what length push rod?
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From: niles,mi
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.
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...
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.
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.
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.
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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.
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Brett Foote 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.
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.
I used this pushrod and it worked perfectly!
http://www.jegs.com/i/JEGS/555/80681/10002/-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
http://www.compcams.com/v002/Product...Tech%27-0.aspx
Thread Starter
On The Tree
Joined: Apr 2010
Posts: 130
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From: niles,mi
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
http://www.compcams.com/v002/Product...Tech%27-0.aspx
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.
Link to Adjustable Pushrod Instructions
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 (?)
Last edited by Jim_PA; Jun 7, 2010 at 10:29 AM.
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
Link to Adjustable Pushrod Instructions
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.
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.
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.
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.
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.
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.
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.
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).
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.
OP, sorry for the highjack here.