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Merc 225 3.0 Piston replacement

T

terk

New member
Hey Merc experts, I have a 3.0 225 EFI (1998). I have slightly low (75) compression on one hole. It had an oiling problem that has been resolved.Power is great, but will smoke and start missing a little at idle. Is it possible to rering or change a piston without pulling the powerhead. I have access to all the measuring tools and a fixed hone. I am a Diesel Mechanic by trade and just can't stomach paying 5-6K for a powerhead if I can repair it myself. Any advice would be appreciated.
 
What are the other holes compression? Really what matters most is how even the cylinders are, generally speaking 75 lbs is real low but compression gauges are often not very accurate.

If you can rebuild a diesel these are easy but I've never heard of a reasonable way to fix a scored cylinder or replace a piston without pulling the powerhead off.

Jon
 
Thanks Leaky, the rest of them run around 110. If I had to do them all I would pull it. Just asking if there might be an easier way for one hole.
 
You may have carbon build-up in the ring grooves- start with a good de-carbonizing treatment and see if the numbers improve. I would suggest Techron, by Chevron, or Yamaha Ring Free +. Both have a high percentage of PEA, the only decent carbon remover.
 
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