[Jack Gifford]

Originally Posted by Bill Hanlon

... Valve Rocker Arm for 56 (not 55) through 59...

Bill- do you know how the '55 arm differs from '56-59? Or is it just a matter of some of the "kit" parts being different, such as the pivot ball or nut? I've only run one '55 engine and never modified it- and didn't pay much attention to details of the rocker arms. Or, I've forgotten over the last fifty-plus years!

[Bill Hanlon]

Sorry, I do not know. May have to do with the ball as the 55 stud had 3/8x24 thread (and was "adjustable" if I remember correctly) while the 56-58 (and probably later) stud had 5/16x24 thread (and just torqued down to 20 [?] ft/lbs) according to the 55-58 GMC Master Parts Book. Neither the GMC MPB nor the 1960 Pontiac Master Parts Catalog list the rockers separately.

[Jack Gifford]

MJ- I poked through boxes tonight.

First- A measurement that may be of help to someone someday: Early rocker arms ('55 through I-think-'60) are about 2.9" long; later ('61? through '79) are about 3.1" long. These are merely rough overall lengths to identify whether early or late- I made no attempt to measure actual center-to-center dimensions of valve tip to pushrod seat, etc. And I measured only 1.5 ratio late arms.

Second, I realized that I never did do any swapping-around of any 5/16" stud Pontiac rockers, so I have no experience that would help you with direct replacement arms for the existing studs of your '55 heads (which are 5/16", aren't they?).

Third- I'm puzzled to find a set of early rockers with oil holes for 3/8" studs. I honestly don't remember what I used them on or how I came up with them. Maybe I figured a way to drill oil holes in them (and since forgot)? Maybe Pontiac or the aftermarket offered them at some point? Maybe someone else remembers such an animal?

[tom s]

Jack,67 and newer are much diff.I guess that was when they changed the valve angle?Tom

[Jack Gifford]

Yeah, in '67 the valve inclination went from 20 degree to 14 degree.

To continue "categorizing" various Pontiac rocker arms: can anybody put a '66 arm next to a '67 & later and describe the differences, if any? If different, is the '66 arm about 2.9" long?

[MJVAUGHANS]

Jack--I beleive my studs are 3/8" and are straight of course. Your measurement sounds correct and is also my difficulty.

My plan is to get a single 1.5 ratio, 3/8 stud, roller-tip, chevy rocker arm and see if the stud to valve spacing is correct, and if so then try to check the pushrod length(geometry?) and see if it is possible to make something fit. Since the pushrod guide holes are round and not elongated I don't have much room for error there.

*IF ANYONE KNOWS FOR SURE THAT THERE IS NO WAY THAT THIS COULD WORK ON THE 1955 WITH OUT HEAD MACHINING PLEASE GIVE ME A HEADS-UP BEFORE I WASTE ALOT OF TIME EXPERIMENTING WITH SOMETHING THAT I DON'T UNDERSATAND FULLY-PLEASE*

[MJVAUGHANS]

OK guys here is my latest update:
I bought a Chevy rocker arm(non-roller) because they look very close to the pontiac ones, Sealed Power part# R-826, rotated the engine until on the #1 Cyl. one of the pushrods was all the way up and one of them was all the way down(to simulate both extremes), colored the valve stems with a Sharpie, installed the rocker with both the stud oiling hollow ball and then later the chevy one and installed the nut until there was a little preload. Then I wiggled the arms back and forth several times to mark the valve stem and the rocker arm.
The 2 pics show the tell marks and the rocker and valve stems. Do you think these are acceptable or is the one on the left(pushrod all the way down) too close to the edge?

[Jack Gifford]

That doesn't look good, but- without first determining the appropriate pushrod length, it's not meaningful. What application is that SBC rocker arm?

Edit: first read my next post.

[Jack Gifford]

Originally Posted by MJVAUGHANS

... rotated the engine until on the #1 Cyl. one of the pushrods was all the way up and one of them was all the way down... installed the rocker... and installed the nut until there was a little preload...

If you did exactly as you said, the adjustment wouldn't be near correct. Or did you separately rotate each lobe to its base circle before adjusting its rocker, as you should have?

[MJVAUGHANS]

Waiting on parts, will report back later.

