BS bent exhaust valve? Why? Just replace?

Bob in SD

Member
Hi all,

I don't think I've posted on the garden tractor forum before--please let me know if this is the wrong place.

I've got a Briggs and Stratton "ELS 500" "OHV" powered riding mower that started on the first crank after the winter. I put it away correctly, drained tank and bowl in he fall and started it with new gas two weeks ago. My daughter used it for an hour or two and I put it away--seemed to be running fine.

Last week it wouldn't start, zero compression. I eventually took the head off, and the exhaust valve is not closing, even without the rocker arm. I took the valve out, but don't have good machinist tools to determine it's bent or not (I'm thinking it looks a little bent, but I may have convinced myself of that since I can't think of any other reason I can't even push it closed with my thumb with the head on the bench and no spring or keeper).

Should I just replace the valve (re-lap, etc) and try again? The pushrods look fine and nothing else looks out of place?

What could cause this to happen? I'll re-check all of the cooling fins and such, but it had oil and seemed to be running OK prior to this? I'm not familiar with OHV lawnmower engines and let a machinists deal with my automotive and tractor heads, so I want to make sure I'm not missing something obvious.

Thanks,
 
Did your valve guide move in the head ? Check it against the height of the intake guide. If you want to see if the valve is bent just chuck the end of the valve in your drill turn on drill watch the valve spin that will tell you real fast. More that likely the valve guide moved then just order a new complete head assembly from briggs and be done with it . Also check your push rods for straightness while you are at it.
 
I think you are right, Kurt. The casting is different on the intake and exhaust sides, so it isn't real obvious (exhaust has a fatter support coming up about 1/2 inch whereas the intake is flush, with the guide coming up inside the valve cover part). I pounded the exhaust guide "up" (towards the rocker arm side). Even just getting it flush with the top of the head let's the valve close.

Thanks for saving me from ordering the wrong parts-I might need that mower if spring ever comes back (hard freeze tonight). I'm guessing there's no way to secure that guide in the right place and continue to use this head?

Thanks again!

Bob
 
As Kurt pointed out, my valve guide had moved from within the head. After replacing the head, what should I do to prevent this happening again? It hasn't been run low on oil since I've had it (year or two?). It did start using oil, and need topped off for the first time last fall--was this a sign? What else do I need to know?

Thanks,

Bob
 
Just keep cooling fins clean and don't overheat the engine. Like cutting tall heavy wet grass and just keep pushing the mower. Don't travel as fast in conditions like that. Keep your rpm's up when mowing.
 

I had a guide on a B&S move the other way, causung the rocker to not be able to push the valve all the way down, which caused the push rod to bend. I pushed the guide back down and staked it with a chisel. Still working fine many years later.
 

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