Briggs engine knock help

belairbob

Member
I have a 10 hp Briggs horizontal shaft engine with a date of 1969. I removed the head. The knock sound happens when the intake valve is open and starts to close. You can feel the knock when you touch the valve. I removed the side cover and do not see anything wrong with springs. Any ideas what the problem might be? Thanks!
 
Is the valve seat tight?? I have seen on those where the valve seat has come loose and causes odd problems
 
Yes, all appears ok. The valve is still open. When it starts to close is when I hear and feel the clunk.
Only happens with the intake valve.
 
You could also have a loose valve guide or a broken cam shaft where part of the lob has broken off
 
Given the age of eng you may have carbon buildup on valve stem causing valve to stick/bind in guide,try removing valve & clean stem,see if that cure's problem.
 
You don't say this one has a stator for the charging system on it, but did you remove the flywheel and look underneath and where the magnet passes the magneto to be sure its not hitting? Also, Is the connecting rod tight on the crank? There should be no or almost no discernible play in the rod bearing. Is anything wedged in the timing gear teeth?
 
Thanks to all for the possible causes! This one has a coil. The flywheel passes by it without interference. I?m now going to roundup a valve spring tool and check for carbon problems as suggested. If no problem there then I will open up the bottom end and check for cam problems, connecting rod problems, etc. It may take me a few days but I will reply back with what I find.
 
I agree. Since you are where you are, removing the valve and cleaning up the shaft and the guide wouldn't be that big of a problem. If you keep Seafoam in the gas it will clean up a lot of what leaded gas did to old engines. Directions on the can.
 
Removed the valve springs today. The intake valve does have a good bit of carbon buildup. Also the intake valve guide is much closer to the valve seat than the exhaust valve guide is to its seat. Are they suppose to be the same? If so, how do I proceed? I do not see any problems with the internals. The piston skirt and cylinder are smooth. The rod end and crankshaft are smooth. I do not see any problems with cam, lobes or teeth. I attached pics of valve and guides. Thanks!

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