low compression in cylinder #1

S

salmonkiller

Recruit
Joined
Mar 13, 2009
Messages
2
looking at a boat to purchase and the info I get is " THE CLOSED COOLED MERC 488 ENGINE ALLOWS FOR SALTWATER USE WITH NO NEED TO FLUSH OUT THE SALTWATER. EXTREMELY FUEL EFFICIENT AND QUIET THIS IS A GREAT BOAT FOR A DAY WALLEYE OR PERCH FISHING OUT ON THE LAKE. OUR TECHS TOOK THIS BOAT INTO THE SHOP AND IT STARTED RIGHT UP WITH NO PRIMING OR ANY OTHER TYPE OF ASSITANCE NEEDED. THE BOAT IDLES GREAT AND APPREARS TO BE IN GREAT RUNNING CONDITION. A COMPRESSION TEST WAS DONE AND SHOWED THE #1 CYLINDER WAS A LITTLE LOW (90, other cylinders around 150), BUT AGAIN THE ENGINE STARTED RIGHT UP AND RAN GREAT"
Is this something I should be real concerned with?
 
Silvertip

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: low compression in cylinder #1

Considering the cylinder is more than "a little low" (actually it's about 60% of what it should be) yes, it is something to be concerned about. Next step is a leakdown test. If the shop has a bore scope they might take a peak through the spark plug hole to see if there is anything that might point to the problem. Leakdown tests can determine "where" the problem lies. Compression merely indicates the cylinder is not up to snuff. Leakdown can tell you whether it is valve related or ring related, or both. That engine may "sound" ok but that cylinder is making far less power than the others so this issue needs to be investigated further. A valve issue generally only gets worse and dropping one into a cylinder makes a horrible sound and will destroy the engine if you happen to be at wide open throttle and only slightly less damage if anything less than WOT.
 
Bondo

Bondo

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Apr 17, 2002
Messages
71,487
Re: low compression in cylinder #1

MERC 488 ENGINE
Click to expand...

Ayuh,... You do Not want that boat....

The 470s are a Troublesome motor with Many known Issues....

Many of it's parts are NLA....
 
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