i have a 1977 150 mercury inline 6 out board .i did a compresion check on it, all the cyclinders have around 125psi except for the #3 it only has 5psi. Is this a ring or pistion problem and if so can i repair the #3 cyclinder only or should i rebulid all the cyclinders .can i test to see what the problem is with out tearing down the whole powerhead .this all started after runing out of gas it ran great untill then then started loosing major power
My merc 200 had one bad cylinder. and it turned out to be a broken ring. If there is damage to the cyl. it will need to be bored out and fixed, the ring will need to be fixed and hopefully nothing else past that. You will need to tear it open and look for damage. You can fix just the one bad cylinder only.
Hi JohnYour #3 hole is probably toast. Here's a long shot. Get a jug of Yamaha's ring free. Soak that cylender over night. Then see if that brings up the compression. Once in a while you get lucky.
I have a Merc 140 1978, actually new ring and pistons are not a big deal of $$ if you just replace them. It's not very difficult neither, you'll just need somebody to re-insert crank+pistons into cylinders, since they are 6 inline, and it's a pain to squeeze rings and line up pistons to reassemble. Everything else is farely easy. I already did 3 of my motors this way, and never had problems. These motors are farely simple and good workhorses. Don't take a chance, just rebuild it, unless you want to do more damage to motor, it'll take a weekend, and probably $ 100 of parts.Val
thanks for all the info sounds like i will be tearing down the motor to see what the problem is are there any little tricks i need to know to make my live easyer .
mercury low compresion
Your #3 hole is probably toast. Here's a long shot. Get a jug of Yamaha's ring free. Soak that cylender over night. Then see if that brings up the compression. Once in a while you get lucky.
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