Unlike me others (eg 'rjb') went ahead and actually made and fitted such things and made it work. {I will post a link to the thread in which this is discussed, when I've found it https://forum.cyclinguk.org/viewtopic.php?f=5&t=61819&hilit=Suzue.]
IIRC the recipe used was to take an imperial sized 'R6' bearing (3/8" bore, 7/8" OD) and fit it to a modified freewheel, with a shimano extractor spline (or similar) . The last few splines in the freewheel body were ground down to accept the bearing. Provided you have a deep freewheel extractor tool, or you have not ground off too much from the spline this still leaves enough of the spline to allow the freewheel to be removed, and of course the 3/8" bore on the bearing is a perfect fit on the intended hub axle, being a Suzue tandem hub.
I've gone a slightly different route, given that freewheels vary and QR hubs use 10mm axles.
I bought a packet of R6 sized bearings (I have hubs with 9mm, 3/8" and 10mm axles that need outrigger bearings) and I've done the following (in this example for a 10x1mm threaded Maillard/Normandy axle).
a) Ground the bore of the bearing to match the axle
b) Ground the OD of the bearing to match each freewheel
c) cobbled together revised spacers and locknuts for the hub.
Photos below;
- The modified axle with the outrigger bearing is in the foreground
- The modified axle with the outrigger bearing is shown in position inside the 'mock-up' freewheel body centre
In the photos above the axle with the outrigger bearing is for 120mm OLN, 5s. The other maillard axle is a longer 126mm one, showing that there is greater need with ~6s/7s spacing, and bags of room for threaded spacers etc. Also shown is the 7s shimano freewheel body centre used for mockup. If I get brave enough I may try with an 8s freewheel.
The bearing bore was ground out to ~9.8mm using a dremel tool, at which point it became a snug fit on the chosen axle. The OD was ground down to about 22.0mm using an angle grinder, to match the intended freewheel. In both cases the bearing was mounted such that the part that was being ground could spin freely; the grindstone/wheel was varied in approach angle so that the bearing was spinning but there was still not pure rolling contact (which might result in no material removal).
The spacers either side of the bearing might have needed a relief on them, but in fact flat-faced spacers didn't drag on the seal. The RH cone is locked via a separate locknut behind the bearing, so that it can be as tight as it needs to be without overly clamping the bearing. Belt and braces means the RH cone is threadlocked too. The RH outer locknut is a shimano one, which is made of harder steel than Maillard ones (so may not deform under QR loading) and has a heavier texture on it (so ought to grip the inside of the horizontal dropouts better).
This was all made easier by the fact that lots of hubs use 10x1mm threading, so there were lots of spacers, locknuts etc in my bits box that I might have used. However this is not so much the case with 10x 26tpi threaded campagnolo axles; the outrigger bearing may have to be placed further leftwards if (say) campag Nuovo record locknuts are used (because they are thicker) and if a threaded locknut/spacer for the cone is required, it may have to be manufactured from an old cone or something.
cheers
