As it always seems with my simple little projects, this one has snowballed into a problem. The vette had a miss, so I thought I would go through the basic tune up items, since I recently bought it and have no idea when the points etc were changed. Today I replaced the points, condenser, rotor, and dist. cap. Everything was going well until I went to set the dwell. I was using my dads old meter and it was bouncing anywhere from 30 to 34 degrees. We thought it must be the 30 year old meter, right, so I ran to advance auto and pick up a new actron multimeter with dwell function. When I hook this up I get the same thing, its varying anywhere from about 31 to 34 degrees? Anyone have any ideas? Also when I check the timing it seems to vary at about the same rate as the dwell, which sort of makes sense? Any help is appreciated, thanks

by the way, this is a very stock 69 350/350hp

 

Looseness somewhere in the distributor. It could be worn shaft bushings, 'slop' somewhere in the advance plate system, or some kind of binding in the flyweight system. Others may have some additional suggestions. If you have some variation in the vacuum level on your engine, that could cause the vacuum cannister on the dist. to fluctuated; but you can check that by pulling the hose of the can and plugging it [to limit the vacuum loss]. If fluctuating vacuum is the problem, it should not vary with the advance hose removed.

 

loose breaker plate, worn point cam,bad bushings in the dizzy.....good luck

 

thanks for the quick responses! I figured it was probably just general wear in the distributor/bushings, but I didn't want to jump to those conclusions without posting on the forum and seeing if I might be missing something simple. I have a new distributor shaft/bushings/cross gear etc to completely go through the distributor this summer and get my tach working...maybe I better get to it sooner than later thanks again, Jeremy

 

Don't forget to check out your vacuum situation. If that's the problem, you'll be "chasing your tail" working on the dizzy.

 

Don't rule out some slop in the timing chain... I was amazed at how slack mine was when I tore it down.

 

You said the dwell was moving from 30-34. Is this a constant move or a move that occurs when you raise the RPM’s.

My Reason for the question:

Dwell that expands during acceleration is usually a upper bushing failure in the distributor as mentioned above.

Dwell that bounces all over the place during idle can be the result of the lower plate being worn (also mentioned above) so here is a picture you can use to see.



or worn lobes on the upper cam which should be about .997 on a used unit and 1.0 on a new one. Here is another picture so you can check. (You should check Dem. in the middle where the points ride).



One thing that I’ve seen and I’m not saying you did this. . .are you sure the point mounting screws are good and snug? This would also cause you a problem but usually this will just keep opening up the points until the car will not run.

Post again. . .

Willcox Inc.

 

I tried this right away, but unfortunately I'm still getting about 3 degrees of fluctuation...

I did take the cap and wires off again and check to make sure everything is tight...same problem. The fluctuation stays pretty constant at 3 to 4 degrees at idle and on acceleration. I did notice that the breaker plate seemed a little sloppy when I put the points in...that was one of the few parts I didn't order from you guys recently so you will be getting an order soon for one of those. Are the upper cams available now? On your website last I checked it said they were on indefinite backorder? When I take this thing apart to rebuild it, I really only want to do it once

Thanks Jeremy

 

Good time to change to HEI or a mallory unilite. Points are always a pain. Others will tell you they are great. If they were they wouldn't have went to HEI in 1975 and never looked back.JMHO

 

One other area to check is the end play of the drive gear. You want about .007" -.010" end play.

 

That was to comply with federal mandates for tune up intervals, and irrekevent to performance.

 

It's your breaker plate. Just get a socket that fits the plate center tight, and whack it with a hammer to shrink it. A new plate is not needed.
Upper bushings fail one in 100.

 

I had the same issues and went straight to an HEI conversion. I have not and will not look back. The improvement in overall performance and mileage was measurable, and now considerably less ignition maintenance. I plan to rebuild the original and keep it around but it probably won't go back in the car anytime very soon.

 

Right. Go to any track event in any type of racing and see how many guys are running point distributors that would be allowed by the rules not to. Why do you think all the real race engines Chevy built were not single point distributors, even in the 50's dual points were used on the highest performance factory models. The real racers of the day went to Magneto's. Then TI was used in the factory high performance models because it was a better system. This proves GM engineering knew there were issues with running points in a performance application. Once HEI came along points were history. HEI provides a hotter spark that allows more complete combustion. Your A/F mix burns more efficently and completely making more power. That is a good reason to run it right there. Less carbon buildup in the cylinders and on the plugs, due to the hotter spark and more complete combustion, which led to less frequent tune ups required. Tune up mandates were not the reasonfor elimination of the points system in 1975, Emmisions requirements and progress in engineering were. This is one emission improvement that actually leads to better performance, MPG and less maintainance. You would think a rocket scientist would know better.

 

Dual points, Magnetos, and TI's are for higher reving engines. They are not necessary on this stock 69.

 

Those noticable improvements were on a stock 350-250 HP car with a performer intake and upgrade exhaust. HEI is not necessary on a lower reving car but will still burn more efficently yielding noticable improvements in fuel economy and power with less cylinder build up and lower maintainance. Dwell variation, burnt points and diminished spark intensity will be a thing of the past. I used to drag race my Camaro in the 70's, Super Stock class. At the time it had a stock 350, 300 HP hydraulic flat tappet cam. We were allowed 3 modifications. Mine was headers, high rise, holley 4 bbl. I could install new points, set the dwell and timing and would have to replace points at least a couple times during the season to maintain my times. This was not a high rpm combination.

 

I had a feeling this would end up in an HEI vs Points battle I run MSD on my Nova and like electronic ignition, but the bottom line is that when I started working on the corvette, I decided I would try to rebuild and restore whatever I could to keep it as much like it came from GM as I could. I am aware of the benefits of HEI vs points, but I think the stock distributor is sufficient for the stock setup, and I don't mind changing points, so that is the direction I decided to go.

All the help is appreciated,
thanks,
Jeremy

 

Jeremy,

No they are still out of stock. I doubt this is the problem though, it would be rare for sure.

The lower plate if loose or rocking would be where I think I would check and inspect first!

This plate rides on the upper part of the top bushing and it is possible the plate has worn a groove in the bushing but this too would not be a common problem.

If you can't figure it out, send me the distributor and I'll put it on our sun machine and figure it out for you.

Willcox

 

No battle on this end. Just offering options and opinions. (cause we all know folks on this forum are NEVER opinionated!)

I fully agree you can restore your stock unit. I too have many miles under me with points fired ignitions. For me it's the cable drive tach I refuse to give up...but went HEI with no hesitation. (go figure)

 

Understand that point too.