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Adjusting reluctor gap with vac advance problem

Posted By: hooziewhatsit

Adjusting reluctor gap with vac advance problem - 01/07/13 09:18 AM

A while back I did a normal MP electronic ignition swap on the 318 in my work truck. Shortly after I got a mity-vac and pulled the (brand new) distributor so I could adjust the reluctor gap on the bench and do it right.

Long story short, to have 0.008" clearance with the vacuum advance engaged, I have ~0.020" clearance with no advance. If I have 0.008" without the vac advance, then the reluctor collides with the pickup when the advance kicks in. It's been running in the summer with 0.020" gap seemingly just fine.

There's also a couple thou difference depending on where the roll pin is on the reluctor. It sits slightly off-center.


It looked like the pivot point was pretty well fixed which would make it hard to true up. Is there any way to get it closer to 0.008" throughout its travel?

Also, can I just file down on some of the reluctor teeth to make them uniform length?


Now that it's cold out, I'm having a hard start issue. But I'm not sure if it's related to the gap being too big, or to IGN1 not having power during crank (ECU gets ~7.5v backfed from the BR). If I jump +12v to the ECU, it starts right up. But that may be a separate issue
Posted By: NachoRT74

Re: Adjusting reluctor gap with vac advance problem - 01/07/13 02:08 PM

tipically.

by geometric is nearly imposible to keep the gap the same allong his travel. Pickup and reluctor, get both diff circunference radious.

what I have done with success is bend the pickup coil bracket back and forth, here and there, until get the best gap relation in both positions. Made to get 7-8 gap without vacuum and maybe 9-10 with full vacuum. Thats was with factory vacuum setup, which gets A LOT OF ADVANCE ( maybe up to 10 degrees )... then shortened the vacuum advance to maybe just 4 or 6 degrees.

needs patiente for that... is a tryal and error process.

Sometimes the vacuum pivot and pickup coil bracket assembly gets lots of play due the vacuum stud and hole on bracket doesn't match perfect. I have filled it with teflon tape over the vacuum stud.
Posted By: RapidRobert

Re: Adjusting reluctor gap with vac advance problem - 01/07/13 03:41 PM

Quote:

Long story short, to have 0.008" clearance with the vacuum advance engaged, I have ~0.020" clearance with no advance. If I have 0.008" without the vac advance, then the reluctor collides with the pickup when the advance kicks in. It's been running in the summer with 0.020" gap seemingly just fine.
There's also a couple thou difference depending on where the roll pin is on the reluctor. It sits slightly off-center.
Also, can I just file down on some of the reluctor teeth to make them uniform length?


Pull & cap the vac adv then set the gap at .008" & see if it will start which will take the gap change out of the equation & although I dont think there's enough cranking vacuum to actually activate the can but I'm not sure on that but one thing at a time & just capping it will eliminate the gap change & will tell you in seconds if the gap change was the culprit. Then you can check cranking vacuum and compare that to the vac needed to activate/pull the can enough to significantly change the gap if you have a Mityvac or similar vac pump to see if the gap is actually changing during cranking or not. You could chuck the reluctor in a drill press then bring a smooth file at it from the side & just keep it perpendicular would be the hardest part. I want to try Nacho's trick to cut down some of the vac adv gap change just haven't got around to it yet.
Posted By: NachoRT74

Re: Adjusting reluctor gap with vac advance problem - 01/07/13 07:29 PM

need to note that you need to be sure all reluctor points are set at same height too
Posted By: 6PakBee

Re: Adjusting reluctor gap with vac advance problem - 01/07/13 08:23 PM

I always have just applied vaccum to get full vacuum advance and then set the reluctor gap. Never had a problem so far.
Posted By: hooziewhatsit

Re: Adjusting reluctor gap with vac advance problem - 01/07/13 10:49 PM

Quote:

Pull & cap the vac adv then set the gap at .008" & see if it will start which will take the gap change out of the equation


I hadn't thought about doing that.

I do have a vacuum gauge in the cab. During cranking it bounces up to ~3"hg. With my previous testing on the bench that's not enough to move the can at all.

Sometime soon I'll pull the distributor again and file on half the reluctor teeth to give them uniform heights.

Quote:

I always have just applied vaccum to get full vacuum advance and then set the reluctor gap. Never had a problem so far.


