Suggest you read the "Timing 101" and "Mapping Advance" articles at the links below; they'll give you a better understanding of how the centrifugal and vacuum advance systems work, and how to optimize them.

http://www.lbfun.com/warehouse/tech_...101Article.pdf

http://www.lbfun.com/warehouse/tech_...%20ADVANCE.pdf

 

John Z and all: I just want to give you an update. Still no backfires since adjusting dwell, timing and installing new resistor.

I also read the 2 attachments that John recommended. OK, I am beinging to learn. Some might say I now know just enough to be dangerous.

While doing the latest round of timing I realized I did not have any change in engine rpm regardless of the vacuum hose being attached or plugged. I rigged up a very simple, crude vacuum tester (squeeze bottle with hose attached) If I squeeze the bottle and plug the end of the hose, the bottle does not inhale. If I squeeze the bottle and put the hose on the distributor vacuum advance, the bottle will inhale. To me this indicates the vacuum advance has a leak somewhere and answers why no change in rpm.

I purchased a new vacuum can and did the same 'test' and the bottle did not inhale.

I started to install the new vacuum can but do not know what to do. I removed the distributor cap and rotor but do not know how the remove the centrifical weight plate and the breaker point plate. (I have pictures but do not know how to attach here, so send private e-mail and I will send).

Primary Question: Does the distributor have to be completely disassembled to install the new vacuum can?

As I mentioned much earlier, another issue is that the vacuum can touches a hump in the intake manifold preventing advance much beyond 8 deg.

Secondary Question: If I pulled the distributor up out of the block and rotated clockwise the outer body with vacuum can attached, but kept the rotating group in the same position, can I then reinstall distributor and have timing be basically the same but vacuum can now away form intake manifold hump?

Thanks again to all. With all your help, we are making progress.

Bob

 

you do not have to pull the dizzy to replace the vac can, but if you want to re clock the dizzy then pull it anyway and re new the vac can.....you can leave it in the car , remove the screws by manually advancing the points plate to get it out of the way of the screws....good luck

 

Bob, the plate to which the points are attached rotates. There is a single screw that holds the vacuum advance in place.

Remove the screw, the vacuum advance will be loose. Then you may need to rotate the plate a little to create clearance to allow you to push the vacuum advance rod off of the point plate.

 

Jeff62: Thanks for yesterday's input. Everyting worked exactly as you described.

Installed new vacuum canister. Now have very noticable RPM difference when vac. line is removed. Reset dwell and timing as previously explained. A side 'fix' was also achieved in that I now have maybe 1/4" gap between the edge of the vac. can and the hump in the intake manifold.

Results of this latest fix can best be described as WOW has the car come alive like never before in the almost 3 years I have owned it. Amazing what happens when all the parts are working as they should.

Now then as so often when you fix something you learn something also. And that in turn creates questions.

While drive the car today I noticed the temp gauge was just below 180. The outside temp was in the low to mid 70's. The other day while driving the car with the bad vacuum canister, outside temp was it was in the mid 80's and the temp. gauge was above 220 and approaching 240.

QUESTION: Does correct timing and timing advance affect operating tempature? If 'yes' why and how?

Heading out to Carlisle Chevy weekend tomorrow AM. Don't have a travel computer so can't answere any of your questions until later in week.

Thanks to all the uniform vets for your service

Regards from a retired Navy Mustang Pork Chop!

Bob

 

If your timing is retarded you can generate more exhaust heat that the cooling system may or may not be able to handle depending on the condition of everything else in that system.

 

Yes - adding vacuum advance (which you essentially did by fixing your non-operational vacuum advance) will promote somewhat cooler running.... That is a big discrepancy in your temps before and after though. I'd still keep an eye on the temperature for a while...

 

The first link in post #41 will explain what retarded timing does to operating temperature.

 

After reading that article, I have to wonder - what did GM do to keep the mechanical advance distributors (like the dual point) from creating overheating conditions at idle?

Or since they were high performance distributors, was there no realy expectation they'd be sitting in traffic?

 

Basically the same as using the port vacuum with no vacuum at idle.

 

Yes, which made the cars run hotter, correct?

I guess I'm wondering why a mechanical advance distributor from the early 60s would not run hot at idle, considering it's effectively operating with parameters similar to a pollution-engine.

 

Probably would be OK as long as the cooling system was sufficient same as the pollution cars. Is that about the same time they started improving the radiators? I'm don't have my books handy but did they run more initial with the mechanical distributors?

 

I'm not sure. I was just thinking that if a vacuum advance is supposed to help keep the car cool at idle, then what did GM do with non vacuum-advance distributors to keep the cars cool at idle? Or is it not possible to keep a strictly mechanical advance car cool at idle using 60's technology?

Jeff

 

Cars with centrifugal-only distributors require more margin of cooling capacity at idle; 283's didn't require the same cooling capacity as the later 327's, and didn't overheat at idle if the cooling system was in good shape.

 

I think what you are saying then, is that 283s didn't overheat at idle which implies that a 327 with a mechanical-only distributor, likely will overheat at idle given enough time?

 

The average intiial timing difference between the non performance engines and their hi-po counterpart is around four to ten degrees depending on the year. The hi-po 283 (RPO 354) had an initial advance of 18 degrees which, I believe, was the highest initial advance of any of the 283 engines

 

I don't recall any of the dual-point centrifugal-only distributor engines calling for 18* initial; all of those distributors had between 22* and 30* of centrifugal advance in them (depending on application) and 18* initial would have put any of them "off the chart" in terms of total advance.

 

If the distributer rotation is such that it vacuum diaphram hits, try moving all sparkplug wires one hole CW or CCW and turn the distributor in the needed direction.

 

That may work, but it results in the wires being mis-indexed in the cap. Normally, if the can hits the #8 intake runner or the plug wire support when setting initial timing, the distributor drive gear is assembled 180* off on the mainshaft, and re-orienting it will solve the problem.

Photo below shows a correctly-installed distributor and correctly-indexed wires in the cap.