Melonized Distributor Gear - Team Camaro Tech
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post #1 of 22 (permalink) Old Jun 9th, 06, 10:33 PM Thread Starter
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Melonized Distributor Gear

Hello,
Is it really necessary to swap the gear offa my Pertronix distributor and replace it with a GM Melonized one?

I have the recommended melonized gear, problem is, GM's largest diameter is 31/64" ID and the aftermarket distributors all run a 1/2" ID. So to get the bugger on there, I'd have to drill/bore out the gear which might screw up it's heat treatment anyway.

So....I'm told that the one on the Pertronix is OK to use...just want a few more opinions before I drop this into my ZZ502 with the OEM steel roller cam shaft.

Any thoughts?
Tim

Meanchicken
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post #2 of 22 (permalink) Old Jun 10th, 06, 12:16 PM
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Re: Melonized Distributor Gear

I am using the one that came on my Pertronics HEI in a 355 with an Elgin solid cam and haven't had any problems.
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post #3 of 22 (permalink) Old Jun 10th, 06, 12:20 PM
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Cool Re: Melonized Distributor Gear

It depends upon the core of your camshaft. If it is billet steel it requires a softer gear to drive the distributor and oil pump to prevent wearing out the cam gear and creating havoc with ignition timing. If you have a cast iron core cam (generally only roller cams are steel) then you do not need a brass or Melonizedô gear.


Larger Dave
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post #4 of 22 (permalink) Old Jun 10th, 06, 12:29 PM
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Gary
 
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Re: Melonized Distributor Gear

I was under the impression that all GM factory cams are compatible with stock distributor gears. As I understand it, GM's use a plain steel core, not a billet core which is the one that requires bronze or melonized gears. I have a Lunati billet that requires bronze although the two techs I've talked to have remarked that folks have been reporting long-term successes with melnoized gears.

Gary Adrian
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post #5 of 22 (permalink) Old Jun 10th, 06, 01:27 PM
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Re: Melonized Distributor Gear

From the GM parts catalog, their words, not mine.
10456413 Distributor Gear
This melonized steel gear is required on all crate engines and roller camshafts that are made of steel. If engines are assembled not using this gear it may affect your engine warranty.
For aftermarker roller cams, it depends on the roller cam itself. Most steel billet rollers will need either the melonized gear or a brass gear. However some biller cams have a pressed on cast iron drive gear and they normally are compatable with the normal stock distributor gears.
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post #6 of 22 (permalink) Old Jun 10th, 06, 03:03 PM
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Gary
 
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Re: Melonized Distributor Gear

c byrd, I'd missed that when I read the description of the melonized gear awhile back, thanks for the tip. Is the cam in GM's crate engines different from production engines? All the cams I've taken out of hydraulic roller engines were steel - have all of the distributors in production hydraulic roller engines had the melonized gear? Can a novice recognize one?

Gary Adrian
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post #7 of 22 (permalink) Old Jun 10th, 06, 04:05 PM
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Cool Re: Melonized Distributor Gear

If it has roller tappets from the factory it shipped with a melonized gear on the distributor. Unless you have swapped out the distributor for an aftermarket there isn't a problem. Even then some, not all, not even a lot, but some are built with a melonized gear on it when sold to be as user friendly as possible. I doubt if you would recognize a melonized gear by sight as it is a metallurgical process (kind of like powder coating) which puts a softer covering on the wearing surfaces.


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post #8 of 22 (permalink) Old Jun 10th, 06, 04:44 PM
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Re: Melonized Distributor Gear

I thought melonizing is a hardening process? Here's a good read:

http://www.trutecind.com/heat/melon.htm

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post #9 of 22 (permalink) Old Jun 10th, 06, 08:00 PM
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Cool Re: Melonized Distributor Gear

Melonizing doesn't harden the part were by the whole part is uniformly harder as in tempering, it is a chemical reaction involving Nitrate salts. Back in the early seventies GM used to nitrate their forged steel crank shafts using a vacuum deposit technology that took days to build up a couple of microns thick coating. The trouble is its is only a couple of molecules thick. The melonizing acts like a Teflon coating increasing wear by being slippery not increasing the hardness of the product (which technically it is so saying softer was a poor choice of words). The way to harden a part to make a wearing surface is to induction harden it with a high frequency transformer. This yields a thick hard machineable surface with a soft untempered core as is found in the Spicer C-clip style axles.

