Valve adjustment on 89 L98
12-31-2015, 12:51 PM
#1
Burning Brakes
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Valve adjustment on 89 L98
OK, So I had done a full top end rebuild about 3 years ago and added 1.6 roller rockers, I adjusted at that time and honestly don't remember the specs I used. But I did it using a feeling guage and then tighten like 1/2 or 3/4 just don't remember.
Several weeks back the engine start to clatter and I suspected a big problem but found that one intake rocker had just backed off the nut and things were loose. Nothing broken and the push rod was still perfectly true.
So I'm now going back and installing and doing the adjustment. I'm using the technique now like this:
So when I do this for the valve that had backed off I notice that I can still move the rocker left-right with a light to medium amount of pressure. I'm just not that experienced with these adjustments to know if that movement is normal? Or am I still too loose?
I took a video to show this movement
In the video the intake is the one on the left that I just adjusted and the exhaust to the right was still tight from 3 years ago but it still has that movement. I know the engine is cold but not sure if this is a good adjustment or not.
While rotating the engine i did notice on other cylinders I could also move them left-right? Overall after the rebuild I was not terribly happy with the performance and I now wonder if the valves are not adjusted well. I'm leaning towards them being to loose, which would translate to extra noise and reduced lift I believe.
Just want to do it right this time before I close it up!
Thanks for any help you can pass along.
Several weeks back the engine start to clatter and I suspected a big problem but found that one intake rocker had just backed off the nut and things were loose. Nothing broken and the push rod was still perfectly true.
So I'm now going back and installing and doing the adjustment. I'm using the technique now like this:
- Working on a full cold engine
- Rotate engine until intake is goes down, then another 90 to get onto base of cam
- Then spin and jiggle push rod and tighten until it stops, then add 1/2 turn preload
- Then tighten allen lock nut inside holding outer nut in position.
So when I do this for the valve that had backed off I notice that I can still move the rocker left-right with a light to medium amount of pressure. I'm just not that experienced with these adjustments to know if that movement is normal? Or am I still too loose?
I took a video to show this movement
In the video the intake is the one on the left that I just adjusted and the exhaust to the right was still tight from 3 years ago but it still has that movement. I know the engine is cold but not sure if this is a good adjustment or not.
While rotating the engine i did notice on other cylinders I could also move them left-right? Overall after the rebuild I was not terribly happy with the performance and I now wonder if the valves are not adjusted well. I'm leaning towards them being to loose, which would translate to extra noise and reduced lift I believe.
Just want to do it right this time before I close it up!
Thanks for any help you can pass along.
12-31-2015, 01:56 PM
#2
Le Mans Master
I have a issue with your #2 direction....turning another 90 degrees. Below is the standard method used my GM for years. You line up the timing mark and adjust half and then turn 360 and adjust the other half. No guess work for "another 90 degrees".
Adjusting valves on the 1985 Corvette or a L98 engine:
1) Remove the spark plugs. This makes it much easier to turn the engine by hand.
2) I believe that the nut in the center of the bottom pulley on the balancer is 5/8”. Use a six point 5/8” socket to turn the engine over by hand to line up the timing marks. Place a finger in the spark plug hole for plug #1 as you turn the engine over. You are trying to determine if the engine is on compression as you line up the marks. If you feel the air pushing against your finger as you line up the marks, you have compression in cylinder #1. Align the timing marks. I have found that the slot on the balancer is often hard to see if the engine is running and you have a timing light attached trying to set the timing. This is the time to clean the groove in the balancer and use something like paper white out or a little white paint in the groove. Makes the timing job much easier.
3) Loosen all the lock nuts in the center of the rocker arm 4-5 turns.
The exhaust valves in the SBC Head are right next to each other for the 2nd and 3rd cylinders back. So if you were to start at the front of the engine the layout of the valves would be: ext, int int, ext ext, int int, ext
4) Now adjust the valves as follows:
Intake #1, 2, 5 and 7 then adjust Exhaust 1, 3, 4 and 8.
Note: If you are not sure which valve is the intake and which is the exhaust, look down at the exhaust manifold. The exhaust valve will be right above the exhaust pipe for the cylinder you are looking at.
5) Turn the engine 360 degrees (one full turn) and line up the timing marks again. Now adjust the following:
Intake 3, 4, 6 and 8 then adjust Exhaust 2, 5, 6 and 7.
You are now finished with your adjustment. I usually tighten the lock nut 3/4 turn after adjusting to zero lash.
If you are adjusting roller rockers with a locking Allan nut inside the nut, turn the adjusting nut about 1/2 of a turn and then tighten your Allan screw. Now turn the nut and the Allan screw at the same time the additional 1/4 turn. This will lock them tight.
Once you have adjusted the valves, it is likely that one or two that you have adjusted have loosed up a little and you will find a little slop between the rocker arm and the pushrod. DO NOT re-adjust. What has happened is that the lifter has bled down a little. If you re-adjust at this point, once the engine is running and the lifter has pumped up to full again, the valve will be too tight and be partially open as the engine runs. The engine will run rough…so don’t do it!
Here is a write up from Forum member JoeC on adjusting the valves using a feeler gauge. I have found that it works great and there is no confusion about reaching zero lash.
