i have a 2001 z06. i am installing livernois stage 2 heads and MTI stealth II cam. i dont have the car apart yet, but was going to order pushrods so i have them before the weekend. do i just get the stock length pushrods?

 

Definitely not. You need a pushrod length checker. Once you check the proper length, then order those. There are too many variables that affect proper pushrod length. You can cause problems by putting in the wrong length. Stock length is 7.400 If your heads are milled and the base circle on your cam is different from stock, it could change it to where you end up needing a 7.250.

 

We typically run 7.400 when used with our camshafts, but as BLOWNBLUEZ06 mentioned, you should get a pushrod checker and measuer for length.

Regards,

Rick LeBlanc
Livernois Motorsports

 

Pushrods are the last part I order, and only after everything is together so I can measure with an adjustable pushrod.

 

Any advice on whats the best way to check the length? Say with Crane cams $20 adjustable?

 

Good question. Someone here can correct me if I am wrong, but I would set the number 1 cylinder to top dead center on the compression stroke (both valves closed). Then install the adjustable pushrod into either the intake or exhaust side and adjust it out until it just barely overcomes any up and down play, but will still spin (zero lash). Once this is done remove the adjustable pushrod and add the required preload for your particular lifter to the pushrod length. Again someone here with more experience than I (Vettenuts)can add to this if I missed something.

 

Comp Cams 7702-1 pushrod checker. I would set up rockers for proper sweep across valve stem and then insert checker and 0 out the lash. Take reading on pushrod length and add .050" for lifter preload.

 

I use the Comp, which is 6.800" closed.

How to use

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.

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 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 0.100" lifter preload, you add that to the measured number and you end up with 7.425" 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.

 

What are the symptoms of wrong sized push rods? Valve train instability? Does it show up on a dyno graph? Top end issues?

 

A little short would result in more noise, a lot long could hold valves open. Stock lifters are pretty forgiving, just try to hit 0.080" - 0.100" preload and you will be fine.

 

MTI recommeded 7.40" with thier cams unless you've got the heads milled

 

Almost all tuners do. That doesn't make it right. It's a quick one-size-fits-all solution, and all these tuners will also tell you the "sewing machine" valvetrain noise is normal for heads/cam cars too.

There are just too many variables for ANYONE to simply say "you need 7.xxx" length with our cam".

The variables involved:

Cam base circle dimension
Lifters, and their particular optimum preload
Rocker arms, and any shimming of them.
Milling of the heads (flat or angle mill also matters)
The heads themselves (if not a stock casting)
Head gasket thickness
Valve stem length.


If you alter several of those things that directly affect optimum pushrod length and still end up with 7.400" as perfect for you...buy a lotto ticket, it's your lucky day.

If you're only changing one of those dimensions, (ie: a cam-only install) you might get by with calculating the longer length needed based on the base circle difference (typically, 7.425 works well for cam-only installs)... Get any more involved than that and measuring is the only way to truly know what's best for your engine.

 

While those who suggest that you check your pushrod length after your new cam, etc., I am puzzled why no one has suggested to you the correct type of pushrod to install after you know the correct length.

I would suggest that you purchase a set of Smith Brothers 5/16 x .116 inch wall, oil flow restricting pushrods. The stock pushrods flex like a piece of spagetti at high RPMs and the LS Engine's oiling system puts too much oil in the overhead.

You can contact Smith Brothers through their web site - www.pushrods.net.

Good luck with your decision.

 

Interesting bit of information, Terry Manton makes custom length 11/32 X 0.120" wall pushrods. I had him make me one so I can see if it will cycle without contacting the heads. It has 5/16" ball ends. This may be the perfect setup, much stiffer than 5/16" diameter and if it works out, no head modifications to fit. Only issue is the increased weight.

 

The increase weight on the short side of the rocker arm is not an issue.

The best solution for LS series engine owners that are willing to open the pushrod hole in their heads is a Smith Brothers 3/8 inch x .144 inch wall, oil flow restricting pushrod, with 5/16 inch ends.