Ok, I am almost positive about using stock length pushrods, but I have heard to re-check this. When do you switch pushrod length? I have beehive springs, cc pro mag 1.6 rrs, fel-pro (stock style) head gaskets, gmpp lifters and I think that is all the mods that apply. Can anyone tell me why I would switch pushrod length? I know the heads have not been milled down, and the head gaskets are stock style, so any reason besides those 2 is appreciated.

thanks

 

You can guess or you can get Einstein to calculate it for you but it still comes down to checking it. Start with your stock push rods and use this method.

http://compcams.com/technical/Catalogs/106-07/264.pdf

If they are the wrong length then estimate the length and order a push rod length gage near the estimate and try it using the same method. Once you have the correct length according to the new dialed in length tester, measure it and look for the rods with the same length. Warning, measuring the length of a pushrod is not easy. Try this
http://compcams.com/technical/Catalogs/106-07/265.pdf
for measuring the correct length.

 

When I installed my Comp pro-mags 1.6 I had to switch from stock 7.200" rods to 7.050" push rods to get the correct rocker geometry. The stock length cause the geometry to be very low on the valve stem.

If you only change springs then pushrod length should not change, however if rockers are changed then it should be checked.

 

Are you sure the only thing you changed is Pro Magnum Rockers?? I mean .150" is a big difference for rocker changes.

 

Stock lengths should be good with most rockers (stock or aftermarket).
The length changes when you use heads that are cast/machined different
from the stock heads, use thinner/thicket head gaskets or use a cam with
different base circle or lift.
If in doubt, mock up the components and use a pushrod length checking tool.

FWIW I used 7.150" with "Impala" (.029") gaskets for my LE2.1HL setup,
with stock gaskets (.051") those heads (even milled .010" - .015")
would have used stock length pushrods.
I used 1.6:1 Comp ProMags on this build.

I think most people with LE's setups end up with 7.150" with .029" gaskets.

 

I used 7.200" with Milled heads and 0.100" longer valves and Morel lifters.

 

BTW don't get me wrong, I saw your picture while you were measuring the lenght. Your current pushrods (7.050") are the correct size, I just wonder if you changed other than Pro Magnum rockers.

 

you shouldnt need longer/shorter rods if you're using the same thickness gaskets and havent had to mill them down. i'm running a bored/stroked 383 with stock ported heads, stock replacement lifters, 1/6 pro magnum rockers and hardened 7.2" puthsrod with guideplates. double springs with IDK what kind of retainers...i just know i can't run with SA rockers.

 

Heads are all stock except for the LT4 springs and Comp pro mags. I used the adjustable pushrod and a super light test spring and the pest geometry was clearly with the 7.050" push rods.

Here is a link to that post:
http://web.camaross.com/forums/showt...light=pushrods

There is absolutely no way the 7.200" pushrods will work with my engine. In fact I am convinced they caused my excess wear on the guideplates which resulted in a rocker slipping of the valve stem.

Left valve- 7.050
Right valve- 7.200 (stock) for reference only



This appears to be dead centered on the stem and slightly wider sweep than stock. I can only assume that the CC Pro-mags are needing this .150" shorter pushrods.

 

I have a question for wrd1972, Does it matter how tight the rocker arm nut is? I am thinking that when it is too tight it might move the mark? I am about to go get a marker and try your technique (that was a great post thanks, http://www.carcraft.com/techarticles...th/index1.html) and hopefully they are dead on w/ stock length (7.195"). If not, a few more days for pushrods to ship and another 100$ or so deposited into my motor (which hasnt started even yet...)

 

Yes it matters in the sense that over doing it will preload the lifter too much. You have to find zero lash (tighten the nut till you cant spin the prushrod with you fingers) and apply an aditional 1/4 to 1/2 turns to preload the lifter correctly. I prefer 1/4 turn past zero lash.

I dont have rocker nuts, I have poly locks which make this a ton easier.

 

till you can feel the resistance. You should spin it by feeling the resistance.

 

blah I have to take out my plugs to do this huh... I just got my plug wires routed and just put the plugs in. One plug wouldnt even be enough would it, it would have to be one plug per cylinder? I can find the zero lash so thats not a problem and I have the poly locks as well.

thanks again

 

For the record, we just mocked up my 396 using ported LT1 head castings... 6.986"... we'll be going with 7" push rods.

Why so short? here's our theory:
1) the block was zero decked during machining... 0.025" lower than stock deckheight (9.000" vs. 9.025")
2) the valves are 0.050" longer than stock.
3) the 1.6 Pro Mag rockers change the geometry somewhat...

So there you have it... push rods UNDER 7" for a LT1 head casting... wierd.