Pushrod Length Question

[AlexTJ]

My block had .028 taken off for a deck height of 9.422 (~.008 deck clearance)

I'm using the Mopar Performance head gasket for another .008 off. So total I've removed about .036 in height.

I'm using a Lunati 63502 cam (.507/.527) and Johnson-Hylift lifters. Stock rocker arms.

I used two push rod length checkers and a length of 9.550 gives zero lash, but 9.6" gives a better sweep across the valve stem tip.

Which should I go with?? Longer sweep or less preload??

[SilverXJ]

How much preload are you getting with each?

[AlexTJ]

I don't have a dial indicator so I can't measure that.

[SilverXJ]

Yes you can. Find 0 lash. Scribe mark on push rod using a straight edge off the valve cover rail on the head. Torque rocker arm down to spec. Scribe new mark on push rod. Measure distance between marks with calipers. That is your preload. There is also an option to measure using turns to torque, but I don't go for that.

Besides, how do you think one push rod gives you a better sweep across the valve? Are you using adjustable rockers?

[AlexTJ]

Yes you can. Find 0 lash. Scribe mark on push rod using a straight edge off the valve cover rail on the head. Torque rocker arm down to spec. Scribe new mark on push rod. Measure distance between marks with calipers. That is your preload. There is also an option to measure using turns to torque, but I don't go for that.

Besides, how do you think one push rod gives you a better sweep across the valve? Are you using adjustable rockers?

I'll try that method. What should I shoot for?

I'm using stock rockers. I read that a longer pushrod on our rockers moves the sweep towards the port-side and a shorter the opposite. I found that to be true when I lengthened the rod.

The 9.6" rod put the rocker arm on the port-side of the tip at maximum lift and at the opposite side at base circle. The 9.550" rod put maximum lift @ about 2/3 the way to the port side

[AlexTJ]

I would spend $20.00 and buy a pushrod length checker. That way you know what size pushrods you need. Comp cams 7704-1 is good for 8.800 to 9.800 length. One turn of the pushrod is +.050. Start at 8.800 and count how many turns you need to get the length you need. Summit sells them for $16.95 plus shipping.

Are you using stock rockers? If so, install the rockers, adjust the checking pushrod untill it just touches the rocker, and then add .040-.060. That should give you the correct lifter preload. You can add shims to the rocker stands if you need to increase length or buy custom length pushrods(if you need shorter or longer than stock). Trend pushrods sells one piece, 5/16 diameter, .080 wall, chrome moly pushrods for $5.60 each. They stock them from 6.00 to 10.00 inches in .025 increments. They were shipped to my door in 3 days after my order.

from http://www.jeepstrokers.com/forum/viewt ... 32&start=0

If I followed dwg's advice there the pushrod to choose would be the 9.600"

[SilverXJ]

I read that a longer pushrod on our rockers moves the sweep towards the port-side and a shorter the opposite. I found that to be true when I lengthened the rod.

Not on ours. All the push rod length does is adjust preload. If you had a valve train like some chevies, where you can adjust the rocker at the bolt then, then yes, but not on ours. If you want to adjust the sweep on ours you would need to change push rod length in addition to shimming the rocker, or shaving the pedestal. Even with teh Harland Sharp style of adjustable rockers I can't change the sweep with out shims as the adjuster is over the push rod.

The 9.6" rod put the rocker arm on the port-side of the tip at maximum lift and at the opposite side at base circle. The 9.550" rod put maximum lift @ about 2/3 the way to the port side

I don't know what you are seeing, but something is wrong. How are you checking this? Are checking it with the lifters dry, and using regular valve springs?

[SilverXJ]

If you are checking it with a new, unprimed/filled lifter and a standard valve spring what is happening is that when you go full lift the lifter is compressing fully. This is not how that lifter will behave in a running engine. If you had a dial indicator you would see you are missing about 1/8"(or whatever it is from preload to bottoming out the lifter) +/- the different push rods length. That would account for you seeing the different sweep pattern.

With a hydraulic lifter the only way to check sweep, valve to piston clearance, and retainer to valve seal clearance is to replace the standard valve springs with checking valve springs. They have a very light spring rate which won't compress the lifter. You can't simple prime or fill the lifter as there is a chance it will either be pumped up too much or bleed down.