lr172

During the build of my 496, I decked the block to 0 deck. Upon final assembly, I used a Nylon spacer for the distributor. While cranking it, I noticed the distributor spin. I figured that I didn't have enough shims, so I added another. This time I was a bit more careful, ensuring that I saw it bottom out and then adding another shim.

I broke in the cam for 20 and have about 40 miles on it. I pulled the distributor today to fix the mech advance and found the distributor gear has about 5 thousands of wear off the teeth. I don't know if this was from the initial cranking or has been continuing to wear over the hour or two of running. The wear is somewhat rough and not polished, leading me to believe that it is from the initial tightness.

Any thoughts here? Any suggestion for the proper amount of clearance when adding shims to the distributor? The gear on the cam looks clean, with no wear.

Thanks for your assistance.

Fonz69

What kind of cam are you running?

Cam thrust button not on backwards right? Or missing?

gingerbreadman1977

did you have cam lube on everything for initial start up.

lr172

It is a Lunati Solid Flat Tappet Cam. It has no cam button, as I was told they were not necessary for FT's.

The oil system priming pretty well soaked the cam gear and I covered the dist gear in oil before assembly (1 hour before starting). The cam lobes were coated with Lunati's Moly.

I took a close look at the cam gear as best I could and it doesn't appear to be worn, as the dist. gear is. Is the Iron in the cam gear harder then a stock GM dist. gear?

I think I will gamble on the cam gear being good and just installing a new dist gear. I really don't like the idea of pulling the cam on a motor with 1 hour run time.

Any suggestions on clearancing the new distributor so that I don't repeat this error?

540 RAT

From what you wrote, it sounds like you shimmed as needed so that the distibutor wasn't held up by the oil pump driveshaft, and then it would clamp down OK. So far, so good, right? But it looks like there may be another issue here. The picture is so blurry that its a little hard to tell for sure what exactly I'm seeing, but it appears to be an aluminum distributor housing, and it appears you have a ton of shims between the distributor gear and the housing. In any case, with an aluminum housing, you should shoot for around .015 distributor shaft end play. This accounts for the expansion due to heat of the aluminum housing, which is greater than the steel distributor shaft inside. If you had much less end play than this (only iron distributor housings should ever run less end play), then the distibutor was almost certainly binding, which would cause a lot more load on the gear to turn it. That could well account for the excessive gear wear. Check it out, maybe that's all you need to do, to correct your problem.

Its also a good idea to drill a .030 hole or file a .030 wide and deep groove at the very bottom boss of the distributor housing, directly above the cam gear. This will provide pressure fed oil to the cam gear/distributor gear interface, for optimal lubrication.

Ironcross

You may need a bronze distributor gear,...Some aftermarket cams creat excessive gear wear...

80TexasC3

I had the same problem with my brass gear. Went with the composite comp gear and the problem went away. More dollars to purchase but worth the pain and time it would take to tow and repair again in the future.

lr172

I think your are on to something here. Not all of the wear could have come from the couple of revolutions when it was too tight. I had my end play clearance around .008, based upon some advise I got. It is aluminum and my recent research also shows a need for a looser tolerance, as you suggest. I see how binding there could cause very accelerated wear.

The Lunati guys suggested the composite gear. They thought it would wear enough to mate with whatever wear that I put on the cam gear and then survive. However, it is $110. I wound up buying a new distributor due to some problems with the adv mechanism. I will try the iron gear that comes with it and check for wear at 100 and 200 miles. If it is wearing, I 'll replace it with the composite. If not, I'll consider myself lucky. They say once the cam gear is worn, it will forever wear dist. gears. I guess we'll test that theory.

Thanks for your help.

540 RAT

I actually bought a Comp composite gear for my 540 build. But in the end I didn't use it because of too many failures (breakage) reported over on the Chevelle Forum. So consider yourself informed about that as well. I ended up going with a bronze gear afterall.

lr172

Thanks for the tip. Can you use a bronze gear on a FT cam with an iron gear? I thought they were only for steel gears on the billet cams.

I thought about the bronze instead of composite, but the Lunati guys discouraged it, saying it would likely wear too quickly with the iron cam gear.

Fonz69

Interested in the breakage issue

I ran a bronze gear on my 540 since new and did see some wear in it in the low hours of use so now that the motor went into the vette I switched to the comp cams composite gear.

I have yet to do more than fire up the motor and run the antifreeze thru the motor so who knows how the gear is going to hold up.

540 RAT

An iron cam gear is fine with a stock GM distributor gear, they are designed to be compatible. Any problems between the two is not due to material types. There would have to be other issues such as the wrong (too tight) distributor end play as I mentioned before. Also don't forget about the extra oiling that I also mentioned, that is a definite plus for any engine, mild to wild.

540 RAT

I sanded the cam gear smoother on my billet steel solid roller cam. It didn't look rough, but felt a tad bit rough. Then after sanding it, you could see high and low spots left by the maching. And now it feels much smoother. That plus drilling the extra oiling hole in the bottom of the distibutor, along with running super slick synthetic Royal Purple XPR Racing Oil, should keep my bronze distributor gear going for a long time.

lr172

I wished I had sanded mine. I put in the new Distributor with a new gear on Friday and I am still getting some wear. It is nowhere near as bad as before, but it did put some wear on it already. On close inspection, it appears to be galling from a edge and not traditional wear. I will keep pulling this dist every hour or two of running and see if it settles down. I hate the idea of pulling the cam to clean up the gear.

Do you think it is worth getting the GM Melonized gear to survive this?