1966 L36 Vacuum advance Mechanism

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Duke, I know enough to be dangerous.

So the basics, yes, but I don't do 5000rpm on an original motor. 4000 is as high as we've had this one running and that's plenty fast, perhaps 100mph fast.

Yes within the accuracy of the measuring device on the motor we have about 8* initial at idle of 700rpm.

The mechanical is essentially all-in by 2000rpm and that kicks us up to 24*

Then for the third dimension, we plug in the vac advance and go on our merry way.

I can't set a surface, only key reference points that generally have a condition (RPM) tied to their value.

I am interested to learn more and perhaps set this up so it does liven things up, when hot, it still is pretty lame. I do have a new spring kit, w/o explication it seems one of the three springs are set up to not be fully advanced until you are way above 5000 rpm, the low end set looks to be all-in by 3000prm. It is a re-packaged Accel point & weight kit.

[John H.]

Re: 1966 L36 Vacuum advance Mechanism

Yes within the accuracy of the measuring device on the motor we have about 8* initial at idle of 700rpm.

The mechanical is essentially all-in by 2000rpm and that kicks us up to 24*

Then for the third dimension, we plug in the vac advance and go on our merry way.

Ron -

24* is WAY short of where you need to be for total timing; that's why it feels like a slug.

With 8* initial, you need the centrifugal to ADD about 26*-28* to achieve 34*-36* total timing (initial + full centrifugal), and that's measured with the vacuum advance disconnected and plugged. "All in" at 2000 rpm is pretty aggressive, but you're way short of full advance anyway.

Forget any readings that include the vacuum advance, except at idle; that should read your initial plus the amount added by the vacuum advance, assuming you have it connected to a full manifold vacuum source.

[Timothy B.]

Re: 1966 L36 Vacuum advance Mechanism

Ronald,

Short of a distributor machine you can try the following. The first step is to verify TDC mark on the balancer to make sure the factory settings are close enough. Check archives for piston stop method but be careful as you can damage a piston turning the engine to fast. The engine needs to be turned by hand to use this method.

Next, remove the small springs on the weights inside the distributor and time the engine for total timing. You can move the damper to read TDC then go up 12* and mark the damper then move that 12* mark to TDC and repeat until you get 38*.

Start the car and rev the engine to about 1500RPM and time to the 38* mark. This mark on the damper will be lined with TDC mark on the timing cover. Let the inital fall where it will and you can check it after you reinstall the springs on the advance weights.

If at that point you want to increase the inital timing you should reduce the centrifugal timing by limiting the slot length on the weight base cam inside the distributor. You want to maintain approx 38* total timing.

Lots of archive info if you like to read..

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

John and Tim,

In my previous post I neglected to put in the total timing.

8* initial
24* with mechanical and that is in by 2000 rpm, maybe as low as 1200 or 1500 and that I will look at more precisely.

38-40 with vac

Ran real nice when cooler, but at the hot temperature range and after a hot soak (half hour stop) on hard acceleration it did sputter. Hard being defined as essentially wide open an hitting the gears fast.

I'll go back over the set points again to see if anything changed, I doubt it.

I also have a weight -spring set that Paragon sells, ACCEL brand, has dark, silver, and copper colored springs with no indication on what is what, any suggestions on which to use or what curve to set this at?

[Timothy B.]

Re: 1966 L36 Vacuum advance Mechanism

Ronald,

Don't include vacuum advance in your timing yet. It plays an important role but it's important to get the WOT timing correct first. WOT timing is inital plus centrifugal and this should be in the range of 38* all in approx 3000RPM (IMHO) for your stock engine.

Total timing includes vacuum advance and is the sum of inital, centrifugal and vacuum advance so you could actually achieve 52-53* at high speed CRUISE. As soon as you put the engine under load like WOT, the vacuum drops and you loose this vacuum advance so the timing retards to the WOT (inital and centrifugal) settings.

If you mark the damper like the above post, and remove the weight springs, the WOT timing can be set without free reving the engine high.

As far as the repro spring set, I have found the light silver springs to give the fastest advance with the stock weights and I would try these first. If you hear ping under load then switch only one spring but I bet with the stock weights you can use the light springs.

Don't throw those original springs out, you can't buy these anymore so save them with your other parts on the car..

After correcting the WOT timing, taylor the vacuum control to be fully pulled at approx 2" vacuum less than idle vacuum so it's completely in at idle.. This will help cool the engine and provide the needed 15* extra timing at IDLE so your engine could actually see 23-25* idle timing, (inital plus 15* vacuum advance)

If you decide at that point to increase the inital timing, you need to reduce the centrifugal the same amount so the engine at WOT will operate at approx. 38*.

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Tim,

I'll pull the springs, and try it this way, but I don't believe I've see more than 24* at 2000~3000rpm - under any circumstance with no vac advance.

And from other threads I understood total advance should not be more than 38* total, perhaps 40-42* with the big block.

[Timothy B.]

Re: 1966 L36 Vacuum advance Mechanism

Ronald,

There are three terms with regard to timing to keep in mind on your car..

Idle timing= inital setting plus vacuum advance and on some cars that idle on the curve there can be a few degrees centrifugal.

WOT timing= inital setting plus centrifugal advance provided by the distributor weights and springs.

Total timing= inital plus centrifugal and vacuum advance. This can vary with RPM but can be as high as 52-53*

The vacuum advance is used to help advance timing in low load conditions (idle and cruise) where the mixture is lean and needs more time to burn so the fire is lit earlier.. When the engine goes under load, the mixture is richened and the engine does not need this lead time provided by vacuum advance to burn the mixture.

