Mechanical Rocker Arms and Hydraulic Cam

[bwhitejr]

Edelbrock Performer RPM heads require mechanical rocker assemblies when you use have larger than stock cam. Can someone tell me how to set up the rocker arm assemblies to work with hydraulic lifters. The mechanical pushrods I bought are just under 7 1/4" long. Are these the correct ones for my application? Some say preload, Mopar says no pre-load??????????


bwhitejr

 

[63dartman]

do you mean adjustable rocker assemblies? If your running hydraulic lifters you have to use preload, I believe most call for .050 preload. Your pushrods need to be measures for proper fit with a length checking pushrod. Also most rockers need to be adjusted so you don't have too much or too little of the adjuster on the pushrod tips. I know on crane gold series they call for 4-5 threads showing on the bottom side of the rocker where they contact the pushrod tips. You could try one of the pushrods you have just to see if it fits. You may get lucky on the sizing.

 

[daredevil]

If the pushrods are close you could shim the pedestals instead of buying new pushrods and be sure to check the centering of the roller tip on the valve. I just snugged my rockers with the motor warm when I ran that set up

 

[moper]

You dont say what kind off cam, lifters, or rockers you have. That makes a difference. As was said, youwant to set the proper preload, as preload is a lack of space between the lifter and cam, and lash is the space you leave between the two. Preload makes the hydraulic lifter function right. The type of lifer is very important. Stock lifters can deal with preload from about .020 to .060. Fast rate of lift cams that use anti-pump-up lifters use much less. Like .005-.020 preload. You need to check every lifter, and being as temp doesnt effect this much unless it's aluminum heads, it can be done cold pretty easy and accurately. Also, like was said, you want the minimum amount of threads showing on the adjusters below the rocker arm. I use from 1-4 as ok. Some guys like no more than 2 showing. Some guys dont care, and leave 5-8 where there is very little left above the rocker...

 

[bwhitejr]

It is a CompCams Xtreme Energy hydraulic cam. The rocker assemblies look like the ones for the 273 (all arms are straight malleable iron). Mopar says the stock lifters have 0.180 travel. I measured the ComCams lifters and they appear to be the same. Mopar says with zero lash turn the adjusters 1 1/2 - 2 turns tighter. I measured 1 turn is 0.0435, so it looks like about 1 3/4 turns would put the adjustment in the middle of the travel range. Is something wrong with this approach?

bwhitejr

 

[C130 Chief]

I would sure run less than 1 3/4 turns (which will put you in the .075 range) go for more like 1/2 turn preload and run it for a while (probably around .020). If it is noisy, try another 1/4-1/2. Factory preload was always pretty deep to soak up manufacturing inaccuracies, and run quiet for a long number of miles. With that cam, a deep preload like that will probably lose you some upper RPM performance to lifter pump-up induced float. Heck even the stock cams would rev a little higher with shimmed rocker shafts which reduced factory preload.

This is not a situation where more is better. As for pushrod length, make sure the rocker tip is centered at 50% lift.

 

[bwhitejr]

The real issue is the the first 20 minutes of an engine's life. My son and I are about to fire this rebuilt engine up and want the lash setting acceptable enough to get it through the initial start-up. I would like a "safe" setting, but I would also like it not being noisy (there are noises the valve clatter may mask). So, will zero lash and a half turn on the rocker adjustment be quiet enough or is more required?

bwhitejr