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I am working on a B&S 21HP single cylinder model 331877 1449g1 and noticed while checking valve lash that at TDC between the compression and power stroke the gap was good however after rotating the engine to TDC between exhaust and intake, both rockers are tight. Is this correct? Thanks.

Between the end of the exhaust stroke and the start of the intake stroke there is an overlap in the valves which is very normal on most engines.

Okay thank you. Next step is compression and it sits at 125 but I seem to remember that below 135 is bad. I know these are hard on gaskets.

Sorry if you think I’m being a jerk, but are you sure you are measuring the clearances on the strokes you say. Won’t be the first time someone has gotten them backwards. Intake stroke, exhaust clearance should be .005-.007”. Exhaust stroke, intake clearance should be .003-.005”. Between the compression and power strokes you may find intake loose and exhaust tight, due to the ACR release on your engine.

Oops, I set the lash at TDC on comp and power stroke. Did I do it backwards?

Some engines are TDC on compression stroke.

Another way is TDC compression stroke and 1/4" into the bore.

Another is one valve fully open, SET the other CLOSED valve and vice versa.

Read your engine manual on the correct procedure.

Well my owners manual states which end of the mower is the front and how to operate the key and to not run over your kids. I’ll try and find a shop manual for the engine.

Bwells said:

Well my owners manual states which end of the mower is the front and how to operate the key and to not run over your kids. I’ll try and find a shop manual for the engine.

Click to expand...

Looks like you read it all LOL.

Here is my problem which I should have asked first. I was mowing just fine when the mower quit like the key was turned off. I cranked it again and it started and mowed another hundred feet and died again. I noticed the fuel filter had no fuel in it. I cranked a few more times and it started so I headed to the shop. Turned it off and the fuel level in the filter was barely visible. I figured the fuel pump was bad so I replaced it along with the fuel line back to the tank and fuel filter. Same story happened. Next thought was not enough pulse from the crankcase to operate the pump so I checked the compression assuming a blown head gasket and got a reading of 125 psi. I then checked the valve lash and here we are are. The compression seems low to me so I do have a head gasket set on the way but is there anything I'm missing? I did do the head gasket about two years ago. Thanks again for your time.