Can you recommend a service to rebuild a tach drive distributor?

[Jeff P.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Dave Fielder rebuilt my 68.

[Joe R.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Rebuilding a distributor without a distributor machine makes about as much sense as an amateur rebuilding a speedometer without the proper equipment. I might add that it's takes thousands of dollars for the distributor and speedometer equipment to do the task properly.
Changing the shaft and or the weights, springs etc. without knowing the distributor curve when finished is a waste of time. Each motor has a proper curve set via a distributor machine. The weights and springs along with the contour of the shaft constitute the curve that timing is applied to the engine. And yes, there are several different springs, weights and distributor shafts that in combination will work for each engine.
The reason for people such as Dave Fiedler charging a premium price is because he has invested thousands in tools and test equipment to give you a perfect distributor for your engine each time.

JR

[Duke W.]

Re: Can you recommend a service to rebuild a tach drive distributor?

If the shaft bushings, shaft, and tach drive gear are okay, rebuilding a Delco single point distributor is easy. The procedure is in the 1963 Corvette Shop Manual and later COMs. Before removal check end and side play. Almost all will have excess end play, and if there is no or just barely detectable side play, the bushings are probably okay.

I posted a couple of threads in Dec. '12 on rebuilding a L-79 distributor that was basically okay other than the ground wire breaking on disassembly, which was an easy fix.

You don't need a distributor machine to set up the spark advance map. A dial back timing light will work just fine. Most OE spark advance maps can be improved on as discussed in my 2012 San Diego National Convention presentation, which is posted on the TDB and can be found on the Web with a simple search.

We set up the dist. using my recommended VAC (which is different than OE) and the lightest springs in the Mr. Gasket 928G spring kit that brought in maximum centrifugal at 3500 rather than 5000, and most of it is in by 3000. The engine ran very strong with better low end torque and did not detonate on 91 PON fuel!

A distributor test machine is certainly convenient, but unless the guy running is knows a good starting point spark advance map for the specific engine configuration (and most don't) you won't get an optimum setup. It's analagous to wheel alignment. Modern alignment equipment is wonderful, but most techs don't understand suspension geometry or the machine and have no idea what specs vintage Corvette alignment should be set to.

[Joe L.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Rebuilding a distributor without a distributor machine makes about as much sense as an amateur rebuilding a speedometer without the proper equipment. I might add that it's takes thousands of dollars for the distributor and speedometer equipment to do the task properly.
Changing the shaft and or the weights, springs etc. without knowing the distributor curve when finished is a waste of time. Each motor has a proper curve set via a distributor machine. The weights and springs along with the contour of the shaft constitute the curve that timing is applied to the engine. And yes, there are several different springs, weights and distributor shafts that in combination will work for each engine.
The reason for people such as Dave Fiedler charging a premium price is because he has invested thousands in tools and test equipment to give you a perfect distributor for your engine each time.

JR

JR-------


If the distributor is original and is rebuilt using the original springs, weights, auto-cam (with or without the original main shaft), and an original spec vacuum control, it will have the same specs as it originally had. In this case, no distributor machine set-up is required. The springs, weights, and auto-cam are essentially non-wear parts, so they can be re-used. If one does not have the known-original aforementioned components but one can obtain NOS original components for the particular distributor part number, the same thing applies.

[John D.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Try Don Baker. 1-815-498-9522. He did my 66 TI and my 67 point distributor over winter last year. Excellent work and I couldn't me more pleased. An honest gentlemen to work with.

I also highly recommend Don Baker. He is the best Corvette fuel injection distributor restorer in the world and also does a ton of carb distributors both points and TI. You will be pleased and his prices are fair. I have had 100% positive feedback on the FI distributors that Don has restored for my customers. They are a work of Art and are tested extensively. You will get a card with the original specs on one side and your restored distributor specs on the other said. You don't get it back unless it's perfect. John

[Joe R.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Joe & Duke,

Your defense is noted BUT when replacing the shaft there are only two available. One for a lower performance motor and one for a high performance motor. Those two cannot possibly replace the ones available to SB and BB across the board.
Also Joe, the cam is brazed on the shaft. I don't expect everyone to have the knowledge to swap the cam to a new shaft. As for finding NOS distributor shafts! Good luck!

