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If this subject has come up recently, please excuse me.
Recently I got lucky and got a steal on a Sun Distributor Machine ($30 on Craigslist). Does a great job on synchronizing the points on my ’29. But when I checked the amount of mechanical advance measured on the Sun machine compared to the amount in the specifications that I had, there was quite a variance.
According to the specs that I had, at 1000 RPM there should be 2 degrees of advance, at 1500 RPM 4 degrees, at 2500 RPM 7.5 degrees, and at 3200 RPM 10 degrees. With the springs that were installed, I got 1,2,3,and 4.5 degrees respectively. The weight pivots were lubed and everything was moving freely. I measured these (stock?)springs to open with 32 oz. of tension.
I then picked up several sets of springs at a speed shop to compare. The next set were 15 oz springs. I now got more advance-2,3,4 and 5 respectively. A road test seemed to indicate better throttle response with this setup. I haven’t tried the 10 and 5 oz. springs yet since they are so much lighter than the ones that came on the car.
Does anyone have any thoughts on this? Am I measuring the amount of advance incorrectly?
Thanks in advance.
Greg,
I collaborated with Arnold Romberg a couple of years ago on a PASB article (PASB 2007-6) on the advance issue in my Delco 668-E distributor (same as yours). It’s NOT among the PASB issues currently on the website).
The short version is that I found that some previous owner had substituted weight springs, so that my 1930 Model B distributor achieved only 6 degrees of DISTRIBUTOR advance vs the 9 (or 9.5, or 10, different sources) required by published specs. The data published in the PAS Wiring and Tuneup Guide uses ENGINE rpm/advance–18* at 3300 (which is equivalent to 9 degrees at 1650 DISTRIBUTOR rpm. Suggest checking advance at published MAX rpm; advance at lower rpms will take care of itself. Remember that ENGINE degrees and advance have twice the values of DISTRIBUTOR degrees and advance.
The guy who did mine substituted springs from wrecking yard takeouts until he got proper advance. What a difference in performance, and it improved cooling at speed on hot days because the spark was no longer retarded! Be sure to re-bush the distributor if necessary while it’s out.
I know of a 1931 restored Model 41, using the same distributor, that I could tell was very retarded, and the car had cooling and performance issues. I suggested that the advance springs be checked. The existing springs in that distributor were later described as “miniature garage door springs”” that allowed minimal advance! Substituting proper-weight springs greatly enhanced both performance and cooling.
Good luck!
George”