Compression Test Readings

[Raggy1071]

I am having some crazy compression test readings and I was wondering what others may think this could be. I would think just something in the heads, but reading are crazy. I was expecting low compression on 1 or two cylinders but its the other way around, only getting normal compression reading on two cylinders.

a week prior to testing Engine was started and ran on muffs (but not under any load) no smoke noticed and it actually sounded fine at idle.

Engine is a 1990 5.7 Mercruiser in a Bayliner Capri , testing was done on cold engine, it was not run before testing.

cylinder 1 150 dry good, pressure leak down test 75 psi applied 68 psi held light hiss from oil fill
cyl 2 84 dry 86 wet 75psi applied 15psi held hissing from carb
cyl 3 0 dry 0 wet 75psi applied 15psi held hissing from carb
cyl 4 100 dry 100 wet no pressure test ran out of time
cyl5 0 dry 150 wet ?? WTF 75psi applied 15psi held hissing from carb
cyl 6 95 dry 95 Wet no pressure test
cyl 7 0 dry 0 wet no pressure test
cyl 8 145 dry good

Lastly, I pulled the left valve cover and although not seen on cap, underside of cover was milky white. did not find any milky white on dipstick or oil fill cap.

 

[alldodge]

Was all the hissing with each cylinder at TDC? If not then doesn't matter

The heads have to come off to determine if the motor needs rebult of just refresh heads

 

[Raggy1071]

Was all the hissing with each cylinder at TDC? If not then doesn't matter

The heads have to come off to determine if the motor needs rebult of just refresh heads

Yes, had each cylinder at TDC. I am getting ready to pull heads now, seems that's the best way to determine at this point.

 

[alldodge]

With all being at TDC then valves are damaged, or not adjusted correctly

 

[tank1949]

I am having some crazy compression test readings and I was wondering what others may think this could be. I would think just something in the heads, but reading are crazy. I was expecting low compression on 1 or two cylinders but its the other way around, only getting normal compression reading on two cylinders.

a week prior to testing Engine was started and ran on muffs (but not under any load) no smoke noticed and it actually sounded fine at idle.

Engine is a 1990 5.7 Mercruiser in a Bayliner Capri , testing was done on cold engine, it was not run before testing.

cylinder 1 150 dry good, pressure leak down test 75 psi applied 68 psi held light hiss from oil fill
cyl 2 84 dry 86 wet 75psi applied 15psi held hissing from carb
cyl 3 0 dry 0 wet 75psi applied 15psi held hissing from carb
cyl 4 100 dry 100 wet no pressure test ran out of time
cyl5 0 dry 150 wet ?? WTF 75psi applied 15psi held hissing from carb
cyl 6 95 dry 95 Wet no pressure test
cyl 7 0 dry 0 wet no pressure test
cyl 8 145 dry good

Lastly, I pulled the left valve cover and although not seen on cap, underside of cover was milky white. did not find any milky white on dipstick or oil fill cap.

Make sure tester is not defective. One gave me false readings due to Shrader valve leaking. I almost pulled head.

 

[QBhoy]

Were the plugs wet ? Does this engine run at all ?

 

[tpenfield]

Wow . . .

I'd run just the compression test again. Never mind the cylinder leak testing at this point.

If the results hold true, you've got . . .

2 'good' cylinders
3 dead cylinders
3 marginal cylinders

Does the engine actually run?

 

[Scott Danforth]

with readings that bad, time to pull the motor

 

[QBhoy]

with readings that bad, time to pull the motor

I’m guessing the valves are stuck badly. Surely the only explanation for an absolute zero reading

 

[Scott Danforth]

I’m guessing the valves are stuck badly. Surely the only explanation for an absolute zero reading

Or holes in the pistons from running lean and detonation

 

[72fj40]

#5. 0 dry. 150 wet. Rings. Might want to recheck that one. I agree with pulling the engine. The rest points to possibly heads. The #s are all over the place, I'd rebuild or replace. If your doing just heads then your probably polishing a turd.

 

[ROY WILLIAMS]

did you test the engine compression correct ?

 

[Raggy1071]

I pulled the heads and here are the gaskets. I do not notice any missing material, but do notice some Dark areas between cylinders.

 

[stresspoint]

i posted in your thread on THT a few suggestions , guessing you found the problem gaskets are leaking between cylinders enough to create the dodgy readings. , while the heads are off check the valve seats as well , fill the ports with fuel to see if the seats leak.

 

[Raggy1071]

Thanks, I have to have 10 posts on THT before I can post pics. I will do it there tomorrow. I really am not great at reading a used blown gasket. Even though there is no material missing. I am assuming those dark spots between cylinders is where compression is leaking.

 

[stresspoint]

those head gaskets would most defiantly be leaking across cylinders , hence whey the compression numbers were all over the place .
use OEM Mercruiser gaskets , they are made specifically for use on marine engines , each gasket is sold separate 2 head , 2 intake , and 2 exhaust , it may cost a little more than a AM VRS set ,but IMO well worth the expense

 

[tank1949]

I pulled the heads and here are the gaskets. I do not notice any missing material, but do notice some Dark areas between cylinders.

leakage? Have shop do heads and slap new head gaskets on.

 

[Lou C]

Looks like one is a GM original gasket and the other looks like an aftermarket, could be Fel/Pro. Someone might have been in there before you...how do the mating surfaces of the cyl heads and block deck look?
Judging by the gaskets looks like an overheat, at least once, evidence on both gaskets.

 

[Raggy1071]

Good catch, I noticed as well, looks like someone had issue in past and just fixed the side that had trouble. I also found it is a Remanufactured short block and pistons are .060 over. It’s a 32 year old boat lot of things have been done over those years I may never know about.

 

[Raggy1071]

Another thought, the .060 bore could be causing more heat hence cylinder gasket problem