With the vacuum advance control plugged, if you are only seeing 24* when reving the engine the timing is not set correctly. That's why I suggested removing the springs and setting the WOT timing at 38* This way, you know it's not to high. After reinstalling the springs, you can check the inital setting to see where it falls.

[Duke W.]

Re: 1966 L36 Vacuum advance Mechanism

Ronald,

There are three terms with regard to timing to keep in mind on your car..

Idle timing= inital setting plus vacuum advance and on some cars that idle on the curve there can be a few degrees centrifugal.

WOT timing= inital setting plus centrifugal advance provided by the distributor weights and springs.

Total timing= inital plus centrifugal and vacuum advance. This can vary with RPM but can be as high as 52-53*

No, you're using confusing terminology. Look at post #15.

Duke

[John H.]

Re: 1966 L36 Vacuum advance Mechanism

I don't believe I've see more than 24* at 2000~3000rpm - under any circumstance with no vac advance.

And from other threads I understood total advance should not be more than 38* total, perhaps 40-42* with the big block.

Ron -

And therein lies part of the problem. If your initial timing is 8*, your distributor centrifugal advance needs to supply an additional 28*-30* to get you to TOTAL TIMING of 36*-38*. Vacuum advance has NOTHING to do with this, and must be disconnected and plugged while measuring it. If all you're seeing now is 24* at maximum initial+centrifugal advance, your distributor is 12*-14* shy of providing what you need.

Vacuum advance is a separate system, and you can only measure/map it at idle; measuring it under any other conditions is meaningless and just confuses things.

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

OK,

Not only was today a good day to twiddle with timing, it was also a great day to get out with the top down and cruise.

So - Duke, and others, here is how I set the timing up - let me know what you think.


Weights banded shut.
30 dwell that did not change ever so I won't mention it further
vac plugged, but vac gauge plugged in
idle 700
6* initial timing
Hg 13"
Timing stayed at that 2000 & 3000 RPM

Then - the old weights came out, and a paragon "Accel" kit went in, the issue that Duke you did not know what I was saying nor do I still understand, they have three colors, three lines on a chart, that starts at 0,2,4,6,8,10,..20, that can't be RPM - who knows, they dont say, the Y axis is timing deg. Dist. mech. advance.

So with the spring colors not matching the paper, I did it the old way - chose the middle set, one set seems easy, the other real stiff, so the middle ones went in.

rpm jumped on restart to 850
18* advance - all measurements at the crank
we moved the idle speed back to 750 and the timing went to 16*

26* @ 2000 w/ 19.5"Hg
36* @ 3000 w/ 20" Hg



Then the vac can was reattached, the idle went to 900

we adjusted the idle to 750rpm
32* advance

46* @ 2000rpm
at 3000rpm was at the end of the strip + 36* advance.

Runs pretty good.

Here is a picture of that mysterious accel chart, the gold weights are the tough ones, the dark brown the easy ones, silver ones are in the car, not shown. And the weights and springs that came out are here too, now sure if they are OEM or not. I let my spare parts get away from me many years ago for these parts.

When hot, on one cruise style trip, I might be bold enough to say the temp dropped to 205 from before when warm, it was easily 210.

If this set up sounds good, next we will lose that Edlebrock intake and put the original cast iron intake back in its place.

[Clem Z.]

Re: 1966 L36 Vacuum advance Mechanism

to mark the damper for "power timing" the engine measure the circumference and divide by 10 and this will be 36 degrees

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Clem, got that there, need to extend it beyond 36*

[Clem Z.]

Re: 1966 L36 Vacuum advance Mechanism

Clem, got that there, need to extend it beyond 36*

you can use the timing marks on the timing tab for additional degrees

[John H.]

Re: 1966 L36 Vacuum advance Mechanism

vac plugged, but vac gauge plugged in
idle 700
6* initial timing
Hg 13"
Timing stayed at that 2000 & 3000 RPM

Then - the old weights came out, and a paragon "Accel" kit went in.

rpm jumped on restart to 850
18* advance - all measurements at the crank
we moved the idle speed back to 750 and the timing went to 16*

26* @ 2000 w/ 19.5"Hg
36* @ 3000 w/ 20" Hg



Then the vac can was reattached, the idle went to 900

we adjusted the idle to 750rpm
32* advance

46* @ 2000rpm
at 3000rpm was at the end of the strip + 36* advance.

Runs pretty good.

Ron -

When you added the kit, it put you 10* into the centrifugal advance curve (added 10* of advance) at 750 rpm idle. You need to tune that out by replacing one or both of the springs with stiffer ones so the centrifugal curve doesn't start until 800 or so.

The 36* @ 3000 (no vacuum advance) sounds good - did it advance any further at higher rpm? You need to find the rpm at which it stops advancing to map it properly.

When you added the vacuum advance and timing jumped to 32*, that shows the VAC is adding 16*, which is about right (but it's 10* higher than it should be because of the increase from 6* to 16* in idle timing due to the early-starting centrifugal curve, which needs to be corrected).

Forget the 46* @2000 and 48* (+) @3000 with the VAC connected - those readings are meaningless; all timing measurements are made with the VAC disconnected and plugged (except to verify VAC operation at idle).

The weights in the photo aren't GM weights - they're some funky long-tail aftermarket things.

[Ronald L.]

Re: 1966 L36 Vacuum advance Mechanism

Hi john,

I am pretty sure those weights are one of the reasons I was not getting advance. I can change springs to the heavier pair, or mix them, will be interesting to see as I did not like how WOT performed.