tg580

How do you determine what length push rod you need? I have Patriot stage 2 heads and a 224/226 cam with .581 lift and 112 lsa.

vettenuts

iTrader: (4)

Best way is to measure but a lot of guys use 7.400" pushrods.

MPFD

iTrader: (5)

measure and then tell us.

http://msperformanceonline.com/pulech.html

tg580

ok. Here is where I am. I have 7.4" push rods. The spec we were following said to hand tighten the rocker arm down until the rocker doesn't wiggle anymore. Then torque them down to 22ft/lbs. It said that you should get about 1-1/4 to 2 turns. If you only get 3/4 of a turn then you need .025 longer push rods. If you get 2-1/4 turns then you need .025 shorter push rods. I was only getting 1 turn on my intake rockers and 1/4 turn on my exhaust rockers. By that spec I am thinking that I need 7.425" push rods. What do you guys think? Is that spec correct? Patriot Performance Said 7.4" push rods.

MPFD

iTrader: (5)

This Comp Cam pushrod length checker is the way to go when checking for the proper pushrod length. Check and see what the correct length is before you order the improper length pushrod. Saves time and effort.---or so the ad says...

LSXNV

iTrader: (1)

well, since you have it all together, go ahead and check rocker travel over the valve tip. the travel from fully closed to fully open, to back closed should stay centralized on the valve. if it tends to prefer one side of the valve or the other you have the wrong size. its best to use a marking fluid or thick oil of some sort. grease can work in a pinch.

LS-1Z28

iTrader: (6)

do you have stock rocker arms? If so...

I measure my pushrods by using an adjustable pushrod. I adjust the pushrod to zero clearance between the base circle of the camshaft to the rocker arm. Once you've measured the zero clearance you need to add your lifter preload... I add 0.05'' preload to the overall pushrod length for my setup but I've heard others using 0.10'' (manufacture suggested preload 0.05''-0.08'').

I'm no mechanic though... just what I've gathered.

Darkman

iTrader: (2)

Based on this, wouldn't you need 7.450 push rods? The 7.425 would put your intake at 1-1/2 turns, which is okay but would put your exhaust at 3/4 turn which is still 1/2 turn out of the 1-1/4 to 2 turn window. Did I miss something?

LS-1Z28

iTrader: (6)

I'm not familiar with this method.

your intake and exhaust base circles should be the same so it's strange that you're getting different readings. I would go with an adjustable pushrod to measure the correct pushrod length.

LS-1Z28

iTrader: (6)

I didn't have much luck with that adjustable pushrod... Both threaded pieces are not exposed when you have it installed so it makes it difficult to adjust without pulling the rocker off every time.

I used this pushrod and it worked perfectly!

http://www.jegs.com/i/JEGS/555/80681/10002/-1

LSXNV

iTrader: (1)

when you are measuring for proper geometry, you are making sure the rocker does exactly what i described. thats it. with proper preload, if your rocker tip goes through the motions and stays centralized as described you are good to go. check out this link, and don't over think this. 0.025 is REALLY splitting hairs here.

http://www.compcams.com/v002/Product...Tech%27-0.aspx

tg580

I couldn't get the link to work. I know that the .025 seems pretty minor but if I'm thinking of this right being .025 short on my pushrod would take my cam lift from .581 down to .556 wouldn't it?

vettenuts

iTrader: (4)

Pushrod length will not effect the wipe pattern on an LS1. You need to shim or adjust rocker height to do this. Pushrod length will only alter the lifter preload. The correct way to set up the valve train is to set the wipe pattern first, then measure for pushrod length because any shimming required (or lowering if that is what is necessary) will change the pushrod length by approximately 60% more then the shim value.

vettenuts

iTrader: (4)

This is how to use the adjustable pushrod. You may in fact need to remove the rocker to make each adjustment. It will take time and needs to be done carefully. You can end up with two different length pushrods, depends on the cam. Some cams use a different intake and exhaust lobe.

Link to Adjustable Pushrod Instructions

Jim_PA

iTrader: (9)

As long as your push rods are able to mate with the lifter when the cam is on it's lowest point of travel, push rod length will not affect lift. Now, if your push rods were like an inch too short, I could see where you might lose some lift.

All we're really trying to do here is get the proper amount of lifter pre-load. Rocker arms are attached to the top of the head, and can't really move up or down, they just sit there and rock back and forth.

As you might be able to imagine.... When the push rod is too short, and you torque the bolt to 22ft/lb, the push rod has barely (and in extreme cases, not at all) pushed down into the hydraulic lifter, resulting in too little lifter pre-load.

In the other case, if your push rod is too long, you torque to 22ft/lbs, but this time, the push rod has extended farther into the lifter body, giving too much pre-load.

At the end of the day, there's only one thing we're trying to do here with stock rocker arms and push rods... getting the lifter pre-load somewhere between.... .050 and .100 (?)

66 BADBOY

iTrader: (2)

Thank you for that link!! I've been reading along in this thread and found it to be pretty informative, especially that link of yours. Thanks!!

LSXNV

iTrader: (1)

so every thing i have learned about valvetrain geometry does not apply to LS style engines? why are they different?

i cant get the link to work properly. anyway it is on comps website under pushrods, then pushrod tech. but either way i guess it would not apply to your engine.

vettenuts

iTrader: (4)

The LS1 rockers bolt tight against the head and once bolted down won't move. So a longer pushrod either increase the lifter preload or if too much will start opening the valve when the plunger in the lifter bottoms. But because the pivot point of the rocker is fixed (bolted down) the wipe pattern will not change.

On the small block, the rocker floats and is supported by the valve stem and the pushrod and the pushrod length will then determine both the wipe (geometry) and the preload of the lifter. The stud mounted setups (Crane/Comp) for the LS1 work this way and the pushrod length will indeed change the wipe pattern.

LS-1Z28

iTrader: (6)

+1

if you have the stock rockers torqued down you will want to zero out the clearance between the rocker at the hydraulic lifter at the cam lobe's base circle and then add a little extra for lifter preload... you DO NOT want to collapse the lifter with pushrods that are too long! When you install your new pushrods you should be able feel the travel of the lifter plunger when you rock the rocker back towards the pushrod (this is if you've given ~10min or so for the lifter to bleed all its oil out).

LSXNV

iTrader: (1)

this is great info, dont know why i havnt caught this earlier. so factory LS engines, more or less, use a shaft mount style valve train? i cant wait to finally get my hands on one. but since all but a few engines i have built were solid cammed, how do you set lash?

OP, sorry for the highjack here.