Custom Pushrods / Preload

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360duster

360duster

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Hi Guys,

next step in my engine build is to measure / order pushrods for it. Can you tell me some good vendors for these?

For the lifter preload: i use hydraulic rollers (factory ones, LA Roller cam block). I want to measure the length of the pushrod when it´s at the cam´s base circle, how much should i add to preload the lifters correctly?

Thanks for Info!

Michael
 
I use Smith Bros. for the last couple sets. Nice product, fast delivery, reasonable price.
You get everything torqued in place and use a pushrod length checker (available from Comp, or make your own) to get it set with the preload the lfiters you're using requires. Stock roller lifters I run .040. Performance lifters go by the manufaturer's spec.
 
check page 3 of this article.
Lots of good info that you will use in your build for the valve train.

onig
 
wow are you looking for proper push rod length or rocker geomitry they go hand in hand and to get proper push rod lenth you need to use a solid lift but we need more info. before we get into this.???
 
Geometry on a stock shaft rocker design has nothing to do with pushrod length. They only transmit (most of) the lift of the cam lobe. Geometry on a Mopar with shaft rockers depends on the valve job, the length of the valves, and the placement of the centerline of the rocker shaft.
 
you could shim the shaft and that would change it and if his heads are cut would change the angles i would think but i could be wrong and if its stock you would just buy the same length no???
 
The relationship between the centerline of the shaft, and the valve stem tip is "geometry" on a Mopar. If you draw lines straight up thru the valve, and straight up the pedestal thru the shaft (the angle of the hold down bolts) you'll see the two lines are not parallel. They lean in towards each other. That's a big deal. That means if the shaft goes up (as with shims) or the valve tip goes up (as with poor valve jobs and/or worn parts) the distance between the two is changed. That change ruins the geometry the rockers need to have. The height of the shaft from the head gasket surface is irrelevant except for the pushrod length figure. Because you're moving both the valve and the rocker in the same direction and the same amount when a head gasket sruface in milled, the geometry is not affected.
 
well wouldent milling the head for number wise ,change lets say his head is cut .060 it would drive the push rod into the bottom of the lifter and that would change the angle of the rock would it not buy giving it more lift in which it would change the angle . or am i wrong??
 
You're correct, although technically excessive milling means you need to replace the pushrods with shorter pushrods so the plunger isn't "pushed in" so far giving too much lifter preload. As the lifter is already absorbing a tiny amount of lift just doing it's job, a change like that would be almost immaterial.
What you're talking about has nothing to do with what is considered valvetrain geometry tho. Valvetrain geometry is bascially the motion of the rocker and it's interaction with the valve tip and as I said, cut all you want. Unless you sink the valves, use longer ones or don't trim the stems as part of the valve job, or raise or lower the centerline of the rocker shaft, you will not change the valvetrain geometry.
What you're actually talking about with the pushrod length is affecting "pushrod angle". That's the difference in angles between the lifter centerline and the rocker's pushrod seat's centerline. Not to be confused with "lifter angle" which is pre-set when the block was designed and not very adjustable.
 
so in turn if you go to a 1.6 or a 1.7 rocker all that is doing is giving you more lift with out going to a bigger cam.??
 
It does a few things:
In terms of rocker geometry it changes the place the pushrod cup is.. .Which means you may lose more lift due to angularity issues.
It will give you more overall lift.
It will give you more mid-lift duration but no more total.
It will open and shut the valve faster (quicker rate of lift).
It makes the lifter, pushrod, and rocker effectively lighter because the leverage is greater on the valve side of the rocker where the spring sits. conversely that leverage is less on the pushrod side so the valve spring is effectively heavier in terms of the force required to open the valve.
 
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