Melonized Distributor Gear [Archive] - Team Camaro Tech

: Melonized Distributor Gear


Meanchicken
Jun 9th, 06, 09:33 PM
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

deerhunter
Jun 10th, 06, 11:16 AM
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.

Larger Dave
Jun 10th, 06, 11:20 AM
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 Melonized™ gear.


Larger Dave

Busted Knuckles
Jun 10th, 06, 11:29 AM
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.

c byrd
Jun 10th, 06, 12:27 PM
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.

Busted Knuckles
Jun 10th, 06, 02:03 PM
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?

Larger Dave
Jun 10th, 06, 03:05 PM
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.


Larger Dave

SIDEWAYS
Jun 10th, 06, 03:44 PM
I thought melonizing is a hardening process? Here's a good read:

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

Larger Dave
Jun 10th, 06, 07:00 PM
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

pdq67
Jun 10th, 06, 07:49 PM
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

67FamilyFun
Jun 10th, 06, 08:00 PM
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

Meanchicken
Jun 10th, 06, 09:20 PM
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

Meanchicken
Jun 10th, 06, 09:25 PM
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

pdq67
Jun 10th, 06, 10:58 PM
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

camcojb
Jun 10th, 06, 11:05 PM
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

Larger Dave
Jun 11th, 06, 08:15 AM
I use a bronze gear on the street (I have three still carded hanging on the door post to the tool room). It is a consumable part (just like Gas Tires and Oil) so you have to look at it occasionally (about every 6000 miles for me) just like you have to check your valve springs and rockers for wear and adjust them. It is part and parcel of living the high performance life (yes it is a chore, but so is mowing the grass).

By the way I usually get about 15,000 miles to a gear (before I replace them) though the car is still running fine; by then I can see about 4° of variance in the timing when I blip the throttle.

Larger Dave

pdq67
Jun 11th, 06, 08:58 AM
OK.

Sorry about throwing out the crude the gun thing, but I guess I always thought of "melonizing" as just another form of surface "case-hardening" is all??

pdq67

camcojb
Jun 11th, 06, 10:48 AM
I use a bronze gear on the street (I have three still carded hanging on the door post to the tool room). It is a consumable part (just like Gas Tires and Oil) so you have to look at it occasionally (about every 6000 miles for me) just like you have to check your valve springs and rockers for wear and adjust them. It is part and parcel of living the high performance life (yes it is a chore, but so is mowing the grass).

By the way I usually get about 15,000 miles to a gear (before I replace them) though the car is still running fine; by then I can see about 4° of variance in the timing when I blip the throttle.

Larger Dave

You must be doing something right. I've never seen one go much past 1-2000 miles, most less. Great if you check them often like a drag car. Of course many failures that are blamed on them are due to improper cam end play, dist height issues, etc. I just see no reason to run them as they are constantly wearing and there are options that don't.

Malitude lost his engine on Power Tour last year due to that gear, and the motor was done by Nelson Racing and had been checked by Wheel to Wheel I believe; those guys know how to set them up. It had very few miles on it.

I am glad yours work, and if it works keep going that way. But nowadays I've been able to get any roller cam (even billet) made with a cast dist gear, and that and the modded GM gear has not had a failure in many engines for me. No reason in my case to put an additional wear item back in the engine if I have other options.



Jody

BPOS
Jun 12th, 06, 02:21 PM
I could not get a cast gear on my cam - a Comp custom billet HR on a reduced base circle. (or so they told me at Comp - unfortunately you could ask the same question to three different techs there and get three different answers) I ran my old GM melonized gear on it for about a thousand miles and pulled it to inspect. I found a very few small pits, so I ditched it in favor of a Comp polymer gear.

zdld17
Jun 12th, 06, 05:03 PM
I just got into this with a gm gear as I installed it on a .500 MSD dist. I drilled out to .500 , about a .006 differance from the GM id and the .500 msd shaft... Good snug fit. Pinned it and its done.
My problem was that the gear teeth on msd was too sharp when compared to the GM that had a bevel cut, this GM bevel cut steel gear is easier on cast stock , non billet roller cams. Save the brass for the billets. There is a poly gear out on market but I have never used them.. $$$$

Just be sure to get the correct end play between the gear and the wear washers on the dist base when you put it back together.

Meanchicken
Jun 13th, 06, 10:03 PM
Thanks, guys.
I took the melonized gear to a precision honing shop today. They're going to hone it out to 0.50" for me at a charge of $35.

Tim

Motorhead62
Jun 14th, 06, 07:52 PM
The melonized gear is recommeded for use with hardened cast roller cams such as what the ZZ engines are equipped with. MSD sells the proper gear for you application. You can use a GM gear for your MSD and modify it as you plan.

The use of bronze gears is NOT recommended for street use as they wear too quickly. They should be used for race use only and inspected often.

The smart move is to order billet roller cams with pressed on iron cam gears. This solves the problems with compatability.

I hope this answers your questions.

Good Luck :D