Merc 240efi rebuild - spec clarification required

[busterthejetboater]

Hi All. My Merc 240efi Sport Jet would not start. Traced to low compression on #6 cylinder. At strip down I found #6 piston crown missing a piece and the barrel scored.

Decided to rebuild the complete engine. I have had the block bored out to 0.015" O/S on all cylinders. I am using the WSM pistons with coating and thin rings. The Merc service manual does not give a piston to cylinder clearance but if I subtract my coated piston size from bore diam then my smallest cl is 0.0068" and the largest is 0.0071". Any idea on this?

The Merc service manual indicates that ring end gaps must be in the range of 0.010" to 0.018". The gaps I am getting 0.021" to 0.022". Will this cause excessive blow by and low cyl pressure readings?????

Any feedback will be highly appreciated.

Thanks

 

[Dr Honda]

Standard piston clearance on the 240 engine is 0.007". BUT... it depends on where you measure it. The factory pistons are slightly oval'd. SO... your measurements are in the spec.

AND.....

Actually, the ring spec is 0.018" to 0.025". So... you are fine there.

Post up some pics of the build. It gets slow in the winter time, and it may help spark conversation.

 

[busterthejetboater]

Thanks Doc. Really appreciated. I purchased all my parts in the good old USA and am very happy with the service that I received from my chosen supplier.

I have also purchased all the required parts to service/overhaul things like the VST and fuel pumps. My motor is one of the latest that has the electrically controlled oil pump and it has tested good and I will not be replacing it. Based on info from this forum, I will also be replacing temp senders. I will post pics as I go along.

Included with my engine parts purchase, I got a service kit (including bearings) for the jet pump. I still have to remove and inspect this to verify my impeller and wear ring condition.

 

[Dr Honda]

I see you are new to the board, so I thought I would link my old rebuild thread. Can't believe it's coming up on 4 years with it now.

I was always anti-Merc in the Seadoo's... but the wife thought an Islandia would fit us. So I drove 10 hr's to get this one, with a blown engine.

Enjoy

http://www.seadooforum.com/showthre...ndia-Project-(Engine-rebuild-and-other-stuff)