Pushrods for milled heads
I don't know if anyone else has contributed their wisdom on
length, but here is my understanding of it.
Theoretically, at half lift, the valve tip, the center line
rocker shaft, and the pushrod end should be in a straight line.
So looking at the rocker position, one end at a time............
The alignment of the valve stem and the rocker shaft are determined
by the valve stem length, the depth of machining for the valve seat,
and the height of the rocker stands. The alignment is achieved by
making the rocker stands taller or shorter. (Note -- with roller
rockers, it is proper to have the centerline of the roller horizontal
to the rocker shaft centerline, rather than having the contact line
of the roller in line with it).
At the pushrod end of the rocker, this means that the centerline
the ball should be aligned with the centerline of the rocker shaft.
Pushrod length has no effect on alignment on the valve side
rocker. The length of the pushrod depends on how much has been taken
off the head and how much has been taken off the cam base circle by
the regrinding. To make it theoretically correct, you must assemble
the engine, position the valve halfway down, and measure the length
required for the pushrod. This is done with an adjustable pushrod. At
the valve end, the spring is replaced by a very light one to make the
In real life, some builders go to all this trouble to measure
pushrod length, but many do not. Many just look at whether or not the
adjusting screw is reasonably centered in the rocker, so that there
is enough for the adjusting nut on the top and no interference of the
pushrod on the bottom. Interestingly, it is often the case that about
the same amount is milled off the head and is ground off the camshaft
base circle, in which case, a stock length pushrod is just fine.
Jack's got it. And, that's the name of that tune.
> I'm shaving a GT6 head and need to
know where to find shorter push rods to keep the rocker
> geometry correct. So far I have been unable to find the right
The tubular pushrods are produced with an insert ball and cup
that has a portion that goes up into the tube. This is NOT welded
in place but simply pressed in. SO.......you can pull out the
insert and shorten the pushrod as you need then just press the
insert back into place. I generally did this in a lathe using
a parting tool and therefore did not have to remove the insert
I just tooled off a bit of materiel right up next to the insert
joint, tested it for length and then went on as needed, recording
as you go and then make all the rest the same length. It's just
not a big deal.
Usually making the pushrod shorter by 1/2 the amount milled
form the head will work.
On my daugter's tr6 - '74 with .102" cut from head yielding
9.42 in case anyone is interested - we used the stock length pushrod
(part #V618) and an S2 cam and still had valve adjsutment.
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