compression lock B&S 21hp 540cc platium with XRD

[oldie]

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

 

[Scrubcadet10]

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.

 

[oldie]

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?

 

[Scrubcadet10]

Try looking on the valve cover

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?

 

[oldie]

Nothing on the valve cover.

 

[Scrubcadet10]

How to Find Your Model Number | Briggs & Stratton

Need help for your Briggs & Stratton engine or product? Locate your model number here to search for your owner's manual, order replacement parts and more.

www.briggsandstratton.com

 

[StarTech]

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

 

[oldie]

70 year old eyes, thanks I found it

Model/type 331877 1371 B1 code 1006117ZD

 

[Scrubcadet10]

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.

 

[ILENGINE]

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.

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.