1951 Bianchi Stelvio - Chain and Brake Bits

Published on 14 August 2023 at 19:21
1951 bianchi stelvio primary drive chain and clutch
fabricating parts for a 1951 bianchi stelvio motorcycle
rear brake adjuster for a 1951 bianchi stelvio motorcycle
replacement seat for my 1951 bianchi stelvio motorcycle

Yesterday was a good day - got loads of bits from the auto jumble - some were what I had gone there for, some were impulse buys, some were speculative. All in all a pretty good haul including a knurling tool for my lathe, something that I needed if I was going to make a reproduction rear brake adjuster.

today, however, was the complete opposite of yesterday with every job turning in to a disaster and everything I touched turning to rat shit in double quick time. Most of my pain has been centered around the chain, I have now discovered what my problem is but it's only half fixed.

On the Stelvio the front sprocket sits behind the clutch housing, you can't see it, you can only just about feel it if you contort your body in the correct way. to get at it properly you need to remove the clutch and then remove a steel plate, it's a very odd design. Anyway, I had tried everything to avoid such shenanigans but when I came to fit the chain it just would not go on properly. I had a rush of blood to the head and decided the clutch had to come off - huge mistake. Turns out there are loads of roller bearings in there that fall on the floor as soon as you withdraw the clutch basket. It also turns out there is a locking nut that requires a special tool to undo it, which is of course unobtainable and would be very difficult to make without getting the thing off first - for which you need the special tool.

I spent the next 3 hours attempting to reassemble the clutch, I had to stick all the rollers to the inner race with grease and then carefully fit the basket with the outer race without disturbing any of the rollers. it was an absolute nightmare. I thought I had it once but the sun came out, heated up the grease and one by one all the rollers fell back off. some dielectric stuff did the job in the end, the relief when the basket clicked back in to place was enormous.


I discovered what my initial problem was - the chain I had purchased was a 122 link 420 sized chain to match the rear sprocket. The front sprocket, however, is for a 428 chain. The rollers on a 420 are 1/4 inch wide, on a 428 they are 5/16ths of an inch so a 420 chain will not fit over a 428 size sprocket. I have concluded that the large sprocket on the rear wheel is not the correct one for the bike, it should be 428 ie 5/16 inch wide not, the 1/4 inch of the one on there. 

Another new chain is on order, it will work but I will have to look for a sprocket of the right thickness to make things right.

I did get the adjuster made, it looks pretty good, the brake pull rod is now complete and awaiting fitting.

OH - before I forget, I found a different seat, it's nowhere near as wide as the one on there, which is great but it's a bit stubby at the front so I'm not totally sure I will fit it yet. It was cheap so it's no big deal if I have to sell it on. Maybe something better will turn up, I am still not certain as to exactly what the original looked like.


Tomorrow is a day away from the workshop, my mate has invited me to watch his Grandson testing out a new race car and to be there as pit crew in case anything goes wrong. My mate Russ will be there as the main man but I will support him as and when needed. I have seen video and the lad looks well quick, his Dad - Danny Watts - teaches f1 drivers and has had one hell of a racing career so no doubt will pass on some of his wisdom. His Mum is none other than Fiona Watts / Leggate of BTCC fame so a lot rests on his young shoulders. Definitely looks like he has the talent though, I reckon he will go far.

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