Hawk73ku

1996 LT1: Something is bothering me about the valve rocker arm/ push rod adjustment in the manual. Basically it says take out lash and then 360 after setting correct firing position. I would expect the number of threads exposed would roughly be the same. Most of them are and have about 6 threads exposed except #8 cylinder which doesn't expose any at all.

Off the top my head I don't remember if it was exhaust or intake but the one furthest back and closest to firewall.

This is my first ever head replacement and am naturally worried about screwing up. No threads exposed after adjustment really bothers me. Could I have something wrong to cause this?

PatternDayTrader

That doesn't sound right to me. Verify that the piston is at TDC on the compression stroke and try again.

Paul Workman

All things being equal (e.g., valve stem length, rocker stud length and depth, etc.) They should all be pretty uniform. You are right to be skeptical.

It is important the geometry relationship of all the valve train components be within spec. Things can get "interesting" if the angles are not right. As long as that geometry is OK, the number of threads showing above the individual rocker adjustment nut is not in and of itself an issue, but I'd want to know why before moving on!

What would cause the anomaly could be valve stem length variance, the depth of the valve seat if reground a bit deep, the length of the rocker stud, a dissimilar rocker nut or half moon pivot bearing, etc, etc.

If the geometry checks out, you'd want to verify the piston is truly at TDC on the compression stroke before setting the valve. Was it?

Q: Are these new heads, or re-worked heads?? Were the valve seats and valves re-ground, I wonder?

Tom400CFI

Are you sure the push rod is seated in the lifter cup?

I agree that all should have about the same number of threads exposed.

PatternDayTrader

:I agree with everything posted in the quote above.

Hawk73ku

Q: Are these new heads, or re-worked heads?? Were the valve seats and valves re-ground, I wonder?[/QUOTE]

They are reworked by local machine shop. I just mounted.
Yes the valves were ground and reseated.

Is rod seated in lifter cup? Hmmm. I hope so but can get back to TDC and take it out and reset it. That would certainly throw things off. The nut is just flush with top of bolt whereas others have about a 1/4" or more thread showing. All but that one are pretty uniform.

Thanks for the feedback. I'll let you know what I discover.

Paul Workman

Then I'd be getting the machine shop involved, first off.

With the rockers removed, some measuring would be in order; 1/4" height variance!? (Yikes!) Yeah, if the pushrod is not seated in the lifter cup, i.e., riding on the edge (?) that would cause the pushrod to be up too far...and too the rocker would be tipped and/or riding high compared to the others.

I'd be very curious to see how things measure up with the rockers removed. And, just for "peace of mind", are all of the pushrods the same length?? (might as well eliminate the easy stuff, is my thought there...)

Some good news... You can be glad it isn't an LT5, cuz if there were a problem with the valve stem length or the seat, for example, the head would have to come off...after you pulled the engine first! (Ask me how I know...)

Like I said, the shop that did the work should be very interested in what you're experiencing. It may be something simple as a new rocker stud that is too short...or the like. But, they should have all the tooling to take precise measurements and make proper adjustments as needed where there is a problem.

Hawk73ku

After finding true TDC and placing in #1 firing position I stepped through it again and same result. So I took off both rockers on #8 and measured the studs. They were same length. Compared push rods and they were same length. Did adjustment again and same result. When I moved to #6 firing position the #8 exhaust that this thread is about was extremely sloppy. Much more so than any other rocker in it's sloppiest point.

Repeated adjustment and added an additional turn. I now have a few threads showing.

Would someone confirm valve order in the head please. I adjusted as the order Exhaust (E) Intake (I) from 1 to 7 is 1:E:I 3:I:E 5:E:I 7:I:E

I couldn't find a picture of it in the shop manual.

Assuming I have the valve order right and the adjustment right, is it possible the lifter isn't fully seating on the CAM or something weird? I'm a rookie so I'm grasping at straws.

PatternDayTrader

Screw all that for now.
Here's what I think you should do because this is what I would do.
Put a breaker bar on the crank bolt and turn the engine over until you see the intake valve close. Once the intake valve closes you know that the piston is coming up on the compression stroke. Now turn it over maybe another 120 degrees (it doesn't have to be exact) or so to be certain the lifters are on the cam heel. Now set the lash for both valves on that cylinder and live happily ever after.

PS - With hydraulic lifters be sure to read the instructions on the amount of preload required. Nine times out of ten it will be something like zero lash plus 360 degrees. This means turn the pushrod gently with your fingers as your tightening the rocker nut. Once you feel slight resistance go another full turn (360 degrees) and lock it down, your done, move to the next, but be sure to read the manufacturers instructions because some of them are different.

PSS - The intake valve is the valve directly inline with the intake port. Not surprisingly, the exhaust valve is directly inline with the exhaust port.

PSSS - Any other questions just ask. Someone will be helpful, but don't come back whining about how its to hard to use a breaker bar on the crank bolt and that you want to just hit the key but you cant see the valves when your turning the ignition. Pull the spark plugs if you have to.

Ziggy*

Are these new lifters? did you soak them in oil before install? Had my share of rebuilt/ new ready to install lifters????? ziggy

ghoastrider1

I was kinda thinking along the same line.. collapsed lifter? I hope haven't bottomed out the lifter . The hot thing for the hotrodders back in theday was to turn the adjustment 1/2 more turn after contact was made, not the full turn.BUT, that was with flat tappet cams, not the rollers.

Hawk73ku

Resolved! Yeah!

The resolution was going to a different procedure. I went back to the machine shop as was suggested and described the problem. He asked me how I made the adjustment and I told him I used the Corvette shop manual where it adjusts all valves at TDC in firing positions 1 & 6. Take out lash of specified valve and turn additional 360.

He told me it probably wouldn't run like that and gave me a procedure which he says will work on any engine using hydraulic lifters.

Rotate engine until the exhaust lifter of the desired cylinder begins to move. Take out lash of INTAKE valve plus 1/2 turn. Then rotate engine until intake rises to highest point and then begins to fall and adjust exhaust just before intake reaches bottom. Take out lash plus 1/2 turn.

It's certainly a lot longer procedure but seems to be far more accurate. I found several valves that I adjusted under the Chevy procedure that had considerable lash at it's adjustment point and others that were to tight.

ken4

I used the 1 tdc and 6 tdc method and then checked that method with another method when setting zero lash. They were both the same so I then went with the full 1 turn.