Since it is so thin you can literally see the underlying metal, so you can not see that part that has been melonized visually. Since it is only a couple of molecules thick the Brinell test will not work either as any attempt to scratch or abrade it would damage the surface.

From what I've read on the web site they have greatly enhanced the technology of how they deposit the nitrate salts with some kind of hot metal spray and quenching. If you have ever gotten Mercury into a gold ring you know how they do it. It is like a soldering process were by one metal (or metallic salt in this case) is melted at a temperature well below the melting point of the base metal and allowed to flow into the base metal (there is a chemical term for this process that escapes me). Once inside the metal it is uniformly heated and quenched to distribute the metallic salt and temper the part so that it doesn't otherwise effect it's metallurgical properties. At least that is how I interpret it.

I also have not mentioned this before now as it is also controversial and I prefer to help by clarifying issues rather than muddying the waters with my own opinions.

But I take the melonized gears off of my distributors if and when they come with them, and throw them away. I then replace them with an "Old School" brass gear that I know is the same hardness from the outside to the inside; and isn't relying upon a "crunchy candy shell" to keep a part from melting inside my motor.


Larger Dave
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post #10 of 22 (permalink) Old Jun 10th, 06, 08:49 PM
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Smile Re: Melonized Distributor Gear

I saw a documentary on TV on Afgahnistan(Sp?), and Tribesmen were making guns out of steel and then throwing the homemade gun parts into a coffee can filled with lit charcoal to case harden them!!

Crude, but it worked fine for killing people guns!!

pdq67
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post #11 of 22 (permalink) Old Jun 10th, 06, 09:00 PM
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Re: Melonized Distributor Gear

I have the same original question as Meanchicken...and seem to have gotten confused reading this post...(although I learned what "Melonized" means...and something about gun making...)

So in a GM Performance crate engine, with a roller hyd cam that has the "GM requires melonized gear part number XXX...", do you need the melonized gear or will a brass one work just as well?...(warranty is not a concern).

Thanks,
Scott

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post #12 of 22 (permalink) Old Jun 10th, 06, 10:20 PM Thread Starter
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Re: Melonized Distributor Gear

Ya...thanks guys....I still seem to have the question tho'.

I bought my ZZ502 without the heads on it or intake, carb and factory dist to save the $. I installed the heads myself along with an RPM Airgap intake and I am reusing my fairly new Edelbrock Performer 850 carb since I plan on going EFI down the road.

Anyway...I went with the Pertronics FlameThrower II distributor thinking I could just swap the dist gear, and that's when I found the issue with the GM Melonized gear having a slightly smaller ID than the Pertronix gear.


So Larger Dave...how durable are the bronze gears you use? Are they good for street use?
I've sean them in the Summit and Jegs catalog with the 0.5" ID.

Do you think I'll screw up the melonized gear I already have by drilling it out a little on a drill press, or honing it, or having it thrown on a lathe and opened up a tad??

Tim

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post #13 of 22 (permalink) Old Jun 10th, 06, 10:25 PM Thread Starter
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Re: Melonized Distributor Gear

Quote:
Originally Posted by Larger Dave
I doubt if you would recognize a melonized gear by sight as it is a metallurgical process (kind of like powder coating) which puts a softer covering on the wearing surfaces.
Larger Dave
Actually there is a visual difference. The Melonized gear is darker and has rougher texture than the gear from my Pertronix. If I knew how to post a pic, I would post one showing them side by side.

Tim

Meanchicken
68 SS
ZZ502; TKO-600; 3:73 Moser 12-bolt w/Detroit TruTrak; SSBC Force 10 4 wheel power disks;QA1 Coil Overs; Global West Tubulars;GNX Quick Ratio 12:1 PS; Hotchkis Front Sway Bar
87 Buick Grand National (does 10's)
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post #14 of 22 (permalink) Old Jun 10th, 06, 11:58 PM
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Re: Melonized Distributor Gear

Guy's,

I have a brand new, el-cheapo, Hotrodsusa HEI dizzy in it's box in my car's trunk and if I even think that it's new gear won't work, I will pull a used one off my point dizzy's and make it fit!!

And be done with it!!

pdq67
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post #15 of 22 (permalink) Old Jun 11th, 06, 12:05 AM
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Re: Melonized Distributor Gear

You can have a melonized gear honed to fit the aftermarket distributors at most machine shops. I would NOT use a bronze gear in a street application unless there was no other choice (billet cam, etc.)

Jody
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