Cracked pistons

[Michael Buchanan]

1. I just pulled the head off one of my ’97 6bta 370 hp engines w/1350 hours due to a coolant leak at the right front of the motor. I have had no overheat issues but I haven’t had the boat that long, and it still ran up to rated 3000 RPM with no smoke. I found two cracked pistons in cylinders 1&6. I have attached the worse of the two below, which was in #6 hole, furthest away from the leak. Does anyone have any idea what could cause this? I showed it to the machine shop surfacing the head and he says he’s never seen one crack this way, and I have two. I’m worried about what’s going on in the other engine. It was no small feat pulling this head and I don’t want to do it again but also don’t want a piston coming apart 60 miles offshore. Thank you.

Topic

[JimmyK]

Amazing that the engine was still able to make rated RPM w/no ill signs.  I would bet the coolant leak is a separate problem.  Take a look at the head gasket.  Typically these engines first leak from coolant passage to outside, not to the combustion chamber, near #1 cylinder.

[Author]

Replies