Im helping a friend with his charger and we installed a new cam and lifters. Comps instructions for these particular lifters says to preload the lifters .002-.004. Which is roughly 1/16 of a turn on the adjuster which by the way is another recommendation for lifter preload. Anyways, we fired the engine and this thing had very noisey valve clatter. I decided to preload the lifters to .014 which is 1/4 turn preload and now all the lifter noise is gone and the engine runs smooth and starts perfect. Has anyone else experianced this. Is there a possibility that there is a typ-o in the instructions? I usually just set the lifter preload on all other lifters to .030 or 1/2 turn preload and have never had any issues. Just wanted someone elses view on this lifter if anyone else has used them.

They want the low preload to prevent any lifter pump up during valve float. Makes it as close to a solid lifter as you can get with a hydraulic. It's gonna be a bit noisy.

Thats what I have heard as well. Had an issue with a 351 windsor that had too much preload, was pumping the lifters and had a backfire at 5000 rpm. When testing spring pressures on the car the valves were hanging open because of the lifters pumping up and too much preload. Once the oil bled out after a few minutes the valves would slowly close?
This was with a hyd roller.

Like I said, the instructions called for .002-.004 or 1/16 of a turn of preload. I thought that was a little light and sure enough it was loud clatter. WAY worse than even the loosest lash solid flat tappet cam! I said to heck with it after inspecting the rest of the valve train and I just gave it a 1/4 turn of preload which was .014 and it is now quiet. I just cant see the manufacturer producing these lifters to install at this recomended spec and be this noisey.

How long did it run with the lower tightening?

I have had some hydraulic lifters that took a very long time to pump up. The lifters in my current 360 were that way. It took a 30 minute break-in and a couple days of driving to work and such for them to quit down, now they are fine. I thought I was just going to have to live with them but they finally started quiteing down and are now very quiet. I don't remember the brand, some generc ones I am sure.

I think those particular comps are desighned to use in a hydraulic application when you would really prefer a solid but rules prohibit them.

Believe it or not, my friend broke in the cam with the lifters clattering like they were. It ran for 25 minutes or so. The tech instructions say nothing about them taking along time to pump up. I always run the oil pump with a drill motor and rotate the engine a few revolutions prior to starting the engine and I have never had an issue in the past dealing with the lifters needing to pump up. I will call CompCams on monday and see what they say. Strange.

My friend talked to the Comp phone tech and they stood behind the .002-.004 preload. THey said it would be a little loud, but this was ridiculous. It sounded like a mechanical cam that was lashed at .080. My buddy told them we preloaded the lifter to .014 and the noise went away, the engine started right away, idled great and it revved very nice and didnt break up at high rpm. The tech guys said .014 was ok, so thats where we are leaving it. So anybody that buys these lifters and experiances the same issues, this may be a remedy for your situation. Now at .014 preload, the valvetrain is very quiet.

I have these and I'll run them at spec regardless of noise (which is minimal). I'd be concerned about high rpm pump up/ which is what these lifters are intended to eliminate. Maybe there are other issues?

This is from comps website.

The following instructions cover the correct guidelines for installing COMP Cams® Pro Magnum™
Lifters. All Pro Magnum Lifters™ require an adjustable valve train for proper operation.
Through various testing we have discovered that lifter preload should be set between zero and 1/8 of a turn for optimal performance.

I have used these in alot of motors for people and set the preload from .000 to .002 and they are all happy. Just my

I have seen this issue with the Lunati brand version of the Pro Comp hydraulic lifters on one of Steve and Linda Myers 340 stocker motors, it was noisy on the dyno, we made several pulls with the preload set the way your doing, set it at .002 lash and finally at 1/4 turn preload (all hot adjustments) and the 1/4 turn preload made the most power and torque. that was when you could buy both the Johnson and Eaton brand hydraulic race lifters, I'm not sure which company made all of those type lifters for ALL of the cam companys back then but they all had the same true arc snap ring retainers