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Helpful ReplyBriggs 19.5hp won’t turn over on compression stroke

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2019/03/17 13:21:23 (permalink)

Briggs 19.5hp won’t turn over on compression stroke

I have b&s model 31p677-0912-g5
It drags on compression stroke, I’ve changes starter, solenoid, battery. Still does it.
I put my hand over carb intake and it will start when I do that. It still drags a lot but will end up firing over.
Take spark plug out and it turns over fast.
I’ve read about compression springs inside of some higher hp motors. Does my motor have one and do you think it’s the compression spring? Is it part of the camshaft gear?
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Re: Briggs 19.5hp won’t turn over on compression stroke 2019/03/17 13:43:19 (permalink) ☄ Helpfulby kshansen 2019/03/18 07:14:22
5 (1)
Hopefully you are not buying new items. What you replaced has little to do with the problem.
First thing to do is to adjust the valve clearances. OHV engine tend to open up these clearances causing the the ACR to no longer work. ACR = Automatic Compression Release
This ACR is on the camshaft. On this particular camshaft it bumps the intake valve right at TDC to relieve starting compression. If the bump is not present after adjusting the valves clearance then the ACR on the camshaft has failed. This particular camshaft ACR (793880) is know for this to fail too.
Valve clearance is .003-.005 Intake and .005-.007 Exhaust. The adjustment is checked and done with piston 1/4" pass TDC compression stroke.
post edited by AVB - 2019/03/17 13:44:43
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