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Old 07-08-2022, 08:02 PM
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Default Weird distributor cap wear

Getting late timing wear marks on HEI distributor cap ďtangsĒ. Car runs ok, but trying to chase down WOT issues. Timing set at 16 initial plus 12 vacuum advance (manifold vacuum) and 9 mechanical adv. All in at 2500 rpm. Wear indicates rotor is past cap tangs when firing. Timing chain is tight both directions. Am I reading too much into this? My guts telling me I have more of a fuel problem.
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  #2  
Old 07-08-2022, 10:46 PM
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you advance weights, numbers up or down ?

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Old 07-09-2022, 06:27 AM
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It would really help us to not so much guess if we knew more details about the motor!

Out of gear and with no vacuum advance Have you confirmed that above 4000 rpm to 5000 rpm that no additional timing is coming in?

Also needed to be confirmed is that in the above conditions that the timing is not bouncing around when the motor is at a steady rpm above 4000 or so.

I have found that some brand of rotors are truly garbage!

I have a old HEI cap that I have jig sawed out two wire terminals such that I can see how close the rotor tip is to the wire terminals.

All too many times this gap is more then what your running for a plug gap which is not good in anyway!

With some rotors you can bend them to extend them closer to the wire terminals.

Just make sure that the rotor tip does not then run below the wire terminals making for a gap in that regard .

Can you post up some photos of some of your plugs so we can look at the coloring and heat range?

Also what issues are you experiencing at WOT?

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Old 07-09-2022, 08:47 AM
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needs phasing: rotor to posts. Sacrifice a cap, put a hole under #6 post and shine time light into hole to see spark phasing. remount Vac ADV canister to rephase.

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Old 07-09-2022, 08:56 AM
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Your rotor is out of phase just a bit.

Something is not correct with the vac advance whether you have it connected or not. If itís connected the slot must be very large.

If it has a block off plate installed the pin is not located properly causing the rotor phasing to be off.

Several other things can contribute to this also.
Iíve seen cheap caps that had the locating lug for the distributor housing notch be so shallow that the cap wonít locate correctly on the housing and cause the phasing to be off but when you set timing with a light it ends up looking right at the balancer.

The large caps are more forgiving with this.

Very likely an incorrectly made cap. Not a Stansard ignition cap is it???

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Old 07-09-2022, 08:59 AM
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Also with those on the edge ware / arcing marks that your seeing in the cap I would double confirm TDC on your balancer.

At true number 1 TDC number 6 exh valve will have no rocker play , or be showing that the valve is open some depending on the cam your running.

In my post #3 I am talking about the gap distance left to right between the tip of the rotor and wire terminal, not the phasing of the rotor to terminal.

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Last edited by 25stevem; 07-09-2022 at 09:06 AM.
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Old 07-09-2022, 09:19 AM
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The Carb Shop in California used to make a big deal of the rotor phasing on HEIs being “corrected” when they built them.I guess this was a big selling point to the potential buyer. It does make a difference if it’s off, however in my experience the phasing right from the factory was just fine.

What I should have explained better in my earlier post was how the phasing should be to begin with. If anyone wants that done I’ll be glad to lay it out for everyone, if not I’ll save the bandwidth and not bore everyone with the details.

If I were to guess, I’d say the OP hasn’t really changed anything and is using the vac advance. With that said he’s likely got a bad cap. When I say bad cap I mean I’ve had lots of trouble with Standard Ignition products lately since they bought 5 -6 other competitors out. Modules being the biggest issue followed very closely by caps next. The Ford distributor caps are the very worst issue wise.

But that’s a separate post. Back to the OP issue.

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Old 07-09-2022, 09:37 AM
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Steve brings up a good point here, and one that I’ve been monitoring around here for many years now. Although the burn mark on the OP terminal clearly shows a phasing issue, the rotor air gap won’t have any measurable effect due to that alone….

However, as Steve mentioned, that air gap is or has gotten to be a very big thing in the last 30 years with these rotors. If you want a treat, do as he says and take a cutoff wheel to a cap. Cut a window in the side. Then go buy about 4 different rotors and install them on the distributor and look at the air gap between the rotor tip and the cap terminal…all over the place.

Back in the days of Sun ignition scopes this “air gap” distance was actually a test checked with an oscilloscope.. the bigger the gap= the more firing voltage was required and seen on the scope. Somewhere over the years these rotor tips kept shrinking until some of these air gaps are near close to 1/4”. Now the ol HEI will quite easily jump that gap but they’re not supposed to be that way. These manufacturers are getting awful loose with the quality control here lately.

Given the fact that different manufacturers make replacement caps, and we all understand that each cap mfg is not made in the exact same size mold, I think we can figure out there needs to be some rub room here on the rotor tip length. That way if you mix and match disastrous results don’t happen to rip the tip off a rotor. I would think these cap terminals should all be within a few thousandths of each other so that the rotors could be fairly close….
But this stuff for the last 15 years for sure has been all over the map. So I think they’ve been cutting the rotor tip back to compensate.

