Compression test - feedback

Not a big fan of doing just a top end rebuild... plenty more boats out there......sorry
 
Just got the oil analysis results and metals reads quite low across the board. The port engine has 2.5% fuel, however the lab indicated that its normal operation as fuel was present in both engines. The genset results were excellent. Compression test result were from the port engine. Thoughts?
 
Unless the engines were rebuilt since your first post a week ago, your compression numbers suck.
Now if you want to get serious about why your numbers are so low....do a leakdown test.
 
Boater71 said:
Looking for some guidance, did a compression test and results were: two at 100, one at 115, and three at 120. The others are 140 and 135. I'm looking to buy this boat and this is my initial test - will do another compression test after the sea trial in a couple of weeks. Engine is Mercruiser horizons 6.2 with 224 hours - 2008. This was out of the water test. The port engine broke the sparkplug so we could not so the compression test at this time. Oil samples being tested. Looking for guidance on this.

I figured they needed to between 140 and 150.
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Guess I was thinking after sea trial numbers.
 
I agree with scoflaw.... Those number's ain't great if you can do a leak down test go for it.... Otherwise i would start with a Top end and while ur there do manifolds and rises...
 
Thanks for the great feedback. I received all the maintenance records, the boat (SR310 2008 powered by 6.2l - SC & Axius) was maintained and repaired by the shop (looks like with open check book). The shop is going to do the prep, detail and necessary repairs, do the sea trial, WOT and then perform the compression test again.

Sounds reasonable? What else should I be asking for?
 
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Like it has been suggested before a leak down test is a true indicator of where a problem is compression test is just a snapshot of overall health you are at the low-end of normal for a motor that’s not that old ,this are my compression numbers of my port motor last year upon inspection of the cylinder heads the exhausts ports were no looking to good so I replaced the motor keep in mind my motors were 20 years old with better numbers than what you’re looking at
 
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Had a motor couple of boats ago, that had
#2 175
#4 150
#6 150
#8 175
#1 180
#3 150
#5 150
#7 175

Boat ran alright, I thought, pulled engine out to do a rotten oil pan. Had the exhaust manifold off and did a leakdown, and could see into the ports that the exhaust valves were leaking. Pulled the heads and discovered both heads had a crack between the center exhaust valves, from a previous overheat that was recorded with the dealer that had been doing the PO's work.

A healthy vortec headed engine should be 175 +. They are thin castings and it doesn't take much to crack them
 
Not a mechanic. Was told consistency is more important than the numbers as one may have a gauge out of calibration. One is 140 the rest around 100+. I would assume 140 was last tested and oil may have filled voids in cylinder. I once had twin 3.8 V 6s on a 28 footer. Some how one spark plug tip got bent in and shorted. We were at the north end of Vancouver Island and the person beside be at the dock was a Class A Drag racer with his mechanic. His comment was it was probably a brass screw form the carburetor that went through the engine. Took out plug bent tip back engine did not sound correct. He asked if I wanted to take the carbon out of the engine. Yes. He told me to hold RPM at 1500 while he poured a quart of water over 10 minutes into the engine. He said the water turned to stream and would loosen the carbon in the rings and valves. It worked. More power. I had done a compression test a year before and readings were 95 to 120. I did one again and they were 145 to 160. Was it a good idea? After he did it he said you can blow an engine doing that if it is not in good condition. He said they use the water trick for the last run of the day if the engine does not seem good.
 
northern said:
Not a mechanic. Was told consistency is more important than the numbers as one may have a gauge out of calibration. One is 140 the rest around 100+. I would assume 140 was last tested and oil may have filled voids in cylinder. I once had twin 3.8 V 6s on a 28 footer. Some how one spark plug tip got bent in and shorted. We were at the north end of Vancouver Island and the person beside be at the dock was a Class A Drag racer with his mechanic. His comment was it was probably a brass screw form the carburetor that went through the engine. Took out plug bent tip back engine did not sound correct. He asked if I wanted to take the carbon out of the engine. Yes. He told me to hold RPM at 1500 while he poured a quart of water over 10 minutes into the engine. He said the water turned to stream and would loosen the carbon in the rings and valves. It worked. More power. I had done a compression test a year before and readings were 95 to 120. I did one again and they were 145 to 160. Was it a good idea? After he did it he said you can blow an engine doing that if it is not in good condition. He said they use the water trick for the last run of the day if the engine does not seem good.
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thanks for sharing, that sounds very interesting, how did you pour into the engine?
 
I'm trying to educate myself by reading and watching youtube about leak down test. The low compression number indicate an air leak and by doing a leak down test the mechanics are trying to identify where the leaks are. There could be a number of reasons why and where. since the shop said they will do what it take to address this, i will defiantly suggest or ask if they have done a leak down test, what followup questions should I be asking?
 
The 3.8 V6 were carb engines. No idea how one would do it on a non carb engine and what effect it would have.
 
Boater71 said:
I'm trying to educate myself by reading and watching youtube about leak down test. The low compression number indicate an air leak and by doing a leak down test the mechanics are trying to identify where the leaks are. There could be a number of reasons why and where. since the shop said they will do what it take to address this, i will defiantly suggest or ask if they have done a leak down test, what followup questions should I be asking?
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They don't have to do all 16 cylinders, do your worst ones, and it will tell the story. I would want to be there so they don't BS there way out of it.
 
Boater71 said:
Just got the oil analysis results and metals reads quite low across the board. The port engine has 2.5% fuel, however the lab indicated that its normal operation as fuel was present in both engines. The genset results were excellent. Compression test result were from the port engine. Thoughts?
Click to expand...
 
Make sure whom ever is performing the compression test takes the boat out for a drive first and puts some good heat into the motor specifically the exhaust. I have seen several times some mechanics just warm the engines in the slip for 7-12mins; then poor readings result. Why because boat motors, unlike cars, have exhaust systems that use an intake water system to keep cool and when not heated properly it tends to impact the compression readings of the cylinders accross the engine. I always test in the following manner:
1.) Heat motors with a good cruise
2.) Test in order 1-8
3.) Heat motors again with a good cruise
4.) Test again but in reverse order 8-1
5.) Compare testing results and retest any cylinders which have a number that is 12-20% below your highest number.
Two other important factors when testing:
(1)make sure the oil in the engine is clean (testing after a oil change is ideal)
(2) Testing at WOT
 
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