MTFCA Forum

I got this question from another T'er and thought it might benefit someone else, so here goes:

Hello
I am in need of a source of the rivets which hold the individual brush holder on the assembly or if not available what people are using to repair it. Any help would be great. Thanks , John

Good discussion of some of this is here. viewtopic.php?f=2&t=25880#p210525

Specifically, I use #6 flat head screws from McMaster Carr on generators (anyone have a source for domed head screws like the original?)
McMaster Carr: Steel Slotted Flat Head Screws, 6-32 Thread Size, 5/16" Long

On starters, I grind off the brass rivets holding the brush plate and replace them w/ solid copper rivets. More info coming soon.
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When rebuilding brush plates on both units, I use 1/8" rivets with backing washers on the new insulators and I peen the rivets.
. .
For the brush holder, its a delicate operation. First you carefully grind off the back of the holder rivets making sure when you pop the holder out you save the metal backing plate that invariably goes zinging across the floor and behind your machines. Also, leaving part of the post intact gives you a "center punch" you can use on the next step.

Then I carefully drill and tap 6-32 holes where the rivets were. I use Steel Binding Head Slotted Screws, Steel, 6-32 Thread Size, 5/16" Long on the posts AFTER I use some Loctite. There's no room for split washers here so Loctite is a must. I've fixed a few of these failed repairs when they short out when the screws back out from vibration.
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There needs to be enough clearance so the new screws don't short out when reinstalled.
. Hopefully this helps someone in the future!

AdminJeff

Very nice tutorial there, Chief !!!

For better or worse, I cut off the part of the new insulator that goes under the stationary brush and use only the portion that goes under the moveable brush. Naturally, the old insulator under the stationary brush, needs to be in good condition yet.

Yeah, Steve, thanks to YOU, I had good instruction.
And Ron Patterson's posts on the old forum are worth their weight in good Babbit

My original info on attaching the starter brush plate was incorrect. Ron recommends using solid copper rivets. More info soon.

AdminJeff

Jerry VanOoteghem wrote: ↑

Mon Feb 28, 2022 12:50 pm

For better or worse, I cut off the part of the new insulator that goes under the stationary brush and use only the portion that goes under the moveable brush. Naturally, the old insulator under the stationary brush, needs to be in good condition yet.

That's one way to do it, but if you're going to the trouble of doing the repair in the first place, it's much better to replace all the insulators. I've seen this type of repair on some cores and invariably the insulator on the fixed brush that wasn't replaced is what failed. So, why take the chance?

AdminJeff wrote: ↑

Tue Mar 01, 2022 6:37 am

Jerry VanOoteghem wrote: ↑

Mon Feb 28, 2022 12:50 pm

For better or worse, I cut off the part of the new insulator that goes under the stationary brush and use only the portion that goes under the moveable brush. Naturally, the old insulator under the stationary brush, needs to be in good condition yet.

That's one way to do it, but if you're going to the trouble of doing the repair in the first place, it's much better to replace all the insulators. I've seen this type of repair on some cores and invariably the insulator on the fixed brush that wasn't replaced is what failed. So, why take the chance?

I have not had that failure yet. But, there's no saying that I won't, especially since it's now been brought up. Irony always wins!

Jerry VanOoteghem wrote: ↑Irony always wins!

Always!

Thanks for the information.
It works fine on the starter brush bridge too.
The only difference I do, is drilling a 2.5mm hole in de riveted parts of the brush holder before I grind of the rivet.
In the hole I tap a M3 thread (metric I live in Belgium). The screw I use are m3 x 10mm

Here a few photos of a starter bridge watch for the locktide.

Good luck
Andre
Belgium

Andre,
While it may seem like a good idea at first glance to drill and tap the holes for an M3 screw, there are practical and mechanical issues here that indicate that it probably wouldn't be a good long term solution unfortunately.

It is common practice that the minimum recommended thread engagement to make a strong mechanical connection for a component with a tapped hole is approximately 1 times the nominal diameter in steel. Nice source that explains this in gory detail is here:

https://www.nord-lock.com/insights/bolt ... pped-hole/

A metric M3 bolt has a nominal diameter of 3 mm. That means that to hold that size bolt without the chance of stripping under stress, and the torques involved inside the starter when engaged are absolutely insane, the minimum thread depth for that screw on the brush plate should be 3mm. There is nowhere near that much material on the brush plate, so these tiny bolts run the real risk of stripping and backing out. I suppose you could use nuts on the back of those bolts but that might interfere with the clearance of commutator. I'm not sure, but I know there's not a lot of room in there.

I'm taking a leap and guessing that Ford (or whoever built the starters for Ford) knew this and therefore, unlike on the generators where there is very little stress on the brush plate, they used solid rivets both for mechanical strength and superior electrical conductivity, which are both an absolute necessity in this harsh application. I have never seen a brush plate fail at these rivets.

Of course, as always, your mileage will vary!

AdminJeff