pushrod adjustment

[66 buick guy]

Hi everyone I have'nt been on the site for a while, been busy with work now that summers almost here its time to get the GS out. I have a 66 skylark gs w/Nh 600 poston cam & the rockers seem to be tapping more than usuall when I start it. My question is what should the clearance be between the rockers and the valves when I adjust my pushrods? any replys helpful.

thanks 66 buick guy

[Dr. Frankenbuick]

You should have between .020" to .080" preload on the lifters. I would stay on the lower end of that if you have adjustable pushrods or rockers. You may just have some dirt in the lifters if it goes away after running it.

[66 buick guy]

How do I figure out the 20'' to 80'' preload on the lifters with myself just being a backyard mechanic. Im assuming you meen some pressure on the lifters all the time, but I cant think of any way to measure that.

[Dr. Frankenbuick]

Well, the best way to do this would be to use an adjustable pushrod on the base circle of the cam with the rocker arm in place. Then adjust it back until the plunger in the lifter is just at the top of the lifter (0 lash), but the pushrod is not loose in the rocker (almost loose, but not loose). Then measure the length of the adjustable pushrod against the pushrod that was originally from that lifter. The difference is the amount of preload on the lifter. You would then go on to the rest of the lifters and repeat the process. Keep track of the 0 lash #s for all of the lifters. Order pushrods that are about .030 longer then the longest (largest) 0 lash pushrod length. This way you will have the minimum preload on the longest distance and a little more on the shorter distances. Keep your current pushrods if the preload range is within the specifications in my first post.

Again, I think this is a case of dirt in your lifters. You may want to take them out, disassemble and clean them. Be sure to put the lifters and pushrods back in the same place they came from. The cam lobes, lifters and pushrods wear in as a unit.

[66 buick guy]

Thanks dr. Frankenbuick that will help me out.

[telriv]

Or you could just buy a set of my Adjuatable Roller Tip Rocker Arms. Besides being adjustable they will increase your performance.

Tom T.

[66 buick guy]

Well i started my pushrod adjustment project sunday and i might have a problem not sure though. Most of the lifters are stiff When they are off the cam lobes but on a couple of them I can twist the rocker and depress the lifter almost a quarter inch, the pushrods seem to be adjusted equal though is this normal or do I have a problem? Any replys will be helpfull

Thanks, 66 Buick Guy

[Dr. Frankenbuick]

Those lifters may have been on top of the lobe when you stoped the engine. They can drain down in that position. It sounds normal. The problem is when the lifters will not pump up or drain down too fast when running. Dirt, once again, can be a major contributor to these conditions.

[66 buick guy]

Actually I have the valley pan and intake removed because the pushrods are in upside down and I'm changing the intake, but getting back to the lifters I checked each one of them when they were off the cam lobes and most of them were very stiff but their was a few I could depress by hand almost a quarter inch by pushing down on the rocker. I'm wondering if some of my lifters are bad or could some have more oil inside of them than others?

Thanks, 66 buick guy

[Jim Carmichael]

Some have more oil in them than others. When I worked for Buick many years ago I found most lifter noise came from the rockers wearing out the shafts. For some reason the steel shaft would wear faster than the aluminum rockers. As I recall that was on the 340 350 400 430 & 455 engins but I think the nailhead may be the same. You have to push the rocker over to the side to see the worn area and I think you can still buy the plastic guides.