240 EFI Mercury Has No Compression on 5 and 6 - Pics Attached - Next Steps?

[ctc1111]

I posted this in the premium members section, but cannot get a response. Figure I'll try here.

I had the engine on my sea-doo die when going down the river a year or so ago. I went over the basics, fuel, filters, plugs, etc... Upon doing a compression check I found that 5 and 6 have almost no compression.

Its been a big avoid the situation and let the boat sit type of thing, but its time for the boat to go and me to fix it and move on. So I pulled the heads today to see what was going on. I found that 5 and 6 are broken on the top end of the pistons. The are both almost at the end of they're stroke, so I cannot see the entire cylinder wall yet. Attached are pictures of the two.

What could have caused this? Also, what should my next move be? I'm trying to determine if it is worth pulling the engine and doing a rebuild, and if I do that, what should I do to fix this issue/prevent it from happening in the future?

Thanks in advance for any help, I really appreciate it!

 

[ctc1111]

An update since I posted this earlier today... I pulled the flywheel cover and rotated the engine. Doing this showed me that there is slight build up on the cylinder walls, and some very minor scratching that I cannot really see, but can very lightly feel. Its not enough to make me overly concerned, and given the condition of the pistons, it not as bad as I would have expected.

Attached is a photo of the worst of the two pistons...

 

[Dr Honda]

I'm seeing a light lean run, and a bunch of hours on a 2 stroke.

If you just need it to run again... I would bore #'s 5&6 for the next size piston, and change the 2 bottom crank seals. Then, while it's apart... just look for anything else that needs changed.


Is there any scaring in the other Cyl's? Also... what year is the engine? If it's a 2001-1/2 and earlier... It could be lack of oil. The oil drive gears are known to give out.

 

[ctc1111]

There is no other scaring in the other cylinders, from everything I can see during the whole cycle everything is perfect besides 5 and 6. The boat and engine is a 2001, I'm really not sure if its a half year or not.. Even on the inside of each head, there is no difference in the appearance of the spark plugs, carbon build up, or anything else between the good cylinders and bad ones.

I've read quite a bit on here about the oil gear.. Do you think that low oil could be a cause, even though its only 2 cylinders and not all 6? Also, I've been really wondering if there is any significance to the fact that its the bottom two cylinders that are bad, 5 and 6. Are they last to recieve oil, or first to recieve water due to gravity? Really just thinking out loud here... I just want to make sure I determine and fix the cause, instead of just the damage, as I would not want to sell it to someone and have the same thing happen again..

If the cylinders measure out ok, will I still need to bore to the next size?

I'm just going to get the boat in good running condition, then sell it as I want to move on to a different type of boat anyways. I'll be pulling the engine this weekend most likely.

Thanks again for your help! Very appreciated.

 

[Dr Honda]

Just as an FYI... the engines seem to be one year older than the actual boat year. That's partly because the engine was made by someone else (prior to the construction of the boat)... and seadoo will generally sell a "2001" boat in 2000. My 2002 Islandia has a 2001 engine. The 2001-1/2 year engines got rid of that mechanical oil pump system (with the internal plastic gear) and went to an electric pump. Right now... the electric pumps seem to be better... but then again... they are still a couple years newer. So they may start to fail soon too. (but that's a debate for later)


The oil'ing of the cyl's is all together. Basically, the pump puts oil into the vapor separator... and then it goes out the the injectors. BUT.. the reason the 2 bottoms could give up first is because they are directly influenced by a lower crank seal. If it burns out (and they do eventually) you can have an air leak, and then they run lean. (and melt the crowns) It can happen to the top 2 also... but there is an inner crank sealing ring to protect it.

The cause will become more apparent when you get it apart.

Make sure you down-load the Merc manual. It will answer a lot of Q's. BUT... I just finished a full resurrection of a blown (rod sticking out of the block) Merc 240... so I should be able to cover your Q's here.

 

[Mayerichm]

Make sure you down-load the Merc manual. It will answer a lot of Q's. BUT... I just finished a full resurrection of a blown (rod sticking out of the block) Merc 240... so I should be able to cover your Q's here.

I'm proud to belong to a forum where people are so willing to help. Kudos sir!