[Sun Tuned]

After being on this site and others for a long period of time, I've seen , read, and heard of many different ways to limit the vac advance.

Some of these ways are pretty ingenious and some have bordered on the particular quantity of alcohol consumed beforehand.

Quite simply the easiest and quickest way is to simply place a 7/64" piece of nylon aquarium tube over the pull pin. Done! And with that little maneuver we just knocked off 3 crank degrees of advance. Just like that.

Some will balk at this idea as they say it will fall off just like when GM did it originally. Eventually this may be true but GM didn't use anything but a thin rubber sleeve over theirs. Anyhow a simple check every year or so will ensure it's stays put.

Now for the real dirt.

Normally I just use the correct advance for the application. Luxury of buying up case quantities years back before they started consolidation. For some, this isn't an option. So....

Imagine if we opened a bench vise just a bit and sat our uninstalled vac can hose nipple end straight down into the vise jaws. At this point one of two things will have occurred. You will have opened the vise jaws a bit too wide and the can will fall through touching nothing. Or you didn't get it quite open enough and the tapered sides of the outside nipple side of the can housing hit, requiring you to open vise a bit more. When you get it just right the canister sits in the vise jaws with only the crimped edges of the canister "sitting" on the vise jaws. With the pull pin end of the advance standing straight up pointing toward the cieling.

Now if you look closely you will see the pull rod going down into the canister housing. If you take a small pointed punch(not too sharp now) and you stake a dimple in one side of the outer housing where that pull rod disappears into, you will notice the rod favoring now the same side of the pull pin slot you just staked. Now simply move to the opposite side and do the same again on the opposite side. When you get them evenly punched the pull pin rid will be even in the middle (side to side) of the slot.

A little practice and maybe some retouching of that procedure to shorten the travel a bit more and you'll notice you just limited a vac advance with no power tools or welding. A note of caution. You won't shorten this much more than 5 crank degrees effectively without wrecking operation of vac can so don't get greedy.

Add that aquarium tube, and you have up to 8 crank degrees at your disposal.

Merry Christmas!

[Half-Inch Stud]

All this time i had bent the rod into a Zee to shorten travel, then slotted the VAC mount screw(s) for phasing.

Dimpling the can stop-wall makes sense.
The tubing doesn't sound easy to me; the rod has a 90* bend at the end, so tubing gotto be split or handled tough to go around bent end.

[Sun Tuned]

No, Mark...
The tubing cut length is only just a skosh longer than 3/16".

And it just slides on top of the part of the pin that travels inside the frame rectangle of the advance slot.

Think short leg of the "L"

[Cliff R]

Here's a super-quick way to take a few degrees out without much effort.

I have one HEI advance that I use here a lot because it's still available and has the starting/finishing points in " of vacuum that I like. It adds 14 degrees timing. For a lot of higher compression combo's I often add 10-12 degrees.

I pull down on the rod and swing it out of the "window". Lay that end of the advance on top of the vise and hit it with a round punch at the upper end of the "window". This swages some material toward the pin and reduces the amount of travel. I can easily take 2-4 degrees out with a few hits. I made a rounded end punch just for this purpose and do a lot of them in this fashion.

You can measure the available travel with precision drill bits and compute how much you've taken out........Cliff

[Sun Tuned]

That's a slick one also.

Keep in mind I'm not against mig welding up the slot at all. Very effective. And sometime down the road we all may be doing just that. I've seen quite a few aftermarket advance units that did ok for the vacuum levels they operated at but just had way too much travel. In that situation a limit would have to be utilized.

But for someone who just needs a few degrees peeled off and don't want to source the Crane plate, or have access to a mig, both methods illustrated above, mine and Cliffs, work extremely effectively.

Plus they are cheaper than the crane plate and there's no waiting for it to arrive.

[Formulajones]

Don't even have to buy the Crane plate. I've made them out of a penny and it only costs 1 cent

But these days I don't even do that anymore. I can weld the slot much quicker to limit travel and I'm ready to go.

[Skip Fix]

I want to think when Accel recurved my 409 distributor in the pits at a race in '72 they just added a small machine screw and nut in there.

[dataway]

Got the urge to try this in the shop tonight.

Actually works, fully adjustable for travel. Didn't try it on the engine but I assume you could do real time adjustment while the engine was running.

Unlike aftermarket units this does not effect vacuum start point, or alter initial timing point. All it does is limit max travel.

Installed an 8/32 rivet nut with loctite, picked the right length screw. The screw bottoms on the metal disk in the diaphragm and limits it's travel.

I put it on the wrong side of the nipple though ... under lots of vaccum .. like 15" and above it starts to cock the advance rod in the direction away from the screw (would tend to try to pull it out of the point plate) ... so I should have put the screw on the side that cock the rod upwards into the point plate. It would create a tad of friction, but from my testing the typical VA unit has way more power than you might think. Seems to still move the rod nice and smooth.

The closer I can get the screw to the center the better it would work. The spring inside the can rests on the outside edge of the narrow end .. so you have to make sure and drill close to the nipple as you can and still get a rivet nut in there. Probably also possible to drill a smaller hole and epoxy an 8/32 nut on the outside as close to the nipple as possible.

