1956 BSA B31 Scrambler Rebuild – Part II

When you’re trying to rebuild something which is a little different to the norm, finding exactly the right part can stop you dead in your tracks. As Phillip Rashleigh has discovered…

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So I’d got myself a project bike and had sourced most of the off-road items needed to make a B31 into a scrambles special. What else did I need to find?

A ZB34 head and barrel topped the list. Why? I could just have used the iron ones that came with the bike — but the bike was once fitted with a ZB34 top end (so I am told) and… well… it would be nice to fit one again. This is where the heartache begins. I found the head quite easily which led me into a false sense of security. Locating the barrel proved a little more difficult — in fact — a LOT more difficult. It made me I realise how lucky I was to find the head. However I have decide to push on with the project in the hope that a barrel will turn up at some point.

So onto buying and building. I started by building what I had to then see what was missing, and then move on to buying the big lumps to see what else I needed. This process stared with the tool box to match the oil tank, and alloy rear guard and then by chance I found a 7-inch front hub with wheel and tyre.

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(Great little story that goes with this. A good friend and I had set out to find a classic motorcycle emporium just over the river in Cornwall. We got a little lost and decided to ask for directions [not very manly, I will agree], so the next house we passed with a chap in the garden we decided to stop and find out where we went wrong. We walked up to the chap, past the Messerschmitt bubblecar — should have been a clue — and asked for directions to the classic bike emporium.

He retorted ‘Why are you looking for them?’ I said I was looking for parts for an old Brit bike I had acquired, the chap asked more questions about what bike it is and the like and then said he might able to help with the front hub. To be honest I was doubtful until I followed him into his shed…

Not the right barrel, sadly.Once in the shed I noticed about five pre-war motorbikes and a post-war BSA twin in gold metallic paint. The chap said he thought he had the part I needed in his garage, and in the double garage were a couple of outfits; vintage, classic and modern and a nice Velo single used for continental touring with the classic Craven panniers and top box.

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And up in the roof there were a few more bikes in bits along with about 20 wheels — one of which was the 7-inch drum I was looking for.

A good result for a Sunday drive, I think you will agree!)

Back at my humble garage I put in the front wheel and, for a laugh, I tried to pump up the tyre – it held 30psi and did so until I cut the rim off the hub five months later…

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Now for a bit of eBaying. I found an inner and outer primary chain case, timing side case, 8-inch front hub, swinging arm, and I also found an A65 rear hub and drum which suited my needs better as the sprocket can be changed, which will allow me to play with the gearing when I get the bike running.

Fitting the A65 rear sprocket and brake drum was an interesting experience and required machining off a spigot and getting a bush made. I have since found out this is a common conversion and I didn’t go about in the ‘acknowledged’ manner. Ho hum…

Along the way I have collected a sidestand (centrestands are for road bikes!) and a few nuts and bolts to fix the thing together. So now I have something that looks like a bike and the wife is impressed to say the least. She is less impressed when I tell her that it’s only a rough build to see if I have all the parts.

So there I am one with bike which looks like a BSA B31 with high bars and a knobbly back wheel… I am still missing a few bits, however; most importantly the ZB34 barrel! Any information on how to get hold of these items will be greatly received.

BSA B31 Stuff on eBay.co.uk

Can you help Phillip find the right barrel? If so, please email him ASAP at phillip.
[email protected]

I'd leave the tank that colour, personally.

Looks nearly finished to me…

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