1979 mercruiser 120 with a cylinder with no compression

[fizzle15]

i need help.
i've got this mercruiser 120 with a crappy boat for free - i'm into it for 500 dollars now.
at any rate - the number 2 cyclinder reads absolute zero - the other three will get 150 to 160 psi.
the head gasket had a funky spot - so i replaced it and got the head shaved down to flat at a machine shop - cylinder number 2 is still dead.
i bought new lifters - because at one point i switched them up and got 140 psi out of the cylinder - then got nothing the next day.
at first it would actully get 40 psi if i losened the rocker arm.

Now everyone is trying to tell me that the rings are gone. - i don't believe it.
i've seen the cylinder walls - they are beautiful - I know i wouldn't be able to see if they were gone but the piston seemed just as tight as the others in the cylinder.

i've also tried the put oil in the cylinder and see and check the compression - and i still don't get anything.
i've adjust the valves thousands of times -
i really don't know what it can be.

my last therory is that the cam shaft is screwed up.
does that happen? any other theories?

i just want this in the water.

 

[Bt Doctur]

Re: 1979 mercruiser 120 with a cylinder with no compression

Exactly how are you adjusting the rockers?

 

[EddiePetty]

Re: 1979 mercruiser 120 with a cylinder with no compression

..... at one point i switched them up and got 140 psi out of the cylinder.......Now everyone is trying to tell me that the rings are gone.
i've adjust the valves thousands of times -
i really don't know what it can be.

my last therory is that the cam shaft is screwed up.

....the fact that you once achieved 140 p.s.i. practically rules out completely defective rings and/or camshaft.

...as others have asked, exactly how are you adjusting valves (ya' got 'sumthin' way too tight!) ??

 

[stonyloam]

Re: 1979 mercruiser 120 with a cylinder with no compression

Doesn't seem like a cam would cause that problem. You switched lifters and got 140 once, if rings were bad, that would not have happened. Took the head to a shop, seems like they would have seen a bad valve, burnt, tuliped). What's left? A valve is sticking and is hanging open is my (not too knowledgeable ) guess. Good luck.

 

[ziggy]

Re: 1979 mercruiser 120 with a cylinder with no compression

i'm not the pro either. but maybe now would be a good time to do a cyl. leak down test. or even just injecting some air into the cyl.s like on pp2 of this link... http://www.boatfix.com/merc/Bullet/97/97_25.pdf

could lead ya in the right direction...

 

[picklenjim]

Re: 1979 mercruiser 120 with a cylinder with no compression

When you had the head resurfaced did you have them do anything else to it like disassemble and a valve job. If not you should have. Definitely sounds like it's in the head. Possibly a intermittent sticking valve not closing all the way.

 

[fizzle15]

Re: 1979 mercruiser 120 with a cylinder with no compression

I'm adjusting the rocker arms by this terrible clymer manual i've got.
but i set it to TDC and then i adjust the number 1 cyclinder. I spin the pushrod until its doesn't spin then i tighten a half turn - the book says 3/4 of a turn but i find that i get a tiny bit more compression and no more noise when i run it with the half turn.
then i do something like the intake on the no. 2 and the exhaust on the no.3 and the intake on the no. 4 - or something like that and turn the engine 180 and do the rest of the valves i didn't get before.

Yeah i can't understand how it worked randomly.
I'm so upset.
i just don't know what the secret is. - and how i can have such a finicky cylinder. - i really like the camshaft idea - but everyone thinks that camshafts don't go bad.

oh - and the machine shop said that the valves look good.
and from my own inspection - there definately was not any tuliping or any visibly cracked valve that would allow me to get absolutely no compression.

thank you for your help so far -
i just need more
thanks again

 

[howlnmad]

Re: 1979 mercruiser 120 with a cylinder with no compression

First thing you need to do is stick that Clymers manual under a short workbench leg and get a Seloc. The next thing you need to do is concentrate on the valves of that cylinder. It's not the cam or rings. It's either lifters or valves.

 

[picklenjim]

Re: 1979 mercruiser 120 with a cylinder with no compression

Camshaft would not make it happen intermittently. You need to know exactly how close the machine shop looked at it. Just looking at the valves while installed in the head don't tell the whole story. They need to be removed to check the fit in the guides.

