Compression test readings
#1
VIP Member
VIP Member
Thread Starter
Compression test readings
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
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
Last edited by 35fountain; 11-03-2015 at 05:39 AM.
#2
Registered
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.
#4
Banned
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
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
#8
Registered
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? ?
#9
Registered
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