If heads are milled do I need shorter pushrods?

[eric383]

Just a question for the experts, lets say you mill .015 off stock 440 heads should you run shorter pushrods if you are using the stock rocker setup? Just wondering.

 

[451Mopar]

I use an adjustable pushrod to measure the actual length with the engine assembled. I like to use 0.040" pre-load, but most lifters can handle 0.060"+ of pre-load.

 

[khryslerkid]

Are you milling the heads to gain more compression? If not you could just use a heavier head gasket to make up the difference. If it's more compression you're after, getting an adjustable push rod, like 451 Mopar stated, to check what you have would be ideal.

 

[5.7 hemi]

Also adjustable rockers come into play.

 

[wyrmrider]

do the whole mid lift procedure and get the right length pushrod
you may find yourself shimming your rocker shafts- almost a certainty with roller tip rockers
you want the motion across the valve as narrow as possible
ignore where the pattern is on the valve tip unless it's way off
your valve guides will love you
you do not want to start with this / or end up with this \ (pretend it's a rocker with tip on right and pushrod to the left which can happen if you try and center the pattern
centering the pattern is a mechanical problem and requires moving the fulcurm or valve tip sideways (some shims do this)
you want like this --- at mid lift- --- tangent to the valve stem !

 

[eric383]

Thanks for the replies, I am not doing this now but just wondering what would be done on a typical hydraulic flat tappet motor with a factory style rocker arm setup. Also some of these earlier 440 came with steel shim head gaskets didn't they? So if you use a typical head gasket you would be at .040 thickness, thicker than the steel shim. With this all being taken into consideration there must be wiggle room.

 

[wyrmrider]

Replacement non shim gaskets start at about .028 so you do not have to loose any compression and you are about the same place as a shim after a clean up block deck
using stock rockers or iron adjustable you will be fine as long as the cam is not huge as the extra lift is all at the push down from the same tip height
There are a lot of badly designed roller rockers out there
Some from big names that do not understand rocker geometry or have their own weird ideas (or justifications)
observe that a rocker ratio can be measured many ways
some measure the mechanical ratio at the tangent- the max but observe that the ratio of pushrod motion to valve motion diminishes as the rocker moves up and down from the center (line pushing an arc picture how much the valve would move if the rocker was tilted way up or down for a given pushrod move- not much
one reason that measured lift is not as much as the ratio says it should be
Another way is to compare the cam lift with the valve lift and just divide- this sorta gives an average ratio but the valve lift does = 1.5 x the cam lift (or whatever ratio)
this cuts down on tech calls that the mfg's rocker ratio is not correct

 

[wyrmrider]

https://www.forabodiesonly.com/mopar/threads/valve-train-geometry.407379/

 

[451Mopar]

Yes, there is wiggle room and in most cases, with a mild cam, it is not an issue.
I like knowing where I am at in case of problems. One example was a rebuilt 440 with new cam and lifters and the owner was using the earlier 1967? pushrods that are longer than the post 1967 pushrods. I think the lifters of the original engine had the cup deeper in the body than the replacements.

Unlike a stud mounted rocker system (GM, magnum), you can't change rocker arm geometry with the pushrod length, just the lifter pre-load, or clearance with a solid cam.
On shaft mounted rockers, the geometry height is adjusted in the height of the rocker shaft support, and the height of the valve stem tip. Setting the rocker arm geometry on shaft mounted rockers is done before measuring for pushrod length.
If your using stock valves, rockers, and cam all the "rocker arm geometry" is still the same as "stock", no matter the distance from cam to rocker arm.
The pushrod geometry would change slightly with different length pushrods, but usually not much or worry about under about 3/4" lift.

 

[Cranky]

If everything is stock and is correct from the factory (isn't always right but usually close), a .015 mill on the heads isn't going to hurt anything....unless your lifter preload is already at the max depth. Hydraulic lifters are usually pretty forgiving but if you like to hammer the throttle from time to time, you might experience lifter pump up (if at max depth) which will make the engine run rough once you come back to a slower rpm range. If the engine already has the thicker 'normal' composition head gaskets, then the .015 cut will put you back more closely to what the preload should be. With hydraulics, I like to run them with very little preload. People have told me that's not right but so far haven't experienced any ill effects. It's still a good idea to check what ya have.

 

[wyrmrider]

"just wondering what would be done on a typical hydraulic flat tappet motor with a factory style rocker arm setup."
you should be good to go
it's roller rockers that get you in trouble
also check your stock rockers carefully for wear- more lift can cause binding when the rocker moves more than its used to
the earlier lifters and pushrods also had a smaller ball and cup- they wore, replace with the later stuff always
op check and see where the wear marks are on your valve tips and rocker tips, obviously if the rocker tips are worn they will catch the valve tips with increased lift- also the psuhrod tips and rocker cups- keep all the parts together- if you take the rockers off the shafts put them back the same place if you are going to reuse (which works most of the time but when it does not...)

 

[wyrmrider]

some great pics in the small block thread
https://www.forabodiesonly.com/mopar/threads/valve-train-geometry.407379/#post-1972077748 post 12

 

[BSB67]

If everything is stock and is correct from the factory (isn't always right but usually close), a .015 mill on the heads isn't going to hurt anything...

This

 

[dvw]

I've run into milled head/deck where the pushrod bottomed the lifter. We shimmed the rocker shafts. Still working fine. Motor has been together 15 years.
Doug

 

[eric383]

If everything is stock and is correct from the factory (isn't always right but usually close), a .015 mill on the heads isn't going to hurt anything....unless your lifter preload is already at the max depth. Hydraulic lifters are usually pretty forgiving but if you like to hammer the throttle from time to time, you might experience lifter pump up (if at max depth) which will make the engine run rough once you come back to a slower rpm range. If the engine already has the thicker 'normal' composition head gaskets, then the .015 cut will put you back more closely to what the preload should be. With hydraulics, I like to run them with very little preload. People have told me that's not right but so far haven't experienced any ill effects. It's still a good idea to check what ya have.

I have heard about the theory of running less preload but I wasn't going to throw that out there yet. Thanks!

 

[wyrmrider]

less preload
big cam
stick shift
race automatic (or changed governor weights)
otherwise whatever it is usually works fine
shims are one fix but your geometry may be off
if off tooo much then pushrods