OND, yeah, it was turning 4300 RPM at the time of failure. It had run 6200 earlier that day. I was running a billet connecting rod and billet flywheel.
Chris, yes, I think so. It must have been a hairline crank in the crank case, then spread to the point of failure.
BBQ, sorry it didn't entertain you. I've been working on the motor since Feburary, well documented on my YouTube channel. If this is the first video in the series you've watched, then it was probably boring to you. But for those who've followed the build all this time, I appreciate your condolences.
I just don't think a built 200cc-class motors can handle a marine environment well. water is 800 times as dense as air. There have been several failures on several built 200cc-class mud motors over on the Mud Motor Kit forums. Most guys are going to the 390s and 420s for daily drivers.
Bone stock it's fine, even stage 1 is fine. Once you cross the line by yanking the governor, even with all the billet parts, the little motors just don't hold up in a marine environment, especially when trying to get all that weight up on a plane.
I may just run it at idle speed like they do in southeast Asia.