Briggs & Stratton 12 HP I/C compression release

[oldnslo]

I am working on an older 12 HP Briggs Model 281707-0411-01 that does not appear to have any compression release. The starter turns till compression stroke and stops. I have verified battery voltage and all electrical connections. Actually hooked my battery charger with boost direct to starter with same symptoms. Installed my compression tester and 105 - 110 PSI first stroke when starter stalled. Held release on compression tester open which allowed starter to spin and then released the unload valve and engine would then keep spinning. Pulled valve inspection cover and checked valve to lifter gap. .008 - .009 exhaust and intake. Neither valve bumps open while turning over by hand on compression stroke. Should this model have compression release? I believe yes and I suspect that cam is worn causing this to not work correctly today.

TIA

 

[RandyT]

IN is .005-.007 and EX is .009-.011 And most of the early Briggs L head didn't use a compression release on the camshaft. They used a modified cam lobe that caused the intake valve to stay open longer than it should which caused it to close closer to TDC causing it to bleed off excess compression. They just ran all the time with the compression bleed off.

 

[oldnslo]

Randy
Appreciate the information and I will experiment with reducing the intake clearance to see if that solves the problem .

 

[oldnslo]

Update, I reduced intake clearance to .007 and now starter spins engine over and it seems to run fine.

Randy thanks again for the help.