Sea Doo Utopia w/low compression on 2 cylinders

[Clarkk843]

Hello, I am new to the forum. I have a Sea Doo Utopia with a Mercury 240 EFI (OE410651) when I first bought the boat in December it did about 55mph. A few weeks later it went down to 40mph, so I replaced the fuel pump and lines along with new filters. Boat ran better, but still wouldn't go over 40 mph. Then one day while driving the boat shut off. After I restarted it with wot, the boat would only do about 10mph. Also burns gas like crazy. So I did a compression test. 4 pistons are at 120psi and 2 pistons (both bottom ones) are at 30psi. Also all 6 coils are sparking. Is there a reason why only the bottom ones are at 30? Could the Reed valves cause the compression to be so low? Please help and thanks!

 

[Dr Honda]

The engine is roasted. 120 PSI is low for the 240 EFI engine. When the rings start loosing their seal... and the compression starts to drop... a lot of heat, and combustion blow-by gets past. In turn, it over heats the piston skirts, and displaces the very thin oil layer that protects them. At that point... the pistons melt.

Since the flywheel is at the top of the engine... the bottom 2 cyls can get more timing since the crank can twist a little at full power. SO... they will have a tendency of giving up before the others. (They run hotter)


If there wasn't any bad noises with the loss of power... then you are in luck. It's a simple "Meltdown". Take the engine apart... bore or hone the bad cyl's... install new pistons and bearings... and put it back together.

 

[Clarkk843]

The engine is roasted. 120 PSI is low for the 240 EFI engine. When the rings start loosing their seal... and the compression starts to drop... a lot of heat, and combustion blow-by gets past. In turn, it over heats the piston skirts, and displaces the very thin oil layer that protects them. At that point... the pistons melt.

Since the flywheel is at the top of the engine... the bottom 2 cyls can get more timing since the crank can twist a little at full power. SO... they will have a tendency of giving up before the others. (They run hotter)


If there wasn't any bad noises with the loss of power... then you are in luck. It's a simple "Meltdown". Take the engine apart... bore or hone the bad cyl's... install new pistons and bearings... and put it back together.

Ok so my best bet i's to pull and bore out the engine. I found a rebuild kit on eBay for about $900. Also I see alot of stuff about a oil pump gear, do I have this and if I do what is the part number? I never rebuilt a boat engine so I hope it's not too complicated..

 

[Dr Honda]

It's a big 2 stoke, so it's a simple engine... but there's a lot of stuff bolted to it to make it run.

The kits on ebay are fine. Most of them are rebadged WSM kits. Just get it from a person with good feed back. That way, if there is an issue... they are more likely to take care of it. Also... DO NOT order a kit until you have the engine apart. That way, you can get the right pistons. I'll assume you aren't the original owner... so you don't know if it's been bored before or not.

Yes... you have a plastic gear. (replace it during the build) The new version is stronger than the old one... (p/n 14513A09) but the old one wasn't as bad as people made it seem. Basically... it was the fuse, and it would be the part that would fail. So... when people would have a melted engine, and they would see that gear messed up... they assumed it was the cause. (It generally wasn't) There was almost always some other issue. The most common issue was an overheating issue. When the engine would over heat... the drive gear would bind. In turn... it could strip that gear. But the engine was going to fail anyway, because everything else was getting hot.

 

[RogerS]

I just rebuilt my engine small rotax 787
Plan to work on it for @ 3-4 weeks is a lot timming consuming task. But is fun!