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


eharris

Website 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

Well Known and Active Website User
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

Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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

Website User
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)?
 

vin998

Well Known and Active Website User
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

Well Known and Active Website User
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
 

eharris

Website User
VOC Member
Wow, that level of detail is amazing, thanks!

I do have the thinner 09067 bearings, with the 0.1" spacer.

One side (that had E80 relitavely flush with the end of F39) there was 30thou of shim. On the side (where E80 over hung the end of F39) there is a grand total of 70thou of shim (5+30+35).

Measuring F39/2, it's 4.38" between shoulders and about 6.7" overall (latter with a rule as I only have 6" calipers) and anyway it's a nice fit between FT5 and G50.

So I need to investigate these bearings, as well as the cones in the RFM. I am quite sure that they haven't been out in 60 years, and are not going to want to come.
 

Robert Watson

Well Known and Active Website User
VOC Member
Not to be too pedantic but the cups are the ones in the RFM and the cones are the ones with the rollers in them......
 

eharris

Website User
VOC Member
On further reflection and having looked up RFM pivot bearings in KTB, I see that Stevens seems to be quite casual about using worn bearings in the RFM pivot. So I might just leave the cups (thank you Robert!) alone, reset the preload as per KTB and then concentrate on getting the E80 nuts flush with the end of F39/2. Given I have the alloy 0.1" outer spacer on these narrow bearings I will probably concentrate on shaving a few thou off that.
 

A_HRD

Well Known and Active Website User
VOC Member
Or someone with a lathe can shave a few thou off the E80 nuts - if, as you say, they are overhanging proud of the hollow spindle...
Peter B
 

eharris

Website User
VOC Member
After some time with the micrometer I measured up the nuts, spacers etc (I checked the two E80 off the battery tray and a couple of spare H59/1 that I found) and juggled the shims about until I have a few thou of preload on the bearing but now only 10thou overhang on the end of F39/2 (at one end, the other end is flush).

The biggest problem I'm having here is that the shims are both controlling the pre-load on the bearings and making sure that the nuts come out flush with the ends of F39/2. Where as in the wheels, there's enough flexibility in the RFM/Forks to cope with the variation in length as you shim the bearings.
 

vibrac

Well Known and Active Website User
VOC Member
No dont worry about the cups I have in the past taken a few thou off the inner face of the hollow spindle because you can insert shims there as well
For wheels when a 5 thou shim in out out results in no forward and back movement if in or just a smigin when out then leave I it out, on the RFM I would leave it in then add shims on outside of bearings with the dust washers to even out nuts
 

clevtrev

Well Known and Active Website User
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:
View attachment 28343
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.
View attachment 28344
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:
View attachment 28345


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
How about, they might be that way to improve the chain line ?
 

davidd

Well Known and Active Website User
VOC Member
That could be possible. Because I usually fabricate the plates and spacers on an RFM and transmission, I build everything to the chain line in the dry build from previous measurements. Because I turn the spacers for both sides of the RFM (if there is no F103 in place) I generally do not fool around with the hollow axle itself. I build around it.
DSCN3203.jpg
With no F103 on the left I can shift the chain line easily because there is a spacer on both sides. With an F103, the width of the hollow axle would be the best way to align the rear sprocket to the left.

David
 

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