[SusieQ]

Thank you Tom Vaught! Nice meeting you!

[Tom Vaught]

Originally Posted by Singleton

I believe that the driven gear and the drive gear tooth count of the SD remained the same as standard pontiac engines at 14 for each gear, just at a slightly different diameters

Agree, Singleton. Read this again everyone:

"A larger distributor gear was intended as a solution to issues with camshaft gear wear in high-performance applications. Getting the distributor with the large gear to fit into the block required an oversize distributor hole (10). This was also a feature found on the 303, 366 and Ram Air V 400s. The standard production block's distributor hole is shown for reference (11)." The 303s were Trans Am engines, no real race miles. The Ram Air V engines never went into production. The 366 engines did run for a few races in the NASCAR series with one team, possible two teams.

Rather than utilize a new distributor core casting to accommodate the oversize gear, the SD distributor was fitted with a sleeve. Accordingly, the corresponding cam shaft gear was undersized to match."

I believe the quoted statement in the first paragraph quoted implies this.

a) Dyno testing with the standard sized camshaft gear and the 80 psi oil pump potentially caused durability testing issues on the engines required to prove 50,000 durability on the track for emissions testing.
(Gear wear, the timing on the distributor changes, the emissions numbers change, not good for certification of the 455 SD engines).

So how many actual miles do you have on your GTOs with the 80 psi pump and drive gear system, Formulajones, that you drive daily?

Tom V.

ps Nice meeting you too Susie Q. Have fun with your car.

[Formulajones]

To date, we've put 73,343 miles on the Firebird. This one isn't the only success story either.

[Bill Hanlon]

Originally Posted by Tom Vaught

1) sorry for the confusion, Bill. Would you agree that the 455 SD Block has a larger distributor hole machined into the block and you need a distributor housing "sleeve" to run a conventional Distributor Gear and Conventional Camshaft? Not a Pontiac SD Expert by any means like Tom S, but assumed that the 455 SD camshaft and the 455 SD Distributor Gear were a matched set. And I assumed that when I wrote the post that Pontiac Engineers put a different configuration (sized) gear on both the distributor and the camshaft to handle the higher pressure 455 SD Pump.

What am I missing here? Why recast a new Pontiac block with a different distributor installation hole size for no reason?

Tom V.

I'm the dummy here. Just trying to learn. Seems to me that if you made the distributor gear larger, you'd have to make the cam gear larger to keep the 1:1 ratio required of the gears (same number of teeth on both).

[Tom Vaught]

Help you out Bill.

STOCK Pontiac Distributor Gear Diameter is 1.350 inches
Stock Pontiac camshaft gear is 1.985 inches. .635 inches in diameter difference but same 14 tooth count.

If Pontiac Bored the hole Bigger on the Block and made it .150 inches larger then the new distributor gear
size would be 1.500 inches and the camshaft gear would be 1.835 inches so THE DIAMETERS OF THE TWO
TEETHED PARTS WOULD BE CLOSER TO THE SAME DIAMETER. These are general dimensions and there is
always a bit of room to get the gear inside the block.

So now the tooth spacing (for the 14 teeth gears) would also be closer to the same.

Tom V

[Bill Hanlon]

Still trying to understand. (I'm a bit thick headed)

So if the gears are not the same diameter, but have the same number of teeth, then the teeth must not be symmetrical even though they mesh with a 1:1 ratio. I realize there is a 90 degree change in direction from cam to distributor. I had just never realized that the gears were not identical. Never really looked hard either.

It is a good day. I learned something new.

[Sirrotica]

Helical cut gears just change pitch angles to accommodate for ratio or diameter change.

Think of a rear differential that has the same spacing from pinion center to ring gear carrier surface dimension, but by changing the pitch angle is able to accommodate different ratios within the same dimensions.

Pontiac engineers knew there would be more stress from using the 80 PSI SD oil pump, and wanted more tooth contact area to compensate for the higher stress on the 2 gears. Increasing the distributor gear diameter, and adjusting the tooth angle gave them added strength on the driven gear, and more area.

[formula kid]

Ok, I just took a count of a standard Pontiac distributor gear teeth = 14. I took a count of a extra SD455 distributor it has 15 teeth. Also checked it against a NOS SD455 gear part # 801318 it has 15 teeth. The Number of teeth on a regular Pontiac cam is 14. The number of teeth on a SD cam is 15. Hope this helps in some way.

[Bill Hanlon]

Thanks guys. Brad's explanation of the pitch change as used in a differential finally turned on the light for me.

