I ordered AFR's milled .030
My gasket is going from stock (.054) thickness to .045
My cam is an MTI C1 Lunati grind which obviously has a smaller base circle HENCE the hardened 7.4 pushrods went in when I put the cam in. So now that my head is effectivley .040 lower than before here is my question.......

I already have the 7.4 hardened push rods so can I just shim the rockers and I'm good to go right ?
Is there any negative effect or anything I better to know when doing this?
Nothing popped up on my search, MTI sells shims. It looks like lots of people are going to be running milled AFR's so might as well get this answered. Yes I know you have to measure and ideally use a pushrod checker and whatever but the bottom line is math says the head is .040 lower so I'm just going by the math here.

 

I have AFR's milled .024 with .045 gaskets. When I set my rockers up I needed a .075 thick shim to get the pre-load right. I used the 7.400 PR's and had no problem.

 

Guys...

The amount of "shim" you use under the rocker stands will have a direct effect on the valvetrain geometry and the "wipe" pattern created from the rocker rolling across the valve stem tip as the cam lifts the rocker and sets it down. Ideally, you want this small rectangular patch or "wipe pattern" to be located dead center over the valvestem tip. More shim will move it towards the Exh. side, less shim will move it closer to the intake side. Once you have achieved the correct geometry, the length of the pushrod is determined by simply measuring (with an adjustable pushrod ideally) what you need to provide the correct or desired amount of lifter preload. Pushrod length does NOT effect the actual valve train geometry (in a "shaft mount" style set-up) which is actually more important then the pre-load on your lifters. The correct "geometry" should dictate pushrod length, not the other way around.

BOTH of these issues need to be addressed if your looking for longevity and additional power from correct valvetrain geometry etc...

Hope this sheds more light on the situation.

Tony M.

 

I am thinking less shim and a shorter pushrod might have given you better "geometry" and the exact same lifter preload (.025 shim and a 7.350 length pushrod for example). Pull a valve cover and see if you can see the wipe pattern on any of the valve stem tips....I'm thinking you might see it biased slightly towards the exhaust.

 

Were you using the "R" lifters or stock?

Maybe I'm missing something, but I don't understand the point of the original question exactly. If you have the correct length pushrods for the application and are using stock lifters/stock replacement lifters and stock replacement non adjustable rockers I don't understand the need to shim the rockers? The only times I've heard shimming being done is when trying to get lifter preload exactly right with "touchy" lifters like the R's.

 

Thanks guys, Thanks Tony. I am going to re-read the thread a few times.
I was just planning on tightening the rockers to 22 ft/lb after 0 lash. I was under the impression that there is nothing to adjust (pre-load) with the stock rockers & lifters. The length of the pushrod with the milled heads was my only concern (geometry)and that was evidently misplaced. I did some reading on verifying the wear pattern and using the shims in that respect.

 

The way I was told to figure it is as follows (someone correct me if I'm wrong);

Since the base circle (diameter) of your cam is .030 less than stock your 7.400 PR's were actually .015 too short (1/2 the diameter difference) for your application. It didn't matter because the lifter absorbed it. However with your heads shaved and thinner gasket bringing the head .040 closer ,the PR's are now .025 too long. (.040 too long - .015 too short already = .025 shim) This should bring the preload and geometry back in spec.

 

Tony, in my case more shims moved the rocker tip closer to the intake side of the valve. I have T&D shaft rockers but it shouldn't make a difference.

 

my afrs are milled .024. i had 7.4 rods with a .065 shim with hs rockers. the rockers hit the valve covers. so i had to get 7.350 rods with no spacer and it clears nice

 

Actually, it depends on the fulcrum point (centerline) of the rocker arm and it's position in relation to the valve stem tip....an aftermafket shaft system is much taller than stock and would work inverse of what I described. Maybe someone can chime in that has done a set-up shimming the stock rockers. I utilized the Crane "stud-mount" style rocker arms in my engine build up which set-up completely differently. Pushrod length determines geometry and preload because the rocker arm (and it's fulcrum point) move higher or lower up the stud depending on pushrod length. In a stud mount system, pushrod length dictates both parameters.

Tony M.

 

Aftica, thanks that what I was looking for and you did the math too.
Lastley, where to buy the correct shim material and size wize (Home Depo) and how exactly to install them.
This is only to make sure the "swipe" pattern is good to go. Nothing to do with pre-load.
If anybody wants to make me feel warm and fuzzy about P/V clearance please do. I am not flycutting.

Thanks, PDD is your car all together now ?

*EDIT* Aftica, stock LS1 pushrods are 7.38 I believe.

 

I have some shims for sale right now from Crane Cams. Let me know if you are interested.

 

Tony, the fulcrum height accounting for the moving of the tip in relation to being higher or lower makes perfect since. Good explanation. I was deffinately a little confused. I would guess this. If the fulcrum point is moving higher and was already higher to start with then the plane of the valve stem tip and retainer then it will pull it back toward the intake. If you are moving a fulcrum that is lower to start with then the plane of the valve stem tip upward then it would move it toward the exhaust side.

 

PM Sent

 

I replied.

 

http://www.holley.com/HiOctn/TechSer...ECVTTech1.html

For measuring the PR

 

no not yet. the engine is together. thats it. im workin on the suspension right now. putting in poly bushing. what a **** misrable job. never agian. then i gotta put the tranny and rear back in. then i can finish eveything up

 

That's exactly right....once you have done it, it becomes easier to visualize.

 

I'm also going with afr's with my c1 cam. If I have unmilled afr's and I use .045 gaskets and stock rockers I shouldn't need any shims right?

 

I'm using the Morel lifters, and when doing the 22ft lb's and go method, I had 1 1/2 turns past zero lash. I did not want that much preload. After shimming, I ended up with 1/2 turn past zero, which is where I wanted to be. I probablly could have ran 1 1/2 turns fine, but to much pre-load can rob HP.

Tony, The engine is on a stand, so I'll go do the test you described. I'll report back in a minute......