Dist cap & rotor deposit build up

JPhil

Huh?
Joined
Mar 26, 2008
Messages
1,361
Location
Loveland, Colorado, USA
I have a problem with my distributor cap & rotor building up deposits of crap which interferes with the spark. Every thousand miles or so I have to pull off the cap and scrape it and the rotor because the idle gets lumpy, and replace them every 2 or 3 thousand miles which is more often than it seems I should. I have tried dielectric grease on the contacts but that didn't seem to help. I know the deposits are a given for any electrical spark jump contactor, but this seems a bit excessive to me and gets to be a drag to constantly have to deal with.

I'm running an MSD distributor with 6A box, good plug wires, NGK plugs. The cap has a little vent hat on the top only. I've been told the deposits are from ozone build up in the cap. I'm thinking about drilling a couple of tiny holes on the front & rear of the cap down low to get a little more ventilation through it.

Anybody else suffer from this and/or have any ideas how to reduce it?
 
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LONG ago I found that a multi spark MSD unit was good for ONE thing.....smoother idle with a rich carb.....once FI was on the car, it made NO difference, put it on this vette with DPFI ....no difference the HEI is fine......that's all I know is my own shit.....


:crutches:
 
I had a "Well, duh!" moment this morning and called MSD. They said to drill 4) 1/4" holes at 90* in the cap at the level of the rotor. I will do this with my new cap & rotor this weekend and we shall see how it goes.
 
No, I didn't ask if that's what he thought it was. I told him that's what I thought it was and he suggested venting it. I have installed the new parts, with vent holes per MSD.

I did just come back from the hot rod shop where we looked at my old cap & rotor and he showed me how my rotor is out of phase with the magnetic pickup. The rotor is retarded in relationship to the ignition timing, causing a long spark between rotor and cap pickups, which is eroding the rotor.

So I will now proceed to a new adventure in rotor phasing.

To be continued.....
 
No, I didn't ask if that's what he thought it was. I told him that's what I thought it was and he suggested venting it. I have installed the new parts, with vent holes per MSD.

I did just come back from the hot rod shop where we looked at my old cap & rotor and he showed me how my rotor is out of phase with the magnetic pickup. The rotor is retarded in relationship to the ignition timing, causing a long spark between rotor and cap pickups, which is eroding the rotor.

So I will now proceed to a new adventure in rotor phasing.

To be continued.....

I wonder, seems that many years ago, I had an instance where the gear on dizzy bottom end was outta phase with the rotor output head, it can only go on at zero or 180 out, due to the pin.....now the gear had a odd tooth count as I recall, so if it was out 180, the phase of the spark is off quite a bit with the contacts.....so to put the rotor button on the dizzy, and check that the output aligns with the divot on the timing gear, if it don't....there is the issue....drive out the scroll pin and turn the gear 180*

Gotta scratch my ass over this one, been more than a few year since I faced this problem......worth checking anyway.....

:stirpot:
 
Today's adventure: rotor phasing--

Following the advice given by MSD (see link below) I drilled a hole in my old cap checked it. Sure enough, it was way off. My spark at rev was at least 3/8 inch long in the cap, the rotor was way retarded, probably almost half way toward the next terminal at rev.

The vacuum advance had been disconnected on the engine dyno for a few more horsepower, so since the remedy is to advance the rotor only I used my little hand vacuum pump to suck on the vac advance canister. Sure enough, the rotor came back into line. I hooked the vac advance back up to the carb and while not ideal as pictured below, it is much better. The rotor is now exactly face to face with the cap terminal at idle and retards to about edge to edge on rev.

My idle picked up & smoothed out a bit, to be expected.

Took it out for a test drive, no noticeable loss of power with the vac advance hooked back up. Impressed a couple Harley guys who thought they'd try to keep right up with me when I pulled out onto Hwy 402 and gave it the gas. They just disappeared in my mirror. I heard them laughing about it when they pulled up behind me at the stoplight a couple miles down the road.

So now I just wait and see how the inside of the cap looks in a thousand miles or so.

http://www.msdignition.com/uploaded...port/frm28392_tech_bulletin_rotor_phasing.pdf
 
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Yipes!

Guess I shouldn't be so quick to post---This morning when I woke up I realized I hadn't checked the overall timing again yesterday plus I think I had mis-interpreted what he said about fixing the vac advance rod to adjust the rotor phasing. So I checked the timing this morning---no wonder it ran so well on my test drive yesterday: I was running nearly 50* total advance! Good thing the engine was cool. Oops. Learning experience.....
So I unhooked the vac advance and will get an adjustable rotor instead.
 
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From what I've learned the most common reason is by changing out the distributor drive gear and the new one is not indexed the same to the shaft. I don't quite understand that one, I think I'm not understanding how it was explained. Sometimes it's a manufacturing problem -- most common on aftermarket distributors--where the reluctor and rotor are not indexed correctly. In my case it is because I have disconnected the vacuum advance for a better power curve.

There's three ways to alleviate the problem, one is to remove and re-index the reluctor, one is to permanently fix the vac advance in the advanced position and then reset the timing, but those require modifying the distributor which I don't want to get into. The other way is to install an adjustable rotor so I can align it with the cap terminals. This is the way I will go.

This new to me, I had never heard of 'rotor phasing' till a week ago.
 
OK, I bought the MSD adjustable rotor last week. Using my timing light and the cap with the view window cut in it, I set my rotor to be dead on with the cap terminal at spark. Really simple and easy, although I would caution one to make goddam sure the screw on the adjustable top of the rotor is TIGHT! I won't go into the story of how I got yet another physics lesson about acceleration vs. mass as it relates to spinning objects..... :mullet: Crank it down and locktite that sumbitch!

Anyway, whether or not there is an actual noticeable difference, it just feels better to me now, like the stars (spark!) are in alignment in the distributor cap. With the 4 vent holes & this rotor alignment I should have a happy cap now.
 
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