Bronze distributor shaft gear wear

kenelder said
I have a Comp billet solid roller cam in my 340 with approx 50 miles on it, don't have the cam ID but it's definitely a billet cam. The engine was completely rebuilt by an experienced Mopar builder for another mopar guy, I bought it from him with only run time on the break in stand. All is well and I'm overall happy with it.

But, it ran great to start with then has gotten a little rough, thinking it was either timing or carb I started checking and discovered a worn bronze drive gear. I've learned through reading in this site that bronze gear wear is expected, but not this fast. It was really difficult to get the gear and shaft out- I had to use an old distributor shaft and wrench to turn it but finally came out. The pics show the wear on the gear teeth and also some wear on the seating surface that runs on the bushing in the block. I measured and compared to a new gear this old one is a little over .010" shorter and is missing the beveled edge of the new gear. I have to guess that the worn gear was simply riding too low on the cam gear and that's what caused the quick wear. But that's a LOT of wear for the little time on the engine. I note the shaft also shows scars where it was riding in the bushing, either from particles going through the bushing or it's an old shaft. I didn't assemble the engine so I don't know if that is an old shaft or if the wear happened in this new motor.

I've read here that the bronze gear can wear against the bronze bushing and some folks have used thin stainless shim washers between them. I've also tried to find/buy a melonized gear but I guess Crane Cams is no longer in business and everywhere I've checked has nothing in stock. Hughes shows it in their online site but when I called they said they didn't have any and no idea of when they might have more.

My choices are: put in a new shaft with new bronze gear and hope for the best, or try the Melling IS72 manganese phosphate gear and hope for the best. I'm not real happy with bronze particles in my engine but would be even less happy with iron particles. I really don't want to replace the cam if I can help it- all inside the engine is new including the cam.

If anyone can share any thoughts to help me out, I'd really appreciate it.

Thanks,

Ken

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That contact pattern looks like the bronze gear needs to be shimmed up to position the wear pattern closer to the middle of the cam's gear. Of course you will need a new bronze gear.

Also, you can limit the up and down movement of the bronze gear by using a 1/2" distributor shaft collar. Be sure to locktite it. If you have excessive freeplay for the gear to move up and down when the motor varies rpm etc, it can dramatically increase wear on the bronze gear as it moves up and down. I believe the clearance between the bronze gear and the blade end of the distributor is around .015" with the distributor bolted down. Someone will likely chime in to verify this.

You also need to limit the cams movement for and aft to control the contact pattern between the gear and the cam. These gear interface is very similar to the contact pattern that a ring and pinion gear have. Imaging not controlling the movement of the pinion and ring gear to limit movement in and out of the proper range that controls gear contact pattern. You would have noise and excessive wear patterns resulting in increased gear wear, especially on the softer gear.

I have always wanted to cryogenically treat a bronze gear to see if it would help reduce the gear wear, but ended up using the treated iron gear. Since you have already run a bronze gear on that cam, you are supposed to replace it with another bronze gear, but that mellonized gear might still run fine on there. It's a crap shoot.

On my last build, the wear pattern between the gears was fine, but my shaft was galled. The gear and bushings contact pads appeared fine. It was just the shaft's surface that was course. I installed a new bushing that was installed with the Chrysler tool too. It's supposed to clearance and better seat the bushing too. It looked like there was not enough oil getting in between the bushing and gear's contact surfaces. I'll measure and confirm there is enough room for oil to get in there on my current refresh.