803A Hits a Wall at 9.3kW

Might I suggest that you add a bit of seafoam to the oil before changing it.
It does a great job of cleaning inside the engine and hopefully freeing up piston rings.

Yes it’s safe for that, says it right on the can.
Just can’t run it forever.
I don’t remember the max amount of time it can stay in before dropping the drain plug.

If that doesn’t work, then try the methods already mentioned.

I would try all sound suggestions before tearing down the engine.

The proof will be when you run it under load. If your oil pressure is higher and it will sustain a load longer than before, that’s progress. I would load it to just below the previous max and see what it does.

handyjay03 said:

Got to run it today. Definitely has blow-by. Not as much as some people have posted about on here. Not shooting oil out of the fill hole, and doesn't pop the dipstick out when running, but definitely positive pressure in the bottom end. I can feel each cylinder's compression compression stroke. It's still holding right at 20psi oil pressure.

Since I've put about 6.5hrs on it, would you suspect a full engine rebuild is needed, or just some engine restore and a couple of hours of hard running?

Haven't even begun to look in the manual for engine rebuild instructions and part numbers, so no idea the time I'd have to put into it. Only ever fully rebuilt small gas engines that can be done easily in a day.

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How are you measuring the backpressure? Are you using a manometer, of judging it simply by feel?
The 803 and by far worse, the 802 can be deceiving if you just go by feel with the oil fill cap off because of the crank and pistons pulsing up and down.

To test compression I made a steel tube the shape and size of an injector that bolts right in place of an injector. It has an o-ring on the face to seal to the bottom of the injector hole and the center is threaded with a 1/4" NPT to accept any compression gage.

I have also seen the old school automotive compression testers with a rubber tip that you just push against the hole, but the gages usually won't go up to the needed 350+ PSI and I'm not sure you could old back 350 psi by hand.