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Front wheel speedo drive unit

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honda-san:
So, anyone know how to tell what model a front wheel drive unit is correct for?

Specifically the drive gearbox for the 350-4, 500-4, 750-4 all look the same and can be fitted to any of these bikes. BUT, there are three different part numbers - 350-4 and 400-4 use the same "317" middle part number item. 500-4 uses a "323" middle number item, and CB750 uses a "300" middle number item. That I can see there are no features / markings on these that enable easy model  identification. Most likely the difference will be the internal gear ratio, which is not much help when trying to identify which bike a particular unit came from.

I have at least half a a dozen of these, not all of which are identified as the bike they originated from. It would be possible to to work out the gear ratios by spinning a front wheel an exact number of turns and measuring the corresponding number of rotations of the output tang (that the cable connects to), but actually not so easy to do with the necessary accuracy given the likely subtle differences between ratios.

Any good ideas appreciated!

Orcade-Ian:
Hi Chris,
You've got my inquisitive side motivated!  With the wheel still in and the drive unit connected to a cable, it would be very easy to revolve the wheel 1 complete revolution - with a suitable pointer/marker fitted.  With degree disc mounted on the squared cable end, you could then count the number of complete and partial turns for that one revolution.  Yes, you would have to mount all of your unidentified units to do a full check.  I only have 350, 400 and 550 fours to check but if owners of all models are willing to help, you could end up with a definitive set of results, perhaps for Ash's Dropbox.

Ian

Oddjob:
Is there no physical difference in size? You’d imagine there would be if the internal gears are different sizes. I can’t remember seeing any identifying marks on my 500/550 speedo drives and I took them to pieces.

Johnwebley:
I seem to remember someone saying the front hub on the 500 and 750 are the same

Do they both run 19" tyres?



Sent from my SM-A546E using Tapatalk

Bryanj:
Yes and speedo drives are same

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