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2 brush/3 brush: what is the difference

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2 brush/3 brush: what is the difference


Post by panhead54 » Fri Aug 08, 2008 4:21 pm

hello everyone. can someone help me out with a few questions? first off, i am running a stock 74" 1954 FLE panhead motor. i have a -65A generator which i would like to run. i know the holes need to be drilled out to 5/16. i also ordered out of v-twin the 12v. "look a like" relay # 32-0071............. what is the difference in 2 brush and 3 brush? how do you know when to use them? any tips on drilling the holes or should that have been done prior to assembly? will that relay work for what i am trying to achieve? thanks, and i greatly appreciate any advice from you all.


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Re: 2 brush/3 brush


Post by King » Fri Aug 08, 2008 8:19 pm

Hi Billy

I’ll get you started and hopefully the more electrically advanced will also chime in. The three brush Model 32-E generator is the stock one for your bike. It is a 6V unit and It has two main brushes and a third small movable brush to adjust current. It does not have a voltage regulator only a “cut-out relay” to prevent the battery from being discharged back into the generator when the voltage drops below 6.8V or thereabouts. The 65A is a 12 volt generator that requires a regulator to prevent frying the battery.

As you noted the two bolts that go through from the gear case cover into the generator are 5/16” for the 65A and ¼” for the 32E. I would strongly recommend NOT drilling out the gear case cover. Instead insert helicoils in the generator and continue to use the ¼” fasteners. That way you do not bugger-up an original part.

I am not familiar with the V-Twin “Look-A-Like” Relay. Hopefully it is not just a relay but a regulator.

Of course you will have to change out your lighting and coil to 12V and get a 12V battery. The one most use is a small 5.5AH conventional lead-acid battery which will fit inside the oil tank where the 6V one sat. To use this battery you need a “low output” generator like those supplied by Cycle Electric. If your generator is a standard 65A unit you will need at least a 7.5AH battery to take the charging output. I opted for the “high output” generator and have installed a 12AH battery in one of my metal panniers.

For me the 12V conversion was worth it. I now can see where I’m going at night, keep a well charged battery, and get better starts.

Good Luck


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Re: 2 brush/3 brush


Post by Cotten » Sat Aug 09, 2008 1:50 am

King's reply should be shouted from the mountain tops:

"I would strongly recommend NOT drilling out the gear case cover. Instead insert helicoils in the generator and continue to use the ¼” fasteners."

The 1/4"-24tpi inserts are readily available from vendors who are experienced with vintage USA-manufactured motorcycles. Indian used them as well.
The 5/16"-24 holes in any HD tw0-brush generator accepts these inserts without a special tap.


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Re: 2 brush/3 brush


Post by john HD » Sat Aug 09, 2008 11:11 am

i don't know if anyone has tried this but i have heard you can rotate the generator body slightly and drill/tap a new set of holes for either size.

that way you will have a generator that would work on any kind of cases.

anyone ever do that? did it work?


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Re: 2 brush/3 brush


Post by panhead55 » Sat Aug 09, 2008 3:45 pm

hey fellas, thanks for the advice. first off i heard that the relay is for 6v only so i just learned a money lesson this weekend. im getting mixed ideas from "older pan guys" about the drill/ no drill. i would hate to drill in my nice cases even that little shaving but on the other hand, with a 1/4 in bolt in a 5/16 passage, isn't that going to leave a gap with less support for the heavy generator? i plan on riding my bike a lot more than just to starbucks. maybe i can get crafty and run the bolt through a sleeve to make up the difference. also, is the FLE a more rarer motor? thanks fellas....billy

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Re: 2 brush/3 brush


Post by awander » Sun Aug 10, 2008 1:02 am


The holes in your cases should all be 1/4".

The threaded holes in the later-year generator will be 5/16-24.

If you put the 1/4-24 helicoils in the 5/16-24 threaded holes, you will now have 1/4-24 holes in the generator.

There will not be any 5/16 holes to sleeve; all holes will be 1/4" and you can use the original, early-model generator bolts.

How much did the 6v regulator run you? I might be interested in it-I am considering going to a 2-brush 6V setup on my '52.

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Re: 2 brush/3 brush


Post by awander » Mon Aug 11, 2008 12:40 am


Are you trying to change a 6V 3-brush system over to a 12V 2-brush system? If so, I'm pretty sure that the relay-replacement that you described will work just fine, along with a 12V 2-brush generator, and the 1/4-24 helicoil inserts.

The V-twin catalog describes it as a 12V regulator that looks like the older 6V relays.

You should be good to go.

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