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Distributor Gear - Worn ??


snomobeelr

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I was getting the car ready to come out  she hasn't been started since I put her away for winter. I always pull the distributor and prime the motor. I was looking at the distributor gear and it looks pretty bad.  I have a BBC with a roller cam. I am defiantly changing the gear but wondering what would cause it. Engine has 3500 miles on it but has been together since 2013. My cousin has a scope and from what we can see in the engine it appears to be ok , but I know you can only really know by pulling engine apart. I don't know if others had this issue as well. Its a MSD Billet distributor.  Thanks

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You need a composite gear on that distributor, which I'll assume it is. It would be softer than the cam gear and it can wear over time.

 

I wouldn't worry about it, just change the gear with a new one and do an oil & filter change.

 

If you want extra reassurance all else is well, cut open the oil filter and look for excessive junk. If none, you're all good.

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X2 Paul's answer. The bronze gear is supposed to wear out instead of the cam. It's a common roller cam set up. Not so much with the old school flat tappet cam set ups. Like Paul said, I would change the gear with a bronze or roller cam designed distributor gear, change the filter and oil and continue to enjoy it.

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The shaft is generally small or big, "small" being later GM distributors and "big" being earlier GM and virtually all performance aftermarket distributors.

 

I'd say your MSD unit is "big".

 

Now, "big" has a few different measurements, depending on who you ask.

 

Whatever size it is, the melonized one is probably the more often used.

 

From Summit:

 

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Thank you Paul.  I really wish I could figure out why it is shearing the gear. I rad somewhere someone said if you have a high volume oil pump it could cause this trouble. I don't know if that malarkey or not .  Attached some more pics if your interested.  

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I did not. check for end-play , I dont believe there was any end-play at all when I pulled the distributor  so now I am wondering if the distributor was bottomed out. I also have a slight oil leak I can not pin down and wonder if its from this. I am going to reinstall the old gear and check clearance and see if bottomed out.  

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I replaced the old gear.  There is barely any end-play at all in the shaft on the distributor . So I reinstalled the distributor without the gasket and there is no movement, no end-play. So I am thinking it is bottomed out. The distributor flange is set on the manifold, I do not see a gap but there is no movement up/down.  

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End play is measured with a feeler gauge when the distributor is out of the engine.  Here is a LINK to a photo-illustrated method to check and set end play from the Chevy Talk forum (see third reply down after clicking on the link).  Because of different thermal expansion characteristics between steel (distributor shaft) and aluminum (shaft housing), you need at least .010" of end play but not much more than that or it can affect timing and wear.  Not sure why you removed the gasket ...

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I reinstalled the distributor gear and measured the end-play in the distributor it is at  .012.  I removed the gasket to verify if the shoulder of the distributor mated to the intake and to see if the end-play of the distributor was still there when it was mated.  It was not,  there is no moment end-play it the distributor it was locked. I realize the gasket will come into play but wondering if it needs to be shimmed on top?  I know it is a Bronze - soft metal gear, so it wears out instead of the Cam Gear.  Maybe I am overthinking it I am just trying to figure out why so much wear and  I am paranoid about using a  composite gear and messing up the cam gear.   I watched the video below also wondered about the 

 

I found the video below also wondered about wht he said - to cut a grove in the lower vein of the distributor housing to oil the Gear Or is that Malarkey?

 

 

 

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That's a great video - very clear and professional!  I've not heard of the additional oil groove modification but I can't see any harm in trying it as long as you don't overdo it (.030" max depth) and wash all the shavings off before installation. 

 

Sounds like you will need to add a shim of the correct thickness, as well as, reinstall the gasket.  The combined thickness of the shim and gasket should allow you to observe the the full .012" end play when the distributor is installed and bolted down. He didn't give a maximum shim thickness but I'd stop trying thicker shims as soon as full end play is achieved.  After all you have shared, I suspect that having no effective end play was the major contributor to the excessive wear you have observed.

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I think you're simply overthinking this.

 

With the gasket, you had some play in the shaft so you're all good. To be safe, add a .030 shim with the gasket and you'l be extra good.

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Ya sorry about that  I have a habit of overthinking things. When I frst noticed it I freaked.  I never realized that gear  on the distributor was designed to go out instead of the gear on the cam.  

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