The second rebuild pt1
Unfortunately I don’t have any photos of the state she was in when I got her back, but she was certainly somewhat neglected. All of the stainless hoses had been swapped for plain rubber items, the mirrors were gone and various bits were about to fall off. I did manage to put a few miles on the bike, but it was while going up Rye Hill in Sussex, with my wife as pillion, that I realised why I'd sold it in the first place. The poor old girls meagre 34bhp engine just wasn't up to it.
It was then that I decided I would start over again. This time the bike would be more 'understated' and I had in my mind I to build something that looked more like a factory special.
The need for a more powerful later type engine, with good spares availability, led me to acquiring a T140 motor.
The pokier engine would require better brakes. Through the grapevine heard the Suzuki GS disc fork set up was a good option. Suzuki GS fork and wheel parts are two a penny and many early Suzuki models shared the same parts. I ended up using a GS550 hub and GS750 forks but with the slightly shorter GS550 stanchions. This meant the fork length was similar to the stock BSA A10.
The biggest problem was caused by the choice of an engine with a left foot gear change. I like the single sided rod operated BSA QD rear brake so I would have to fabricate some kind of cross over shaft.
It must have taken me hours of checking, measuring and template cutting to work out the rear engine plate design and also the position of the crossover shaft, which would be mounted to and run through the plates themselves. It was very tight. I got some steel tube and a 3/4" die and threaded the ends. Terry Mead made up the cross over shaft to go through the tube. The shaft was brazed to a brake pivot bracket from a Yamaha XJ750. The T140 brake pedal was reshaped and shortened and a nicer XJ750 'footplate' fitted to the end. The whole set up looks great and works very well.
Terry also modified the Suzuki fork yokes which were too long for the BSA headstock so the steering stem was shortened and a solid sleeve inserted and brazed in for added strength. Top hat inserts were made for the taper bearings to fit the slimmer steering stem as well. Pleasingly, the finished yokes don't look a million miles away from standard BSA items.
To my disappointment the very expensive Converter engine plates didn't all fit. The rear outer pair were miles out. I drew some new ones up on the computer and got a local engineering firm to quote on getting some laser cut. They quoted a staggering £150+ VAT for the pair. On Terry's advice I used a company in Staplehurst in Kent called Sciss. They precision cut a pair of plates for a grand total of £30! At that price it didn't matter if I got the drawings wrong, which funnily enough I did! But I was so impressed that I also got them to water cut the headlamp brackets and instrument mounts and other one-off parts.
The engine build proved to be fairly straight forward with only a couple of hiccups.
The crank was lightened and balanced to the rods and pistons to a balance factor of 85% by Chris Applebee. A three piece timing side roller bearing is fitted to cope with the half race T120 exhaust cam. Cylinder head work was done by Len at the Cylinderhead Shop, having been gas flowed and fitted with 1mm larger inlet valves. A 34mm Mikuni carburettor is fitted along with a custom head steady and carb steady bracket.
One thing I learned was to use original parts wherever possible.
Initially I went for some smart CNC pushrod tubes, but when
I bolted the head down and tried to set the tappets I noticed that a valve on each side would not fully close. It turned out that the internal lip at the bottom of the pushrod tube was too narrow and the SRM pushrods were binding on the inner face of the tube, thus the valve wouldn't close.
The engine went into the frame reasonably easily, although certain bolts had to be inserted in a particular order. I was very pleased as to how the engine sits within the BSA frame.
Modified Suzuki GS fork yokes
Early Katana front caliper
Suzuki GS forks, hub & brake
Rocket Gold Star mudguard & stays
Crossover shaft to allow use of BSA excellent single sided QD brake with left hand Triumph gearchange
RHS rear engine plate showing threaded crossover shaft tube (centre of picture)
LHS rear engine plate showing crossover shaft tube retaining nut
Triumph unit engine sits nicely in the BSA pre-unit frame
Suzuki fork yokes look similar to BSA items
A number of bespoke parts were water cut like this instrument console
Smart battery box re-used from previous build
.... CNC alloy tube v original. Too much crush on oil seal meant it kept popping out. Narrow inner diameter meant pushrod would stick and valve not fully close