Magneto poinst and condenser - where to buy?

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Magneto poinst and condenser - where to buy?

Postby hennesse » Mon Oct 06, 2014 7:56 pm

My 62 XLCH started (pun) getting hard to start. My points were badly pitted, even though they are only six months old. I filed them down, and it now starts easily, but I fear they will end up pitting again soon. They should last years and years.

It seems that points for everything are made today from whatever crappy metal the Chinese decide to make them out of this week. My Ford NAA tractor was getting hard to start, and the points (probably 20 years old) were badly pitted. I replaced them with a set from Carquest, and 2 weeks later, it was no-start again. The new points were burned black. I got a set from Napa, and they've been running fine for 2 years.

I got my CH mag points, condenser and cap from Mainely Magnetos. Maybe just a bad batch. But I'd like to get a new set from someone else. Any recommendations?

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Re: Magneto poinst and condenser - where to buy?

Postby dr dick » Thu Oct 16, 2014 9:18 pm

nos fm points come up on ebay from time to time. usually around $45.
these are the best ive found.

the rubbing block is clearly marked fm
the fixed point has a slot at wick holder screw. un like the am sets that have a large round hole.

early pitting can be from:
too small a cond for rpm useage
or condensor infiltrated by moisture.

white stuff on point faces is water contamination
black is usually oil, grease, or gas.
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Re: Magneto poinst and condenser - where to buy?

Postby hennesse » Wed Oct 22, 2014 1:04 pm

dr dick wrote:nos fm points come up on ebay from time to time. usually around $45. these are the best ive found.
the rubbing block is clearly marked fm, the fixed point has a slot at wick holder screw. un like the am sets that have a large round hole.

early pitting can be from: too small a cond for rpm useage or condensor infiltrated by moisture.
white stuff on point faces is water contamination black is usually oil, grease, or gas.


Thanks Dr. Dick,
After filing down the points, it started easily, but then started getting hard to start after a few days. The points had re-pitted badly in the same place. I put in a new set of (aftermarket) points. The problem could have been from an impurity in the point material (like in my tractor situation), but I changed the condenser too - using the one from when I bought the bike. It again starts easily, but time will tell.

I also started looking on fleeceBay - and I found an original set that are exactly like you described. I bought them.

Which brings us to the matter of condensers and how to test them... I tested both the suspect one and one from a K/XL distributor according to the directions here. I used my digital multimeter set on the 20 Meg ohm scale, and got similar results as described for an analog meter - I got a 1/2 second "swing" for normal polarity, and a 1+ second "swing" for reverse polarity, and infinite resistance after that. No short or leakage, right? But as mentioned in that article, this isn't stress testing.

The article mentions a "real" capacitor tester (that applies a substantial AC voltage). I see some antiques on Ebay, but of course, who knows how/if they work correctly. (Side note: I picked up a free Sun VAT-28 with problems. I contacted a guy who has done beautiful restorations on automotive test equipment - his advice to me: "first, change all the capacitors in the unit - they're probably all bad by now") So any antique capacitor tester will probably need its capacitors changed. Quis custodiet ipsos custodes?

I do see some capacitor testers like a Fluke 12B or this one but it seems like these are more "capacitor identifiers" rather than "capacitor testers".

Any thoughts on capacitor testing?
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Re: Magneto poinst and condenser - where to buy?

Postby dr dick » Sun Oct 26, 2014 12:17 pm

1st id like to talk about some things that are idiosyncratic to the f-m mag.
understanding these differences (compared to a battery system) usually helps in keeping your bike starting and running right.

in a battery system the juice for starting comes from a storage battery. a mag has no external electric supply. it needs to make its own electricity.

there is a lot going on in a mag that isnt going on in a battery system, the biggest difference is that your mag reverses magnetic polarity during each rev of the rotor.

in the battery system the flow of current is always in one direction coming from the battery. (this is a generalization as a capacitor flows current in and out during each spark cycle). as far as breaker points are concerned the major juice flow is always in the same direction. that tends to erode the metal from one contact face and deposit it on the other. = pitted points.
if you reverse battery polarity the transfer also reverses = the pit is on the other point face now.
one of the jobs the capacitor does is to 'soften the hit', to keep hi temperature arcing (and the subsequent metal transfer) across point faces as they break to a minimum.
got that?

now to the mag-
because it needs to make its own juice, it needs a coil to turn magnetism into electricity. this happens in the primary side of the mag coil.
as you feed magnetism of a given polarity into the coil, you get current of a given polarity out.
when you reverse (each 1/2 turn of rotor) the magnetism into the coil you also reverse the current flow out of the coil.
that means the flow across the point faces reverses in a mag this keeps pitting to a minimum.
and
it also reduces contact face temperatures as arcing is reduced by less (or no) pits.
low contact temperatures can "foul' points. seen as black (oil based) or white/grey (water based) residue on contacts. once points are dirty pitting is gonna follow. and so is hard starting.
dirty points dont come from capacitors, they are from dirty mags. or low purity contact faces.

when you get capacitor faiure on a mag you will get:
1) no spark (capacitor is shorted)
2) high rpm misfire (broken capacitor mount or an 'open' capacitor with reduced capacity)

if you have a good proven capacitor i seal the wire opening with sealer to moisture proof it. it should last for decades then.

personally i dont use the foil/paper caps i use foil/mylar. the fully epoxy encased units being bullet proof.
Image
these were commercially available in the late 70's. i have no idea where to find them now.
ive been running them, with no change out, since then.

in closing
your mag is a a/c permanent magnet altenator that suppies ac spark output with the frequancy of the rotor rpm.
you really need to understand ac electricity and apply that knowledge to you mag building and operation. dc knowledge is a poor fit here.
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