Mercury 75 hp compression difference

[ultra353]

I'm looking at buying a boat that has '91 Mercury 75 hp on it , it's just a bit out of the 10% rule on compression . Top and middle 120 lbs, bottom 105lbs, walk away or see if some engine tuner brings it up. I'll see if I can look into the cyl for any scoring

 

[robert graham]

Run some heavy Ringfree through the motor and re-check it.....the readings can vary between tests/testers....so multiple checks might be good....

 

[Faztbullet]

Walkaway as way over 10%.....jmo

 

[ultra353]

Thanks for the feedback. Because of the engine issues what do you think is a acceptable amout off the price, $500-$1000 or more for motor repairs. The boat is a 17.5 deep and wide aluminum fish and ski style.Hull is super clean not a scratch or ding on it Same for trailer, interior just needs to be cleaned as it's been sitting in a building for awhile. There asking $2500 , or just keep looking as it will just be a bigger problem

 

[robert graham]

If you like the rig and the price then go back and double/triple check your compression readings....to be sure you're not passing up a good rig....

 

[boobie]

Food for thought. BRP says no more than 15 psi between cylinders. You're right on the line. Check it with a different gauge. They do vary.

 

[racerone]

That lower compression should be a concern !!!

 

[boobie]

How's it run and idle ??

 

[ultra353]

Seems to idle and start good, gonna get another gauge and try it along with looking into the cylinder with my bore light to see if I can see any scoring or piston damage. I'll offer $1500 -1800 if the cylinder is toast and if they say "no" then I'll walk away.

 

[boobie]

After you check it out and it seems okay, do a GOOD decarb on it.

 

[ultra353]

Update: I went and did a compression ck with my gauge, did it twice to make sure.
These are cold readings, no oil as it sat.
Top 124
Middle 123
Bottom120, so it was the same each time I checked it, I think the guy doing it before didn't spin the motor enough times to get a peak reading . If I only hit the starter to spin it maybe 3 or 4 crank revolutions I got the low results as givin to me.plus he told me he wasn't positive that the gauge was screwed in tight because of the clamshell cover design. Thanks for everyone's advice!