SWEET98SS

iTrader: (8)

So I am in the process of rebuilding my motor, AI 219 high compression ration ported 853's heads and cam, head gasket, pushrods, stock rockers with trunion upgrade.

Now I was told that he could calculate my pushrod length and then just send me the correct size.

I have stock rockers so there is no way to adjust lifter preload is there?

outkast6991

iTrader: (34)

Pr length will dictate preload on stock rockers

SWEET98SS

iTrader: (8)

So I just torque them down and I should be all set then. Thanks !

soundengineer

iTrader: (16)

well...sort of.....
you need to measure for pushrod length...
and with an aftermarket cam you should shoot for around .030 preload...

its a 1.25 pitch if I remember correctly...... so one full turn is .049212

to measure... you can torque down a rocker to 22 ft lbs...
then measure.. and take away .030 to get your correct pushrod for your aftermarket cam..
with a stock cam you shoot for .080~.100

SWEET98SS

iTrader: (8)

So I need a pushrod length checker?

soundengineer

iTrader: (16)

personally, I would use one....
but many people do not...


the other option...is to buy some pushrods as suggested by the place you buy the cam from...or do some simple math to find out how much different you need based on the base circle...
the cam grinder can tell you the size of the base circle...

Stock Base Circle Diameters:
'97-'04 LS1 = 19.7mm / 0.776"
'01 LS6 = 19.3mm / 0.760"
'02 -'04 LS6 = 19.0mm / 0.748

then its simple math to get a longer pushrod....and a little more simple math to get it closer to the desired preload..


but its still best to measure

you probably will not get an exact match pushrod...
but its better to err on the low side of .030 when possible, but not less than .020...
shoot for inbetween .020~.040

vettenuts

iTrader: (4)

You need to correct the thread pitch with the rocker ratio as well using parallel triangles from the valve stem if calculating using bolt motion. Also, some of the bolt rotation is due to bolt preload where the bolt rotates and no rocker motion takes place because it is bottomed. On my motor, I found this to be 1/3 turn which is another correction that must be used in the calculations. I agree that it is best to measure than order pushrods.

As for the rockers, you should set the geometry first (wipe pattern) then once that is corrected you measure for the pushrods as any geometry correction will affect the final pushrod length. With an aftermarket cam (smaller base circle) and higher lift, this might require lowering the rockers rather than shimming them up. That being the case you will need a different stand and have to mill the stand to the proper height.

baxsom

iTrader: (6)

.030 for aftermarket cams? almost every post here on lifter preload says to use the .080 number for aftermarket too. where did the .030 come from.

soundengineer

iTrader: (16)

from the cam grinders....optimum around .030
the ranges they say to be within that are still ok..
Cam Motion says .020~.060
Comp Cams says .020~.070
Lunati says .020~.060

they say this for both stability and cam lobe life

most engine builders will tell you the same thing, to shoot for .020~.040

mark21742

I found for me the best setup is around half turn 0 lash to torque.