Valve lash on a 25 horse Briggs&Stratton?

Tractorguy24 · Apr 18, 2019

Does anyone know the valve lash on a 445777 25hp briggs Stratton OHV? Its installed in a gs6500 craftsman mower.
Ive had problems with it starting and think its due to a loss of compression thru the valves at operating temperature and would like to adjust them properly.
Thank you

tomplum · Apr 19, 2019

.004" Intake .006" exhaust set at 1/4" past TDC after the intake valve for the respective cylinder closes. If it cranks over well, you likely have other fish to fry. While under the valve covers, compare the valve guides that protrude from the head. They should be relatively equal figuring in the seal on the intakes. Also rotate the engine comparing the amount of lift, (the amount the valves open).

Tractorguy24 · Apr 24, 2019

Thank you for the reply, tomplum
I just reread my post and noticed for some reason I forgot to mention that im only having trouble starting the mower while hot. This should be valve related, no?

tomplum · Apr 24, 2019

Define what trouble you are having. The engine cranks well, but is an extended crank or it is difficult for the starter to crank the engine over...

Tractorguy24 · Apr 25, 2019

It cranks we値l it just won稚 fire
I知 thinking the heat from the engine expands the valves and causes them to open prematurely, reducing compression which causes it to not fire.
Might do a compression test at temp later to confirm this

RandyT · Apr 25, 2019

Probably wouldn't hurt to check and adjust valve clearances just as a possible issue. I would think it would at least start and try to run on one cylinder if it was just a valve issue. Shouldn't effect both cylinders equally. I would be looking at a loss of spark at the spark plugs due to either heat sinking of the ignition modules causing heat related failure.