Wheelchair stem bearing kit spec ?

Following the temporary removal and in-situ (i.e. no chance to see any markings) lubrication of the front stem and castor, the actual job to replace them seems quite straightforward. Except ...
The kit number is "1510219", but I have a feeling that the two bearings in it could be purchased for less than the $35 (i.e. at least £50) which pops up when googlging.
I have every piece of publicly available literature about the product, but nothing in any more details.
So I thought I'd tap the hive mind of uk.d-i-y ...
(What's the groupthink on "caster"/"castor" ? You can tell I've been on US sites this afternoon).
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On 17/12/2017 16:04, Jethro_uk wrote:

Not enough information.
If you get the bearings out, you only have to measure the OD, the ID, and the thickness and that will give you a very good start on finding commercial replacements. The dimensions are almost certainly millimetre integers. It is possible that you have angular contact ball bearings, or roller bearings, but they are almost certainly ISO-series deep groove ball bearings.
There are *usually* some markings on the races to help you identify them.
It's Castor in the UK, Caster in the States. Just as "Berkeley" is "Bark" in the UK and "Burk" in the US.
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wrote:

Wotesaid. Tables with dimensions and their bearing numbers available by google for free, with many options: seals rubber or metal, one side or both, pre-greased or dry, loose/tight/regular, stainless or steel, (none of which matters much in a wheelchair).
Probably just get what fits and is available in shop near you, wrapped in waxed paper (1-2 € or pounds apiece, going from ebay prices).
Thomas Prufer
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On Sun, 17 Dec 2017 20:33:06 +0000, newshound wrote:

The problem with that is there is a slight risk that attempting it will leave the assembly unable to be reassembled which in the absence of a spare wheelchair is not an option. Otherwise I would have done it when I was greasing them.
The moment I notice that the manufacturers are coy about specs, I know it's because their price is going to be a *lot* more than the actual component cost, which is why I was hoping someone had encountered this before.
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wrote:

The plans look like there is a bolt/screw that goes through a retaining washer into the "Front Pin". So, I'd say: remove bolt and washer, pull "Front Wheels -- Fork" from the "Front Pin", and the bearings could just drop out, or be held with a benign C-clip.
If they need to be pressed out (and in), proceed with caution...
It might suffice to flip the wheelchair over and approximately measure them -- it's probably something straightforward like ID 9 mm, OD 26 mm, 8mm thick.
Thomas Prufer
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On 18/12/2017 14:23, Thomas Prufer wrote:

This is a third party supplier, looks like it *might* be a non-standard imperial bearing
https://www.southwestmedical.com/Wheelchair-Parts/Wheelchair-Bearings/Invacare-Caster-Fork-Stem-Bearings-Pk4/20448p
Do you have any more details of the wheelchair apart from the bearing set number?
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On Mon, 18 Dec 2017 14:35:19 +0000, newshound wrote:

Invacare-Caster-Fork-Stem-Bearings-Pk4/20448p

Yes, I noticed that US sites were much more loaded with data. However that leads to a metric/imperial situation ...
The wheelchair is a Kuschall compact. But I am willing to bet a pound to a penny that the stem bearing kits are universal ... if only I knew the actual specs.
With Xmas upon us, it's dropping to a low priority. Hopefully the grease I put in will give us a few more months. In the meantime, the whole chair- needs thing should be re-assessed anyway.
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On Mon, 18 Dec 2017 14:41:02 -0000 (UTC)

We've got a Kuschall somewhere - if I can get to it I'll pop the bearings out and measure them. (Measuring is preferable to just reading the size printed on the side, I've encountered bearings that weren't what they said they were.)
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On Tue, 19 Dec 2017 13:42:11 +0000, Rob Morley wrote:

If you could, I'd be grateful (virtual beer grateful :) )
TBH I'm of an opposite mind, and prefer numbers to measurements, although I accept that does rather put you at the mercy of the catalogue/manual.
I know for a fact that the Invacare/Kuschall parts list has an error, and has done since I told them 2 years ago. I have a feeling I am not on their Xmas card list .....
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On Tue, 19 Dec 2017 14:32:55 +0000, Jethro_uk wrote:

Remember BSA. They're probably regarded by the company as their "Shining xample of just how far you can under-engineer a product before the customers actually sit up and take notice". Sadly these days, customers need considerably more prodding before they can even be arsed to sit up and take notice.
--
Johnny B Good

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On Tue, 19 Dec 2017 13:42:11 +0000, Rob Morley wrote:

That was a trick used by BSA Motorcycles. They ordered bearings from the manufacturers, specifying that they be supplied with 10 thou ground off the inner or outer (or both) journals to match the custom sized shafts or housings (or both) in their engines so as to monopolise the spare parts trade. They also used sub-standard materials in their engines which is why any attempt to "Tune for performance" usually ended in "Tears Before Bedtime".
Confirmation of this attitude, "Use the cheapest materials and see what we can get away with before it breaks", happened when the crank pin snapped on my 13 month from brand new Bantam D14 purchased in January 1968. Despite being a month out of warranty, BSA did provide a warranty replacement but when I had to buy a replacement head a year or two later due to the original overheating and distorting beyond effective repair, I noticed it was the version used in the later production run where they'd dropped the compression ratio from 10:1 down to 9.5:1 in order to prevent the crank pins from failing.
All of this "Just in Time" automated production technology today is being used to create under-engineered product after the philosophy pioneered by BSA over half a century earlier, including the business of making otherwise standard parts like bearings just ever so slightly non- standard as you're very likely to discover in things like low volume items such as wheelchairs and mobility scooters.
--
Johnny B Good

