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New starter, battery and adjusted valves to .005 but motor won't spin. Pull plug and it spins fine . External examination of push rods and valve spring movement looks fine. Ideas please

give us the engine model number, it should be stamped on the Valve cover.
first guess i would say the compression relief failed on the cam shaft.

The model and serial number is on a white label on the engine cover which is damage and unreadable. Is it anywhere else on the engine?

Try looking on the valve cover

oldie said:

The model and serial number is on a white label on the engine cover which is damage and unreadable. Is it anywhere else on the engine?

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Nothing on the valve cover.

If you have re-install the valve cover try looking on the bottom side.

70 year old eyes, thanks I found it

Model/type 331877 1371 B1 code 1006117ZD

that engine uses the Briggs 793880 camshaft, which is known for the compression relief mechanism to fail, causing this issue they upgraded it to part number 84005207, to help diagnose the cam problem, i usually remove the valve cover, and spark plug, and turn the engine over by hand, i believe on this one watch the exhaust INTAKE valve, on the compression stroke, the rocker arm should bump the valve open. if you don't see the bump most likely the compression relief failed.

Scrubcadet10 said:

that engine uses the Briggs 793880 camshaft, which is known for the compression relief mechanism to fail, causing this issue they upgraded it to part number 84005207, to help diagnose the cam problem, i usually remove the valve cover, and spark plug, and turn the engine over by hand, i believe on this one watch the exhaust valve, on the compression stroke, the rocker arm should bump the valve open. if you don't see the bump most likely the compression relief failed.

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Keep in mind that most of the single cylinder OHV engines use a cross flow head and the bottom valve is the intake, which is the one normally opened by the ACR.

I have been reading about this problem and I understand what you are saying about the jump in movement. Is that p/n for an entire cam or just the relief valve?

I also read somewhere about doubling the head gasket to lower the compression, so the starter can rotate the engine. Has anyone tried this trick?

My neighbor was throwing this machine out so I decided I would use it for parts, but it has had such little use I hate to tear it apart before trying to get it to run.

Thanks for the help

that is the part number for the whole camshaft. the compression relief isn't available by itself.

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