Engine compression tests

[jacobmorin]

What is a good reslut for a compression test? I am not fimiluar with how the results are tabulated; numeric grading, alphabetic grading, pass or fail? I am getting ready to bring my engine down to my local mechanic to be tunned up and I want to have this test done, however I want to have something to compare the results too.

Also, is there another test that can be done on an engine to tell the owner if the engine is worth putting money into or being put to bed?

Thanks for any help you can provide.

 

[duff]

Re: Engine compression tests

as a rule of thumb you want 100+ on all cyl. but you do not want more than 5-10% differance on any cyl.

example

my 1979 80 hp merc has 4 cyl
#1 140
#2 145
#3 145
#4 140

if # 1 was 120 there is a big differance and something is not right.

there is also a leak down test they can do ( i might be off on the name of that test) they say that is the better test to get a real picture of the inside of the motor.

hope this helps

duff

 

[Silvertip]

Re: Engine compression tests

If you have a two stroke with a fair amount of run time on it, you would probably get a more accurate compression test if you decarbed the engine before having the test done. Carbon build up can result lower compression on one or more cylinders giving the impression something is wrong. Clearing the carb from stuck rings often brings the compression back into the normal range.