I suppose I'd better start a thread on this build. I aquired a B31 rolling chassis, I scoured the internet for an engine and sourced a reasonable unit, so I have the start of yet another project. 1955ish BSA B31. 350 big fin (iron) engine bored out to 400cc using Triumph T140 piston. Gold star headlight brackets, mudguards, chainguard, clocks, rearsets etc I am modifying a Suzuki GS750 clutch to suit the BSA gearbox. carb will be a Mikuni TM32. I hope to get it to the other side of 100mph with a little work. The std B31 was good for about 70-75mph. When funds permit a full fat, fire breathing gold star engine will be installed...........................
Cylinder head went on a little holiday to Roy Shearwood (R S Motorcycles). Exhaust valve seat suitable for unleaded, Inlet ported to 32mm (from 1"), Gold star valves I have brazed the lugs onto the frame for the rearsets, repaired the brake pedal stop which had broken off and repaired the missing tank mount. I have bought a set of needle roller bearings for the swing arm pivot to replace the BSA rubber bushes. I will turn up some bronze spacers to take the end thrust with O rings to keep the water out Yesterday I cleaned my crank cases, Mr muscle oven cleaner works brilliantly on Villiers cases, It turns BSA cases dull grey and blotchy. I am informed its due to the silicone content of the aluminium. Oh well into the blast cabinet and a good boil in soapy water and rinse. Then into the oven for bearing fitting
It appears that if I use anything hotter than Gold Star touring cams I risk breaking my cam followers. So I have ordered a set of Gold Star cam followers which have a thicker stem. I am converting to eccentric rocker shaft instead of the (heavy) lock nuts on the cam followers. The main bearings are now fitted and the crank is temporarily in the cases, I have sorted the shims and spacer to get it central.
The frame etc is back from Triple S in lovely shiny black, yokes fitted with taper roller bearings and I have converted the swing arm to needle roller pivot bearings from the original rubber bushes (yes seriously). The rear end is being kept in check by Ikon (formerly Koni) shocks
There is significant wear on my gearbox layshaft where it runs in the bronze bushes, I was thinking of machining the shaft and making some undersized bushes. However, I have been informed I am due a tax refund (5 digit), so I have bitten the bullet and ordered a Nova 5 speed cluster. The layshaft runs in needle roller bearings and the gearbox itself is a more modern "dog ring" type Nova
I machined a steel sprocket blank to mate up with the Suzuki outer basket, then bored it to take the bearing. On the final cut I got some chatter, as a result instead of the bearing being a press fit I can throw it in from t'other side of the workshop, first cock up. So I bored the sprocket out to 70mm and made a bearing holder a nice snug fit in the sprocket. The bearing holder has a flange which is fixed to the sprocket with 6 M5 cap head screws, on the other side of the sprocket is a bearing retaining plate held on by 6 M5 countersunk screws.
All that is required now is to reduce the basket and drum down from 8 friction / 7 plain plates down to 7 / 6 to clear the outer case. I also made a bracket which bolts to the bottom gearbox bolt to support a GPZ500 starter motor, A bearing housing in the rear of the primary chaincase supports a shaft with a sprocket behind. Inside the chaincase is a sprocket with a pair of sprag clutches driving another sprocket bolted to the crank sprocket. Then the second cock up, the GPZ500 engine runs BACKWARDS!!! I drilled the starter body to relocate the power connection stud 90 degrees round and rotated the brush gear 90 degrees. The motor now rotates forwards. The state of play now is :- 1955 BSA B31 overbored to 400cc DB32 goldstar valves Pearson crank with Carillo rod ABSAF high volume oil pump ABSAF vernier gold star cams Morgo oil filter Nova 5 speed gearbox Powerdynamo electronic magdyno Suzuki GS850 clutch Electric start
Yes the crank dropped straight in. I had to make the spacer between the two bearings on the drive side. The timing side shaft is 25mm dia instead of 7/8" dia. The drive side shaft is 30mm/25mm diameter instead of 25mm. Phil supplied the bearings, the timing side roller bearing is a sleeved metric bearing