I recently found out the hard way that camshafts and distributor gear materials have changed over the years.

The older flat tappet camshafts were made from iron and were matched with iron distributor gears. This was standard from the 60's to the 90's.

In the late 80's to early 90's the auto makers switched to roller cams which are made from steel. These camshafts are not compatible with the old iron gears. You must use a hardened steel (melonized) distributor gear. (Melonizing is a fancy term for a proprietary hot salt nitriding process)

I was not aware of this and paid the price. Sat on side of the road 24 hrs waiting for replacement distributor drive gear, one of very few parts I did not have in my spares.

Steve G linked an article on this subject. They list 3 different cam materials and 4 types of gears! A good discussion, however, the GM melonized gear (#19052845) they recommend does not fit the .491 OEM distributor shaft, it has a smaller inside diameter.

http://www.onedirt.com/news/it...-gear-compatibility/

The correct GM melonized gear is part #10456413 Can you find the iron gear?



Another example of what you don't know can hurt you. When I replaced my 454 with a factory GM crate 454HO there was a recommended distributor but no mention of the need to have the later style gear, even though the engine is specifically designed to replace early pre-emission engines which all had iron gear distributors.

The crate engine has camshaft #24502611. If you go to the GM parts website (and others like JEGS, etc) they warn that you must use gear 10456413, but not in the factory "Installation instructions" that came with the engine!

Meanwhile, I replaced the gear on the distributor with the proper gear and I will monitor for gear wear. Hopefully the camshaft gear is not too worn. Also, I posted a warning in the 454HO engine swap thread to check which gear you're using.

Hello Steve, have you pulled your distributor lately to check how it is wearing ? The issues I had with my 460 came back in bit me and caused me to miss the 100th running of the Indy 500 about 4 hrs from home on our way to Indy without any warning the motor made a pop and died leaving us on the side of I 80 for 24 hrs before I could get a heavy hauler to tow it back to Long Island. The cam and distributer gears were wiped out.

Oh crap. Welcome to my world.

I pulled the distributor after about 1000 miles. Very little wear on the new gear, slight shiny wear areas. Pulled it again in Florida, still looked good. When I got home I looked again. It still shows very little wear after about 5000 miles. It looks like I got away with it and may be OK for a while. I'll check it every 5000 miles or so to be sure.

Based on reading the chevy gear head sites they recommend a modification to the distributor to improve gear oiling. There is a pressure gallery around the shaft housing, just above the gear. If you cut a small groove in the shaft housing it directs oil onto to the gears below. I did this, it may have helped, can't be sure. Maybe you can do something like this with yours?

There is more to shaft and gear compatibility than I thought. Looks like we are both learning the hard way. Good luck with your project.

Now I am worried about the drive gear on my new distributor! The seller says it is hardened steel nothing about melonizing, The articles I have looked at said with my old Cam with any of the 3 gears would work, Composite, Iron or Melonized. Nothing about hardened steel, now what the hell do I do!!!!

I will cut the little groove that is recommended.

quote:

Melonized

Does his explain anything?

https://www.onedirt.com/tech/e...-gear-compatibility/

quote:

posted 07-05-2019 04:17 PMHide Postquote:Melonized Does his explain anything?

Dick, that was the article that was the most confusing because they never mention harden steel at least that I could find!!!

From what I've read , the "hardened steel" gear is harder than the crankshaft gear and will result in destroying of the crankshaft gear.

I have been researching a distributor for my truck and was warned of this.

quote:

Originally posted by Harold,Cat&Sam:
From what I've read , the "hardened steel" gear is harder than the crankshaft gear and will result in destroying of the crankshaft gear.

I have been researching a distributor for my truck and was warned of this.

That is my fear too, my stribby drives off the cam and that gear they say is iron, I hope the oil groove will help it out. We shall see!

There is a chart in the URL Dick mentions that says it is ok but I wonder??

quote:

Dick, that was the article that was the most confusing because they never mention harden steel at least that I could find!

." Both GM and Ford used a heat treating process called melonizing to harden the distributor gears. At least for the GM pieces, these gears were easy to identify with a light silver cast to the material. For many years, these gears were only available through Ford and GM.

Crap!! the only introduction to a distributor I ever had was replacing a cap or a rotor.. oh and messin' with the timing.

Use this https://www.holley.com/product...utorless/parts/60151 and your issues are over. It can be moved from one engine to another if you swap or replace. Not sure how you seal the distributor port but MSD will answer questions.

Holey Moley $1300 for a stribbie, Yikes. It still has a gear and drives the oil pump! I think the oil pump causes most of the gear wear.

I wonder if Melonizing and the harden gear in the stribbie I bought is the same process?? I hope the oil groove works, better than that I hope new wires, plugs and distributor, get the nose back on its feet, aka Tires!

I got burned on this one, too. The old iron camshafts will run with any of the gears. The problem came with the steel roller cams used later. They will eat anything but the melonized gears.

The replacement distributor worked fine with the old OEM engine. When I installed the modern roller cam 454HO I assumed the distributor could be used but the steel cam ate the gear. The melonized gear worked fine. When I later replaced the cam for tuning reasons I found minimal wear.