Bronze distributor shaft gear wear

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kenelder

kenelder

70 340 4spd 6 pack
Joined
Aug 14, 2018
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Location
Largo, Florida
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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Luckily I was able to find a Crane melonized gear myself, but yes now they are unobtainable. I’ve read on various sites of people carefully radiusing the edges of the teeth on the cam as a means to help prevent the shaving of the bronze.
Could maybe source and send a new steel gear (once removed from the shaft) off to be melonized (or a bunch, keep a couple for future, sell the rest) that might be an option? An answer is out there just might mean $$$
 
From your description, it sounds to me like the intermediate shaft is binding. When installing a new bushing it needs to be reamed to final size, otherwise the type of shaft and gear wear that you are describing can result.
 
Might have been a tight bushing, I do recall when I put the dist in before starting it the first time the gear slot was not aimed to cyl #1 and I was able to easily turn it out with a screwdriver and when I tried to reposition it and missed, it would not come back out. Almost like it was too low even then.

I’ll check the bushing, maybe put a new one in but I’ll need to get the tool to burnish it.
 
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

View attachment 1716037714

View attachment 1716037715
Click to expand...

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.
 
The shaft collar is a good idea. Not only will it help with reduced wear by stopping/limiting bouncing caused by a hp cam, it will steady your timing marks on the harmonic balancer making it easier to set timing at idle with your timing light.

Rick eherenburg has them for sale on his eBay store, ricks mopars. They are like $20.00 or so.
 
ch1ll said:
The shaft collar is a good idea. Not only will it help with reduced wear by stopping/limiting bouncing caused by a hp cam, it will steady your timing marks on the harmonic balancer making it easier to set timing at idle with your timing light.

Rick eherenburg has them for sale on his eBay store, ricks mopars. They are like $20.00 or so.
Click to expand...
Those collars are also available at McMaster-Carr and other places on-line for less $.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
www.mcmaster.com www.mcmaster.com
 
I agree it looks like it needed to be shimmed up, but that is likely because of the wear on the bottom face of the gear. I have a new gear, but need to get a new shaft too- don't want to use this shaft with the wear marks on it where it goes into the bushing. I have a hard time believing worn bronze particles scored the shaft like that. I think maybe it was an old shaft. Anyone replaced the bushing while the intake was on? If so, what tool did you use to take it out? I'm believing if the gear is correctly meeting the middle of the cam gear wear would be minimal.....
 
ch1ll said:
I believe the one rick has comes with a Torrington bearing, I may be mistaken though.
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The shaft and the gear are locked together with the tang and slot that connects them, so no need for a torrington bearing there. Might be for under the gear, but that would scare me to run a needle bearing there although they run those between the thrust surface of the upper cam gear and block.
 
Rick’s collar uses a set screw to a flat you put on the distributor shaft. A little loctite and its not goint to move. Carr McMaster one just grips the shaft and that might move.

735DB9FB-F6B3-4931-93E1-9AD9B3F9EDF3.png
 
Ricks does not have a Torrington bearing, just looked. His price is $18.17 shipping included and comes with instructions, just saying.
 
You may need a new intermediate shaft, drive gear, and in the block bushing by the looks of these parts.

Make sure the in the block bushing spins freely on the intermediate shaft with engine assembly lube on it, before installing.

Then check the bushing fit again once it is installed in the block.

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Expand these ^^^ photos up and you will see what I mean. Not looking good.
 
What actually happens if you use a treated standard gear such as the Melling IS-72? I find it hard to believe it would damage the steel gear on the cam. Anyone have experience?
 
Engine is in the car and I’m not interested in taking it out right now- has anyone replaced the bushing without taking the engine apart?

If taking the engine apart is the solution then I’m going to get a different cam…without this problem.
 
kenelder said:
Engine is in the car and I’m not interested in taking it out right now- has anyone replaced the bushing without taking the engine apart?

If taking the engine apart is the solution then I’m going to get a different cam…without this problem.
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Can make up a little slide hammer like the head of a carriage bolt that just fits down inside the bore of the block bushing.

Push it down in the hole then off to one side, then pry the bushing up and out.

_________

Here is a comment from a YouTube How to video:

Screenshot_20230121-135337_Gallery.jpg
 
Oil pump/intermediate drive shaft Bushing install

It is not a given that you will have to burnish/ream the new one, the Durabond version. I’ve installed them in two different engines recently and that step was not required. (I also use some green Loctite bearing retainer for good measure) Some may say that’s pure luck not having to burnish/ream.. Whatever, it didn’t need doing in both my cases. I use an old intermediate shaft to tap the new bushing into place. You might be able to use a slide hammer and use a blind bushing puller (I think that’s what its called) or as mentioned above to pull the old one.
 
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Ok it sounds like the bushing can be done with the right tools. I might just replace the shaft, gear and bushing as recommended above and give it a try again. I’m still puzzled over the scoring on the shaft though, makes me think it’s an old shaft.

Thanks everyone for your recommendation’s!!
 
I’d still like to know what happens using a steel billet cam and a standard gear…….actual experience not just what everyone says
 
Ran a bronze gear on several rollers for about 20 years (racing, not significant miles, but a lot of runs) and still good. My experience was on some of the blocks/bushing set ups, was there was more likely a vertical too tight condition that needed to be corrected when the dist was tightened down, than too much clearance. I always fit the dist with the intake off to verify while doing pre-assembly and check that there is enough clearance.
 
Outsder, that makes sense. I believe the first time I inserted the dist it was difficult to get it all the way down. I’m going to have to check that for sure. Thank you for that!
 
kenelder said:
I’d still like to know what happens using a steel billet cam and a standard gear…….actual experience not just what everyone says
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That’s going to take finding someone who disregards the advice of cam manufacturers among others about what gear to run with their billet cores, right? Most say use bronze and/or a melonized, that a standard gear should not be used. Wear.
For what a billet cam costs these days who would chance it? Why? There’s too much information and accessible knowledge out there explaining the reasons.

The articles discussing this are plenty:

Properly Matching Your Camshaft and Distributor Gear - Engine Builder Magazine

Distributor Gear Compatibility: How to Choose Which Distributor Gear to Use
 
kenelder said:
What actually happens if you use a treated standard gear such as the Melling IS-72? I find it hard to believe it would damage the steel gear on the cam. Anyone have experience?
Click to expand...
I used standard gear with a billit rollar cam. I really have a hard time believing that it will be a issue, so much oil back there. No problems yet, but still under 500 miles...
 
When I built my 434 I used a hardened valve spring shim deigned for a motorcycle engine between the bronze bushing and the bronze distributor gear to hopefully slow the wear on both. I'll have to wait until it needs to come apart to see if it worked.
 
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