Hello everyone,
I have a Craftsman lawn mower with a 18.5 Briggs single cylinder that will not crank over. Have replaced the starter with a new one and it still does not crank over. Someone suggested checking the values and the valves were a little off so we fixed them. Sometimes it will crank over just fine as long as it is cold, but once the engine is warm it acts like the starter does not have enough strength to turn the engine. When we try to turn the engine by hand it seems to have a lot a of compression. Would this be caused from the compression release not working? If so how can this be fixed?
Any suggestions..

Far

Valves were a little off... They were set to the spec'd clearances correct?
If they are the little bit off, and almost on the compression stroke, it will not turn past it without help.

Right on the money.. One of the few times that when we set them they were according to spec.

So you did put them to spec?
If you did, I'd make sure the rockers aren't getting loose while running (go back and redo them to see if they have)

New battery?

New Bat.. Which valve does the compression release work off. Is it the intake or the exhaust.

Will check on the rockers.

Exhaust... for the compression release.