[kenneth77]

last summer i had a rocker arm failure,so i have changed the valve train in the engine.
engine is a 1966 ws 389,093 heads,sum2802 camshaft,rhoads lifters.
since last summer the mechanic have changed original rockers with prw 455 7/16 1.52 rocker arms. he also have pulled original studs,and mounted adjustable studs. the metal where the studs is screwd in,is not machined down,to compensate for the lenght of the guide plate and the new adjustable stud. today i mounted the pushrods,and they was to short,approx 0,5".i need to order new push rods ( and guide plates).

how do i measure up,to get the correct lenght of the pushrods?
do they have to be of hardend steel?

the guide holes in the guide plate did not line up with all the guide holes in the head,so i have to get new guide plates also,that fit the 389 engine.

is there guide plates made for the 389 engine,or do i have to do some work on others.

thank you

[Mr. P-Body]

Kenneth,

You officially have a "bag of worms" on your hands.

Changing the rockers (if true Pontiac) should have no affect on pushrod length.

389 and 400 have different spacing between the valves and between rocker studs. 400-455 guideplates will NOT fit. Correct 389/421 guideplates dried up years ago.

The alignment slots in the heads are there because there was no guideplate. If you add guideplates without modifying the slots, you WILL have pushrod "bind".

We've been through this before. Your best solution is to remove the heads. Have the slots drilled to a round hole about 1/2" in diameter. Machine the stud bosses flat. HeliCoil the stud holes for 7/16" threads (7/16-14). Get a set of BBC rocker studs. Use Isky "adjustable" guideplates. A good machinist will be needed to help you get everyhting "square". Once the guideplates are properly spaced, tack-weld them together (they're two-piece).

Jim

[kenneth77]

the guide holes in the heads are slotted out. the original studs have been pulled,and mounted 7/16 studs with poly locks.the guide holes in the guide plate,dont line up with the guide holes in the heads.some of the guide holes in the plate,are off 3mm of the center of the guide holes in the heads,so i think there have been mounted 400 or 455 guide plates.i have to change them with 389/421 guide plates. the stud bosses have not been machined down( do you have to machine down stud bosses,when changing to adustable rockers/guide plate).

my problem is that i have to get new pushrods,and i have to measure to get the correct lenght.i also need to order new guide plates. i have ordered some parts from pontiac dude before,so i think he have the parts..

[PONTIAC DUDE]

The problem is the valve spacing and trying to use the later wider spacing guideplates.

I'll PM ya.

[kenneth77]

valve spacing:do you mean the lenght between intake and exhaust valve on the head?

does anybody have a link to how measure measure pushrod lenght

[Mr. P-Body]

Kenneth,

We use an "adjustable" pushrod. That is, one that has been cut, tapped and extended with a threaded rod in between. Comp and others sell them, in sets and as individual sizes. Jim Hand's book "How to Buld Max-performance Pontiac V8s" has a step-by-step set of instructions for how to measure the length properly.

And yes, spacing is the distance between the studs (more important in this particular matter than the space between the valves).

Jim

[kenneth77]

i have jim hands book,so i guess i have to read.

[kenneth77]

in the pics you see that the guide hole is off center of the guide hole in the head. in the pic with the rocker arm,i have pushed the pushrod up in the rocker arm,see how off the rocker is

i need to modify or remove the guide plate

[PONTIAC DUDE]

Those holes aren't elongated. Someone drilled them out when you had the guideplates installed. You have 2 choices now. Find a set of pre 66 guideplates out there or cut the later ones shorter & weld back together to line the rocker back up.

[kenneth77]

i will cut them,and weld them back together.
do i cut them so the center hole in the guide plate is center of the stud bolt?

[Mr. P-Body]

Kenneth,

Maybe you missed it, but... Iskendarian sells "adjustable" guideplates for small block Chevys. They can be made EXACTLY right for the early heads. They're a whole lot better than trying to cobble something together. We've used them MANY times, and never had a fitment or wear "issue". We've tried in vain for years, to find the "real" Pontiac guideplates for the early heads. Don Roberts got the last set about 9 years ago...

FWIW

Jim