Compression test.. Bad news!

[traben]

I have a 91 glasstream with a 3.0 mercruser... Did a compression test today... Reading cylinder one below 90 psi dry no real change wet.. 2nd cyl 150 dry little change above 150 wet... 3rd cyl below 90 same wet.. 4th cyl below 90 dry no change wet...Does this sound like a valve problem or possible rings or both... I think maybe valves or hoping and praying just valves.... Any suggestions?

 

[TilliamWe]

Re: Compression test.. Bad news!

Well, if you did the test right, and there was no change between wet and dry, that sounds like valves to me. A leakdown test is in order, I think.

 

[Don S]

Re: Compression test.. Bad news!

How long had the engine been sitting when you did the test?

 

[traben]

Re: Compression test.. Bad news!

put cyl 1 in up position applied air thru and had air coming thru some of the other cylinders where the spark plugs go... Think maybe blown head gasket... gonna take head to be checked for cracks and for bad valves... hopefully this is all that is wrong

 

[traben]

Re: Compression test.. Bad news!

we took the boat out about 2 weeks ago for a test run boat ran pretty good except wot rpms were low to my ears since tach doesnt work just didnt sound like it was getting enough spin at prop thought it was the prop pitch size but found it to be 17p so reading up on here seems like i should be running at the top of the engines wot rpms worried me till i read some more on here about what would cause this.. so i got a tester and went from there .. but to answer your question i ran the motor with muffs about a week ago ..... so by reading more i should have run the engine till it warmed up right but anyways it shouldnt be getting air between cylinders... my guess i hope is a blown head gasket or cracked head

 

[Don S]

Re: Compression test.. Bad news!

put cyl 1 in up position applied air thru and had air coming thru some of the other cylinders where the spark plugs go...

When you do that test, similar to a leakdown test, you MUST have it on TDC on compression/firing stroke (both valves closed) if you are 1 revolution off, you will have both valves slightly open. And it sounds like you do.

 

[traben]

Re: Compression test.. Bad news!

would it hurt to run the engine on the water with low compression?

 

[Bondo]

Re: Compression test.. Bad news!

would it hurt to run the engine on the water with low compression?

Ayuh,... It'll just have No power...

 

[jerryjerry05]

Re: Compression test.. Bad news!

Marvel Mystry Oil in the cylinders for a few day and then remove the oil and start it. Then do a compression test.No change.Then remove the head and see what the problem is.J

 

[nrmi76]

Re: Compression test.. Bad news!

i have a 1969 evinrude 115 hp i just checked the compression i got 110 psi on all 4 cylinders. i was told the compression should be at 120 psi, but if it reads within 15 psi of 120 psi it ia ok is this a true statement?

 

[traben]

Re: Compression test.. Bad news!

my serial number on the engine i have is 0D500626 anybody have any links for service manual on this engine... thanks in advance.. i ordered a manual on amazon but got the wrong year its 1964-1989 do i need the one that goes to 1991 or will this one do, it looks really similar?

 

[traben]

Re: Compression test.. Bad news!

ok fellas did a no-no and posted a new question about the same engine.. sorry...

 

[traben]

Re: Compression test.. Bad news!

ive took the intake/ exhaust manifold off as well as throttle and shift assembly on rocker cover... took rocker cover off and pulled the pushrods out and labeled them ...the head bolts are pretty stubborn so what would be the best method of breaking these loose without breaking them in two ... found a machine shop here in town that will check the head for cracks and so forth...will keep yall posted.. are there any telltale things i need to look for on the pistons and cylinders to tell that i need rings?

 

[ebrich2]

Re: Compression test.. Bad news!

spray the bolts with pb blaster and use a hammer drill with a socket to loosen, just a thought

 

[traben]

Re: Compression test.. Bad news!

Got head off.. Head gasket looks good block looks true no dips or cracks as i can see... checked head looks good not warped using straight edge some of the valves look burnt and not seating..taking the head to be check for cracks and see if valves need work....

 

[achris]

Re: Compression test.. Bad news!

If the rings are ok, get a can of Power Tune (Merc product) and shoot a load of that around the cylinder walls and let it soak into the ring lands. It may free up a stuck ring...

 

[traben]

Re: Compression test.. Bad news!

Can you get the quick silver thread sealer for the head bolts at an auto parts store or will any brand of thread sealer work?

 

[Bondo]

Re: Compression test.. Bad news!

Can you get the quick silver thread sealer for the head bolts at an auto parts store or will any brand of thread sealer work?

Ayuh,... Plain ole plumbers pipedope will work, just Fine...

 

[traben]

Re: Compression test.. Bad news!

Thats just plain ole pipe thread sealer you brush on, or is it like thread tape, bond-o ? Im just getting ready for my head when i get it back from the machine shop...no word yet as to if there was anything wrong with the valves or if the head was cracked or not.... to my eyes it looked as tho the valves were nor seated all the way and some looked burnt.... Im hoping nothing was wrong on the bottom like rings... all looked good to me.. but im not an accomplished machanic either...so hope im in luck ... thanks

 

[traben]

Re: Compression test.. Bad news!

Got head back and nothing wrong with it..so im looking at maybe bad or stuck rings...