alright, i received my comp cam pushrod checker, but how do i go about using this tool correctly. btw i tried searching but i couldn't find anything. i also have the stock rockers


thanks,
albert

 

This is assuming you have the Comp Cams adjustable pushrod, which at its shortest length is 6.800".

Each turn of the adjustable pushrod is 0.050". When fully closed, it is 6.800". This is pushrod "gauge length" so you can't measure it directly as the pushrod length is actually based on the length between the ball ends where the ball end measures 0.140" in diameter. Assuming you are using stock rockers or a non-adjustable rocker.

1. Open the adjustable pushrod to the same length as your stock pushrods
2. Close it down two turns
3. Put your rocker rail on the head
4. Make sure your cylinder (typically #1) is at top dead center on the firing stroke so both valves would be closed
5. Put the pushrod in place on the intake valve and make sure it is in the lifter cup
6. Install the rocker and snug down the bolt (don't need to torque, just make sure it is snug)
7. Lift rocker tip up and down, if it "ticks" the pushrod is too short. If you can't easily move the rocker the pushrod is too long.
8. You can try and adjust the pushrod in place but my fingers are too fat so I end up pulling the rocker and adjusting the pushrod length. Go either shorter or longer 1/2 turn and try again.
9. You are trying to get to the point where the lifter doesn't "tick tick" with the pushrod in place nor is the rocker snug. When you get the pushrod length such that you just barely get rid of the "tick tick", you have found "zero lash".
10. When you have found zero lash, carefully remove the rocker and pushrod without rotating the pushrod.
11. Tighten the pushrod until it is fully closed counting the turns as you go.

To figure out your pushrod length you do the following. Let’s assume it took 10-1/2 turns to close the pushrod down to its shortest length after you reached zero lash. Each turn is 0.050".

Your length is then: 6.800" (fully closed length) + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So for this case:

6.800 +10.5 X 0.050 = 7.325"

This is the length you measured to zero lash without any lifter preload. Now let’s say you want to have 0.075" lifter preload, you add that to the measured number and you end up with 7.400" pushrods.

Now repeat for the exhaust valve to verify the length. If you have something like Yella Terra's, it is the same procedure but you must snug down the rocker pair rather than the single rocker.

 

alright, im still a bit confused, i took some video of the different length's. what would be the best pushrod for me




7.425





7.450





7.475

 

Not to make you sound like a fool that just wants to get it over with because I was in your exact same shoes not horribly too long ago. It's better to understand what the heck you're doing rather than just having someone say use that pushrod length in my opinion. So what don't you understand about vettenut's post ?

I don't know what all you did or what type of cam you tossed in there but you might be able to use stock pushrod length, adjustable rocker arms are the bomb as well. If you follow the steps in the guide above it's pretty simple though, you should have your new head gaskets and they should be torqued. Hopefully your cam is installed properly and then it's just a matter of having the valves you're checking shut so having the cylinder top dead center.

Like the guide says though the tool doesn't have a lock so it may turn slightly, put the tool where you think you need it ... snug eveerything up ... if you need longer try it again, if it's too snug ... shorter.

Don't quote me on this and do your own research always and use common sense, the beautiful thing about these engines is they've been around for a long time and pretty simple.

 

no worries, ill learn eventually, it just has me very confused, plus i dont have a garage and its 115 outside so the heat is starting to get to me . i tried the stock length pushrods but there is to much play. the heads are torqued down and they are stock 317 heads with mls gaskets, and i also installed ls7 lifters. the cam thats in there is a 224 228 114, and i installed it almost two years ago so i know it is installed correctly. im trying to understand how the actual lifters work, like the plunger inside the lifter also what has me confused is step 7. if someone can explain it that would be great, i dont want to have a collapsed lifter or worse.

 

Of your three video's, the answer is "none of the above". You are pushing at the pushrod end of the rocker. What you want to do is lift very gently at the valve end of the rocker (opposite of the end you are pushing, but lift instead). Don't lift hard, do it very gently. Also, make sure the lifter is on the base circle and the rocker is snugged down.

If this doesn't make sense, let me know.

 

well it looks like my stock length pushrods will work just fine, thanks for your help

 

Subscribing for info.

 

Not sure what information you are seeking, but this thread is seven years old. I doubt there will be any more posts. If you have a specific question I would either post it here since the thread was revived or start a new thread to get answers to your particular question.

 

I saw it's seven years old; just subscribing so that your posted info remains in my user thread subscriptions for reference.

 

Reviving an old thread, rather than creating a new one...

So I have the Comp Cams 7702 pushrod length checker. Went through the whole measurement technique. I understand all on that just fine. The question I have relates to the actual dimensions of the checker.

​​​​​​Closed it is supposed to be 6.800", but when I measure it with calipers, it measures 6.815". (I have 2 of the 7702,and the both measure the same - 6.815")

And... Therefore, when I find the perfect length pushrod to give me zero lash, by calipers, it measures 7.755". But when I count turns, it is 18.8 turns which calculates out to 7.740" so which is the correct pushrod length? (yes, I know we are only talking about 0.015", but in some cases that would make a difference in pushrod choice)

 

The difference is the measurement methods you are using. Using the turns of the pushrod is done because the pushrod is measuring "gauge length". Gauge length is the distance between the two ball ends where the ball is 0.140" in diameter. This point on the ball end (0.140" diameter) is impossible to find with a caliper and that is why they count turns. You are measuring "Overall Length" with the caliper, which is the distance between the ends of the *****. Trend (who makes most of the aftermarket pushrods for other vendors such as Comp) doesn't believe this is accurate since this measurement is very sensitive to the way the ball is machined into the end of the pushrod therefore they use gauge length. Manton, on the other hand, uses overall length.

The difference between gauge length and overall length is typically 0.013" - 0.017" so your difference of 0.015" is right in the middle. In essence the pushrod measurements you are taking are the same length when you account for the type of measurement you are taking.

Note also, the tolerance on length is typically 0.005" so even if all your pushrods are 7.400" there might be some variance in length between them.

Hope that all makes sense.

 

Thanks. Makes perfect sense. Appreciate the explanation.

 

HPR had this explanation over on the C6 side too. All is clear now...