Moulton TSR rear pivot

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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

Just upended the bike and measured the width of the frame where the bushes fit.
49mm wide.
Take off 0.75mm off each side, and it comes down to 47.5mm.

Hardly worth worrying about as it's not much in the grand scheme of things, though the hard part would be getting the same off on both sides to preserve the frame tracking.

Also, the tube isn't central, due to the extra metal for the bolt securing threads on the drive-side and the clearance for the chainset.
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Mick F. Cornwall
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

The more I think about this, the more the idea is a good one.

Trim the frame, and fit standard bushes ................. forever.
Buy ten pairs from Simply Bearings and you'll be fine for up to 40,000miles. I'll never ride that far on Moulton .......... so buy five pairs at £3.80 each which will give me 20,000miles.

Yes, the frame will need to be modified a tiny bit, but it's easy I reckon.

What's not to like?
Mick F. Cornwall
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

You'll need to check you don't run out of insertion depth, if the frame tube isn't reamed to 3/4" all the way through.
fastpedaller
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Re: Moulton TSR rear pivot

Post by fastpedaller »

Could the hard pin be 'extended using a small washer?
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

That would spread the "ears" of the rear triangle, if you could get it in at all.
fastpedaller
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Re: Moulton TSR rear pivot

Post by fastpedaller »

Oh yes, of course - please forgive (forget) - I had a 'senior' moment!
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

Keep them coming...I've made several "impossible" things work with a bit of lateral thinking!
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

I'm out riding the beast this morning for a few hours, but tomorrow (weather permitting) I take the bike outside in the sunshine and strip it down. Do a bit of maintenance on the front suspension, and then remove the rear triangle.

Then, I'll pump grease in and allow the bushes to come out, then remove spindle and the grease nipple, clean out all the grease, and inspect the tube to see if it's possible (with ease) to reduce the length of it. I'll check the internal surface and diameter at the same time.

If I achieve nothing else, the bike will have had some TLC, and I will know if my idea is possible or not.
Mick F. Cornwall
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

Mick F wrote: 13 Apr 2021, 10:48am 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.
Stripped out the pivot.
Photos and removal technique at the end of this report.

Measured:
Bushes have a "shaft" of 375thou long - as measured by me and as stated by Simply Bearings.
The internal tube of the frame has narrower bores at either side, obviously 500thou diameter to fit the bushes.
The 500thou "land" inside the tube is 470thou long meaning that there is (470 - 375) 95thou to play with on each side.

Already said that the bush flange thicknesses had been trimmed taking 29thou off. This means that the un-trimmed bushes will go in if the frame tube had 29thou off each side.

Therefore my idea WILL work. All it needs is to get the frame cut down 29thou each side.
Not easy, but it can be done.

How to take out the bushes ..............
1. Remove the rear triangle.
2. Connect a grease-gun to the nipple and pump.
3. One bush will move under the pressure.
4. Pull out the one that's moved using fingers.
5. Remove the grease nipple as it protrudes inside.
6. Withdraw the spindle.
7. Fit a 3/8" drive 1/2" socket to a short extension and insert the socket into the tube to abut the other bush.
8. Tap the extension end firmly with a mallet to drive out the other bush.

Note.
I have a copper washer on my grease nipple because the grease leaks out without it.
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Mick F. Cornwall
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

All this talk of untrimmed bushes reminds me of a film I once saw when (that's enough - mods)
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gazza_d
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Re: Moulton TSR rear pivot

Post by gazza_d »

All joking aside, this is interesting and you wonder why the factory didn't go down this route. I cannot imagine it's to lock into a lucrative parts market as there's simply not the volume.

Although the thought of taking a file or grinder to that tube would strike fear into me in case I got it wrong. Easy to chuck a fiver's worth of bush away and start again. It has to be bang on otherwise you'll have slack and end with wear
rogerzilla
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Re: Moulton TSR rear pivot

Post by rogerzilla »

Mick, was the paint already cleaned off the ends of the tube? I have a feeling mine still has powdercoat on there, which is thick old stuff.

It may be better to determine how much clearance you need for a location (or sliding) fit, and work to that. Forget what the factory did.
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Mick F
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Re: Moulton TSR rear pivot

Post by Mick F »

I'd never looked specifically at the ends of the tube in the past. I imagined they would have paint on them, but no, there's no sign of paint at all.

Never looked before today, but no paint and no sign of paint. I looked, because the subject was raised up thread.
All back together now.

As for removing 29thou (which is 0.74mm) accurately and parallel with the other side, I'm thinking about it. It could need a workshop milling machine to get it spot on .......... but how accurate does it have to be?
From what I saw today, the sleeve is only a tiny bit protruding from the bush surfaces. How little (or much) can the system handle? So long as the sleeve protrudes, how much tolerance would there be?

Possibly, when Pashley/Moulton designed this, they planned on getting the frame tube in the right ball-park and knew that skimming bushes to suit their sizing would have been easier and cheaper than a complete re-design of the bare frame.

It was a cock-up in my humble opinion.
Mick F. Cornwall
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gazza_d
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Re: Moulton TSR rear pivot

Post by gazza_d »

I've read previously in the Moulton club instructions for servicing the rear suspension http://www.moultonbuzz.com/resources/te ... /apb-rear/ that the spacing and dimensions are key. It basically needs to be able to pivot, but not swing. If you have access to a milling machine then that maybe the best approach as the ends will need to be faced to be vertical too.
5. Using a soft-faced hammer, knock the pivot sleeve into place. It can be a tight fit. The pivot sleeve should protrude a small amount either side of the bushes when pushed into place. This may not be visible to the naked eye. Test for pivot bush protrusion by placing two straight edges against the bush. If a little movement sideways of the bush is possible before the straight edges touch the phosphor bronze bushes, there is sufficient protrusion. If not, remove the phosphor bronze bushes as described in 4 above, clean some paint from the edges of the pivot housing and reinsert the bushes as described above. Recheck for sufficient protrusion.
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Re: Moulton TSR rear pivot

Post by jb »

rogerzilla wrote: 15 Apr 2021, 2:07pm All this talk of untrimmed bushes reminds me of a film I once saw when (that's enough - mods)
Confessions in the topiary class?
Cheers
J Bro
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