Valve lash. Need help.
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Instructor
Joined: Sep 2015
Posts: 143
Likes: 25
Valve lash. Need help.
92 lt1. Installed head gasket drivers side. Turned rocker nuts down till they stopped spinning. Rotated harmonic balancer till arrow was at 12 o'clock. Number one cylinder both lifters down , rockers up , both valves closed. Number 3 , intake open, exhaust closed, number 5, exhaust open, intake closed, number 7 intake closed , exhaust open. I think this is what I'm looking for but, The book says back off rocker nut and take out valve lash and then one full turn on center of plunger . I'm good with that, however there's a lot of play in the pushrods right now. So tighten when the valves down ? which means very tight when open. Sorry for the novel. All I have to go by is from before, and the rockers where loose when closed and tight when open. That's how it was to begin with.
Race Director
Joined: May 2006
Posts: 10,691
Likes: 71
From: Phoenix Arizona
There are lots of methods, probably the easiest for a new guy is, rotate the engine to each cylinder so one of the valves is all the way open, make sure the other valve is loose, and then tighten the valve lash to zero clearance and then go 3/4 turn more (tighter). repeat through all the cylinders.
Last edited by zr1fred; Feb 27, 2016 at 08:11 PM.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Adjusting valves on the 1985 Corvette or a L98 engine notes on LT1 in red:
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. The LT1 has a triangle on the balancer...turn the balance until the triangle is at the 12 o'clock position and you have compression in cylinder #1. 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. LT1 position the triangle at the 12 o'clock position 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!
The traditional method is to twist (rotate) the pushrod between your thumb and forefinger while very slowly tightening the lock nut. When there is resistance in rotating the rod, you have reached zero lash.
Make sure the nut is loose on the rocker before you start to adjust the valves.
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. The LT1 has a triangle on the balancer...turn the balance until the triangle is at the 12 o'clock position and you have compression in cylinder #1. 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. LT1 position the triangle at the 12 o'clock position 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!
The traditional method is to twist (rotate) the pushrod between your thumb and forefinger while very slowly tightening the lock nut. When there is resistance in rotating the rod, you have reached zero lash.
Make sure the nut is loose on the rocker before you start to adjust the valves.
Melting Slicks
Joined: Jan 2009
Posts: 3,482
Likes: 196
From: folsom california
no, no, no. if by "till they stopped spinning" you mean the pushrods, that's way too tight ; slowly tighten the adjusting nuts only until you feel the first SLIGHTEST resistance to spinning freely, they're still gonna turn , that indicates zero lash; adjust from there.
Last edited by mtwoolford; Feb 27, 2016 at 10:01 PM.
