new omc crate motor rocker arms loose

[michaelrj9]

I just bought a 1985 27' bayliner which has a 260hp omc
from this guy and it has a new crate motor But the rocker arms are tapping.
I got it cheap because the guy could not figure out what is wrong with it.

I went to a boat repair place by me he let me look in his repair manuals but only had it for a 1990

Would the 1 turn past 0 lash be the same for the different years.

Is it possible to adjust the rocker arms while the engine running,if so would it still be 1 turn past the no tapping of the rocker arms?


Thanks

Michael

 

[KaGee]

Re: new omc crate motor rocker arms loose

Each cylinder must be Top Dead Center. Chevy lifter initial adjustment is to tighten the rocker nut just until you can no longer turn the pushrod between your thumb anf forefinger. Then add an additional 1 turn.

There are shortcuts, but some people find it hard to understand.

Once a cylinder is done, DO NOT go back to it later and check it or further adjust it.

Then of course, there's the messy way... do it with the engine running... oil everywhere!

 

[whywhyzed]

Re: new omc crate motor rocker arms loose

For static set , I'd recommend a little less than 1 turn...more like 1/2 to 3/4...
I always do it running though. I loosen till it ticks, tighten till the engine rpm stumbles (valve not closing), and split the difference. PITA on marine though, you have to pull the exh manifold to get the valve cover off with the factory OMC manifolds... but I like to watch everything in there running after I build a motor...

 

[Haut Medoc]

Re: new omc crate motor rocker arms loose

If you are referring to a GM 5.7, then the correct procedure would be to bring the engine to TDC in the #1 firing position....
Then adjusting Intake #'s 1-2-5-7 & exhaust #'s 1-3-4-8
Then turn engine one full turn to bring it to #6 firing & intake 3-4-6-8....Exhaust 2-5-6-7
I Believe "Zero lash" is achieved when there is no up & down movement of the pushrod, but it can still be turned...
Someone correct me there if I am wrong.....
With the engine running, zero lash is when the rod stops clattering from being tightened.....
Then, 1/4 turns at fifteen second or so intervals until a total of 3/4 turns is achieved......JK

 

[michaelrj9]

Re: new omc crate motor rocker arms loose

Thanks for all the help everyone....

I found out I have a bigger problem going on..

It is the Gm 5.7 engine

Last week when we picked up the boat I took one valve cover off (heard it tapping)and noticed 1 rocker arm stud came loose (it was threaded so we locktite it in ) Today I pulled off the other side (heard it tapping)and 1 stud on that side was loose also but no threads on it.(except the top to hold the rocker arm on (Don't know if it broke off inside the head) don't seem like it is broken but not sure.
Does anyone have a length they supposed to be?
This one is 2 7/16" long
Do they supposed to be pressed in or threaded in?

Why is 1 pressed in and the other one threaded?

What could be causing 2 different studs to come loose?
It supposed to be a ctate motor from some place in Flordia but I don't know if I believe the guy I bought the boat from.

But there is not a speck of sludge in the head so it apears to be rebuilt.

Thanks
Michael

 

[Reel Poor]

Re: new omc crate motor rocker arms loose

Possible incorrect valve adjustment or overreving the engine. Since you have the valve covers off, I would recommend backing all the rocker adjusting nuts off (at least to the top of the stud) and doing a cylinder leak test. There is a good possibility that there has been some valve to piston contact, that contact is most likely what has caused the studs to be pulled out, If this is what happened the chance of bent valves is highly probable. A cylinder leak test as I described will show if this type problem/damage exist. If it does exist the cylinder heads will have to be remove for further inspection.

 

[Silvertip]

Re: new omc crate motor rocker arms loose

Some vintages of small block Chevies had pressed in rocker studs. They can be replaced with screw in studs but the bosses need to be machined on top and then threaded. The tools are not (or at least they weren't) terribly expensive. Pressed in studs can be replaced and overreving or over tightening the rocker nuts can pull them loose.