72 -115 hp Merc Compression question

[SHUMAKEB]

I just bought this motor yesterday for 900 with powertilt and trim. The man started it up and ran it put it in foward and reverse and it worked. I get home and test compression on it and it's a 6cyl the highest cylinder tested 125 and the lowest one tested 98 should i take this motor back or not?

 

[DHPMARINE]

Re: 72 -115 hp Merc Compression question

98 to 125 is a stretch,but not all that bad.Was the 98 psi reading the last cylinder?If so the battery may have been down and causing a low reading.<br />DHP

 

[SHUMAKEB]

Re: 72 -115 hp Merc Compression question

The first time i checked that cyl. the battery was going dead but it read 95. Then i re-charged the battery and then was able to do the whole test with the exception of that cyl...needless to say the last cylinder i tested the 2nd time was that cylinder and it read 98. Yeah I hope... Is 3/8 bolts big enough to mount that on the back of a 16ft Starcraft Tri-Hull?

 

[Clams Canino]

Re: 72 -115 hp Merc Compression question

IMHO any cylinder under 100 is cause for pause.<br /><br />If you keep it, run a can of Mercury Power Tune through it as directed on the can. If that brings up the readings do it again. Stuck (or sticking) rings are pretty common in those critters. The Power Tune stuff helps to free them up. (and is good preventive maintanence)<br /><br />-W

 

[SHUMAKEB]

Re: 72 -115 hp Merc Compression question

What does IMHO mean.... I have a can of Engine Tuner but its not mercury. Im gonna hook it all up and take it out then re-test the cylinders and document every-thing with a video camera, so there are not any questions.

 

[Clams Canino]

Re: 72 -115 hp Merc Compression question

IMHO = In My Humble Opinion<br /><br />FLMD = Friendly Local Merc Dealer<br /><br />POS = Jonnyrude <br /><br />-W