Initial timing

[Steve D.]

Ok, following up on a previous discussion today, I set the total timing at 36 degrees advanced as follows: took the springs off of the distributor, marked the balancer at 36 degrees, started and warmed up, revved to max advance, adjusted 36 degree mark to zero, tightened distributor hold down, bumped several times to make sure there was no additional advance. Then I put the springs back on, started it, set the idle at 800 and checked the initial timing: 2 degrees retarded. I then checked a few more points to see (approximately) what the curve looks like: -2 @ 800, 3 @ 1000, 8 @ 1500, 15 @ 2000, 20 @ 2500. Looks like the curve needs a lot of work.

Steve

[William C.]

Re: Initial timing

Did the advance stop at 2500, or is that just all the farthur you ran it up?

[Clem Z.]

Re: Initial timing

this is a pretty good sign that the mechanical advance stop bushing has come off the pin. seen lots of race engines blow up from this happening back in the late 50s and early 60s because back then GM use a rubber stop bushing and it would go away with the heat on a race engine. we use a 3/16" ID ferrel from a swedge connector soldered to the distributor advance pin to prevent this. the ferrel was larger OD so it allowed more initial advance without going over the total of 40 degrees at speed. the later ones GM put a nylon bushing with a snap ring to hold it in place

[Steve D.]

Re: Initial timing

Bill

That was just the last point that I noted. A number of posts have indicated that a desirable curve gets to full advance at 2500 - 3000 and I was checking to see how close it was at 2500.

Steve

[William C.]

Re: Initial timing

I think Duke is likely correct that your dist appears to have lost the bushing that goes over the stop pin to control the max advance. Better to correct that before drawing any conclusions about the curve.

[Terry F.]

Re: Initial timing

Bill,
It has been a while since I took a dist apart. Can you refresh me on this bushing. I assume it is used to stop the weights from over advancing the engine. But, I don't seem to recall seeing them. Were they used in 68? Terry

[Steve D.]

Re: Initial timing

Clem
I pulled the distributor and the bushing is indeed missing. Here's what I don't understand; my "curve" indicates to me that something is limiting advance (strong springs I thought), but that suggested to you that something that limits advance was MISSING. Can you help me understand why a missing bushing that LIMITS advance would result in a seemingly limited curve?
Thanks.

Steve

[Clem Z.]

Re: Initial timing

if the power timed the engine to max advance and at idle you have negative timing the advance curve is too long for some reason. could be incorrect weights,advance plate,incorrect advance stop or distributor shaft.

[Michael H.]

Re: Initial timing

Steve,

Clem has it right. I'm sure the problem is the missing bushing. The distributor should be providing somewhere around 24-26 degrees of advance, internally, while the initial timing setting of 10-12 degrees, when added to the cent amount, should provide a "total setting of 36 degrees. The fact that your timing plot is showing 38 degrees just from the distributor means that there is actually far too much movement of the cent advance. Adding a bushing to the pin would limit the travel of the pin in it's slot and reduce the distributor degrees to something closer to the 24-26 figure.

The total timing figure of 36 degrees should be divided between initial setting (10-12) and the mechanical advance (24-26).

Michael

[William C.]

Re: Initial timing

Just one, on the pin that fits in the slot in the mechanism that contains the cam to activate the points. The pin is on the bottom side of the piece attached to the main shaft containing the pins that the springs attach to on the top side. Just look under the plate the weights sit on and you will see it. It moves in a slot, and as described earlier, the metal pin has a bushing around it to help limit the advance. Any late 60's-early 70's passenger car distributor can be used for reference.

[Terry F.]

Re: Initial timing

Thanks, I will check it out. I rebuilt my dist years ago. One of the funner things to do. But, I don't recall a bushing in that area. I will be looking into it. Thanks, Terry

[Steve D.]

Re: Initial timing

I robbed a bushing from another distributor and installed it and left the springs off to check maximum advance. Before the bushing was installed I had matched my 36 degree mark on the balancer with the zero mark on the timing tab. After I installed the bushing, the closest to the zero mark on the tab that I could move the 36 degree mark on the balancer was the 14 degree advanced mark. Does this make sense? (36 + 14 = 50 degrees advanced ?)
I guess I could have missed a tooth when I reset the distributor after installing the bushing, but it started immediately and ran smoothly.

[Timothy B.]

Re: Initial timing

Steve,

If you can't move the distributor to set total advance because of interference with the vacuum advance can then lift the distributor and move it one tooth clockwise. When you time total advance at 36 degrees, lock the distributor and hook the weight springs up then check and record inital timing at a very slow idle. Make sure the vacuum can is not hooked up for this entire process. The 36 degrees minus the inital timing reading will tell you the centrifugal advance in your distributor. The total advance (36) is the sum of inital and centrifugal not 36 + 14 as this is way to much.

[John H.]

Re: Initial timing

Terry -

Here's a photo of the pin in the slot - this one has the limiting bushing removed from the pin (and is the later style where an E-clip retains the bushing on the pin).

[Terry F.]

Re: Initial timing

Man, I never would have thought that was suposed to have a bushing on it. I can see where it would easily fall out. I am almost certain mine is missing. Where can I get such a bushing and clip? Thanks for the picture, Terry