aaronware76

iTrader: (2)

hey guys, i'm doing heads and cam on my 99 ls1 trans am and i'm trying to determine proper push rod length. i need to know what the proper amount or range of preload should be on the lifter after i've found zero lash. my length checker is at 7.310 at zero lash, i measured with calipers. any idea? i don't know at all. any help is greatly appreciated.

vettenuts

iTrader: (4)

Couple of things to be aware of. First, if you are using the Comp adjustable pushrod, it measures by counting turns and figuring out the length. Bottom line is Comp is trying to give you "Gauge Length" which is how they (and Trend who makes the Comp pushrods) determine length. The length you measured is "Overall Length". There is nothing wrong with that but Overall Length is approximately 0.017" longer then Gauge Length of the same pushrod so be aware of that when you order off the shelf pushrods.

There is a GM Engineer on Corvette Forum who recommends 0.060"-0.100" as GM lifter preload.

Also, if you order Manton pushrods (which I would recommend) they use Overall Length (which you measured) to make the pushrods. Manton has an 11/32" OD pushrod which is a killer pushrod and it fits most heads without any machining. 3/8" OD pushrods do not fit all heads.

aaronware76

iTrader: (2)

ok so my gauge length is 7.293 plus .080 preload to split the difference. i have comp 7.400 rods now, think they'll work? or should i go with 7.350? they'll be comp pushrods again, thats all i can get over the next 2 days and this needs to be done by monday night.

vettenuts

iTrader: (4)

The 7.400" will put you at 0.107" of preload. I have run more then that with a prior setup. One thing to consider, order from Manton and temporarily assemble with the pushrods you have then swap them when the Mantons come in.

joecar

vettenuts, do you have a link to this please, I searched and can't seem to find it.

hiltsy855

iTrader: (35)

Patrick G recommended .080" to .100" preload in this thread.

joecar

There's a thread on CorvetteForum where a GM engineer produced a chart of various lifters showing maximum plunger travel, this is what I'm looking for.

joecar

Ok I was searching in the wrong place (yes please slap me)...

I found it the chart in this thread (see the post by Matt/TSP): https://ls1tech.com/forums/advanced-...-question.html

Sales2@Texas-speed

iTrader: (5)

I'd go with 7.375" based on your zero-lash measurement!