That's what I was thinking too, but with a 0.020" gap with no advance, and my hard starting issue, I'm not sure if it's related to the gap or the ECU having low voltage during cranking.
Posted By: Jeremiah

Re: Adjusting reluctor gap with vac advance problem - 01/08/13 05:29 AM

I know a guy that might have some OEM reluctors hanging around his shop...
Posted By: hooziewhatsit

Re: Adjusting reluctor gap with vac advance problem - 01/08/13 06:49 AM

Quote:

I know a guy that might have some OEM reluctors hanging around his shop...



Really I'd have to check again, but I think mine is otherwise fine, it's just not centered on the shaft properly. The side with the roll pin sticks a couple thousandths farther out. Just enough to be annoying.
Posted By: hooziewhatsit

Re: Adjusting reluctor gap with vac advance problem - 01/20/13 07:14 AM

It finally warmed up and got nice today (hit 32*F ), so I took another look at it.

I have a couple problems:
1 - The reluctor teeth. Measuring from the ID (where the reluctor touches the shaft) to the outer edge of each tooth, there is a ~0.005" difference from the shortest to tallest tooth. This is noticeable when looking at the gap and spinning the shaft.

2 - I did a few things to the entire pickup mechanism, and got it to have 0.008" difference between vac and (0.016") with no vacuum.

The big gap with no advance is definitely the issue. It's currently gapped to 0.008 +5 slop, and it fires up cold GREAT. But, I don't have vacuum advance.

Quote:

what I have done with success is bend the pickup coil bracket back and forth, here and there, until get the best gap relation in both positions.


Nacho, are you referring to adjusting the bracket that the two wires go to?


Edit: Just drew a picture and figured out 90% of the problem with #2. Will try to verify it tomorrow. #1 is still a problem though.
Posted By: RapidRobert

Re: Adjusting reluctor gap with vac advance problem - 01/20/13 03:30 PM

Quote:

Just drew a picture and figured out 90% of the problem with #2. Will try to verify it tomorrow.

Post how that works & what you bend
Posted By: NachoRT74

Re: Adjusting reluctor gap with vac advance problem - 01/20/13 04:39 PM

Quote:



Quote:

what I have done with success is bend the pickup coil bracket back and forth, here and there, until get the best gap relation in both positions.


Nacho, are you referring to adjusting the bracket that the two wires go to?






that OR the bottom section where magnet is. As I told you is a tryal an error method.

If you find can remove the coil from bracket and reinstall it without problem ( usually is posible ) you can work there, removing the coil to save from damage on it.

talking about tooth height. You must consider the reluctor can get a small difference mounted on shaft due the pin is pushing out one side of reluctor. I adjust the tooth height MOUNTED, using a fine file, setting the height against the pickup ( no matter how much is the gap at this moment )
Posted By: hooziewhatsit

Re: Adjusting reluctor gap with vac advance problem - 01/21/13 12:17 AM



10-12 clearance on all teeth, with and without the vac advance engaged.

Later tonight I can make a picture, but the short version is that you have to shorten and/or lengthen the arm for the vacuum advance to get more uniform gaps as the advance engages. A drawing really helps show how this works.

I also clamped a file to a board and adjusted the height of the reluctor teeth. It does seem to idle better already, so I wonder if that was the cause of my rough idle when it was cold.
Posted By: hooziewhatsit

Re: Adjusting reluctor gap with vac advance problem - 01/21/13 05:16 AM

Let's see if this makes any sense.

Like Nacho mentioned, the reluctor and the pickup travel on different curves because their diameters are different. Like the picture shows, this puts the pickup a varying distance from the reluctor, depending on the length of the vacuum advance arm. Initially, my arm was too long, which is why the gap got a lot smaller when the advance was applied.

The only thing that changes this is the length of the arm going to the vacuum advance can. I tweaked the Z portion of the arm to make it ~0.050" shorter. This put the pickups' travel over B, rather than A->B.

This is mostly trial and error until you find the sweet spot. Some distributors have an alignment pin to keep the vac advance can in one spot. Mine didn't, which allowed a little bit of adjustment, but it still wasn't enough.

Attached picture 7555323-vacuumadvancePickup.jpg
Posted By: 1_WILD_RT

Re: Adjusting reluctor gap with vac advance problem - 01/21/13 05:26 AM

Which is why Ford & GM pivot their breaker plate on the same center as the shaft... But Chrysler had the best engineers... I love my old Mopars but some of the stuff they did really sucked...
Posted By: NachoRT74

Re: Adjusting reluctor gap with vac advance problem - 01/21/13 05:59 AM

Interesting method HOWEVER I think bending the vacuum advance link, will affect the phasing IMHO
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