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On Tue, 19 Dec 2017 16:18:35 GMT

The bearing story I liked concerned Norton, who had a problem with main bearings failing on their early 750CC engines (which were IIRC basically a bored and stroked version of the 500CC pre-unit twin). Having determined this was due to the bigger top end causing excessive flex in the crank and/or crankcase, they fitted roller bearings with barrel- shaped rather than cylindrical rollers which could cope with the flex, rather than making the crank/crankcase fit for purpose.
Chronic under-investment, probably.
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On Sat, 23 Dec 2017 02:06:43 +0000, Rob Morley wrote:

That problem was endemic to most of British industry pre-WW2 through to its demise in the 80s and 90s (by the end of the 90s there was SFA left of "British Industry" to be under-invested in).
That anecdote about flexing crankshafts and roller bearings reminds me of the great mistake made by BSA when they took over production of Triumph Motorcycles around 1970. Presumably, they must have thought replacing the drive side crank ball race bearing with a roller bearing was "A Good Thing" to counter the extra stress from the primary chain sprocket side thrust.
Unfortunately, they'd forgotten about the crankshaft flexing at very high revs (6000 to 7500 rpm) being a far more serious issue with a roller bearing than it was with a ball race which could tolerate this abuse far better. This resulted in the need to replace the drive side bearing every 14000 miles. The timing side bearing didn't suffer but would still be replaced during such a major service since it would be stupid not to shell out the tiny extra bit of cash as a precautionary measure when it would add so little extra time to take the opportunity to do so.
What makes this mistake even more egregious is the fact that at high rpms, the forces resulting from a 70% balance factor typically used on the crank of a single or parallel twin engine make the side thrust from the primary chain sprocket totally insignificant. The Triumph Motorcycle company's engineers had good reason to stick with ball race crank shaft bearings.
Unfortunately, circumstances intervened at the 28000 mile mark and I never did get round to fitting the pair of ball race bearings I'd intended to fit on the second major engine overhaul so I never did get a chance to prove my theory about BSA's mistake.
Although the welded twin downtube, "oil in the spine" frame vastly improved the poor handling inherent in the original Triumph frames and was the only good thing BSA ever did for the design, you can add to their list of "wrong doing" the classic choice of cheap substandard materials in the clutch centre hub where they replaced case hardened steel with cast iron which meant that instead of having to file the notches in the outer drum clutch plate splines every 10 to 15 thousand miles, you got to do this job on the centre hub splines every 5000 miles as well - original Triumph clutch centre hubs *never* needed such work doing *ever*.
TBH, I don't believe BSA Motorcycles ever employed a qualified design engineer. They probably did what the Japanese were accused of, copying, and even then, unlike the Japs, did so in an extremely incompetent way. If the "design" wasn't quite up to the job, they just detuned the engine until it stopped falling apart.
--
Johnny B Good

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On Mon, 18 Dec 2017 15:23:53 +0100, Thomas Prufer
If it's this,
<https://www.southwestmedical.com/replacement-parts/tilite/tilite-zra/front-casters-forks/caster-pin-locks/caster-pinlocks-for-bearing-fork
the parts are
SPACER .750" OD X .500" ID X .125" INTERNAL RETAINING RING 1.125" BEARING 1/2"ID X 1-1/8"OD X 5/16"
Bearing is 1.70€ in Treznal.
"Retaining ring" means it'll probably come quietly.
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On 18/12/2017 14:37, Thomas Prufer wrote:

Well done!
Wheelchair makers seem to go for some bizarre bearings, e.g. these mixed imperial/metric, also one with a bore of 12.5 mm. God knows what the widths are.
http://www.epc-wheelchairs.co.uk/wheels-wheel-parts/rear-wheels/wheel-bearings?original_route=wheels-wheel-parts%2Frear-wheels%2Fwheel-bearings
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On Monday, 18 December 2017 14:40:50 UTC, newshound wrote:

ront-casters-forks/caster-pin-locks/caster-pinlocks-for-bearing-fork>


rings?original_route=wheels-wheel-parts%2Frear-wheels%2Fwheel-bearings
probably to ensure their dealers get heavily paid every time it needs fixin g
NT
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On Mon, 18 Dec 2017 15:37:16 +0100, Thomas Prufer

Argh, hit send too soon.
"ball bearing r8 zz"
for the shielded one. If it has a flange or ring, it's FR8 ZZ.
7 quid for 10 from China, 1,65€ here: <http://shop-rc.causemann.de/Miniatur-Kugellager-R8-ZZ-127x2857x793-R-8-ZZ
tp
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On Mon, 18 Dec 2017 15:47:59 +0100, Thomas Prufer wrote:

front-casters-forks/caster-pin-locks/caster-pinlocks-for-bearing-fork>

ZZ>

many thanks and at those prices (note my suspicion about keeping the spec on the QT also keeping the price high looked right) no harm if it's wrong ...
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On Mon, 18 Dec 2017 15:37:16 +0100, Thomas Prufer wrote:

The assembly has one bearing inside the housing held in with a circlip. This slides over the other bearing which is held on the actual pin of the stem.
However, looking at the parts list/service manual that pin is actually threaded into the block which mounts on the frame.
So with a bit of luck (or to be more accurate, two contra-tightened nuts :) ) I should be able to remove the pin completely making it easy to knock that bearing off.
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