Current setup

SBC 383
Hydraulic flat tappet cam
New Melling pump (M55)
"Z28" valve springs
Cam, lifters, and distributor gear had moly grease applied prior to break-in.
Distributor is shimmed for 0.010" up-down play.


Some background.

Prior to this engine go through, a lifter and cam lobe wore out. Enough of the lifter's bottom wore away so that the spring within the lifter became exposed and unraveled. The steel wire from the spring found its way to the oil pump and managed to get caught up in the rotors. I believed the intrusion caused excess pressure on the distributor/cam gear which in turn wore out both the distributor/cam gear.

After disassembling and cleaning the engine, I replaced the cam and lifters with new ones. I also replaced the distributor cam gear with a used one that was in good shape. I finished breaking in the cam/lifters (2500 RPM for 20 minutes) and checked the lash and nothing was giving me an indication of premature wear out. This was based on loosing the poly lock that same amount needed to set the lash to prior to cam break-in.

I pulled out the distributor to make sure that it is wearing correctly only to find premature wear. As seen in the pic, the wear is similar on all teeth (right side). I did not check the distributor shaft or oil pump shaft for straightness, but visually I did not see anything odd about their appearance.

The only thing I noticed during engine assembly was that the distributor took a "little" effort to get into it's bore. It just didn't fall into place, but needed a little pressure to seat on top of the intake manifold.

Before these last two failures, the engine has never had any "funky" cam/distributor wear problems. So does anyone have any thoughts to why I am having this quick cam/distributor gear wearing problem. And is there any fix like using a different material distributor gear to minimize this problem.

 

Here is the pic.

 

The distributor appears to be sitting too high. If it is difficult to get into the manifold hole, that may be your hint.

 

This distributor has worked for years in this engine. Also the photo is a bit deceptive for when I look at the wear pattern, it is within the center of the gear teeth.

I looked at the distributor a little closer and found what was causing the distributor not to "fall into place". The outer adjacent side to the mating surface of the intake manifold and distributor was rubbing against the intake manifold, so I ground some of the distributor that was contacting and now it installs with no effort.

Now only a little of distributor housing was contacting the intake manifold and it was not difficult to install the distributor, it just took a little force and a slight twist. I don't believe that removing a couple of 0.010" will fix the problem.

A closer look at the wear pattern of the distributor gear reviles that one side has worn more than the other, so I'll set up a dial indicator to measure untruness.

 

So is there any other input out there?

What about running a different material for the distributor gear? I do understand that a bronze distributor gear is for a roller cam and the melonized gear is for a factory roller cam. What harm would come from running one of these type of distributor gears with a regular camshaft?

My other thought is to replace the distributor housing and shaft (along with a better gear ).

 

I thought we were waiting from more data from you.

Anyway, looks like there are two wear patterns on that gear, if the photo can be trusted.

Bronze gears are expected to wear out and be replaced often (remember, we're talking about race car engines with that combo).

Melonized won't help if you've got a set-up problem.

 

Upon further inspection I found the distributor shaft and the bottom bore of the distributor had a lot of wear (about 0.025" play). So replacing just the distributor gear was not enough.

Hopefully this other distributor with 0.007" of play will take care of the problem. [/fingers crossed]