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1987 5.7 350 Crusader compression test

J

junior4597

Contributing Member
New to this so I am hoping to utilze this as a continued resource

I am looking at a 1987 boat with twin inboard Crusader engines with approx 650 hours. During the compression test we had anti-freeze in one of the cylinders #8 - turned out to be a blown head gasket. This has since been repaired so now I would like the compression test run once again before the sea trial. The original test produced these results:

Cylinder #1 170/170, #2 180/180, #3 160/170, #4 170/160, #5 170/170, #6 165/185, #7 170/170, #8 185/170 these are starboard/port readings

I am wondering if A) these are good numbers on the original test and B) what would good or relatively good numbers be after the gasket has been repaired and the second test. I have been unable to find any usefull info so I am hoping ot get an idea in this forum.

Any help or thoughts would be greatly appreciated. Oh, and would there be any other "typical" tests that shold be run on the engines other than the compression test that I should be aware of and run?

Thanks!
 
The cylinder pressure readings will be a result of engine build (i.e., which pistons/combustion chamber volume) and condition of the valves, etc.
Those numbers sound like fairly good numbers.
However, the general consensus is.... no more than 10% differential between the lowest and highest reading per engine.

Safe to assume that these were cold/dry readings???? No oil added to each cylinder????

Let your sea trial influence your decision also.
And don't fall the ole "lighten the boat up for the sea trial" thingy.
Do the sea trial with the boat loaded as you would intend to load it.
 
Hi Rick - thanks for the response. Yes, these were the "dry tests" no oil. Should I really do the "wet" test as well? I know that cylinder #8 was high at 185 due to the gasket blowout. So if I use the high number in that engine of 185 and the low of 160 I get a differntial greater than 10% - I get 13.5% - if my math skills serve me right! I believe those numbers will change on #8 now that the gasket has been repaired so the jury is still out on that. But, on the port engine I get similar numbers of high at 185 and low of 160 - again about 13.5% - should I be concerned here? I will try to bring friends with me for the sea trial to give her a full load - good point! Any other thoughts on tests for the engine or is it really just a compression test and see how she runs out of the hole in full throttle and under load?

Again - thanks!
 
GM redefined acceptable compression test results a while ago...If you search this forum, I'm sure you can find the pdf I uploaded a while ago.

The 185 number is a little higher than normal. A leakdown test will give you a more detailed assessment of the engines' health. You may want to consider an engine survey as well as a hull survey, especially if you aren't handy with tools and repairs. I'd also pressure test the cooling systems and ask to see the maintenance records.
 
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