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Cam gear for distributor
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Nor Cal CJ5 View Drop Down
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    Posted: Sep/14/2020 at 11:00am
Here is a picture of the original cam gear.  

I replaced the distributor with a Pertonix unit 5 years ago and no issues.

I recently rebuilt the motor (no short block) and after about 8 hours of running time, the original distributor drive gear on the cam wore to a knife edge and eventually jumped a tooth.

During the rebuild I replaced the timing cover, rebuilt the oil pump, installed the distributor and clearances were checked.

I followed Rick Jones' advice and aligned the cam oiling hole with the new timing gear, fuel eccentric, and distributor gear.  

I used a good conventional 5w-30 oil and an additional zinc additive.

With the wearing of the cam distributor gear, the cam wore into the timing cover a bit.


What is the consensus on the reason for the issue?

Should I just replace both cam gear and distributor gear (Pertronix gear looks fine) or is there something else that needs to be done?

Thanks in advance.
1972 CJ5 304 2 barrel 3 speed
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Points: 9082 		Post Options Post Options   Thanks (1) Thanks(1)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Sep/14/2020 at 11:16am
From what I gather most distributor drive gears on aftermarket distributors are hardened. Never mix different harnesses. Mallory and MSD have good gears, both in brass and iron. Their distributors come with the proper gear. I obtained a newer (2018) iron gear that has proper hole locations and depth. No guarantees just be sure with any gear obtained to check thoroughly.
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Did you replace the timing cover with a OE part or a aftermarket one?
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Originally posted by SC397 SC397 wrote:

Did you replace the timing cover with a OE part or a aftermarket one?

It was a used OEM cover from a member here.

My first thought was some sort of alignment issue - the distributor is bolted to the timing cover and the cam gear can move back and forth.  However, these two gears have been working well and have had no significant wear when pulled for rebuilt.  The only difference is the timing cover.

I don't know what the original cam gear is made from, but I know that Pertronix makes good quality parts.

Is a hardened cam timing gear available?  I'll definitely get both gears new this time.


Edited by Nor Cal CJ5 - Sep/14/2020 at 1:17pm
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That gear in the picture is worn on the inboard side on each gear tooth face and the outboard side of the opposite side of the gear tooth face. 
This indicates that the gears were not a matched set, or at least not cut correctly.
If this was oil or even different hardness issues, the gear teeth should be worn equally on each face.
If it was the cam had walked, the teeth should be worn on the inboard.
Next gear set, mesh them by hand so they roll nicely and use a good square to ensure you have a 90 degree angle between gear faces.
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Originally posted by Trader Trader wrote:

That gear in the picture is worn on the inboard side on each gear tooth face and the outboard side of the opposite side of the gear tooth face. 
This indicates that the gears were not a matched set, or at least not cut correctly.
If this was oil or even different hardness issues, the gear teeth should be worn equally on each face.
If it was the cam had walked, the teeth should be worn on the inboard.
Next gear set, mesh them by hand so they roll nicely and use a good square to ensure you have a 90 degree angle between gear faces.

The gear is worn on both sides of the tooth - to a knife edge.  EDIT - Sorry - you are right, The gear is mainly worn on one side, just where it wore thru and jumped the tooth is it worn on both sides.
 

Where can I get a good matched set of gears?


Edited by Nor Cal CJ5 - Sep/14/2020 at 12:33pm
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I still reuse factory gears so cannot help with new sets.
If you know a wrecker with a few 304's or 360's - that's were I would shop.
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Here are some better pictures:

Outboard side:





Inboard side:





When the timing cover was removed, oil was apparent on the gear.  The depth of the groove shows approximately 1/2 of the cam gear was engaged.  One thin gasket at distributor base.
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To me it looks like the distributor gear is too hard, if it is in near perfect condition. Like others stated, could be gear meshing issues, due to not being matched.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Originally posted by 304-dude 304-dude wrote:

To me it looks like the distributor gear is too hard, if it is in near perfect condition. Like others stated, could be gear meshing issues, due to not being matched.

The distributer is a PerTronix with a steel gear on it.  It is pretty much flawless.  I've used the Pertronix and the original Cam gear since 2016 and the cam gear was ok when tore down for rebuilding the top end recently.

I've looked around for a new set and all I see is the Crown and Omix-ADA stuff.  

I did see that MSD has an iron cam & dist. gear set 8005 & 8007 that seems to work for people with AMC motors.  I'm trying to figure if that is the route to go right now.  Checking with MSD...

The distributor gear on the PerTronix shaft is .500 where a standard AMC distributor shaft is .491. 
1972 CJ5 304 2 barrel 3 speed
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