Gas in the Crankcase? Rotax 657x

[Tysonk]

Hello,

I had a piston fail in a motor I just rebuilt. I should have bored the cylinder and did'nt. Won't make that mistake again.

However, I pulled the motor. When pulling off the flywheels I tipped the motor on its side (carbs removed) and fuel poured out of the exaust ports. After removing the jugs I found there was fuel in the crankcase.

I am very familiar with these carbs and motors. The only decent theory I can come up with is that the fuel pump diaphram may have ripped, and the pulse line from the crank sucked in fuel. Or possibly the needle and seat stuck open. But if that was the case I would not have been able to run the motor before it failed. One other unlikely theory is that after cranking the failed motor over ALLOT trying to start it again, fuel from the carb'd air fuel mixture built up in the crank. I would guess-timate that there was about a 1/2 cup of fuel that ran out when the motor was tipped.

Any ideas or experience with this one before I start to rip the carbs apart?

Thanks,
T

 

[Bills86e]

Rrrrrrippp'm down. 'Couse ya new that!:cheers:

 

[captain scale]

Probably the needles and seats or insufficient pop off pressure. Did you ever leave the fuel valve open for a prolonged period. Cranking it without it starting several times may have caused it too.

 

[Tysonk]

Is it possible to flood the crank by turning motor over?

Well.. Broke down the engine in prep for rebuild. When taking the rotary valve cover off fuel came out once seal was broken.

I opened the fuel pump to take a look. I don't have a local place to get a rebuild kit. I would have the order it and the summer is dwindling. So I didnt want to go too deep. The fuel pump diaphrams look fine. The clear disk check valves look fine. I cleaned the fuel filter while I was in there. I rebuilt these carbs last season and have not put many hours on after due to blowing the engine the first time.

In total there was about 1/2 cup of fuel in the rotary valve and crank. Is it possible, that much fuel can build up in the engine from cranking it over many times without ignition? I killed my battery tring to start the engine before I put the compression test on it.

I guess I am unsure how much fuel can build in the crank when turning it over withough ignition. I have heard of "flooding the engine" but this is more fuel than I pictured.

Thoughts?