JR

JR-------


If the distributor is original and is rebuilt using the original springs, weights, auto-cam (with or without the original main shaft), and an original spec vacuum control, it will have the same specs as it originally had. In this case, no distributor machine set-up is required. The springs, weights, and auto-cam are essentially non-wear parts, so they can be re-used. If one does not have the known-original aforementioned components but one can obtain NOS original components for the particular distributor part number, the same thing applies.

[Duke W.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Joe & Duke,

Your defense is noted BUT when replacing the shaft there are only two available. One for a lower performance motor and one for a high performance motor. Those two cannot possibly replace the ones available to SB and BB across the board.

JR

If the shaft has to be replaced then one may well have to accept a compromise. I don't know the specifics of the centrifugal curve between the two, and I don't know if the vendors even publish it.

Also, I think it was noted a couple of years ago by someone that a "repro" shaft actually had the football brazed onto the shaft upside down... another example of "repro" parts designed, manufactured, and sold by the blind leading the infirmed.

If faced with a shaft replacement, I would recommend first trying to find a serviceable used shaft of the same type as original before going with one of these poorly designed and manufactured replacements.

Duke

[Joe R.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Duke,

I totally agree with you. My only concern was the shaft is usually replaced because of bearing failure or tach gears being stripped. When it is replaced with one of the repos available you don't know what your getting unless you put it on a distributor machine and see when the timing advance starts and ends. The entire curve of the distributor and purpose is then unknown.
Thanks for jumping in to clarify.

JR

If the shaft has to be replaced then one may well have to accept a compromise. I don't know the specifics of the centrifugal curve between the two, and I don't know if the vendors even publish it.

Also, I think it was noted a couple of years ago by someone that a "repro" shaft actually had the football brazed onto the shaft upside down... another example of "repro" parts designed, manufactured, and sold by the blind leading the infirmed.

If faced with a shaft replacement, I would recommend first trying to find a serviceable used shaft of the same type as original before going with one of these poorly designed and manufactured replacements.

Duke

[Duke W.]

Re: Can you recommend a service to rebuild a tach drive distributor?

If someone has installed those replacement shaft assemblies with whatever weights/springs came with them maybe they can use a dial back timing light to determine the centrifugal curve.

I vaguely recall seeing some data a few years ago and IMO neither was very good for the either application.

As I explained in my San Diego presentation, SHP engines with high overlap, late closing inlet camshafts need and can tolerate more low rev advance, so the 365/375 HP engine's OE centrifugal (24 @ 2350) is about ideal and the L-79 can be nearly as aggressive.

The 30 degrees beginning with the 1966 300 HP dist. is about right since they don't need and can't tolerate as much low rev advance. Bringing the maximum in at 3000-3500 rather than the lazy OE 5000 will improve low end torque, usually without getting into detonation.

Big blocks are more suspeptable to detonation due to their larger bore, so 28-30 at 3000-3500 is a good starting point.

All should have initial timing such that the sum of initial and full centrifugal is about 38 as long as there is no detonation.

Duke

[Stuart F.]

Re: Can you recommend a service to rebuild a tach drive distributor?

I should have mentioned in my previous post that another reason I chose not to use the replacement main shaft, even though it was supposedly for an SHP small block such as mine, the profile of the "football" was not the same (close, but no cigar), and it was crudely made with a perlmeter burr above the cross shaft gear. Bottom line for me, replacement would have been the last resort.

Stu Fox

[Joe C.]

Re: Can you recommend a service to rebuild a tach drive distributor?