Try adjusting it like this. With the spark plug out bring the piston up to top dead center in firing position. Both valves will be closed. Now adjust both the exhaust and intake on that cylinder. Be sure you aren't tightening it to tight prior to giving it the final 1/2 turn. Tightening it till it stops spinning may be your problem. You could be forcing the hydraulic lifter in some and not know it. Hold the push rod right below the rocker arm and wiggle it side to side or up and down as you tighten the adjustment. As soon as all the end play is out of the pushrod then give it 1/2 turn.

The spinning method is not good. You can easily start collapsing the lifter and the push rod still be spinning. Merc manual does not say anything about the spinning method. It says determine end play up and down as you tighten the adjustment. When all end play is gone give it 3/4 more turn. I would almost bet this "spinning method" is your problem. You may be actually turning it down 2-3 turns past zero lash with the spin method and not realizing it. That's why you got a little more compression at 1/2 instead of 3/4. Bottom line in the end it's adjusted to tight not allowing the valve to close all the way.

 

[Adirondack]

Re: 1979 mercruiser 120 with a cylinder with no compression

Proper valve adjustment may not be the problem. You can adjust all day, but if your adjusting to a valve already stuck open it's going to stay open.
I would remove the front four rockers, then eyeball the top of the valve stems with a straight edge to see if either of the front two look like they are hanging. After that the head probably has to come back off for closer inspection.

 

[bigdan1]

Re: 1979 mercruiser 120 with a cylinder with no compression

definetily a sticking valve .....

hard time to believe that no one looked at the guides while engine was apart !

 

[Adirondack]

Re: 1979 mercruiser 120 with a cylinder with no compression

definetily a sticking valve .....

hard time to believe that no one looked at the guides while engine was apart !

You would think so wouldn't you? The head is off already. For the amount of time it takes to pop the valves out to check it good? Time and/or money well spent.

 

[fizzle15]

Re: 1979 mercruiser 120 with a cylinder with no compression

yeah i guess i'm an idiot for not doing anything about the valves.
i was really expecting either a hole in the piston or a cracked valve.
and when there were neither i thought the hot spot in the head gasket - and the machine shop guy telling me that "this was one of the most warped heads he's ever worked on" - that i had found the problem.

I think that my next move - other than trying the up and down instead of the spin method - is going to be the air compressor trick that Ziggy suggested / pass on the link for.
- thank you Ziggy -

Then i guess i'll have to pull the head off again.

question:
if i have not run the engine with this new head gasket that i put on - will i be able to reuse it when i take the head off?
or is it no good now?

thank you for all the advice - i'll let you know how it turns out.

 

[fizzle15]

Re: 1979 mercruiser 120 with a cylinder with no compression

i did the compressor - poor mans leak down test.
put 30 pounds of pressure in the the cylinder and i could hear it coming out of both the exhaust and the intake - yikes.
so then instead of trusting that i was able to set it to TDC i took the rocker arms off - and still could hear the air coming out of the prop and the carb.
so i've got the head off
to bad none of the machine shops are open.

 

[Howard Sterndrive]

Re: 1979 mercruiser 120 with a cylinder with no compression

I set valves with a compression gauge- cranking with the starter.

Tighten until comp drops off, loosen until comp drops off. split the difference.

 

[AdellAdam]

Re: 1979 mercruiser 120 with a cylinder with no compression

I use a piece of paper between the rocker and valve and move the paper around while tightening. When the paper doesnt move anymore I go another 1/2 turn past after i take the paper out, of course.

 

[fizzle15]

Re: 1979 mercruiser 120 with a cylinder with no compression

i took out the exhaust and intake valve from the troubled cylinder.

the exhaust valve had a huge deposit around the stem.
i cleaned it off and it feels like the valve seats now.
i want to take it to a machine shop - but i dont' think i can wait until tuesday.

i think i'm going to slap it all together and see if its got any compression.

does anyone know if you can reuse headgaskets if you never fire up the engine?

 

[ziggy]

Re: 1979 mercruiser 120 with a cylinder with no compression

if you can reuse headgaskets if you never fire up the engine?

headgaskets are one time use only. as in, one torquing down. once it's been torqued in place, it's used and should not be removed and used again....

 

[fizzle15]

Re: 1979 mercruiser 120 with a cylinder with no compression

well i slapped it all back together,
retorqued the head - with the used head gasket -
and i'm sure you guessed it -
nothing -
maybe its the head gasket -
maybe its the valved -
i really don't know
i'm shocked about getting 0 psi - it seems like the valves seat.
but i think i'm going to wait till i can get to the machine shop before i buy another head gasket.
this was a felpro kit - cost me 80 bucks - i'm pissed.

I'll keep you posted -
thank you for your help