Thanks for the helpful replies!!!

I took both valve covers off. Embarrassed to say I did not adjust the rocker clearance on the new head. Not sure about "caps"... It came fully assembled. The clearances were too tight (actually non-existent) - so perhaps the valves weren't fully closing for the compression and fire strokes. I've set them to roughly .005" now. Rocker clearance on the other head checks out fine. I'm waiting for my battery to charge because it had trouble turning the engine over now...

By the way - how would it be possible to mix up the intake/exhaust sequence during re-assembly? I checked and it appears the intake valve opens just after the piston reaches TDC and closes near the bottom of the stroke. Both stay closed on the way up. Then stay closed on the downward power stroke. The exhaust valve opens near the bottom of the power stroke and stays open during the upward exhaust stroke...

Not the first, or last person that will do the same thing.
You can cross over the pushrods on most Briggs engines as they run in a common tunnel.
You can also catch the join between the ball & the tube on the edge of the cam follower.
Done both of them.
The little hats that go on the end of the valves are very important ( when they are fitted ) as the rocker arm can touch the spring and cause the inlet spring collar to pop off the valve ( not pretty )
 

FordCook

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  • / Briggs and Stratton 20HP V-twin - firing on one cylinder
Update: I adjusted the clearances very carefully to .005" and it's running well now. There was a bit of a tap on the new cylinder head, so I checked my clearances and adjusted them again. Still a small tap but perhaps it needs to "wear in" (?). THANKS for the HELP!

I did NOT clean the carb - so will spray a little carb cleaner thru the intake today. I did, however, clean the engine pretty well. Very happy to have it running again.

About mixing up the intake and exhaust - this motor has separate tunnels for intake and exhaust push-rods - so hopefully that prevents mixing things up. I did install the aluminum rod to activate the intake valve and the steel one to activate the exhaust. Thanks again guys.
 
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