1963 340HP distributor bushing (timing limiting bushing)

[Joe L.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

That is goo news Tim.
By the way Joe, the 524 is not functionally the same as a 724. My information comes from Don Baker, the FI and Carb distributor restored.
Also at the same time Delco Remy was pushing the 524 cams they were also putting out a generic FI distributor shaft advertised as '62-'65 I believe. It has the incorrect football on top. Says 54W. Once again DR just was using up parts. Like the B1 Vacuum advances in the box for the also service replacements 163's. The 163 was supposed to be used in lieu of a 201. So confusion big time and it's not our fault.
All that superceeding puts a wrench into correct restorations. Like the time I bought a ton of exhaust tips. Found out none were correct for my 63. Thanks everyone. Hope I didn't confuse you. John D.

John-----


So, how do they differ and how does that affect functionality?

[Richard G.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

I have been attempting to decipher how much difference (in timing) the rubber limiting bushing would make if it denigrated and fell off.

I did this drawing;

Given the pin is 1/2" from the center line and the bushing OD is 1/4" and ID is .200.

One would have to double this number to account for the opposite/both side of the bushing.
The difference between having the bushing installed and not would be 6 distributor degrees or 12 crank degrees.
Hope I got this correct.
Rick

[Duke W.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

Sometimes the limit of retraction is not when the pin (with or without a bushing) reaches the end of the slot. In some cases the ends of the weights contact each other and this is the limit of retraction. Be sure to check for that.

Duke

[Gerald L.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

Still talking '63 -340 engine. Does the presence or absence of this timing bushing (sleeve) have any impact on distributor position for initial timing? Everything else being equal as I understand the gear position, VAC arm length, and even the gear end play has an impact? Trying to understand why my '63 340 distributor is just a few thousandths from the manifold. Initial is 10 BTDC with manifold vacuum plugged and weights banded and timing tab spot on. I do get a full 24 degrees mechanical advance. I am looking for essentially 6 distributor degrees to move the distributor to midpoint between the manifold and the coil bracket. I would like to increase the initial advance to 12 or maybe 14 but have no room. Might the cam/weight plate be wrong on a rebuild in the '80s?

[Richard G.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

You need to confirm the gear on the bottom of the distributor was installed correctly.
The dimple on the gear aligns with the rotor tip.
It can be installed both ways.

[Gerald L.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

Dimple aligns w the rotor. Rotating the gear 180 will rotate the distributor about 14 degrees (a little geometry calc) which places it against the coil bracket, confirmed by doing it. Any way I can read markings on the cam/weight plate with distributor installed?

[Duke W.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

Still talking '63 -340 engine. Does the presence or absence of this timing bushing (sleeve) have any impact on distributor position for initial timing? Everything else being equal as I understand the gear position, VAC arm length, and even the gear end play has an impact? Trying to understand why my '63 340 distributor is just a few thousandths from the manifold. Initial is 10 BTDC with manifold vacuum plugged and weights banded and timing tab spot on. I do get a full 24 degrees mechanical advance. I am looking for essentially 6 distributor degrees to move the distributor to midpoint between the manifold and the coil bracket. I would like to increase the initial advance to 12 or maybe 14 but have no room. Might the cam/weight plate be wrong on a rebuild in the '80s?

I'm not sure if the original '63 340 HP engine dist. had a limit bushing or not, but it really doesn't make much difference if it does or not. Use a protractor to make a cardboard template to measure the angular movement in dist degrees. Crank advance is double that.

Is the limit of retraction due to the weights contacting the "football" or due to the weights contacting each other? Again, it doesn't make much difference whether it's 24 or 30 when you use a dial back timing light to set total WOT advance in the range of 36-40 a few hundred revs above the point of max centrifugal.

There have been reports over the years of the dist. hitting the manifold or coil bracket with the dimple pointing the same direction as the rotor tip. This appears to be the case because some aftermarket cams appear to have the gear on the camshaft improperly indexed, so you have to index the dist. gear 180 deg. out from the OE indexing.

You need a B28 (Airtex 4V1053) VAC and the black springs from the Mr. Gasket spring kit are the lightest.

Search for threads started by me and download the "L-79 dist. blueprint/overhaul thread" and the breaker points article.

Duke

[Gerald L.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

Thank you both. My interest in setting the distributor midway between the manifold and the coil bracket (and why it is not) is secondary to my interest in moving WOT from 34, to 36, or 38. I know my cam plate and weights bring 24 degrees mechanical all in before 2400 rpm (two silver springs and original '37' weights), initial advance is 10, and dwell is 30. Since dwell angle actually impacts initial timing I do have that to play with before winter even with the VAC against the manifold. Thanks Duke for the 1:2 relationship of dwell to timing. Definitely acceptable to move dwell from 30, to 31, or 32 (initial 10, to 12, or 14) until I hear detonation.

I do wonder why cam/weight plate PN 1967002 was widely used on Corvette small blocks from '58 to '72? BUT a different part 1966686 was used in '62 to '64 all engines x FI or was available as a service replacement for only these years. Are the slots on these two plates slightly different relationship to the cam lobes, 6 degrees is all it would take to center my distributor. It appears that shaft PN 3998287 applied to all sbc engines with single points. So the football to gear relationship was always the same.

[Duke W.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

Thanks Duke for the 1:2 relationship of dwell to timing. Definitely acceptable to move dwell from 30, to 31, or 32 (initial 10, to 12, or 14) until I hear detonation.

I do wonder why cam/weight plate PN 1967002 was widely used on Corvette small blocks from '58 to '72? BUT a different part 1966686 was used in '62 to '64 all engines x FI or was available as a service replacement for only these years. Are the slots on these two plates slightly different relationship to the cam lobes, 6 degrees is all it would take to center my distributor. It appears that shaft PN 3998287 applied to all sbc engines with single points. So the football to gear relationship was always the same.

It's actually the other way around. Look at it this way. As dwell angle is reduced point gap is wider, so the points have to open earlier, so the timing is advanced.

Not sure about your second question, but there were many different combinations of shafts that have different footballs (not available individually), weights/springs and, it looks like several cam assemblies both with and without the limit bushings. I don't think GM sold shafts individually through service parts. You had to buy the whole assembly of shaft, cam assembly, weights and springs, and there were only a couple of these assemblies available through service parts.

Rotating the dist. gear 180 degrees should be the VAC about halfway between the interference points in the normal initial timing range.

Duke

[Joe L.]

Re: 1963 340HP distributor bushing (timing limiting bushing)

It's actually the other way around. Look at it this way. As dwell angle is reduced point gap is wider, so the points have to open earlier, so the timing is advanced.

Not sure about your second question, but there were many different combinations of shafts that have different footballs (not available individually), weights/springs and, it looks like several cam assemblies both with and without the limit bushings. I don't think GM sold shafts individually through service parts. You had to buy the whole assembly of shaft, cam assembly, weights and springs, and there were only a couple of these assemblies available through service parts.

Rotating the dist. gear 180 degrees should be the VAC about halfway between the interference points in the normal initial timing range.

Duke

Duke------


Distributor mainshafts with attached auto cam were available in SERVICE for virtually all original distributors. Shafts without attached auto cam were never available in SERVICE from GM. There were only a few SERVICE assemblies that also included weights and springs. Weights and springs were available separately in SERVICE for all distributors.