FT: Frame (Twin) Fit of RFM between FT5 and G50

eharris

Well Known and Active Forum User
VOC Member
I am having some difficulty with the fit of the RFM between the two plates FT5 and G50. The issue is that the pivot of the RFM seems to be longer than the gap between the plates and so when I fit it in, the gearbox plate G50 isn't flat any more. With the distortion of G50, the gearchange becomes stiff. Specifically the lever itself, I can change gear with the indicator ok, so presumably the internal pivot and cover bearing have gone out of line. It frees up if I loosen the cover.

I can't see a way that I could make the RFM pivot assembly narrower, as it's all constrained by the fit of the taper bearings in the RFM pivot.
 

chankly bore

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Non-VOC Member
Er, if it isn't the pivot axle itself F39/2 that's too long then it's all to do with the type of bearings in the RFM. Do the E80 nuts extend over the ends of the axle? The standard H22 (SKF numbers 09074/09196) has a cup 11/16" wide and a cone .848" wide The inner and outer grease shields F42 and F42/1 should be 1/16" thickness. Some Korean War era machines were fitted with narrower bearings H22/1 (09067/09195), cone 3/4" wide, cup 9/16" wide. There were spacers 1/8" under the cup and .100" outside the cone to compensate. Are you sure a wide bearing hasn't been fitted with a narrower bearing's spacer sitting in the dark unexplored declivities of the pivot casting? Has anyone out there got the correct length of F39/2?
 

eharris

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Thanks for those thoughts. I'll take it all apart again and measure carefully. It's unlikely that it's a whole 1/8" too wide, as it's would just never have fitted between the plates.

There's a significant possibility I put it back together wrong last time!
 

stu spalding

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You could try measuring F39/2 and check it against a drawing held by the Spares Co. I got caught out by an F40/2 on a friend's rebuild. There is an awful lot of badly made rubbish still kicking about out there including stuff that was "rescued" from the scrap bin at the Vincent works. I've come across a couple of badly machined C3 shoe carriers that would never have made it past inspection. Cheers, Stu.
 

chankly bore

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Obvious next questions, is David's part an unmolested original or does anyone have one such? Is the Spares Co. dimension wrong? Other remote possibility G5 and/or G50 plates too thick. Answers on a postcard, please. This is how we improve the quality of our parts, folks.
 

eharris

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VOC Member
Thanks for that feedback.

Initial investigation so far:
One of the E80 nuts 'overhangs' the end of F39/2 and with the kickstart cover done up tight (previous assembly was without the KS cover) it doesn't want to fit between FT5 and G50. Without the overhang (left the dust cover off) FT39 fits nicely.

One bearing is shimmed out off the shoulder. I need to check to what thickness.

My FT5 is new, but I have checked its thickness with the old one and they are the same (1/4") to within a few thou

I now need to do some measuring and checking of the bearing numbers (thank you Chankly).

As a slight aside, the "F39/2" suggests that there may have been an "F39" and "F39/1". Does anyone know if there was, and if so how they differed (or perhaps I have just misunderstood the part numbering)?
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Moderator
F39 was the part number for the pivot axle on series A machines and is not interchangeable with post war machines as the whole pivot design was different. A lot of part numbers were carried over from the series A's but with a /1 etc added when the part was changed dimensionally or redesigned.

As for F39/1 I don't know where that was used if at all.

I would guess that there is a mixup with the bearings being used as you can get wide and narrow outers and inners and in the hand they can appear to fit if mixed up.
 

davidd

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VOC Member
I don't think that my part is molested, but it is a used original. I have copied it several times in aluminum, but most of my builds are not stock, so it is difficult to compare.

Having measured many hollow axles, I don't think that they are built to the drawing except in the most critical areas. Some have undercuts at the shoulder, some do not. The shoulders themselves are various widths (although the distance between the shoulders is more accurate. The center diameters vary on most. They all seem to work well.

If you buy one at a jumble it is difficult to know which position it is destined for if the seller is not certain:
DSCN3615.jpg

All of the above are stock. There are two more for the front stand pivots, but they are easily distinguished.

The easy ones to pick out of the bunch are the metric hollow axles. They have "step downs" from the bearing pad, which is .786" or 20mm to the stock brake plate hole of .75". It is very obvious on the rear axle at the bottom and less obvious (but identifiable) on the second axle from the top, which is metric. The RFM pivot is the middle hollow axle.

The imperial bearings, narrow or wide, use the same hollow axle. As a result, the narrow bearing has to be positioned in a way so the hollow axle works with the spacing of the narrow bearings widened out to fit the wide bearing hollow axle. As Chankly mentioned, two spacers are needed: one under the race at 1/8" width to compensate for the narrow race, and one under, or in between the brake plate and the bearing cone to compensate for the narrow cone.
DSCN3644.jpg

I could not find a cone easily, but the important items are the spacers, which may be in a box of bits, but remain unrecognized.

Narrow:
67 & 95 Narrow.PNG


Wide:
74 & 96 Timkens Wide.PNG


I would wonder if the E80 nuts are at different positions on each side because the shims were not split between the two sides?

David
 
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