How long would it last, I don't know. Bleeds a tiny bit of vacuum, will bleed down from 20" in about 15 seconds. Could easily be remedied by coating the screw in some non-hardening pipe dope.

Next might make a little jig to do SunTuned's idea except make something so I can tap down on the area surrounding the pull rod both sides at the same time.

This did require a bit of time making temporary modifications to my pop rivet gun so I could I use it as a rivet nut installer and get in tight to that nipple.

Now if I could move the nipple off to the side and put this adjustment in the center I'd be cooking with gas.

[Half-Inch Stud]

Originally Posted by Sun Tuned

No, Mark...
The tubing cut length is only just a skosh longer than 3/16".

And it just slides on top of the part of the pin that travels inside the frame rectangle of the advance slot.

Think short leg of the "L"

THAT is Good. LIKE. I'd probably use a metal tube from a brake line cutting, or ancient electronic chassis spacer part.

[Half-Inch Stud]

Am i the only one that checks Rotor-Post phasing after this?

[RocktimusPryme]

FWIW I used a chart I found that listed what available over the counter NAPA cannisters advertised vacuum added was. Spent like $17 and just swapped in a cannister with the numbers I wanted, and it worked. Lowered my added vacuum to a level that doesn't cause pinging at part throttle anymore.

Im all for learning these tips and tricks but for many people a cheap swap is going to be what they consider easy.

[footjoy]

Originally Posted by RocktimusPryme

FWIW I used a chart I found that listed what available over the counter NAPA cannisters advertised vacuum added was. Spent like $17 and just swapped in a cannister with the numbers I wanted, and it worked. Lowered my added vacuum to a level that doesn't cause pinging at part throttle anymore.

Could you share that chart

Thanks

Greg

[RocktimusPryme]

Originally Posted by footjoy

Could you share that chart

Thanks

Greg

http://www.crankshaftcoalition.com/w...ance_Specs.pdf


My chinesium HEI came with a cannister that added nearly 20 crank degrees. Caused part throttle ping. I switched to the VC1703 unit that allows more like 10* at the crank.

[Sun Tuned]

Take and tap the hose nipple id for a brass setscrew(Allen), drill the id of the setscrew first for a hole.

Since you got access to a lathe this will not be an issue to accomplish if you think about it a bit.

[Sun Tuned]

Look at a set of points, study how that adjustment works and miniaturize that for an external stop.

That's getting into serious watchmaking. But I know how machineshop guys like to "tinker"...a lot.

Sure way easier to select a close candidate and buy one and just install it. Way easier.

You could even make a stop fixture on the points plate or the HEI pickup coil... the choices are endless.

Enjoy fooling with it and have fun with it. That's what the hobby is about anyway.

[Formulajones]

Wow, you guys are making it way more difficult than it has to be.

It's soooo simple to set these things up properly, I've explained it a dozen times on the forums, as well as Cliff and a few others.

[dataway]

Originally Posted by Sun Tuned

Take and tap the hose nipple id for a brass setscrew(Allen), drill the id of the setscrew first for a hole.

Since you got access to a lathe this will not be an issue to accomplish if you think about it a bit.

Hey ... good idea, that would get me my center point on the diaphragm. I can get a small OD set screw up to 2" long .... bore that sucker out, cross drill at the deep end for plenty of air flow and I'd have my center pressure point.

Or go a step farther and move the nipple to the side, I think I could braze one on ... and then I could set it up to adjust while the engine is running and the VA is working.

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Everyone has different means and methods, I'll sacrifice time in fabrication to save time in operation. I'd love to have a VA unit I could adjust while the engine is running at idle, just set initial, fire it up, have someone hold a light on it and tell me when it gets where I want.

Fun to play with the stuff that is simple and inexpensive to modify.

I have that same chart, I didn't really find anything exactly what I was looking for, the B13 VC1675 would probably suffice ... if I could find one. But I'd like closer to 12" HG starting point.

[KEN CROCIE]

Skip: you remember correctly. Had the Accel rep com by my speed shop for a " clinic" and offering free recurves. The little screw and nut trick was employed

[RocktimusPryme]

Originally Posted by dataway

Or go a step farther and move the nipple to the side, I think I could braze one on ... and then I could set it up to adjust while the engine is running and the VA is working.

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I have that same chart, I didn't really find anything exactly what I was looking for, the B13 VC1675 would probably suffice ... if I could find one. But I'd like closer to 12" HG starting point.

I would like to move the nipple to the side on mine to help with HEI heater hose clearance. On a car not designed for an HEI you have very limited space. Before I couldn't get my heater hose on, now I can get the hose fitting in there but my cannister nipple is right up against the intake and Im a couple degrees more advanced than I would like initial and total. If I could cut the nipple off and braze it onto the side it would help.

As far as the list, Im the same as you. 12* at the crank would be ideal, but I went with the 1703 that allows 10* and am pretty happy with it. I cant remember if it allowed exactly 10 at the crank or not.

[dataway]

I'm going to put some thought into a easy way to move the nipple ... something that doesn't involve trying to braze on a tiny nipple. Although it would probably be easy to solder for someone soldering skills. Original hole could just be plugged with epoxy.