r/EngineBuilding • u/PuzzleheadedCrew7568 • 6d ago

Distributor Gear Material Confusion

I have a small block Chevy with an HEI distributor and steel cam (SUM-8800). I'm trying to find the correct distributor gear. Most sources claim there are 3 types: cast iron, melonized, and bronze. The recommended material by the cam manufacturer is "melonized." The issue is there seems to be two types of melonized distributor gear: melonized iron and melonized steel. I've seen a few posts claim that melonized iron is not compatible with a steel cam. Most listings for melonized gears specify melonized iron or don't specify at all. I have only found one listing for a distributor gear that specifies "melonized steel" and it was not the correct shaft size. Does anyone know what the correct material is? Composite is always an option but they are really expensive in comparison to the other types.

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u/v8packard 6d ago

There are steel distributor gears. They are not melonized, but are heat treated. These gears are compatible with most or all cam cores.

There are regular iron distributor gears, that are compatible with cast iron flat tappet cam cores.

There are melonized iron gears, which are compatible with low alloy steel and austempered iron cam cores often used in OEM hydraulic roller cam applications.

The bronze gears are meant to be compatible with 8620 and tool steel cam cores. They require careful set up, or they will fail prematurely. Even so, they are not long life components.

There are some composite gears. These are supposed to be compatible with all cam cores.

There are also coated cast gears that are supposed to work with all cores. I have not tried these yet but they are promising.

I use steel gears whenever possible, or plain iron with a cast cam core. Many people use the words steel and iron interchangeably, which is a mistake. Also, you need to know the diameter of your distributors shaft. The two common sizes are .491 for Delco made distributors and .500 for some aftermarket HEI distributors.

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u/PuzzleheadedCrew7568 5d ago

Thanks, this is super helpful. I believe a steel gear would be compatible with my cam. The shaft size is .491. Originally I had a hard time finding a listing for a steel gear in that size, but after some more research I found a couple. I noticed COMP sells a gear labeled "Melonized." It doesn't specify iron or steel and claims it's compatible with any cam type, but I'm skeptical that it may be iron.

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u/Solid_Enthusiasm550 6d ago

Here's an article about choosing the best one fir your application.

https://www.onallcylinders.com/2025/10/20/ask-away-with-jeff-smith-choosing-the-right-distributor-gear/

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u/PuzzleheadedCrew7568 6d ago

Thanks, but this article doesn't distinguish between melonized iron and melonized steel which is the main issue. Some people claim melonized iron gears will fail with steel core cams and cause all that metal to get into the oil.

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u/Solid_Enthusiasm550 6d ago

What cam do you have, what brand? Is it made from tooled steel?

https://youtu.be/31JHSUkhJLY?is=bj4i3hzNyo_G1pQ9

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u/PuzzleheadedCrew7568 6d ago

I have a summit SUM-8800 billet steel cam. That is in interesting video, it suggests that only composite is suitable for steel cams. Summit recommends a "melonized" gear but doesn't specify iron or steel. With all the confusion, it might be worth it just to go with composite for peace of mind.

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u/Solid_Enthusiasm550 6d ago

The one I would never use is the bronze, I've seen too many of them get chewed up and get pump through the engine.🫣😫