I have replaced the oil seal on my 12hp Power Built briggs and stratton 3 times now, what can cause this?
I've checked to make sure I was installing them correctly.

Is there a sharp edge on the chankshaft that might damage it on installtion, is there a scratch or other damage in the crank surface the seal slides in... it should be smooth as glass.

If that's the problem, I guess the crank will have to be replaced or can it be smoothed out?

If the seal surface is damaged, one of those two, which depends on the extent and nature of the damage.

I'm thinking more likely there is a sharp edge (or even a rusty area) that is catching the seal and damaging it going on. If that's the case... the crank isn't damaged its just machined that way and you need to be extra careful gettign the seal up and over it. Trust me, its unbelievably easy to damage a seal in a situation like that... I have in various different things over the years.

Speaking from experience of other lawnmower, automotive and motorcycle engines I have worked on.

I'll definitely check it out. Thanks for the info.

Hi,
Be sure that it is actually the seal that is leaking! Briggs has mad more porous sump pans that any other manufacturer. Make millions and millions of castings and chances are that sooner or later just one of them will be bad. Most common places are the front right (near the camshaft bosses) or left rear (near the governor bosses.)
Peace,
Clarke