When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Trying to figure out why I can only get max 15 degrees of mechanical advance out of my distributor - I was expecting mid twenties.
- The silver Delco tag is missing. It is installed on a 1969 L36 but the engine is sadly not too original so this might not have been the distributor that came with it.
- The distributor is currently off car and being measured on a Sun distributor machine
- Started with very light springs, and have also tried no springs - in order to establish what the full range of mechanical advance would be before I start adjusting it
- Initially only got 12-13 degrees but was able to squeeze a couple more (15 total) by removing the spacer from the pin that travels through the advance slot
- Vacuum advance not connected
- Cam is CCW 524
I noticed today that when any of the weights are installed, the shape of the weights prevent the pin from starting flush with the near edge of the slot (pic 2). If I remove the weights then the pin is able to start flush with the near edge (pic 1). In either situation, with or without weights, the pin is free to fully travel to far end of slot (pic 3). After chancing upon this, I can definitely see/feel the bind when the weights are installed. But I tried 6 different sets of weights from a selection of spare 60s Delco distributors. The general shape of all the weights is the same, but there are subtle differences, I assume not all are original GM weights but not sure how to tell which ones are. Regardless, 6 different sets tried - all of them created the same problem to varying degrees.
Shape of weights? Shape of football? Something else? Or maybe I'm incorrectly expecting mechanical advance range in the mid twenties? Don't be misled by my mention of Sun machine - I do have access to one but I'm still very new doing anything with distributors so there might be fundamental flaws in my assumptions.
Ugh, not sure - probably distributor degrees as the values I'm quoting are being measured off car on a Sun machine. On the Sun machine there is an RPM gauge which I understand to be distributor RPM - you have to double to get engine rpm. But It didn't occur to me that you'd have to do the same thing with the degrees - is that what you're implying? If that's the case, the numbers would be exactly where I'd expect them, so maybe that's it.
Do you have a bushing on that pin? I ask because I can't quite see it from the pictures.
Your pin diameter WITH bushing should be about .260". On say a #730 CCW cam w/ #37 weights - a slot length of about 0.412" should yield about 15* (or 30* at crank).
If you're seeing 15* on the machine - then that is 30* at the crank.
You can also Google up 'printable protractor' and print it on paper with a diameter roughly the diameter of your distributor (or larger for more accuracy), cut it and tape it on the distributor. Use a paperclick or something on the shaft and measure degrees of advance.
When Lars pops into this thread - send him a PM (I don't have his email handy) and request his white papers on setting up a distributor curve and timing an engine. It's *THE* manual for how to do this project.
Do you have a bushing on that pin? I ask because I can't quite see it from the pictures.
Your pin diameter WITH bushing should be about .260". On say a #730 CCW cam w/ #37 weights - a slot length of about 0.412" should yield about 15* (or 30* at crank).
If you're seeing 15* on the machine - then that is 30* at the crank.
The bushing is not on the pin in pics. I took it off trying to squeeze more advance out before the crank vs distributor degrees con ept was understood.
Agree about Lars'paper - great stuff. I do have a copy.
Distributor Mech Adv Limit
