I have a supercharged small block Chevy that is running a steel mechanical roller camshaft. The engine quit running the other day and it took us awhile to figure out why. At first we thought it was the MSD 6AL box but testing showed it was OK. We finally pulled the distributor and noticed the gear was not turning smoothly. I’ve included a photo of the bronze gear.

This is the second one I’ve installed. I don’t drive this car that much so I don’t know how many miles are on this gear. I am already tired of replacing these gears but I’m not sure what to do. I don’t want to replace the cam to allow running a regular iron gear. Is there another way around this problem?

B.T.

The quick answer to your situation is to replace that bronze gear with a melonized distributor gear. The melonizing process subjects the iron gear to a salt bath nitriding procedure that strengthens the iron to produce a much harder surface and improve its fatigue strength. A melonized distributor gear will be compatible with any camshaft gear material, including high strength steel.

Keep in mind that aftermarket distributors like MSD’s have a 0.500-inch diameter shaft while a stock GM distributor for small and big block Chevys have a 0.491-inch diameter shaft. This means when you go looking for a melonized gear, make sure it will accommodate a 0.500-inch shaft.

There are several companies offering a melonized distributor gear for an MSD distributor. We’ve listed several options below that are available at Summit Racing.

It’s worth mentioning that the metal from your worn bronze gear is now inside your engine. That’s bad. I recommend immediately changing your oil and filter, run the engine for long enough to get the oil up to normal operating temperature (which will take longer than just meeting the coolant temperature threshold), then change the oil and filter again.

If you are running high viscosity oil like a 20w50, you might consider using a lower viscosity oil. When the engine first starts, the oil is cold and will put a much higher load on the distributor drive gear as it spins the oil pump. A 20w50 oil at 50 degrees F is dramatically harder to pump than 10w40 at the same temperature. If you combine thicker oil with a high pressure/high volume oil pump, the load is even greater! It’s something to think about.

It appears from your description like you have quite a bit of money invested in this engine. We suggest getting the used oil from the latest oil change tested. There are several companies that will perform this test. One is SPEEDiagostix run by a friend of ours, Lake Speed, Jr. from Driven Racing Oil. You can get one of their testing kits at Summit Racing. The kit has everything needed to collect an oil sample and send it in, including a prepaid shipping box. SPEEDiagostix uses the same used oil analysis machine that Formula One teams use so you will get very accurate information.

In about a week to 10 days your oil analysis evaluation will be available. You will see the levels of wear metal and contaminants such as fuel dilution, water, antifreeze and airborne dirt that are in the oil. The information will tell you the condition of your engine and any problem spots that need to be addressed. This FAQ from the SPEEDiagostix website details what is in your oil analysis report.

For example, we sent an oil sample from a small block Chevy to SPEEDiagostix. We thought the engine just had a small external coolant leak, but the analysis revealed high levels of sodium caused by an internal coolant leak. If we hadn’t found out, the engine would have eventually suffered serious damage.

Parts List

Summit Racing 0.500″ Melonized Distributor Gear SUM-850467-M                                          
COMP Cams 0.500″ Melonized Distributor Gear CCA-410M
Summit Racing 0.491″ Melonized Distributor Gear SUM-850466-M             
PRW 0.491″ Melonized Distributor Gear PQX-70265491
Driven Racing Oil SPEEDiagostix Used Oil Analysis Kit JGR-10001

Worn bronze distributor gear
This is the bronze gear pulled from B.T.’s supercharged small block Chevy engine. Note that the gear does not appear to have been fully engaged with the camshaft. When installing a new distributor gear, the best procedure would be to apply thick grease to it to evaluate the contact pattern with the cam. (Image/Jeff Smith)
Melonized distributor gears
The melonized distributor gear on the left is compatible with all camshafts. It has a mottled or dimpled surface on the round shank portion of the gear. Compare it to the stock iron gear on the right. (Image/Jeff Smith)
Keywords
distributor gears , distributors
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.