Pushrods for milled heads

I don't know if anyone else has contributed their wisdom on pushrod length, but here is my understanding of it.

Theoretically, at half lift, the valve tip, the center line of the 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 of the ball should be aligned with the centerline of the rocker shaft.

Pushrod length has no effect on alignment on the valve side of the 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 operation easy.

In real life, some builders go to all this trouble to measure the 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 Drews

Jack's got it. And, that's the name of that tune.

Kas Kastner

GT6 pushrods

> 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 length.

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.

Kas Kastner

TR3-4 pushrods

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.

Ted Schumacher

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