Ideally you’d want the rotor tip as close as practical without whacking any terminals. Anything closer than .100 is not going to make any real difference but 1/4” is just dumb.

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Old 07-09-2022, 09:48 AM
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And for sure to the OP….
Be sure your mech advance isn’t bound up. Remove the cap, grab rotor and twist. Quickly release the rotor and look/listen for it to snap back with some authority.

This allows you to know the springs and weights are relatively free and not gummed up or stuck.

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Old 07-09-2022, 11:23 AM
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Quote:
Originally Posted by kuik02 View Post
Car runs ok, but trying to chase down WOT issues.
What engine is this and what is your "WOT issue"?

This a GM HEI or aftermarket?


Quote:
Originally Posted by kuik02 View Post
Timing set at 16 initial plus 12 vacuum advance (manifold vacuum) and 9 mechanical adv. All in at 2500 rpm..
Vacuum advance doesn't count at WOT unless the engine is way under carbureted.

Is that "9 mechanical adv." in crank degrees or distributor degrees?

9į at the crank is 4.5į in the distributor. Centifugal could be froze up and still get 4.5į in the distributor from end play. That's distributor shaft raising up with RPM and dropping back down at idle.

Thread needs details
Clay

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Old 07-09-2022, 06:54 PM
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Quote:
Originally Posted by Sun Tuned View Post
...What I should have explained better in my earlier post was how the phasing should be to begin with. If anyone wants that done Iíll be glad to lay it out for everyone, if not Iíll save the bandwidth and not bore everyone with the details...
Please do. I've got a vague idea of where it should be but not really that sure.

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Old 07-10-2022, 11:01 AM
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Thanks for all your responses guys. Drove the car to 2 car cruises last night and donít think that itís an ignition issue. I think I need fuel injection or an electric fuel pump to push fuel up to mechanical pump. I took cap off of rebuilt HEI to investigate originally and thatís when I noticed the weird wear. Maybe that wear happened when I dropped in the distributor a tooth off last year after installing a flame thrower coil and module with a rev limiter. Would the engine even run if I had the distributor dropped in a whole ďcylinderĒ off? Iím thinking it would be ridiculously noticeable.

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Old 07-10-2022, 11:28 AM
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Quote:
Originally Posted by kuik02 View Post
Getting late timing wear marks on HEI distributor cap ďtangsĒ. Car runs ok, but trying to chase down WOT issues. Timing set at 16 initial plus 12 vacuum advance (manifold vacuum) and 9 mechanical adv. All in at 2500 rpm. Wear indicates rotor is past cap tangs when firing. Timing chain is tight both directions. Am I reading too much into this? My guts telling me I have more of a fuel problem.
Letís see if this works correctly.
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Old 07-10-2022, 11:32 AM
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Damn! I did it!

Ok , hmmm….

Anyhow. Here’s a pic of one that the brand new module wasn’t working correctly. For illustrative purposes here this will work fine.

With the burn pattern way over to the edge of the cap terminal like your first pic. This is what I would be expecting going on inside where you really can’t see. Except in your case I would say the spark kernel is nowhere this long but you get the picture.
I should also mention this is a Chevy distributor.

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Old 07-10-2022, 11:37 AM
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Hereís what happens when it gets too wide. Iíll add this is very erratic at times also.
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Old 07-10-2022, 11:41 AM
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To the OP, your still not being forthcoming in terms of needed details as to what your motors WOT symptoms are that lead you to make a post in the first place !

If your leaning towards thinking you have a fuel supply issue, then exactly what is taking place and at what rpm and in what gear?

I have my crystal ball rented out this weekend so I can’t access it to help you.

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Old 07-10-2022, 11:45 AM
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So your dizzy cut away is showing the spark jumping to two terminals at the same time.
Not good to put it mildly!
Thanks for your efforts on making that!

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Old 07-10-2022, 12:13 PM
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Looked at distributor pick up coil today. The only thing I can conclude is that the inner wheel is not pressed onto the shaft in the correct phase causing the ďlateĒ wear on the distributor cap tangs. Whoever rebuilt distributor didnít press that on correctly. Is that even possible or is it dummy proof? Iím gonna pull distributor to check.

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Old 07-10-2022, 12:22 PM
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Quote:
Originally Posted by 25stevem View Post
To the OP, your still not being forthcoming in terms of needed details as to what your motors WOT symptoms are that lead you to make a post in the first place !

If your leaning towards thinking you have a fuel supply issue, then exactly what is taking place and at what rpm and in what gear?

I have my crystal ball rented out this weekend so I canít access it to help you.
Lol. I appreciate your response but I think Iím dealing with a couple issues. Car runs decent but not as good as it can be. Think I got a fuel and spark issue which complicates things. Wish I could say, itís ďdoing this exact thing all the timeĒ. Itís always been hard on this car to drop distributor in and get to run.

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Old 07-10-2022, 12:23 PM
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Quote:
Originally Posted by Sun Tuned View Post
Hereís what happens when it gets too wide. Iíll add this is very erratic at times also.
Way cool to see that!!

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