[Tom Vaught]

Wow! That is great information.
By increasing the diameter of the SD Distributor Gear and by reducing the diameter of the SD camshaft gear they were able to get another full gear tooth into the Helical Cut Gear "mesh".

THAT is a piece of the 455 SD story that I was never aware of. Thanks formula kid.
Always like to learn something new about Pontiacs.

Tom V.

[Singleton]

Originally Posted by Tom Vaught

Wow! That is great information.
By increasing the diameter of the SD Distributor Gear and by reducing the diameter of the SD camshaft gear they were able to get another full gear tooth into the Helical Cut Gear "mesh".

THAT is a piece of the 455 SD story that I was never aware of. Thanks formula kid.
Always like to learn something new about Pontiacs.

Tom V.

Agreed. I searched and searched this forum for tooth count on the SD gear and came up empty. Same for searches on internet. The only thing I could find was that the SD used a larger distributor gear and smaller cam gear, but no specifics on tooth count. Thanks for the info Formulakid.

[KEN CROCIE]

To enhance wear and break in performance, the SD dist. gear was Cadmium plated, as were std. gears slated for use with the 60 psi. pump

[Tom Vaught]

Thanks Ken, Hope all is well in Cali and Texas

Tom V.

[1968GTO421]

Y'all have convinced me here, I'm going with a 60 psi pump, probably from Luhn or Nitemare. Thanks all.

(Always good to hear of members helping members here. Glad Tom V was able to help member Susie Q.)

[formula kid]

Thank you Ken the cam that I have is your HC-62 still in the box.
Shure would like to raid the old H-O Racing warehouse and get a HC-63 cam!

[Cliff R]

Some food for thought on distributor gears. I've had several aftermarket HEI distributors sent here that showed HEAVY wear on the distributor gear after very short time in service. Enough that it needs to be mentioned here. I get in factory points and HEI's all the time and it's rare to see any wear on their nearly half a Century old gears at all, or at least not enough to be alarming or where they would need replaced.

These aftermarket HEI's are obviously "offshore" parts. The distributor gears are dark black bearing the resemblance of Chinese materials. The most recent one I had in here was for an Oldsmobile, purchased new from Summit Racing. The owner may have said it was a Pro-Line, but not sure. Really doesn't matter, folks just need to know that there is potential for quick wear and failure of those parts........Cliff

[Tom Vaught]

Originally Posted by 69TempestCustomS

I always though you should completely disassemble the pump and then braze the pickup on. then check/correct for any distortion caused by the heat.

copper gasket? never saw evidence of a paper one failing or blocking the flow of oil. somebody is a little OCD here. cant re use a copper one without re heat treating it.

I will pass on another tip the WW-II Instructor (Chief Mechanic at my Uncle's Pontiac Dealership) showed me years ago.

Sometimes, when you are drilling with a small drill bit, the drill bit breaks into two pieces. The overall length on most drills (even small diameter drills) is over 2.0" long.

So I was going to braze up a pick-up on a new oil pump for a Pontiac Engine and he explained there was a better way and no harm would come to the pump with his method. You could also use this method if you did not have a Gas Torch or welded available available.

So what he did was:

a) Carefully drill a hole thru the soft cast iron oil pump pickup boss with a drill slightly smaller vs the broken drill he had available. Clear the drill shavings.

b) The drill needs to enter and exit both sides of the Oil Pump boss.

c) Install the oil pick-up screen to the oil pump in the proper location.

d) Now using the hole previously drilled in the boss as a guide, drill thru one side of the oil pump boss, then thru both sides of the pick-up screen tube, and finally thru the other side of the oil pump boss. Drill slowly and carefully.

e) Install a small drill thru the 4 holes and get a total length for a retention pin (broken drill bit).

f) Trim the broken drill bit to the same length as the outside diameter of the pump boss minus .060" and then tap the broken drill bit into the 4 holes.

g) Take a small Ball Pean Hammer and using the ball end "trap" the broken drill bit inside the boss on each side by peaning the cast iron over the drilled outside holes.

NOW THE PICK-UP TUBE IS SECURED SO IT WILL NEVER FALL OUT FROM VIBRATION, YOU DID NOT NEED A TORCH, YOU DID NOT NEED A ARC WELDER, OR EVEN ELECTRICITY. A simple drill set, a 3 Jaw "Hand Brace"
and a little muscle and the oil pump is ready to go back on the engine. It will never come out again.

Thanks Del Forrest.

Tom V.

[65sport]

Hi Cliff-
I'm needing a new pickup screen for a bone stock application, I think I want a fine screen. I like the set screw idea and will likely do that. Can you recommend a good one ? Thanks.