Cycling UK Forum

ferrit worrier wrote:Mick try a look at

https://simplybearings.co.uk/shop/Beari ... index.html
Might be a lot cheaper , chances are the bush is worn far more than the pivot shaft?

Malc

On the button.

nice detective work. BTW if the sleeve is ductile enough it should be possible to 'resize it' by using a tapered mandrel.

cheers

Brucey wrote:nice detective work.

I had nothing to loose. I figured it was worth a punt.

BTW if the sleeve is ductile enough it should be possible to 'resize it' by using a tapered mandrel.

Yes, no doubt. Give it good squeeze eh?

Moulton back together again. May have it out for a spin tomorrow.

Hi,
Because of the nature of the beast is that the parts will wear oval........?
So reassembly always a bit iffy..............just like diagnosing ball joints.

Whats the verdict on the material?

I would think the wear in the bushes and sleeve would have been up and down (suspension) as well as side-to-side (pedalling forces) plus back and forth (propulsion and braking).

The hollow sleeve is absolutely non-mgnetic and is some sort of stainless steel.

Mick F wrote:Moulton back together again. May have it out for a spin tomorrow.

I had a ride.
20odd miles with some fierce hills.
The pivot survived perfectly, and still no play.

This is the way forward with TSR rear suspension pivots.
Catch it early, and just replace the bushes. The sleeve would be ok.

Next job for me, is to buy a pair of Simply Bearings bushes and fit them to see how they go. Give me a week or two and I'll get onto it.

Had a quick chat with my mate down at the Rising Sun yesterday evening.

Two things:

He uses Simply Bearings quite a bit and has done for years, and he can't get the bushes any cheaper than from SB.
He reckons they must have a huge warehouse!

He says that the stainless "tube" is a stock item and comes in long lengths. He also says that they are made in Imperial sizes and the people who put the kit together must just part short lengths off and finish them off to accurate diameter and length.

Basically, the spare parts kit is a rip-off.

I've just ordered a pair of bushes for both the APB ( 1/2" internal, 5/8" external, 1" long) and a pair for the TSR (based on Mick's measurements) from Simply Bearings. 12 quid for both pairs

I'll update the thread once fitted and tested

gazza_d wrote:I'll update the thread once fitted and tested

Excellent!

It'll be a week or more before I can get anything further done for mine, and I too will be updating the thread about it.

Hi,
You could also take the old sleeve to an engineering works and get it hardness tested, then test any new parts you might fit.
It would be interesting.............

As has been pointed out up-thread Moulton 'fixed' the TSR pivot bearing problem by increasing the bearing surface on the SST frame by '150%'. Looking at the close-up frame pictures on the PortaPedal web site (https://portapedalbike.com/catalog/moulton-sst-alfine-11-airforce-blue/)it doesn't look like the frame has been altered in any way (either the 'ears' or the pivot bracket at the bottom of the seat tube). This leads me to suspect they increased the surface area by speccing different bearings, pivot tube and bolt. There would appear to be enough meat on the bronze bushings to increase the internal diameter, although my maths isn't good enough to work out if there's enough for 150%. Anyway, the point of all this is perhaps there's SST spec bushings, tube and bolt that would be a direct fit on the TSR frame, mitigating the need for such regular inspection/maintenance? This of course assumes the increased bearing surface area is a fix. Perhaps someone with more than my failed O-level maths can work out what internal diameter a 150% increase would be and see if there's a match on the Simply Bearings web site? Mick F's 'Rising Sun' mate can then fashion a batch of tubes to match, get the right bolt and happy days!?

On a related note, I wondered if musical instrument oil, regularly applied, would be easier than wrestling with grease guns, No 14 here looks promising: https://www.thomann.de/gb/hetman_grease_and_oil.html

My engineering knowledge is limited, but I thought that oil filled bronze bushes as described above, were mainly intended for use in high speed applications like electric motors where radial loads are low and further lubrication is not necessary. Would a solid bronze or brass bush be better especially if it was machined with internal grooves to allow grease to reach the bearing surfaces? Such a bearing may have to be specially made on a lathe and it maybe that given the low cost of of the oil filled type bushes the idea is simply a non starter on economic grounds!

Igauk: if the length of a cylinder remains fixed, its surface area excluding its ends varies with its diameter. So a 150% increase in surface area would simply require a 150% bigger diameter.

Does that help? I’m not familiar with the parts in question.

Well the new bushes have arrived although the APB rear triangle isn't back from framebuilder yet.
A visual check and measuring with the digital calipers shows the APB bush seems identical to the Moulton bushes. The stainless steel sleeve fits like a glove and there is just the tiniest hint of play. There is noticeably more play in the bushes I removed.

Visually the TSR bush seems to have wider flanges to what is fitted but they're still in the bike.
The bush is 12.67mm long.
External diameter thats inserted in frame is 19mm.
Internal diameter is 12.6mm
Flange diameter is 25.38mm
Flange thickness is 3.15mm
It's be useful if someone with a set of TSR bushes on the bench could check the measurements

cromo wrote:My engineering knowledge is limited, but I thought that oil filled bronze bushes as described above, were mainly intended for use in high speed applications like electric motors where radial loads are low and further lubrication is not necessary.....

I have seen similar sintered bronze bushes used in upper wishbone suspension pivots on cars. If lubed (just once) and sealed adequately, such bushes were found to have worn ~0.004" in ~160000 miles. I concluded that if lubed better (eg with a grease nipple), they would last even longer.

Sintered bushes work in two ways; first there is always lubricant to hand and second any wear particles have somewhere to escape to, in which they don't cause any further wear between close-fitting parts. Solid bushings lack both characteristics.

Regarding the bushings that are '150% the size of TSR ones' or '150% larger' then someone may be playing fat and loose with sizes; the former would simply be x1.5 the bushing area and the latter would be x2.5 the bushing area.

The TSR bushes are 1/2" bore and 1/2" long; simply upgrading to 5/8" bore, 5/8" long would give a much increased bushing area.

cheers