OMC valve adjustment

[JonF76]

I have an OMC Cobra 3.0 (GM) I just put a head gasket on. I read some of the other threads about setting the valve lash, witch I understand. What I am having trouble with is how do I rotate the engine a half of a turn with it still in the boat? I have tried taking the spark plugs out to keep it from compressing. If I try to "bump" it with the starter its not accurate. There is no nut on the carankshaft pulley and if there was I would not be able to get to it because of the engine mount. Any tips or advice would be greatly appriciated. As soon as I get the valves adjusted I'll be back on the water.

 

[Coors]

Re: OMC valve adjustment

Leave the plugs out, grab the fanbelt
apply pressure, and put a socket on any accessory pulley; Alt p/s etc

 

[whywhyzed]

Re: OMC valve adjustment

......

 

[Don S]

Re: OMC valve adjustment

An alignment bar does not have splines.

 

[JonF76]

Re: OMC valve adjustment

Thanks Coors, Thats what I was looking for. Nowhere in the book does it give you the small important little nuances like that ( I have a clymer book and I dont think its any good, are there other books that might be more detailed?). Moving on, I adjusted the valves per the book , zero lash plus one turn, and it would'nt start so I backed them off a 1/4 then another 1/4 still nothing. I checked the compression and found; #1 90psi #2 110psi #3 90psi #4 110 psi. When I bought the boat three months ago I checked compression and they were all at 120psi. The reason for changing the head gasket was it would'nt start and there was water coming from the manifold gasket. I had the manifold off so I thought I would replace the head gasket also. When I took the head off, the head gasked was find but I replaced it anyway. Could there be something I am missing? Whats the best way to find zero lash? Is it when the lifter becomes just snug? do the hydrolic lifters have any thing to do with it? Is zero lash plus one turn correct for an '89 motor? I'm missing some thing here and I would hate to have to take it to the shop just for an adjustment. Thanks for your help guys.

 

[Don S]

Re: OMC valve adjustment

Back all the valves off till they are too loose to work.
Starting over, get to #1TDC on the compression stroke (That is very important) if you aren't actually on #1 everything after that will be WAY wrong.
Then (when you have it right) turn the nut down to zero lash. Do this only once cause it will change. If you do it 2, 3 or 4 times you mess everything up.
Then turn your one turn down.

 

[JonF76]

Re: OMC valve adjustment

I re-adjusted the valves again making sure cyl #1 was at tdc the #3, #4 and #2. The motor will start and run only at full throttle (at 3000 rpm) and as soon as I drop back to idle it dies. Is the valve adjustment so critical that it has to be just so to run or, might I have another issue?

 

[Don S]

Re: OMC valve adjustment

I re-adjusted the valves again making sure cyl #1 was at tdc the #3, #4 and #2.

Just by that statement, you haven't adjusted the valves properly, only by what you think it should be. Just being on TDC means nothing if it's not on compression stroke.
You need a manual, so, go to this link
http://www.boatfix.com/merc/Servmanl/13/13A3R2.PDF
Go to page 3A-12 and read the procedure.
Read my previous post about removing lash one time only.

 

[JustJason]

Re: OMC valve adjustment

sometimes it helps to do a compression test before you adjust the valves, then redo it after your done. If your compression goes considerably down then you do not have it set correctly.....
ps.... no idle is a good sign of low compression.

 

[Don S]

Re: OMC valve adjustment

What you need to be finding out is if you are up on #1 TDC on the COMPRESSION STROKE.
An easy way to find out, is pull the spark plugs out. put your compression tester hose in #1 spark plug hole, hold your thumb over the hose outlet, and bump the starter over a little at a time with a Remote Starter . When you feel pressure starting to build, continue turning the engine BY HAND in the same direction till the timing marks line up. Then you are on #1 TDC on the compression stroke. Then adjust the valves as explained in the service manual link I posted earlier.

 

[Coors]

Re: OMC valve adjustment

If it runs now, while running; back off the rocker nut until it starts clacking.
then tighten it until quiet, then turn it down for the pre-load.
One at a time. Have rags.

 

[a70eliminator]

Re: OMC valve adjustment

That works too

 

[JonF76]

Re: OMC valve adjustment

Thanks for sending me that link DonS. I have bookmarked it and will get much use out of it. My Clymer book doesn't say anything about splitting up the valves like that, it says go to tdc adjust both valves for #1, half a turn adjust #3, half a turn adjust#4, half a turn adjust #2. That being said, I tried it the way the bookmark stated, tdc on #1 compression stroke(witch I am sure of) adjust #1 E I, #2 I, #3 E, #4 I. Then one full revolution for #4 comperession and adjust the last three. Still only a quick fire up and then it dies. I didn't have much time to check compression because it started raining. Still I am thinking there may be some other issue.

 

[Don S]

Re: OMC valve adjustment

My Clymer book doesn't say

Clymers !!!! that says it all right there. You aren't reading that thing are you? They are to be used as knee pads, not tech info.

 

[JonF76]

Re: OMC valve adjustment

What is the best book? is there a Sierra book?

 

[Don S]

Re: OMC valve adjustment

OMC OEM manuals only.
Since OMC doesn't exist anymore, you can find them on ebay. I know there is a guy that does sell OMC manuals, but not sure who it is.
If Sierra sold manuals, I would bet they would be as junky as the parts.

 

[Bt Doctur]

Re: OMC valve adjustment

Try doing one cylinder at a time. 1 intake & exaust,3 intake/exaust, 4,etc,2 etc. In most cases the amount of threads showing above the rocker nut is a good indicator.Just watch the INTAKE rocker go up and then down ,when it stops moving the valve is closed, adjust both rockers and move to the next cylinder

 

[Coors]

Re: OMC valve adjustment

Clymers !!!! that says it all right there. You aren't reading that thing are you? They are to be used as knee pads, not tech info.

I already stated, a Clymer ain't even good for a kneepad- the spline glue is crap, and the pages start blowing all over the yard.
Include Seloc in that.

 

[Don S]

Re: OMC valve adjustment

Try doing one cylinder at a time. 1 intake & exaust,3 intake/exaust, 4,etc,2 etc. In most cases the amount of threads showing above the rocker nut is a good indicator.Just watch the INTAKE rocker go up and then down ,when it stops moving the valve is closed, adjust both rockers and move to the next cylinder

That would work if he actually had it on TDC of the COMPRESSION STROKE when he first started. If he was not on the compression stroke, all his valves would be adjusted improperly.

 

[Coors]

Re: OMC valve adjustment

I think it's seamanray13 on ebay.
but him or his wife ain't cheap.