The tach drive gears destroyed themselves and thus I am faced with overhauling the distributor. I have read many of the past posts and investigated several services which perform overhauls. It has left me with several questions and I am hoping to get input to help clarify these issues.

1. There are many sources for reproduction distributor shafts. Are they all of quality and do they accurately reproduce the original shaft specs? I have been told that some or all do not and only NOS parts are to spec.

2. If they do not accurately duplicate the "cam" plate what performance compromise are they making?

3. Does anyone have long term (20k + miles) experience with overhauls from any of the major providers Willcox, TI Specialists, Chicago Corvettes or other. Given the difference in their build processes this seems to be the only indication of who is best.

4. The bushings in my distributor feel very good by hand test. Is bushing replacement as automatic as the overhaul providers would lead you to think?

Bill

 

I would do the bushings and have them line bored.

 

...don't know what you mean by that statement, but bushing/shaft clearance should be about one to two thou... basically you should feel no side play or just barely perceptible.

Duke

 

1. The point distributor shafts all look the same. The football is where the difference is. The tach gear heat treat is a gamble (but there is no alternative).

2. The football or cam plates are reported to be the low performance (300hp) profile. Few people will notice a difference (none will notice if they change the springs, unless run on a machine and graphed). You can swap the football.

3. I do not. I rebuild my own (they last).

4. Shaft and bushing removal inspection is needed. Any shaft damage or scoring, or radial play, indicates a bad lower bushing (and the bushing must be removed for inspection & replacement). The bushing & shaft kit is one of the least expensive upgrades to address engine wear.

The kit issues I experience are with the tach cross shaft gear thrust button. Later distributors use a thin nylon button, early distributors use a thick brass button. Neither button works out of the box, unless you get lucky. The last few I have rebuilt (in the last two years) required the brass button to be thinned to provide the correct end play with the tach cross shaft assembly tight. I now use a mill bit, but a file and time will hand fit the button clearance (a winter, time kill, project).

Some recommend line boring the shaft bushings as part of the reassembly. The bushing's ID's are not undersized, and any material removal is added clearance (added wear). Unless you have a tool lathe any slop at one end of a bit will amplify at the far end bushing (too easy to make things worse, IMO).

The shaft should spin free by hand with no radial play if the bushings are aligned correctly. If you experience resistance the shaft or housing is likely bent (not likely with a new shaft). Heating and slight expansion of the lower housing to align the new bushing to the new shaft alignment in the new upper bushing is what I was taught as a solution. Pack grease and oil into the housing above the lower bushing during assembly. There is an oil hole mid-housing.

I have experienced maybe two really bent distributor housings in the past forty years, housings bent enough to bind where lower bushing realignment after applying heat from a propane torch to the lower housing to help the bushing seek and seat in proper alignment to the new shaft did not help. Sometimes a new distributor housing is the answer (but iron housings are tough).

The other thing to check is the advance cam plates, as they get bent if the distributor is dropped or hammered on (people do weird s#it when they don't know how an assembly comes apart). The football and rotating plates should be straight with only the buttons making contact. Binding of the plates will effect the advance curve.

I doubt the rebuilders blueprint more than the advance curve (if that), with minimal attention to bushings other than hand alignment.

Good luck (you really don't need luck, just patience).

 

I have an article I wrote on rebuilding a tach drive distributor. If you want a copy send me your email address.
Joe

 

I do not have proper gaging to measure the side play in the shaft bushings. The application of side load by hand yields no perceptible movement in the bottom bushing and barely any in the top bushing. I realize this not very scientific since the bushing bores may be worn to an elliptical shape. Sounds like it maybe worthwhile to get an accurate measurement of the bores and inspect the shaft for scoring before assuming the bushings are bad.

Bill

 

Find someone with a Sun machine and spin the distributor up with points. If there is excessive play you will see point bounce.

You can also use a regular timing light and watch the timing bounce around timing marks on the balancer at a fixed rpm, if wear is significant, but it is not as reliable as using a Sun machine.

An electronic trigger (Pertronix, etc.) is much more forgiving than points, until the wear is severe. The timing bounce you see with an electronic trigger is usually advance plate disturbance from the shaft vibration.

Did you disassemble the distributor and inspect the shaft?

With the shaft out, you can shine a light down the bore and inspect the bushings.

Replacing the bushings and shaft is less time consuming for most people than tracking down test equipment.

 

Talking about wear items---is there any source for replacement advance weight pivot pins?

 

Since the distributor housing is full of gear teeth, disassembly and inspection is the logical first step.

 

If your gears are stripped, the cause is almost always due to the sidegear having worn itself into the thrust surface of the distributor housing and then locking up. You cannot put a new mainshaft and crossgear in a housing with thrust surface damage. If you have any wear on the surface, you have to machine the housing and install a custom machined thrust surface insert to repair the surface. If you don't do this, the new gears will strip out almost immediately.

Lars

 

Yes there is wear in the housing and the way the gears failed, one spot on the cross gear and the entire shaft gear wiped, would indicate the cross gear froze despite it moving freely in its bore. Proper repair will have to include repair of the casting interior wall and restablishment of the proper end play in the cross shaft. I am going to use an established specialist to get this accomplished.