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Replacement bushings and spring for TU56 drive motors?

TJ_Mossman

Experienced Member
Joined
Dec 1, 2013
Messages
370
Location
Bristol, England
Hi All,

I've had a 2nd TU56 arrive the other week, and I've just got around to giving it an initial look-over before I start refurbishing it.

One thing that was immediately apparent is that all but one of the drive motors had seized up. After getting them out I could see that at some point the bushings had dried out and stuck to the shaft, and that the springs had been bent and snapped. They were really stuck on hard and unfortunately got scored by the shaft on the way out as the set screws for the hubs had roughed them up. (I'll probably have to lightly sand it back down before I replace them)

Damaged_Motor.jpg

Has anyone gone about replacing these? (P/N 12-9926 for the bushings and 12-9917 for the spring)

I see that they're not normal Oilite bushings and springs. The bushings measure ID=8mm, OD=10mm, Flange Diameter=12mm, Flange Length=2mm Length=6mm (total), and have a small hole to retain the spring. The spring has an internal diameter of 10mm and is about 25mm long. One end is bent inwards trap the bushing, and the other end is bent outwards to trap the C-ring on the motor.

I might be able to make the springs myself by finding a similar one and bending it, but I haven't had any luck finding bushings the right size, and lack the tools needed to machine them without damage.

Meanwhile I've stripped down the motors and re-lubricated them. They use standard GMN 608 bearings, just like skateboards.
I suppose I'll move onto the PSU next. As with my other unit, a bunch of wires got burned by one of the dropper resistors. I'm tempted to find some high-temperature cloth coated wire to replace it with, rather than repeating my last kludge where I just put a few layers of heat-shrink over the existing wires.
 
If you do manage to find an Oilite bushing that almost fits, be careful on machining it to size. Regular steel tooling can "smear" the bronze and plug up the "pores" so that lubrication is lost. Some report success in rehabilitating these by burning the old oil out cleaning and re-impregnating by immersing the bushing in oil and drawing a vacuum on the whole setup (removes air trapped in the bushing and fills it with oil).

Springs can be fabricated. There are several good demonstrations of this on the web. Easiest if you have a lathe to spin a mandrel.
 
Regular steel tooling can "smear" the bronze and plug up the "pores" so that lubrication is lost. Some report success in rehabilitating these by burning the old oil out cleaning and re-impregnating by immersing the bushing in oil and drawing a vacuum on the whole setup (removes air trapped in the bushing and fills it with oil).

Springs can be fabricated. There are several good demonstrations of this on the web. Easiest if you have a lathe to spin a mandrel.

That's what I meant by "lack the tools needed to machine them without damage". I've heard it can be done but the tools need to be very sharp.
I might try rejuvenating them, but since the bore is scored already I doubt I'll have much luck.

It turns out there's a company that makes spring local to me, I think I'll ask them for a quote.
I may end up having to buy a lot of them to get a sane price, but in that case I'll be able to pass any extras onto people with the same issue.
 
I see that they're not normal Oilite bushings and springs. The bushings measure ID=8mm, OD=10mm, Flange Diameter=12mm, Flange Length=2mm Length=6mm (total), and have a small hole to retain the spring. The spring has an internal diameter of 10mm and is about 25mm long.
I thought the TU56 drives were made in the US in the 1970s. It seems really unlikely that it would have any metric measurements. Did they also make them somewhere in Europe with locally sourced parts?
 
This one is US made. I gave the measurements in metric because that's what the bushings most closely lines up with (I would have expected it to be imperial too).
The Flange Diameter (1/2") and Total Length (1/4") make sense in inches, but the 13/32" OD and 9/32" ID seem a bit unusual.

Maybe if I did deep enough I'll find the engineering drawings...
 
First off, don't guess or assume what the dimensions are. Get a digital caliper, vernier caliper or micrometer and check them exactly.

The tool that is used cut to size and put a high finish on small diameter plain bearings and bushes is a reamer. They come in fixed and adjustable. Here is one for the size you gave from a UK machine tools supplier, I have purchased lathe tools from them and posted to Oz and they are reputable.
https://www.ebay.co.uk/itm/RDGTOOLS-ADJUSTABLE-HAND-REAMER-1-4-TO-9-32-HV/350643355805

Chuck is correct that machining Oilite will smooth the porous surface over. Oilite is sintered metal and compressed to shape, allowing oil to seep through it. They are great for situations where the bearing isn't going to be oiled on a regular basis, eg. due to lack of access.

If this was my problem I would just use a piece of plain bronze. Bronze bearings often have a crossed LH and RH helical channel cut on the inside face for oil. Put a washer of felt alongside it for the oil. It's light duty and not going to be used heavily. Maybe even a graphite-impregnated polymer would be ok.
 
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