Threaded Mode | Linear Mode

dbl overdrive · 09-11-2016, **(Subject: Overhead )**

No lash in jakes while doing a overhead, what are my options? Cm 871.
Looks like they were hitting the inside of the head.

Signature620 · 09-11-2016, **(Subject: Overhead )**

Reset the running clearance.

Hammerhead · 09-11-2016, **(Subject: Overhead )**

What do you mean by "no lash"?
The rockers do not have the detent position...
Or
From the detent position to the exhaust valve there is no or less than 0.020 after correct adjustment?

The correct valve pin to jake rocker lever clearance is 0.276" or 7mm.

Can you post a pic...I don't seem to follow, the rocker should not contact the head anywhere. It should only have three points of contact, the mounting on the rocker shaft, roller to cam, rocker to valve pin.

Rawze · 09-11-2016, **(Subject: Overhead )**

(09-11-2016 )dbl overdrive Wrote: No lash in jakes while doing a overhead, what are my options? Cm 871.
Looks like they were hitting the inside of the head.

It sounds to me like you are doing something VERY VERY WRONG!

STOP AND SEEK A PROFESSIONAL before you do some serious damage!

dbl overdrive · 09-11-2016, **(Subject: Overhead )**

No or less than.20 after proper adjustment.
When I checked it with a dial indicator, pushing down there is 0 on 2 of the jakes.
I'll post a pic in a bit.

Signature620 · 09-11-2016, **(Subject: Overhead )**

Do they have a lot of travel between detent position and the cam lobe? Sounds like you need to loosen the rocker shafts and rotate them to bring the jake running clearance back into the correct range. I can post the procedure if you don't have access to Quickserve.

Rawze · 09-11-2016, **(Subject: Overhead )**

(09-11-2016 )dbl overdrive Wrote: No or less than.20 after proper adjustment.
When I checked it with a dial indicator, pushing down there is 0 on 2 of the jakes.
I'll post a pic in a bit.

and...

(09-11-2016 )Signature620 Wrote: Do they have a lot of travel between detent position and the cam lobe? Sounds like you need to loosen the rocker shafts and rotate them to bring the jake running clearance back into the correct range. I can post the procedure if you don't have access to Quickserve.

You cannot do this on an ISX 871! -- The valve rocker shafts have flats in them to prevent this kind of adjustment. I would not recommend this, as you would have to leave the bolt loose/under-torqued where the flat is, creating an oil leak at the joint and reducing oil pressure into the rockers.

However .... It is NOT a bad idea to ensure the rocker shafts are in fact seated properly, and aligned with the flats correctly. THIS, you can certainly check/re-set correctly, but NOT purposefully twist it out of alignment with the flats!.

Cummins is FULL OF shi#t ON THAT PROCEDURE!!! -- It only serves to mask other problems like the pistons protruding too far downward from the rocker assembly, broken set screws, flattened bearings, etc. and/or a very worn out head!.

If you are doing everything right, Correct crank position, correct clearance, adjustment, etc... and the engine brake piston (inside the rocker itself) is NOT extended down or damaged,... and you have less than about 0.028" movement in the engine brake rocker after it is set properly between the detent position and the point of contact to the valve,... then your head is done! -- TOAST!. The exhaust valves are riding too high in their seats. -- It is time to replace the head before a valve snaps off and takes the rest of the engine with it. -- Adjusting the rocker shafts back is NOT a good solution at all, and masks the real problem no matter how you look at it!

To me,.. IT STILL SOUNDS LIKE you are doing something wrong, or something is assembled wrong,.. or you are having problems with the engine brake rockers themselves (pistons down, or broken/stretched set screws). It will NOT be that bad to have zero clearance (or even 0.020 for that matter) unless it is a VERY POORLY DONE RE-MAN HEAD, or there is a serious problem with the exhaust valve height!>

Trying to cover it up by rotating the shaft will only compound your problems, and/or destroy something.

dbl overdrive · 09-11-2016, **(Subject: Overhead )**

This is what I thought but I wanted to be sure, I ran the overhead and never seen this befor.
I had to back 2 others off to get the detent but I have 2 that I can't get any out of.
They are not hitting the wall on the side of the head but are very close.
Can I just back then off enough so he can get it to his engine guy ?

Rawze · 09-11-2016, **(Subject: Overhead )**

(09-11-2016 )dbl overdrive Wrote: This is what I thought but I wanted to be sure, I ran the overhead and never seen this befor.
I had to back 2 others off to get the detent but I have 2 that I can't get any out of.
They are not hitting the wall on the side of the head but are very close.
Can I just back then off enough so he can get it to his engine guy ?

Have you checked the bottom of the rocker to see if the piston is sticking down too far? Sometimes this is what the actual problem is.

If you back off the rocker set point so that you have at least 0.025" movement between the rocker detent position and the top of the valve, driving it will not cause any damage, but i would NOT use the engine brake,.. or drive it very far until your problems are resolved.