4-Brush Starter Motor

Wordman

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I purchased a NOS brush plate and armature for my project, and I noted that the brush plate has holes for a second set of brushes. Has anyone successfully added (or experimented with adding) the second set of brushes?

nos-new-yamaha-tx650-xs650-starting-motor-brush-holder-assembly-306-81840-10.jpeg
 
If my rekallecktions about armatures is correct, adding those 2 extra brushes to those empty mount holes will increase the current draw 6x, seriously overheat the armature windings, without adding a proportional increase in starter torque, due to misphasing with the field...
 
If my rekallecktions about armatures is correct, adding those 2 extra brushes to those empty mount holes will increase the current draw 6x, seriously overheat the armature windings, without adding a proportional increase in starter torque, due to misphasing with the field...

Sooooooo.....that would be.....bad - correct?

upload_2019-8-3_8-2-18.jpeg
 
I purchased a NOS brush plate and armature for my project, and I noted that the brush plate has holes for a second set of brushes. Has anyone successfully added (or experimented with adding) the second set of brushes?

View attachment 146696

Perhaps it's to locate the brushes for a reverse direction, while reworking a Mitsubishi ATV starter I found brush frames available to spin the starter either way depending on application.
 
If my rekallecktions about armatures is correct, adding those 2 extra brushes to those empty mount holes will increase the current draw 6x, seriously overheat the armature windings, without adding a proportional increase in starter torque, due to misphasing with the field...

That would depend on how the armature is wound, yes? I ask because adding a second set of brushes is a common upgrade on Norton Commandos and made in Mariden Triumphs (with no change to the armature). Hmmm....
 
Well, go ahead and try it.

Starter armatures are wound with thick wiring, windings in series, joined at the commutator.
StarterArmature.jpg

The layout of the fields, brushes, and current direction have to make up a working combination. Adding those 2 brushes adds 2 opposing current paths, since each +12v brush is now straddled by 2 ground brushes. The starter's windings and fields would have to be designed to allow for this new configuration...
 
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Well, go ahead and try it.

Starter armatures are wound with thick wiring, windings in series, joined at the commutator.
View attachment 146821

The layout of the fields, brushes, and current direction have to make up a working combination. Adding those 2 brushes adds 2 opposing current paths, since each +12v brush is now straddled by 2 ground brushes. The starter's windings and fields would have to be designed to allow for this alteration...

I get that... and I also know that there are several different bikes where a 4-brush kit can be installed, without changing the armature (making me think a lot of armatures are already capable of being 4-brush)... I think (once I am back in the garage) I'll build a 4-brush starter using old parts and see what happens. Should be able to tell pretty quickly if it's a workable idea! LOL
 
Just for arguments sake, let's say the 4 brush idea works... I'm wondering if the starter gear train is up to the task of handling that much extra power...
 
Just for arguments sake, let's say the 4 brush idea works... I'm wondering if the starter gear train is up to the task of handling that much extra power...

By cranking more reliably, it should help longevity by eliminating the speed up/slow down variations in cranking speed. At least, that's my thinking. Of course, I'm also waiting for the Twins-Inn gears to be available.
 
The Norton Commando used the Prestolite starter motor in two brush form, it had barely enough guts to turn the 850 engine over, the exact same starter was used in 4 brush form on ironhead HD 1000cc Sportsters. When i was working on HD years ago at a shop in Kent, we sold all the 4 brush starters we had to Commando owners, who instantly could electric start their bikes.

so yes it might very well work, we are trying it now
 
the standard coil was renowned to be of bad quality, when we first had XS650 ( in the 80s) they always packed up
yes a good coil is a great addition.
However if the compression is high or the engine of large displacement, the coil wont help, as you cant turn the engine over, that's where the more powerful starter will come into its own
 
Sorry, you mention large displacement. I just was pointing out that with a hot spark a motor fires pretty quickly and thus does not strain the starter motor by forcing it to crank endlessly and heating up.
 
The larger displacement, ( we build mostly 880 and a few 1000cc engines) are so hard to turn over it wouldn't matter how good the spark is/was, the 880 i sold recently even with a longer kickstart and one of the XS2 exhaust cover/valve lifters, you kick it as hard as you can, and it comes up to compression and just stops dead. it was running a true 10.5:1 so i wasn't surprised. even the smaller 840 sidecar moto-cross engines we built were very hard to start, with only 10:1

The 4 brush starter conversion should ( we hope) allow the engine to turn swiftly past TDC and then start, we have most likely the same ignition as you with a really good set of coils and a good spark, when we run it on a Honda generator powered external starter it fires instantly.

we have started using an Ignitech programable ( crank mounted) ignition recently, we will report on it as soon as we know how good( or otherwise) it is

the big rephased engines are great fun to ride, but we have found them very hard to start, Jerry Van Der Heiden gets the same thing in Holland, (you may know him or have heard of him, he designed the large fin cylinders that Mikes XS sell ) the 4 brush conversion with welding wire earth and power leads and a good battery might swing it enough that they start well.

of course the common sense move would be to drop the compression ratio/pressure. or fit a longer duration cam, or both !!
 
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