Bad backslap from recoil starter

[Fish]

How much did you shave off? It doesn't take much to throw your compression ratio way up.

 

[greggw60]

Not sure how to measure that. Only sanded till surfaces were evenly shiny. Hard to imagine that I could've taken that much off with sandpaper and block but.....?

 

[greggw60]

Really can't figure why it gets so hard to roll over only on the downward stroke of the power cycle. Would think it would be on the compression stroke.

 

[greggw60]

No decompression mechanism but agree it that's what it acts like. Cam maybe?

 

[StarTech]

Are 100% you on the power stroke? All depend how you are determining you have passed peak compression stroke.

And yes the camshaft has a decompression method. It is ramped and bumped decompression grind on the camshaft lobe. Most likely the exhaust lobe.

 

[greggw60]

I turned the motor manually until it got to the tight spot and removed the head to check the position of the piston. It was just past TDC. Good to know that about the decompression on the cam. Didn't know about that. I have another one I'm going to replace it with. Only thing that makes sense since it's the only part that rotates twice to the four times of the crank.

 

[StarTech]

Yes the ratio is correct but it is 1 full camshaft rotation to two full crankshaft rotations, just to clarify. These engines are four stroke not eight stroke. Each stroke is half of a complete crankshaft rotation.

Intake stroke (piston moves down), Compression stroke (piston moves up), Power stroke (piston moves down), and Exhaust stroke (piston moves up). Then everything repeats.

 

[smithboy]

I turned the motor manually until it got to the tight spot and removed the head to check the position of the piston. It was just past TDC. Good to know that about the decompression on the cam. Didn't know about that. I have another one I'm going to replace it with. Only thing that makes sense since it's the only part that rotates twice to the four times of the crank.

To expand on a previous thought, the engine work along with the light resurfacing may have increased compression by enough to cause (pre)detonation. One thing that may help without modification is increasing the octane of the fuel you are using. Drain the tank and carb, refill with 93 octane and see if the problem persists...the questions about blades and other rotating weight is also important. If you are using new blades that are lighter than the original or something else that is supposed to rotate is now lighter, you may be just noticing the change in the forces that are usually dampened by those weights. I have tried to start a push mower with the blade removed and had the cord snatched painfully from my hand...The blade does more than just cut. It acts as a weighted flywheel.

 

[Hammermechanicman]

It is very difficult to get the compression ratio of a flathead briggs up to the point you need 93 octane fuel. I have chainsaws running 200psi of compression with about a 10:1 compression ratio and they run fine on regular gas. 8hp briggs will have a cast iron flywheel. No need for a blade.

It is simple to diagnose. Remove head and slowly turn engine over. If it binds up something wrong internally.
Put head on without sparkplug. Slowly turn engine over
Does it bind up? If so valve hitting head.
Put in spark plug and slowly turn over. Does it bind up? If so compression issue.

 

[VRR.DYNDNS>BIZ]

If you still feel the resistance with the plug out, and you reused the head gasket and stoned the head/block as you said, this engine has very tight clearances to the head and may be making contact. Loosen all the head bolts and pull slow and feel the head and if problem disappears.