Ok, a couple of weeks ago I had to pull my heads. Had noise in valve train thinking I bent a push rod or bad lifter from bumping the rev limiter on a burn out.

Heads were shaved milled and on cyl #4 the intake valve had to be lapped. (fail vacuum test, passed after lapping)

When I was ordering parts (LS7 lifters, MLS gaskets, Manley Chrome Moly Push Rods 7.40", head bolts) I was told that I didn't need to change my push rod length (7.40") because I was using the stock heads that come on a 98' still.


After it's all together I now am getting noise that can't be pinpointed. Oil pressure reads normal. Sounds all over - behind the timing cover, along the sides of the block and even in the oil pan. At idle no noise, rev to 2000< rpm it makes metallic noise very close to piston slap but not 100% the same sound.


Now here to the point -

Yesterday, I came across that some guys using LS7 lifters have had to change their push rod length to 7.35" because the cup of the LS7 lifter sits a little higher then the LS1 cup. I know both lifters are the same length in size, but the cup position is what I'm concern with.









Could the push rods be what's making the noise?


I've ordered a push rod checker, waiting for it to come in.

 

My cars doin the exact same thing. I changed lifter because of a noise. I have close to the same noise now. I change pushrods from 7.425 to 7.4 because I had them. It had a direct effect on the sound but still their. I have ordered a trick flow pushrod lenth checker I will know something by next weekend. The tool should be here Wednesday.

 

Yes since OP had heads milled I would recheck pushrods for length

 

There needs to be sticky for push-rods. This has to be #1 question asked in this section.

OP, there is no magical formula for push-rod length. People can guess, assume, do some mathematical calculations etc, but at the end of the day measuring with the proper tool is the only error proof method. With your heads milled and now using different lifters, you can bet you will need different push-rods.

 

Yep. I'm thinkin I'm way off from where I should be. I hàve the tool on the way.

 

Thanks guys, just waiting on the mail truck to bring the checker.......




I'll post what I find.







FYI, Only reason I reused the heads is this is to be a temp fix, I have a LQ4 short block waiting in storage to be built, however I still need to use my TA. The LQ4 I have plans for a 408 build.

 

On my otherwise stock motor and LS7 lifters, I needed 7.350" pushrods to get around 0.075" preload. With my heads milled 0.022", I had to go down to 7.325" pushrods to get around the same preload. My valvetrain a still a little noisy but it's probably due to the cam and springs.

 

Can someone explain to me how to do preload?

 

Assuming you bought the Comp adjustable pushrod.

Each turn of the 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 with a correctly established wipe pattern (Note, wipe pattern should be established first.)

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 you 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 buy 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. Lets 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 lets 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.

 

Great write up Vettenuts