BTW, I tried something a little unconventional on adjusting hydraulic lifters. One thing that always bothered me is the statement "spin the pushrod until resistance is felt" that seems a little too subjective to me. So I tried this: I set "zero" lash with a .0015" feeler gauge while slowly turning the adjusting nut. {place the feeler gauge between the top of the valve stem and the rocker arm and pull on the gauge slowly as you tighten the nut.} When I felt the feeler gauge grab, I was fairly confident I was about .001 from zero lash. At that point, I turned the adjusting nut 3/4 turn. I recently read that one turn is equivalent to .040" because of the thread pitch on the threaded rocker arm stud, so 3/4 turn should give you about .030" adjustment. I also read that within a hydraulic lifter there is .060 total plunger movement, and ideally you want to be just about in the middle of that range, or .030 inch. I don't know if I’m out in left field on what I did, but I feel I got a really consistent valve adjustment across the board. if you think you might have a tight cylinder, maybe give this a try - it seemed to work for me...
again, thanks for all your help - take care -
JoeC
Adjusting valves on the 1985 Corvette or a L98 engine:
1) Remove the spark plugs. This makes it much easier to turn the engine by hand.
2) I believe that the nut in the center of the bottom pulley on the balancer is 5/8”. Use a six point 5/8” socket to turn the engine over by hand to line up the timing marks. Place a finger in the spark plug hole for plug #1 as you turn the engine over. You are trying to determine if the engine is on compression as you line up the marks. If you feel the air pushing against your finger as you line up the marks, you have compression in cylinder #1. Align the timing marks. I have found that the slot on the balancer is often hard to see if the engine is running and you have a timing light attached trying to set the timing. This is the time to clean the groove in the balancer and use something like paper white out or a little white paint in the groove. Makes the timing job much easier.
3) Loosen all the lock nuts in the center of the rocker arm 4-5 turns.
The exhaust valves in the SBC Head are right next to each other for the 2nd and 3rd cylinders back. So if you were to start at the front of the engine the layout of the valves would be: ext, int int, ext ext, int int, ext
4) Now adjust the valves as follows:
Intake #1, 2, 5 and 7 then adjust Exhaust 1, 3, 4 and 8.
Note: If you are not sure which valve is the intake and which is the exhaust, look down at the exhaust manifold. The exhaust valve will be right above the exhaust pipe for the cylinder you are looking at.
5) Turn the engine 360 degrees (one full turn) and line up the timing marks again. Now adjust the following:
Intake 3, 4, 6 and 8 then adjust Exhaust 2, 5, 6 and 7.
You are now finished with your adjustment. I usually tighten the lock nut 3/4 turn after adjusting to zero lash.
If you are adjusting roller rockers with a locking Allan nut inside the nut, turn the adjusting nut about 1/2 of a turn and then tighten your Allan screw. Now turn the nut and the Allan screw at the same time the additional 1/4 turn. This will lock them tight.
Once you have adjusted the valves, it is likely that one or two that you have adjusted have loosed up a little and you will find a little slop between the rocker arm and the pushrod. DO NOT re-adjust. What has happened is that the lifter has bled down a little. If you re-adjust at this point, once the engine is running and the lifter has pumped up to full again, the valve will be too tight and be partially open as the engine runs. The engine will run rough…so don’t do it!
Here is a write up from Forum member JoeC on adjusting the valves using a feeler gauge. I have found that it works great and there is no confusion about reaching zero lash.
BTW, I tried something a little unconventional on adjusting hydraulic lifters. One thing that always bothered me is the statement "spin the pushrod until resistance is felt" that seems a little too subjective to me. So I tried this: I set "zero" lash with a .0015" feeler gauge while slowly turning the adjusting nut. {place the feeler gauge between the top of the valve stem and the rocker arm and pull on the gauge slowly as you tighten the nut.} When I felt the feeler gauge grab, I was fairly confident I was about .001 from zero lash. At that point, I turned the adjusting nut 3/4 turn. I recently read that one turn is equivalent to .040" because of the thread pitch on the threaded rocker arm stud, so 3/4 turn should give you about .030" adjustment. I also read that within a hydraulic lifter there is .060 total plunger movement, and ideally you want to be just about in the middle of that range, or .030 inch. I don't know if I’m out in left field on what I did, but I feel I got a really consistent valve adjustment across the board. if you think you might have a tight cylinder, maybe give this a try - it seemed to work for me...
again, thanks for all your help - take care -
JoeC
12-31-2015, 05:34 PM
#3
Burning Brakes
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Well, I went ahead witht he process on just that valve that was the problem and then I checked a few more on that bank and made a slight adjustment to 2 others.
I buttoned it up and all is running fine, might even feel a bit smoother and with a little better power based on a short drive.
So, I'm going to guess that that sideways amount of movement on a cold motor with the lifters mostly all drained is probably OK. But sure would like to hear from some others that they have noticed this as well.
I buttoned it up and all is running fine, might even feel a bit smoother and with a little better power based on a short drive.
So, I'm going to guess that that sideways amount of movement on a cold motor with the lifters mostly all drained is probably OK. But sure would like to hear from some others that they have noticed this as well.