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My engine build is in process and as such I have no running engine to set-up my distributor with, and it seems all the Sun Distrib machines have disapeared over the years.
I would like to rebuild this old vette tach drive distrib I picked up at a Carlisle and see what the current advance curve is like and if it is even close to what I need.
Question: Did (or could) anyone measure their mechanical advance curve slot with a caliper and could give me a measurement?
Something like: "mine is xxx long and that gives me xxx degrees mechanical advance"
Once the engine is running I will have no problem fine-tuning it from there,
Here is a pic of what I have. Without disassembling the distrib, just turning it upside down, I measured from edge of bushing to end of mechanical advance slot, with a dial caliper, and got around .140" Anyone measure theirs and tell me how many degrees advance theirs is?
These are the slots that get filed longer for more mechanical advance, or welded up for less mechanical advance, to change the timing curve.
Mine looks to be un-modified in either direction. Depending on which distrib it was originally, ( I have no idea), it could be good to go, or not. That may mean I may need to weld it up, and would prefer to do that before Dyno day.
Thanks in advance.
It has 30 degrees in it originally. Might be more now with the bushing wear. The stamped number on the distributor will tell you the original application. You can check the tune up specs once you know the application.
I can save you some time.....it was from an engine that originally had an initial timing spec of 6 degrees before TDC at idle.
Last edited by stingr69; Aug 16, 2019 at 02:24 PM.
My engine build is in process and as such I have no running engine to set-up my distributor with, and it seems all the Sun Distrib machines have disapeared over the years.
I would like to rebuild this old vette tach drive distrib I picked up at a Carlisle and see what the current advance curve is like and if it is even close to what I need.
Question: Did (or could) anyone measure their mechanical advance curve slot with a caliper and could give me a measurement?
Something like: "mine is xxx long and that gives me xxx degrees mechanical advance"
Once the engine is running I will have no problem fine-tuning it from there,
No, not all
Nelson Crozier ... have your ducks in a row before you have the conversation ... download & read the worksheet
http://www.nelsonspecialties.com/
--------------------------------------------------------------------------------------
Also Dave Fiedler at TI Specialty
You could just reduce the travel by 1/3 or so and use that as a base line. I just braze the slot up a bit and finish it out with my miniature Nicholson rat tail/flat files to get it exactly where I want it. You should replace that black rubber bushing with the copper one that comes with a recurve kit. Bushing gets pressed on with pair of pliers. I like to make sure the bushing does not come off with a tiny dab of epoxy. The 2 medium springs should be close enough for dyno day. If you are building what I assume you are building you are not really looking for any power "on the curve". The torque and HP numbers you want to see will likely be above 3000 RPM. If the dyno shop will be assisting you with the ignition curve then they can finish that out.
BTW - the last 2 digits stamped into the autocam plate tell you the number of degrees designed into the slot mechanism. The original GM applications of this era used the sum of advance mechanism design degrees plus the initial timing degrees setting equaling 36 degrees. Still true for the GM wedge head design but the newer kidney bean shaped chambers use less total advance. Around 32 degrees or so if you build one of those.
Last edited by stingr69; Aug 17, 2019 at 09:40 AM.
Yes that's basically what I want to do and kind of assumed I was going to have to shrink the "slot" based on what happened when I raced my LT-1 waay back. Just didn't know how to tell what I had right now. I am glad you knew what those numbers meant.
Getting closer to Dyno day! Cam button is in. Valvetrain assembling & blueprinting is next.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Originally Posted by stingr69
You could just reduce the travel by 1/3 or so and use that as a base line. I just braze the slot up a bit and finish it out with my miniature Nicholson rat tail/flat files to get it exactly where I want it. You should replace that black rubber bushing with the copper one that comes with a recurve kit. Bushing gets pressed on with pair of pliers. I like to make sure the bushing does not come off with a tiny dab of epoxy. The 2 medium springs should be close enough for dyno day. If you are building what I assume you are building you are not really looking for any power "on the curve". The torque and HP numbers you want to see will likely be above 3000 RPM. If the dyno shop will be assisting you with the ignition curve then they can finish that out.
BTW - the last 2 digits stamped into the autocam plate tell you the number of degrees designed into the slot mechanism. The original GM applications of this era used the sum of advance mechanism design degrees plus the initial timing degrees setting equaling 36 degrees. Still true for the GM wedge head design but the newer kidney bean shaped chambers use less total advance. Around 32 degrees or so if you build one of those.
I didn't know that. I'm smack in the middle of redoing/reducing the mechanical curve of my distributor. I appreciate the info.
Just find a buddy that will let you stick your rebuilt distributor in his/her car so you can set it up properly. You can "ballpark" it while sitting on the bench, if you have no way to put it in a running engine...then fine-tune it when your engine is ready to run.
Here is a pic of what I have. Without disassembling the distrib, just turning it upside down, I measured from edge of bushing to end of mechanical advance slot, with a dial caliper, and got around .140" Anyone measure theirs and tell me how many degrees advance theirs is?
These are the slots that get filed longer for more mechanical advance, or welded up for less mechanical advance, to change the timing curve.
Mine looks to be un-modified in either direction. Depending on which distrib it was originally, ( I have no idea), it could be good to go, or not. That may mean I may need to weld it up, and would prefer to do that before Dyno day.
Thanks in advance.
This is the only number on the distrib.
This is your lucky day - I found the identical '530' part in my stash and a '722' also. The length of the slot of the '530' is .412"; and the length of the slot of the '722' is .375". The latter is from my L76 327/365 SHP motor; the last two digits being 22 means 22* of centrifugal advance at the crank, which when combined with the 12* initial advance at the crank means 34* of advance.
Alternately, if I use math, with your measurement of .140" of movement, and by measuring that the centerline of that pin is .568" from the axis of rotation; this means that your distributor has an advance is 14.1*, which translates to 28.2 degrees at the crank. Pretty close to the 30 marked on the piece ('530') don't you think?
Terrific info! Thanks. Yes those mid sixties HP engines had much more optimum timing curves, than later ones. before the emissions concerns started kicking in around 68 or 69 or so. IIRC even my '68 295 HP SS350 Camaro had a smog AIR pump.
I believe I would like to have about 22 in the distrib before we start the dyno. Time to start brazing!
So based on both your and my measurements, every .0046" equals one degree advance. I need to shorten mine 8 degrees or .037", from my original .412 length to your .375 length.
Easy bench work and should be real close.
Last edited by leigh1322; Aug 19, 2019 at 08:47 AM.
Distributor Advance Measurement requested