[MJVAUGHANS]

The SBC rockers I ordered were self aligning so they hit on the valve springs so that experiment did not go very far. I measured them and they are shorter than my pontiac rockers so even with changing the pushrods I don't know if I could have gotten it to work. (I am not a machinist or master-tech) I wish I could order just 1 of the rockers I want to play with without having to pay $30 for it with shipping/handling!

[Pontirag]

It was not before too long ago that billet aluminum rockers for pontiacs needed to be massaged between the valve spring cap(retainer) and the underside of the rocker. Not that I would recommend doing any grinding for experimental purposes.

Just curios ? why did you choose the chevy rocker?

[MJVAUGHANS]

I was going to try the chevy rocker because it was for a 3/8 stud and when I compared my pontiac stamped steel rocker to a sbc stamped steel they looked really similar and because the 1955 v8 was unlike ANY of the later years in some ways I was hoping I might get lucky and find that the mysterious first year actually used the same rocker that the chevys went on to use. A longshot, but not impossible. No one sells a pontiac rocker in a 3/8 stud size, only 7/16. I have been looking at the COMP sportsman or PRW rockers-clean, simple and not too big.

[Jack Gifford]

Don't you have a junkyard nearby to grab rocker arms to fiddle with? Or friends with SBC junk bins?

Zillions of SBC engines had non-self-aligning rocker arms.

I believe Pioneer still sells 3/8" stud Pontiac rocker arms, possibly the early ones. If not, I'm sure Kanter Auto has them (but they're typically on the expensive side).

[Pontirag]

The rocker arm nuts for 55's, ...they are common? what kind of part number at an auto parts store? I have a 55, and several of the rocker arms come loose over time, I suspect that when one or more start comming loose they all will eventualy so its best to replace them all at once? Hopefully they are not pricey like lifters and mainbearings

[MJVAUGHANS]

Pontirag,

I have just used regular 3/8-24 thread nuts for a sbc. They are cheap. (Melling part# MRM-1786) If you no alot of adjusting back and forth you may want to double nut them.

[MJVAUGHANS]

Update and observations:
I gave up on the roller rocker idea for now and broke down and ordered a set of stamped steel replacements from falcon global(they get them from Kanter). They have a listing for both the 1955 and the 1956. I ordered the 1956 instead of the 1955 because they would have 3/8" rocker balls and the 1955 would have 5/16" (my studs are 3/8").

Besides the 3/8 vs. 5/16 discrepancies there were a couple of other things to note about them.
1. The rocker balls I got are the same diameter and height, but they are not hollow for the stud oiling.
2. The pushrod sockets have the hole drilled in them for the pushrod oiling.
3. The nuts that came with them are not self locking, crimped or otherwise. (That is probably correct for 1956 since they were just supposed to be torqued down with no adjustment, in 1955 they were adjustable.)

So ignoring that my studs are 3/8 instead of 5/16 for whatever reason(remember first year GMC V8), these rocker sets that Kanter is selling are not exactly correct factory replacements.

My plan for now unless I change my mind is to use the new stamped steel, let them pushrod oil, polish my hollow balls and reuse them so it will also stud oil and use sbc crimped nuts and double nut them.

[Old Goat Racer]

These are NOS-GM. Not sure what year they are. Missing 1 p-rod & 1 rocker.

[MJVAUGHANS]

Here is some interesting info. I contacted comp cams about what I was trying to do, install roller tip rockers like their sportsman series, on my 287cu. a while back and here is their response:

ME Does COMP or anybody else sell a 3/8" stud Pontiac rocker arm? The only thing I can find for a Pontiac is for 7/16" stud. My 1955 287cu studs are 3/8".

If not could I run the 3/8" balls with the 7/16" rocker arms? What I mean is does the size of the pivot ball and locknut designate it as 7/16" but the actual rocker may be the same?

THEM Ihave done some checking, and it will be ok for you to swap the pivot balls.

There will be a little more space between the rocker stud and the slot in the rocker, than on a normal setup, but it should be fine.

The 3/8" pivot balls are part# 1400B-16. A set sells for $10.31.

Thanks,
Matt Maxwell
COMP Performance Group
Technical Consultant.

[Jack Gifford]

I'm glad you've now got a "plan"- hope it works well.
I wouldn't bother trying for stud oiling, as you'll get plenty of oil to the ball/rocker area via the pushrod route. I'd prefer to keep the known-compatible rockers and balls together (the new ones you're buying).