TI Distributor Advance Curve

[Gary C.]

I have a 1111248 distributor that I put on a distributor machine and the centrifugal advance maxes out at about 11 distributor degrees. I think it should reach 16. I had a set of weights and 2 sets of springs that I obtained from one of the corvette parts suppliers, and no combination of those parts are even as close to the factory specs as what was on the disrtibutor to begin with. Am I missing something here, or does anyone have any suggestions for springs/weights?

Also I noticed that the arrows on the Sun machine that would correspond to cylinders #5 and 7 were each off by one degree. Is this within the tolerance of my sun machine or the distributor or does that indicate some wear with the TI triggering parts?

Lastly, does anyone have any experience with reproduction vacuum advance units, the one I bought, a 360 that should provide 12 degrees at 14 inches Hg, does about that but will go on to about 16 degress at about 17 inches. Should the unit provide 12 degrees maximum?

Thanks in advance.

Gary

[Duke W.]

Re: TI Distributor Advance Curve

I haven't committed to memory the specs of the scores of OE distributors, nor can I correlate all the distributor part numbers to the actual engine option - just a select few. Sorry for my feeble level of knowledge.

So what are the centrifugal specs of the 1111248 distributor and what have you measured and what year/engine? Since you are testing on a distributor machine, let's use distributor degrees which are half crankshaft degrees.

Format as:

0 @ xxxx RPM (start)
max @ xxx RPM

for both the OE specs and measured data.

You can also give an intermediate point if you wish.

I believe the 360 VAC should be 0@6", 6 (dist deg.) @12", in which case yours is out of spec.

A couple of cylinders measuring one (distributor) degree off is not unreasonable.

Duke

[William C.]

Re: TI Distributor Advance Curve

1111248 specs should be 0-4 degrees at 1000 engine rpm, and 30-34 degrees at 5000 rpm. It is essentially not a high performance curve by any stretch of the imagination. The distributor advance is established by the length of the slot in the plate the weights pivot on, and the timing of the advance is based on the shape of the mainshaft cam as well as the location of the pivot pins and the spring characteristics. Looking at a point anywhere below 5000 engine rpm will not give you the correct total advance for sure, and requires a major rework to get to a "high performance" configuration. As Duke said, the Repo vacuum can is simply not to spec, an all to common failing or repo vacuum cans. I find about 50% to be off spec and 25% to be way off. As an aside, I do not work on TI distributors!

[Clem Z.]

Re: TI Distributor Advance Curve

install a plastic "sleeve" on the upright part of the advance rod where it comes up thru the slot in the vac can bracket to limit its travel. make sure there is no "play" in the advance plate where the vac advance rod come up thru.

[Joe L.]

Re: TI Distributor Advance Curve

Gary-----

All of the distributor springs and weights that are on the market today are pretty much "generic". Basically, there is one set of weights and 3 different springs. No matter which kit you buy, this is pretty much what you get. I don't think that they are all manufactured by the same source since there are some differences in finish and slight configurational differences with respect to the springs. However, they're all, basically, the same set.

Originally, there were a plethora of different springs, a plethora of different auto cam configurations, and several different weight configurations. Various combinations of these were used by Delco-Remy to create the particular mechanical advance configurations for particular distributor part numbers. There is no one that I know of today that manufactures exact reproductions of all the original weights, springs, and autocams. I've searched for such a source for years and never found one.

I've never used one of the reproduction vacuum controls that are available. However, you might want to try one of the replacement controls that are available and see if it checks out. Of course, there will be some slight "nuances of original configuration" that will be lost, but the conformance with design specs might be better. Try a GM #19138049, aka Delco #D1383X.