Distributor Main Shaft Drive Gear(s)

[Gene M.]

Re: Distributor Main Shaft Drive Gear(s)

Gene,
I put a Comp solid roller cam in my engine and it chewed the shlt out of the stock, iron gear. The cam is made of iron, but is nitrided, so I didn't think there should be a problem. Timing moved about 10 degrees over time so, sure enough the gear was chewed up on the driven side. I installed a GM STEEL gear and now they make nicey-nice together.
Oil pump is standard volume pump with 58# (HP) relief spring. It is NOT a high volume pump.

This is a common issue on performance modified engines. The nitrided cam surfaces is also on it's rear gear teeth. It forms a nice hard wear resistance on the lobes but not good for iron distributor gears as you point out. The steel being harder surface should end that issue for you. It is important to have materials and hardnesses that "play well together". Engineering wise on a 90 degree helical gear set the softer material should be on the driver and if harder than it should be on the driven with constant lubrication.

The 58 pound pump I would assume increases the load on the gearing too. Stock oil pumps are more like 40 lbs at cruise speeds.

Glad you got that solved so the wheels can keep on a rolling..........

[Joe L.]

Re: Distributor Main Shaft Drive Gear(s)

Gene,
I put a Comp solid roller cam in my engine and it chewed the shlt out of the stock, iron gear. The cam is made of iron, but is nitrided, so I didn't think there should be a problem. Timing moved about 10 degrees over time so, sure enough the gear was chewed up on the driven side. I installed a GM STEEL gear and now they make nicey-nice together.
Oil pump is standard volume pump with 58# (HP) relief spring. It is NOT a high volume pump.

Joe------


If you're referring to the GM #10456413 distributor gear, I don't think it's made of steel. I believe it's MELONIZED CAST IRON. The melonizing process hardens the surface of the cast iron. This type of gear is used with all GM Gen I and II small blocks with hydraulic roller cams.

[Joe C.]

Re: Distributor Main Shaft Drive Gear(s)

Joe------


If you're referring to the GM #10456413 distributor gear, I don't think it's made of steel. I believe it's MELONIZED CAST IRON. The melonizing process hardens the surface of the cast iron. This type of gear is used with all GM Gen I and II small blocks with hydraulic roller cams.

That's the one.
When I was doing a search for this gear, half the websites I looked at described it as "melonized iron" and the other half as "melonized steel". Those were probably close to 20 websites. I remembered that you have always referred to this gear as melonized iron. The process of melonizing can be used for any ferrous metal, and so either may be accurate.
How do we know, for sure who's fibbing and who's not? I tend to think that your info is accurate. Where did you learn that the gear is iron and not steel?

[Joe C.]

Re: Distributor Main Shaft Drive Gear(s)

This is a common issue on performance modified engines. The nitrided cam surfaces is also on it's rear gear teeth. It forms a nice hard wear resistance on the lobes but not good for iron distributor gears as you point out. The steel being harder surface should end that issue for you. It is important to have materials and hardnesses that "play well together". Engineering wise on a 90 degree helical gear set the softer material should be on the driver and if harder than it should be on the driven with constant lubrication.

The 58 pound pump I would assume increases the load on the gearing too. Stock oil pumps are more like 40 lbs at cruise speeds.

Glad you got that solved so the wheels can keep on a rolling..........

Gene,
As you know, low horse engines used a 48 or 49 pound relief spring, depending on where you look: GM or Melling. High horse engines used a 58 pound relief spring. HP and LP pumps should both cruise at the same pressure, all else being equal. The higher relief pressure should only be called upon at engine speeds higher than about 5000 RPM. When you say "cruise speeds" you probably mean a car with a 3.73 axle traveling at about 65 MPH, or about 3000 RPM? The "cruise pressure" is also depending on the viscosity, correct?
In any event, mine cruises at 75 MPH at 2250 RPM. Using 20W-50 oil, the pressure is around 40 pounds. The relief spring starts to dump pressure past about 6500 RPM, where it's supplying its rated 58-60 psi. The old 10 psi/1000 RPM rule of thumb is fairly accurate, but not sure what viscosity it's based on. Probably 10W-40. 10W-50 allows for a few more RPMs.

[Joe L.]

Re: Distributor Main Shaft Drive Gear(s)

That's the one.


Where did you learn that the gear is iron and not steel?

Joe-------


GM. The gear is described as "melonized iron" in the GM Performance Parts Catalog. Being that they are the source for the gear (whether or not they actually manufacture it), I consider their information definitive.

To add a little more to this, though, I believe the cast iron is either of the ductile or malleable variety. These kinds of cast iron are often described as "cast steel". It's really a misnomer, though as they're not steel.