35fountain

The boat ran pretty good I was just curious what the readings would be.. Heads were done 150 hours ago.

This test was done when engines were cold. On the 2 lower readings I squirted some oil in that cylinder and retested

Starboard engine
Cyl # 8 --- 165 Cyl# 7----170
# 6 ---- 170 #5---- 170
# 4-----180 #3-----155 with oil 165
# 2-----175 #1-----165


Port engine
Cyl. # 8---160 #7----145 with oil in cyl. 150
# 6---165 #5----170
#4----165 #3----170
#2----165 #1----165
Does anyone see any problems? Much appreciated

Rambocj7

Old school ppl will say as long as they are all within 5-10 lbs of each other thats good. To me compression won't tell you much. You need to do a leakdown test. Although my guess is that one cylinder with 145 lbs has issues. I did a compression test and was 160 on most (with my gauge ). I had some at 145 lbs. The ones with 145lbs had 30% leakdown vs 10% on one's with 160. Needless to say I did full top ends.

donzi matt

iTrader: (1)

Warm em up and try again. I don't like to compression test cold motors as a general rule.

BUP

iTrader: (9)

Comp testing from a fully warmed up engine and with the throttle plate wide open.

Also OEM Mercruiser specs in a Service Bulletins to all dealers that is still the norm all about compression testing and leakdown.

http://www.boatfix.com/merc/bullet/97/97_25.PDF

35fountain

Thanks so I guess no worries here

HyFive578

iTrader: (3)

Agree with Rambo...leakdown test much more meaningful than compression test and will tell you more about condition of top end...

Full Force

iTrader: (5)

Make sure starter is n ot cranking weak or slow that will give you weak readings also...

Rambocj7

I'm sure your motors still run fine - mine did too! But a leakdown will tell you in more detail the real health of your motor. From that service bulletin by merc on compression test readings , apparently I would have been in spec with mine too which is ludicrous! Some of my valves pulled no vacuum at all when i had the head off at the machine shop yet i had 130 lbs compression. This is precisely why I would never trust a merc mechanic. How is 100 lbs on one cylinder still within spec? ?

MDGperformance

Leak down test is a better way of checking engine condition,you want to warm engine either way,i have found if you do a compression check and all cylinders are 150 but one reads 125-130 if you put the leak down tester in the weak cylinder it will show up in the leak test usually showing around 30-40% compared to 10-15% in the good cylinders,motor will still make good power but will need some work in the future