You Need to Know About Cam and Distributor Metals
I don’t write many articles anymore. After decades in this trade, I only sit down to write when I see engine builders walking straight toward a mistake that could cost them real money. The last time I did this, it was about early Quick Fuel carburetor flaws that could be fixed—if you knew what to look for.
This time, the problem is far more expensive: roller cam core materials and distributor gear compatibility. If you have a short attention span, this isn’t the article for you.
A Little Background
I’ve been building street-performance engines since the sixties—sometimes for a living, always for the love of it. Last year, a friend who builds high‑end show cars asked me to help with three engines: two 351 Windsors and one 5.0 SBF roller.
Cam selection is always the most critical decision. I look at everything: vehicle weight, rear‑end ratio, transmission gearing, RPM range, compression, and the overall combination. A good engine is never about one magic part; it’s about parts that work together.
What Cams Are Made Of Today
For years I used Comp Cams and always degreed them. Then I found one that was five degrees off. They replaced it, but that pushed me to look at other brands.
After the flat‑tappet failures around the 2008 recession, roller cams became the only realistic option. Early rollers were billet steel—expensive and aimed at racing. But once rollers became mainstream, companies started using cast‑iron roller cores, which are cheaper to manufacture and more profitable.
I shifted to Howards because they offered more off‑the‑shelf options. Lunati was solid too—until Edelbrock (owner of Comp Cams) bought them and shut them down.
Distributor Gear Materials: Where Things Go Wrong
Everyone knows cam and distributor gear compatibility matters. Comp Cams even has a video tapping different cores and listening to the sound differences. Cute idea, but not exactly scientific—especially when companies invent new terms like “Aussie Tempered.”
Here’s the real problem:
When you buy a cam, the required distributor gear material is almost never listed. Not on the cam card, not on the website.
I usually have to call tech support. And after what I’ve seen, I can tell you: that information is not always reliable.
Distributor gears used to cost $15. Now they’re $50–$110. And if you mismatch materials, you can destroy a cam in minutes.
The basic rule still applies:
Cast‑iron cam → cast‑iron gear
Steel cam → steel gear
But now we have “special hardened,” “melonized,” “Aussie tempered,” and other marketing terms muddying the water.
The Real‑World Problem
When buying a distributor, try finding the gear material in the listing. Good luck.
For our three engines, we used two Howards cams and kept one good Comp Cams roller. I’ve used the Pertronix III distributor before and liked it—multi‑spark through the entire RPM range, built‑in rev limiter, no external box. So I called Pertronix tech support and asked about the gear material.
They told me their gear uses a special Rockwell hardness compatible with any cam.
That turned out to be disastrously wrong.
We finished the first engine—a pristine ’69 Mach 1 the owner has had for 50 years. Fired it up, broke it in, everything sounded great. After about 40 minutes, we pulled the distributor to tweak the vacuum advance.
The “special Rockwell hardness” gear had eaten the cam gear.
We had to pull the engine, buy a new Comp cam with the “Aussie” core, and hope it would live with the Pertronix gear. I’ve run that combo in my Cobra for 13 years, so we took the chance. Still, that mistake cost about $500 in parts alone.
Pertronix tech support had nothing useful to say beyond “that’s what our engineer told us.”
And Then It Gets Even Better
A month later, I was modifying my own Pertronix distributor and checked the gear again—still fine. I also have a new Lunati cast‑iron cam on the shelf and was considering using it.
That’s when I discovered Pertronix doesn’t even sell a cast‑iron gear for their distributors.
Then I measured the shaft: .4645"
Standard Ford size is .467"
Pertronix lists their gears as .467" ID.
I called tech support again. They measured a shaft in their office—also .4645". Their explanation?
They subcontract the shafts, and “that’s just what happened.”
So now the question is:
Do I have to buy a different brand of distributor just to run a cast‑iron cam?
Or am I locked out of using cast‑iron cams entirely?
This is the kind of nonsense engine builders are dealing with today.
Final Thought
If you’re building engines in this “new world,” be careful. Don’t assume the cam card tells you everything. Don’t assume the distributor manufacturer knows what their own gear is compatible with. And absolutely don’t assume “special hardness” means “universal.”
Your camshaft is too expensive to gamble with.
