Once again..
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
Once again..
This has been discussed on this forum many times so forgive me for asking the question again. I understand both the twisty and engine running methods to adjust the valves. What I don’t have a good understanding is how far past zero lash do you tighten the rocker arm nut? There seems to be recommendations from ¼ turn to 1 full turn. I’m running a stock 78 L-82 with ~60K miles on it. I prefer to use the engine running method when adjusting and am currently running at ½ past zero and things seem fine. I tried it at a ¼ turn and it causes the engine to run like crap. So, for the folks that use the engine running method to set preload on stock GM lifters, how far past zero lash do you go?
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Whatever the manufacturer recommends. Most aftermarket cam companies recommend 1/2 turn - but check your install instructions.
Generally, the hardest thing in preload is correctly finding zero lash. For someone new to doing this the "twist" method where the pushrod is twisted while the rocker is tightened works best...the minute you feel ANY drag on the pushrod, that's zero lash.
There's some pushback on using this method...but it works very well.
Generally, the hardest thing in preload is correctly finding zero lash. For someone new to doing this the "twist" method where the pushrod is twisted while the rocker is tightened works best...the minute you feel ANY drag on the pushrod, that's zero lash.
There's some pushback on using this method...but it works very well.
Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
This isn't a new install. It's the original cam and lifters as far as I know. Does that make a difference?
Here's the method I'm using to adjust them except the guy in the video does 3/4 turn. http://www.youtube.com/watch?v=HSR36fmBR6M
Here's the method I'm using to adjust them except the guy in the video does 3/4 turn. http://www.youtube.com/watch?v=HSR36fmBR6M
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
GM says 1 full turn down after 0.They want you right in the middle of the lifer travel and they dont want the engine to over rev.
The lifter depth is about .140 so they want you down .070. One full turn of the rocker nut with stock rockers moves the pushrod down .070.
There is plenty of room.If you happen to go down 1 1/4 turns it wont kill it.
For customer cars that dont get driven hard I go 3/4 turn because if Im off slightly when finding 0 I wont get a ticking lifter.If the customer is going to run the dog out of the car I usually go 1/2 turn.
Going 1/2 turn is great as long as you correctly find 0---if you dont and you are a little loose and the inner cup keeps coming up and banging on the retaining clip you can pop the clip out the top of the lifter.
The lifter depth is about .140 so they want you down .070. One full turn of the rocker nut with stock rockers moves the pushrod down .070.
There is plenty of room.If you happen to go down 1 1/4 turns it wont kill it.
For customer cars that dont get driven hard I go 3/4 turn because if Im off slightly when finding 0 I wont get a ticking lifter.If the customer is going to run the dog out of the car I usually go 1/2 turn.
Going 1/2 turn is great as long as you correctly find 0---if you dont and you are a little loose and the inner cup keeps coming up and banging on the retaining clip you can pop the clip out the top of the lifter.
Melting Slicks
Joined: Sep 2004
Posts: 2,412
Likes: 3
If your lifters are shot, you might need more than 1/2 a turn to jury rig it.
Had this problem recently on my friends Mustang. His 42 year old lifters were in bad shape. They can't pump up enough to hold adequate pressure. We put 1/2 a turn on them, didn't work, went up to a full turn, let the motor run to pump them up for about 15 mins. Runs fine now. He still needs new lifters but it's ok for now.
After you have a similar adjustment on all of them, you don't need to get them all back on the base circle to add more pretension. Just go over them all with another 1/2 a turn and fire it up.
Had this problem recently on my friends Mustang. His 42 year old lifters were in bad shape. They can't pump up enough to hold adequate pressure. We put 1/2 a turn on them, didn't work, went up to a full turn, let the motor run to pump them up for about 15 mins. Runs fine now. He still needs new lifters but it's ok for now.
After you have a similar adjustment on all of them, you don't need to get them all back on the base circle to add more pretension. Just go over them all with another 1/2 a turn and fire it up.
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Thread Starter
Instructor
Joined: Jan 2007
Posts: 233
Likes: 41
From: Simpsonville SC
I think thats what I'm dealing with, worn lifters. I still have some valve noise on initial start. I will give it another 1/4 turn to get me at 3/4 and see if that helps. Thanks for the feedback!