Finding pushrods for my lifters

[jonas454]

My 1999 GMC k2500 7.4 (454 vortec) bent 2 pushrods this happened because of failing lifters. I ordered new lifters and they fit. https://www.compcams.com/oe-style-h...t-96-chevrolet-gen-vi-big-block-and-8-1l.html. these are the lifters and I need a pushrod length for them. The pushrods that were in before seem to work but when I measured them I got 7.5 inches and 8.5 inches for the length. I can't find any and the stock pushrods are a completely different length. Thanks

 

[docstoy]

So have you talked with comp cams about your issue ?

 

[Schurkey]

Are the new lifters the same length as the originals--from roller wheel to pushrod cup? I would expect so, but wouldn't hurt to measure them.

If so, replacement pushrods should be readily available from multiple sources including a local GM stealership.

Make sure you buy HARDENED pushrods, since BBC uses pushrod guideplates.

 

[400Rogue]

I want to make sure I'm understanding. You bought a full set of lifters or just 2? Either way, I'd suggest buying something like this: https://www.compcams.com/magnum-checking-pushrods-select-length.html. Looks like they are temporarily out of stock so you could get a full kit which will give you this tool for pretty much any US OHV V8. https://www.compcams.com/hi-techtm-master-checking-pushrod-kit-5-800-9-800.html

I believe each turn of the adjustable pushrod is 0.050". When fully closed, 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. 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 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. 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.

From here tighten the pushrod down and count the turns. 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: fully closed length + 10.5 X 0.050" (number of turns times the length change per turn) = pushrod length minus preload. So if your fully closed pushrod length was say 7.5"

7.500 + (10.5 X 0.050) = 8.025"

This is the length you measured to zero lash without any lifter preload. Now you need to know what OEM preload should be for your engine. you add that to the measured number and you get your total pushrod length. For example if preload specs are .05" then your pushrod length should be 8.075"

These are arbitrary numbers of course for example and your results will I'm sure be very different.

Now repeat for the exhaust valve to verify the length.

 

[Schurkey]

This is a stock engine aside from the replacement lifters...right?

Assuming the replacement lifters are made to the same length spec as the originals, you'd use original-length pushrods.

If you're seeing "stock" pushrods that are significantly longer than what you have, you're probably seeing stock pushrods for FLAT-TAPPET CAMS/LIFTERS. You (probably) need stock-length pushrods for OEM ROLLER CAM/LIFTERS.

 

[jonas454]

This is a stock engine aside from the replacement lifters...right?

Assuming the replacement lifters are made to the same length spec as the originals, you'd use original-length pushrods.

If you're seeing "stock" pushrods that are significantly longer than what you have, you're probably seeing stock pushrods for FLAT-TAPPET CAMS/LIFTERS. You (probably) need stock-length pushrods for OEM ROLLER CAM/LIFTERS.

Found some that are 0.09 off of the measurements I made and I will be ordering those.

 

[Schurkey]

Are they hardened?

.090-longer is not a direct replacement, especially considering that the newer BBC do not have adjustable valvetrains.