It seems that the 1110984 (1962 250hp single point) distributor doesnt have a set screw to adjust the tach drive cross gear, so cannot install a plastic or brass button. Is this correct?

Without the set screw, which cross gear do I buy? There are ones that have a steel end, ones with a steel end and bore to allow a button, and ones where the button appears to be pre-installed.

Any help would be appreciated.

 

There were no adjustable set-screws on the end of the cross gear cavity until 1972 or so; unless you see major wear in the end of the cast iron housing, you shouldn't need any "buttons".

 

So I assume the gear will be thrust away from the housing (hence the thrust washer on the other side). Would the brass-end cross gear offer any benefit over the ones with a steel end (the one I have)?

i.e. This:


vs this:

 

The cross gear thrust is inward, the hardened washer is simply there to protect the brass bushing from the gear teeth.

Most times you can drill/tap for a set screw through the distributor housing or install a bronz bushing inside the distributor housing. What you don't want to do is not repair the housing if it's wore because the main shaft and cross gears will mis-align and strip causing replacement.

 

GM used a plastic button somewhere around 1969-1970, I never saw a factory installed set screw and have owned quite a few tach drive distributors, send yours out to Lars in CO, he will repair the housing and set the thrust, for a nominal fee.

 

Thanks for that information. I have fully rebuilt the distributor and converted points-electronic. The last piece of the puzzle is this tach cross-gear. There is no wear in the housing but I might drill and install the brass button anyway. I found a good writeup here:

http://65corvette.nonethewiser.net/m...inter03-04.htm

 

I wouldn't recommend it. The brass will get chewed up very quickly, and it will send metal fragments down into the lower shaft bushing, destroying the bushing and the mainshaft. There is a good reason the factory never used brass thrust buttons. I charge people quite a bit of money to fix what you're planning on doing...

Lars

 

Thanks Lars, the housing is not damaged, so it looks like I will just use the steel-end one I have. One more question for you - as I rotate the mainshaft back and forth, the tach gear can slide in and out by about 0.040" as it is thrust forward and backward. Is this normal?

 

Some people have used a set screw with a hardened steel ball bearing soldered on the end to adjust the cross gear end play and prevent wear.

 

Thanks for the advice. I would rather not drill the housing if I dont have to. Is end-play really an issue? If so, maybe I can machine a custom thickness thrust washer to take up the play?

 

See post #2.

 

Yes, .040 is about right and perfectly normal. If you don't have a big worn counterbore recess in your housing thrust wall, you're good to go. Lube it up well and run it.

Lars

 

Thanks Lars!

 

I have never heard of the damage you are referring to with the installation of the brass button. I installed one on my 1967 Corvette distributor and inspected it some time ago only to find what looked to me like a little scratch.

I had installed a set screw that had a plastic tip but it looked terrible as it stuck out of the rear housing. I think most of the vendors sell these brass buttons, can you provide a picture of the damage you have seen regarding this button.

How do you repair these in the shop, I guess you could have one made from steel easy enough. It's hard to see in my picture but I recess the housing .060 so it sits flush and the hardened washer can be used on the gear to protect the brass bushing plus the gear sits centered.

 

I build one to two distributors per week, and I get, on average, one per month that has the brass button installed with severe damage: The brass button is too soft to provide durable service, and I see them fail in as little as 500 miles. Commonly, I see total failure of the buttons, where the crossgear has worn completely through the brass, leaving only the "stem" in the housing pin hole. In every case, the metal shards from the shredded brass end up in the lower bushing, and this destroys the bushing and scores the mainshaft severely.

Here is one that I received just this week: This is from a Forum Member who rebuilt this distributor just a few hundred miles ago, but he was not happy with the advance curve, so he sent it to me for checkout and curve. The crossgear and the thrust surface had plenty of lube. The crossgear end surface was not scored up, yet the brass button is clearly headed for early failure. It's hard to get a 3-dimensional view from this 2-dimensional photo, but the thrust surface is worn almost halfway through. This is one of the better brass buttons I have seen after use:



The brass shavings had scored up the lower bushing pretty bad, but the mainshaft was still in serviceable condition. I replaced the lower bushing, polished up the shaft, fabricated a good, mild steel insert, and got this one set up and tested at a nominal cost.

When I first started rebuilding tach drive distributors about 10 years ago, I thought the brass buttons would be great: I used them in several of my early builds. I received every single one of those distributors back in less than a year with complete thrust button surface failure, and I lost my butt on the work. Needless to say, I don't use them any longer, and I haven't had a failure since.

Lars

 

Lars,

Thanks for that picture, the next time I have mine out it will be addressed. It's always something..