RegisterSearchFAQMemberlistUsergroupsLog in
Reply to topic Page 1 of 1
ZZ4 Valve adjustment procedure?
Author Message
Reply with quote
Post ZZ4 Valve adjustment procedure? 
Hi all
Just found your forum!
I bought a ZZ4 for my '73 Corvette and am having a problem getting the valves adjusted. I adjusted them the way I always do.

Basically I spin the engine to TDC Compression stroke on #1. Adjust exhaust for 1,3,4,8 and intake of 1,2,5,7
Rotate one full turn (TDC Compression #6): adjust exhaust 2,5,6,7 and intake of 3,4,6,8

This has always worked until today. For some reason I believe that when I have the cylinder at TDC, the lifter to be adjusted is NOT on the very bottom of the lobe (fully closed) because after the adjustment (I tried 1/2 turn from zero lash the first time and then a whole turn the second time I adjusted them) because they are even noisier/looser then before I touched them.

Is it possible that the steel roller cam in the ZZ4 is somehow configured differently than other camshafts?
Thanks in advance for any help.

View user's profile Send private message
Reply with quote
Post  
Howdy,
It has been my experience that steel roller cams adjust differently. They need to be on the very base of the lobe and the best way to ensure that is to do each cylinder at TDC between the compression and power stroke. Do both the Intake and Exhaust for each one. You'll be rotating the crank eight increments, following firing order, two full rotations in total.

A half-turn past zero-lash is correct and has worked well for me with 1.6:1 rockers. 1.5:1 ratio rocker will take even more - 3/4 turn.

View user's profile Send private message
Reply with quote
Post  
James B. wrote:
Howdy,
It has been my experience that steel roller cams adjust differently.


Thanks for the reply James.

Is there it physical difference in a roller camshaft that doesn't allow for the procedure I listed in my original post to be used?
Thanks.

View user's profile Send private message
Reply with quote
Post  
There isn't any difference in firing order or base circle, but I think roller cams have a more aggressive ramp angle. When I first did rockers on this I used the tradiaitonal method. I got frustrated and have done it this way ever since.

View user's profile Send private message
Reply with quote
Post  
Yes, they do. The rollers allow the valves to snap open and close instantly, as opposed to non-rollers which allow the lifters to slide on the cam. If the profile is too steep then the lifters will drag on the edges instead of the flats, gouge the cam and wear out in a hurry, and may even destroy the valvetrain. The instant open/close of the rollers also allows a longer full open duration with less overall duration, meaning a smooth idle with the airflow of a lopey standard cam.

Comp does offer some offset firing orders, like 18736542, which is supposed to yield a smoother idle and about 10HP more than the standard 18436572 order, with no other changes.

View user's profile Send private message Send e-mail
Display posts from previous:
Reply to topic Page 1 of 1
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum