Re: 54 Johnson RD15A top seal (still) leaks

[Don]

The engine will still develop crankcase pressure, even with the plugs removed. You could put the gearcase in a bucket of water if you are worried about the impeller. But again, you will need to plug the fuel tank pressure port for this test to be effective, I now recall that both cylinders are plumbed into the pressure port. Simply remove the pressure hose and plug it off, or you could make the tool Frank uses if you have a spare two line tank female connector.
I guess I am trying hard to keep you from splitting that crankcase, resealing it, only to have the same problem re-occur. I really don’t think there is a problem with the spaghetti crankcase seal, only because the pictures show the powerhead has never been split. It would be very hard to find a porous/cracked crankcase by inspecting it visually after disassembly as well. I am hoping that pressurizing the crankcase will help isolate the real leak/problem, seeing exactly wear the leak is occurring will help find/rule out crankcase leaks/imperfections. Mumbles wasn’t spinning his flywheel nut very fast, he might not have even been using an electric drill. You will want to have the carbon seal properly installed for this test though.
The only other issue that may be causing this situation is an engine that is running lean at idle and constantly backfiring. Every time the engine backfires/coughs, a strong crankcase pressure pulse is developed, which may overcome the sealing ability of the carbon seal/drain circuit.