The config of the "football" has very little effect on the advance program. The autocam, springs and weights define about 90% of the program. There is absolutely NO need for a Sun Distributor machine when setting up a distributor, as I always do them ON the engine to be tuned. As mentioned, the original specs are no longer valid in most cases because the gasoline is different, spark plugs are different, and many engines are assembled differently from the way they were originally.

Case in point: I have no idea how long those "High Performance" main shafts were being sold (by every single vendor I contacted at the time) with the "football" attached (pressed on, not brazed as original) upside down, nor how many were installed by unwitting customers. But you can bet yer bippy that nobody noticed any difference in engine performance, nor that any difference in the spark advance program could be measured for that matter. The only one who contacted me later on to confirm what I had told them was LI Corvette Supply. For all I know, the others might still be selling the Hi Perf shafts with the upside down football.

The two most important factors in defining the advance program are the length of the advance slot in the autocam, and the flyweight spring strength. I have a reproduction High Perf mainshaft (with the football installed correctly) in my 1111069 distributor. The football is VERY different from the original one installed in the L76 non-TI distributor but guess what.......................the 24 degree centrifugal spark advance................when my engine was configured as an L76................were set to be "all-in" @ 2350 JUST LIKE IT SAYS IN THE SHOP MANUAL.

No problemo.
Adeste Fidelis.
HAND.
Later.

[Joe L.]

Re: Can you recommend a service to rebuild a tach drive distributor?

Joe & Duke,

Your defense is noted BUT when replacing the shaft there are only two available. One for a lower performance motor and one for a high performance motor. Those two cannot possibly replace the ones available to SB and BB across the board.
Also Joe, the cam is brazed on the shaft. I don't expect everyone to have the knowledge to swap the cam to a new shaft. As for finding NOS distributor shafts! Good luck!

JR

JR------


I do not recommend the use of the aftermarket replacement shaft assemblies with attached auto-cam. ALWAYS transfer the original auto-cam to a replacement shaft. Removing and re-brazing is not all that difficult. However, if one does not have the skill, there are lots of folks around that do and they do not have to be distributor specialists.

As far as NOS shaft assemblies are concerned, I know where there are lots of them. None for sale, though.

[Mark E.]

Re: Can you recommend a service to rebuild a tach drive distributor?

It's fascinating to see the direction a thread can go.

And keep it going! I'm learning a lot about brazing auto-cams and upside down footballs. Whoever I choose to rebuild my distributor, I can dazzle them with my new found ignition jargon.

[Duke W.]

Re: Can you recommend a service to rebuild a tach drive distributor?

The shape of the football affects the shape of the curve. The 365/375 HP distributors have a linear 24 degree "curve" from 700 to 2350. The '66-'68 300 HP curve is non-linear from 700 to 5000, but most of it is in by 4500. With lighter springs that bring the 30 in at 3500 all but two or three degrees is in by 3000.

The non-linear centrifugal curves are a refinement that allow optimum advance at high revs without so much advance on the low end that detonation can be a problem, and it took a lot of geometric analysis to achieve.

If you installed a 365/375 HP dist. in a 300 HP engine and set initial to achieve 38-39 total, detonation would be likely, but it doesn't happen on 365/375 HP engines I've tuned using CA 91 PON premium, and the 375 HP engine had single .018" gaskets, which is an indication that it has never been apart, so the true CR is likely at least 10.5:1 and could be about 10.9 if deck height is nominal.

Duke

[Joe C.]

Re: Can you recommend a service to rebuild a tach drive distributor?

JR------


I do not recommend the use of the aftermarket replacement shaft assemblies with attached auto-cam. ALWAYS transfer the original auto-cam to a replacement shaft. Removing and re-brazing is not all that difficult. However, if one does not have the skill, there are lots of folks around that do and they do not have to be distributor specialists.

As far as NOS shaft assemblies are concerned, I know where there are lots of them. None for sale, though.

The autocam has to be clocked correctly relative to the roll pin hole for the distributor drive gear. Autocam clocking determines cam/plate clocking which determines rotor clocking. And the rotor clocking must be correctly aligned to the camshaft position.