I just bought a 2004 Supra Launch in March. A few weeks ago the engine started to run rough and it sounded like it was running uneven, if that makes sense. I took it to a shop and they said that two of the eight pistons are running at 4 and 5 pounds of pressure instead of 170. Anybody have any idea what the problem could be?

Rings are shot or potentially a blown head gasket. Time for a top end rebuild. Essentially resurfacing the heads, replacing the head gasket and putting new rings on the pistons. Not cheap. <BR> <BR>Pre-mature piston ring wear is usually caused by poor maintenance. Although there are a lot of people on this site that know more than I do about this issue.

I would bet you have a blown head gasket. Are the two cylinders with low compression side by side? If thats the case (and i bet money that it is). <BR>You will need to pull the intake and then the head. Not that big of a deal. Just a pain.

The engine only has 92 hours on it and I know for a fact that the previous owner took immaculate care of the boat/engine with regular tune-ups etc. Plus, I had it surveyed before I bought it and the surveyor said it was in pristine condition. It had been running just fine this whole summer and then this. I am seriously at a loss...

Yes, they actually are side by side

Like Big E has stated, chances are it is a blown head gasket. This is certainly less than needing a rebuild but still not cheap. Take it to a traditional auto mechanic, my experience has been that they are a little less expensive then boat dealerships and there is nothing much different about the engine.

Are you going to try to tackle this yourself? It could be done on a Saturday. Head gaskets normally run around $50 bucks i would guess.

No, I probably won't tackle it myself. I don't know enough about engines to even go there. Plus, I want it done right. Any guess as to how much this could be?

Maybe find a guy in the neighborhood who works on engines and pay him to help you.

That actually might be a good idea. I really want to have it fixed before Labor Day weekend and that's probably my best hope. We'll see, thanks for the tip though!

If you plan on tackling it yourself, even with an experienced persons help, get the shop manual. Seems to me you need to find the cause to prevent a second blown gasket. Did the warning horn ever come on, telling you that it overheated?

It could be a burnt valve as well. That happened to my boat, and they just replaced the valve. It wasn't cheap, but nothing a mechanic does to a boat is. <BR> <BR>(Message edited by psudy on August 29, 2007)

No, nothing came on that the boat was overheating.