Compression issue after rebuild

[casual observer]

Hi,
After reading your issue, , I think your problem is actually your starter motor circuit, could be electrical issue or a broken part or slipping part in the starter motor. A starter motor should always have enough guts to crank engine. The fact that you can turnover engine without sparkplug, but not with spark plug installed, when you get max compression, Also over tightening valves ,even slighty was letting compression out of engine, which allowed to crank.
I suggest you reset all of your original overhaul like you had it, they check out starter system, bad battery, wiring, starter motor, slipping overrunning clutch in starter motor.
If you can crank engine with starter rope, try that.

 

[Hammermechanicman]

 

[doug9694]

Help everyone…. Ok, this is going to be lengthy. I have completely rebuilt my Briggs and Stratton model 31C707-0026-G. It all started with a broken piston Rod arm. I figured while I was rebuilding and the engine was old I replaced multiple parts. (Cam shaft, cam shaft timing gear, tappet valves, all gaskets) I just put everything back together, started it up with out the spark plug, turned the ignition key and the flywheel spins freely. Put the spark plug in, tried to turn it over and the fly wheel doesn’t want to turn. There is a lot of resistance. The flywheel just doesn’t want to turn. I did a little research and found that it could be a valve issue. I have a Briggs and Stratton service manual and adjusted the rocker valves to the required specs. Put the valve cover back on, cranked it over and had the same results. I now have back firing out of the carb and exhaust. It’s also very hard to turn over to the point where my starter was smoking, no issues with the battery and the starter is fine. After adjusting the valves, the flywheel will spin much better when I have the throttle cable to the lowest setting. When it’s at max, flywheel barely turns. I am suspecting that something is messed up with the timing in the cam shaft even though I lined the marks up. Does anyone have any suggestions?

Likely problem is defective decompression system. Old side valve engines had about 9 to 1 compression. OHV has much higher. Instead of putting on a stronger starter and bigger battery. Manufactures chose to add decompression schemes. Valves must be adjusted after the decompression part of the cam is past the valve stem. Or perhaps the decompression system is broke!

 

[casual observer]

Was this comment directed at me

 

[kinsler33]

After you take some time away from your engine, disassemble it and re-assemble, but take an extra look at the carburetor. I'm speculating that you may have assembled something incorrectly and/or the fuel system isn't cooperating.

 

[Hammermechanicman]

Was this comment directed at me

Just the whole thread in general.
This thread is like a guy fell off a boat and can't swim and folks trying to tell him how to swim. Very entertaining.

 

[GDHS]

Methinks maybe the white smoke means something - like maybe the cylinder is flooded with oil.
And since not all of us are experienced mechanics, it would be good if writers (whose input is appreciated) would define the abbreviations they use. And we novices should try harder to use correct terminology. For example, to me, the words 'start' and 'crank' have different, distinct meanings. Like "my engine will crank but won't start". Just saying . . . .

 

[tew45]

someone in the distant past very wisely said: For an internal combustion engine to run it must have fuel, compression, and a spark at the right time. He also said if all these were present it was beyond his expertise to repair. Apparently you do not have a spark at the right time due to cam gear misaligned or timing not right.

 

[Tom O']

Help everyone…. Ok, this is going to be lengthy. I have completely rebuilt my Briggs and Stratton model 31C707-0026-G. It all started with a broken piston Rod arm. I figured while I was rebuilding and the engine was old I replaced multiple parts. (Cam shaft, cam shaft timing gear, tappet valves, all gaskets) I just put everything back together, started it up with out the spark plug, turned the ignition key and the flywheel spins freely. Put the spark plug in, tried to turn it over and the fly wheel doesn’t want to turn. There is a lot of resistance. The flywheel just doesn’t want to turn. I did a little research and found that it could be a valve issue. I have a Briggs and Stratton service manual and adjusted the rocker valves to the required specs. Put the valve cover back on, cranked it over and had the same results. I now have back firing out of the carb and exhaust. It’s also very hard to turn over to the point where my starter was smoking, no issues with the battery and the starter is fine. After adjusting the valves, the flywheel will spin much better when I have the throttle cable to the lowest setting. When it’s at max, flywheel barely turns. I am suspecting that something is messed up with the timing in the cam shaft even though I lined the marks up. Does anyone have any suggestions?

If you have the issue with the timing and flywheel solved and your having problems with backfiring you may need to adjust the carburetor lean/rich settings. The new valves may be mixing less air than the old ones (tighter seating or gap setting or for some reason allowing more air). I'd try adjusting the fuel mixture if you think it's viable.

 

[Appiefromholland]

My first rebuild of an vanguard briggs and stratton I forgot to put the push rods in place