Moulton TSR rear pivot

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gazza_d
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Re: Moulton TSR rear pivot

Post by gazza_d »

I've ridden with slightly worn bushes too and not noticed any issue when actually riding.
However a loose bolt can move and ovalise the holes in the eyelets which is a bad thing.
I suspect that if you ride with worn and moving bushes for a prolonged period, they could end up causing the bolt to move and then wearing the holes which would be a bad thing.

I have had the bolt come loose and actually fall out of my TSR. It happened about 4 weeks after taking delivery and it hadn't even got to it's mileage for the first service.
It came out and jammed the LH crank. The bike stopped very quickly and I went over the bars (I was ok luckily though).
The LH eyelet plate was very badly bent and the whole bike went back to Pashley via the retailer for repair which took about 5 weeks. I was slightly miffed that I didn't even get an apology out of either the retailer or Pashley for such a catastrophic failure on such a new cycle.
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simonineaston
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Re: Moulton TSR rear pivot

Post by simonineaston »

How disappointing!!
I don't recall the torque value for tightening the pivot bolt except that it's quite high, the idea being that the frame ears should render the pivot sleeve immobile, such that there is no movement in the system other than the rotation of the bushes around the sleeve. The sleeve is (or should be) ever so slightly wider than the bushes-mounted-in-the-rear-triangle - all the bolt does is a lot of squishing...
S
(on the look out for Armageddon, on board a Brompton nano & ever-changing Moultons)
jb
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Re: Moulton TSR rear pivot

Post by jb »

As Mick says - a hardened steel bush with a case hardened pin would be be more durable for this application than a bronze bush. The problem being there is next to no movement in the pivot, therefore any lubrication will break down. Taper bearings would be total overkill for the same reason.
Hardened bushes will still wear but at a slower rate.

If there was no reason to rotate the swing arm under the frame as per the Brompton then the pivot would best be replaced by a flat piece of spring steel (of a calculated size & thickness) which would cope with the tiny movement far better than any pivot.
Cheers
J Bro
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

simonineaston wrote: 11 Apr 2021, 9:25pm How disappointing!!
I don't recall the torque value for tightening the pivot bolt except that it's quite high, the idea being that the frame ears should render the pivot sleeve immobile, such that there is no movement in the system other than the rotation of the bushes around the sleeve. The sleeve is (or should be) ever so slightly wider than the bushes-mounted-in-the-rear-triangle - all the bolt does is a lot of squishing...
30Nm, which isn't all that high (at the lower end of the range for fitting a pedal, and about the same aa a nutted axle) but is probably the limit for the bolt size used.
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

When I first took delivery of mine, I stripped it right down to see how it all worked.
Typical of me! :D

When I put the pivot bolt back in, I made it nice and tight.
Torque?
I couldn't care less. Mine is tight and remains so.

As for the front suspension, they reckon that the nylon washers shouldn't be lubricated and assembled dry.
When I pulled mine apart .......... brand new remember ............ they were nicely greased. I clean and grease them every now again.
Mick F. Cornwall
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

One of the issues I have with the TSR suspension is that many of the bearing surfaces, especially on the fork, are painted. Polyester powdercoat is not a good bearing surface!

The powdercoat then rubs off in use, increasing clearances and making a rusty mess.

I am also going to have some bushes machined but I will clean the paint off the seating surface in the frame and measure carefully to ensure the spindle is just longer than the frame tube + bushes. The factory bushes have a flange between 96 and 100 thou thick, and goodness knows what it's supposed to be. About 8 thou difference (0.1mm each side, in new money) seems to be about right to allow the rear suspension to move without binding.
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

I wonder why the makers of the frame used non-standard bushes?

I also wonder if the rear end could be machined a tad narrower to allow for the standard bush flange thickness. It's hardly rocket science to do and could even be done by hand with a file.
Mick F. Cornwall
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

Maybe they cocked up the calculations and ended up having to commission special bushes :D

I wouldn't want the pivot any narrower than it already is. Compared to an AM model, it is setiously undersized.
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

The pivot would be the same size, it would just be that the bronze flanges would be thicker.

Just been looking at the bike. It's the front end with the bushes, not the rear! My mistake! :oops:

I have two pairs of new bushes as well as a fairly new pair fitted. They've only done just over 500miles. Mine have worn after three or four thousand miles, so I have 7,500miles's worth of bushes yet. Three or four years yet and could be much longer as I'm lavishing the things with grease regularly. Only did it a few times in the past.

I still think dressing up with a file would sort the frame to take standard bushes.
Back soon with some measurements.
Mick F. Cornwall
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

The bushes from Simply Bearings are in Imperial sizes.
https://simplybearings.co.uk/shop/p1205 ... _info.html
Flange thickness is 125thou.

The modified/original ones have a flange thickness of 96thou.
Therefore each bush was turned on a lathe taking 29thou off.

Therefore all that needs to be done is to take 29thou off each side of the frame fitting to allow for standard bushes.
29thou per side is a total of 1.5mm ................ 0.75mm per side.
Could be done easily, and then I wouldn't need any bushes modifying ever again.

Food for thought.
Mick F. Cornwall
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

The faces really need to be parallel, especially if the bushes are a bit of a sloppy fit in the frame tube, so I wouldn't use a file. I have a BB facer but it's far too big.
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

Yes, of course they need to be parallel, but with skill of hand, it could be done. It's not much metal to take off, and some of it is paint.

I've already explained how easy it is to get the bushes out, so trial and error would get them seated neatly and at the right width.
Mick F. Cornwall
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

Just measured the original bushes. The originals that were fitted on the frame when brand new.

One is 96thou and the other is 82thou. :shock:
Therefore, the tolerances are a bit liberal ......... to say the least.

All the ones I had modified are all the same at 96thou each.
Mick F. Cornwall
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

I wonder if they're skimmed at the Pashley factory?
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

More than likely yes.
Pity they can't be more accurate though. Maybe they give the job to young apprentice! :wink:

Still don't know why they skim them in the first place.
Possibly they made a cock-up in the plans and needed thinner flanges to compensate.

Another possibility is that they could see a gold mine in selling spare parts. My first kit cost £30, but Fudges (where I bought the bike) wanted £50odd. This is for two bushes, a spindle, a bolt and two serrated washers! :shock:
Mick F. Cornwall
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