I became the owner of two of these machines (actually two frames with nearly enough parts to make one complete bike) after agreeing to buy them for £150. After building the first bike up over a period of about four months, I took the bike for its MOT which it passed with no problems. I started using the B25 to travel to work every day after not having a bike for twenty years. After the first few days I began to wonder where all the vibration was coming from. Merely riding at 50mph produced an effect similar to sitting on a road drill.
As soon as I could I wound her open to an indicated 75mph, the motor seems to like revving, beneath 6000rpm it is lumpy, rough and gutless. I recently lowered the gearing slightly by fitting a rear sprocket with two extra teeth, to try to get the power coming in at 50mph instead of 60mph and was partially successful.
After I started riding it every day things started happening (don’t they always), like bolts coming undone allowing various essential bits to fall off at inconvenient times. There are three possible remedies buy a decent Jap bike, put an extra nut on bolts or use Loctite (this stuff was designed with B25 owners in mind). Anyway, this will stop you losing silencers, number plates and all those little things that make motorcycling so much more bearable. This isn’t to say that the B25 is unreliable, it isn’t but it can’t be ridden willy-nilly without being looked at once a week to see what surprises it’s about to spring on you.
The thing that I recall from the sixties is seeing one of the B25s with a pool of oil underneath it and comparing it with the spotless Hondas, thinking what chance have our lot got if a brand new machine can’t even hold oil the owner told me he wished he'd bought a Honda Dream. It is possible to make the B25 oil tight, but care has to be taken, all joint faces must be absolutely flat and silicone grease and much patience applied. Perhaps BSA were competing for the Royal Oilfield title?
One thing that really enrages me is the fact that some, er, person used BSF threads in the timing and drive side cases. By the time the bike has passed through a few butcher’s hands the threads will be stripped. BSA probably ordered the wrong bolts, the SS B25 models reverted to the usual coarser threads.
If you buy a BSA B25 ignore whatever the previous owner told you and strip down the motor unless you’re desperate to ride the bike (mind you, if buying a B25 isn’t desperate then Christ knows what is) there are three things which need looking at. If the early type of con-rod is fitted then throw it away and fit the SS type - natch this won’t fit unless you machine the flywheel to clear the big-end eye or you can file the rod down, but don’t leave any stress points. If you thrash the motor with the original con-rod it will break sooner or later and unless you're very lucky it will smash the crankcase, barrel, piston and bend the valves and pushrods.
Also check the end float of the crank - you’ll almost certainly find that there is far too much play - however carefully you shim up the crank the bearings will move on the shaft and destroy the shim. The cure is to fit a shim behind the bearing outer track in the crankcase - if this is a loose fit then it must be Loctited. Take the trouble to shim the gearbox shafts properly, so what if it does take an hour or two, it will save the dogs wearing so that you lose 2nd or 3rd gear at a later date.
If you do all this, you'll find you'll have a pretty good bike which will cruise at 60-70mph, handles pretty decently and is quite a good looker. However, there is one more moan - the B25 is not and never will be a Classic British Bike, assuming that such a thing exists - to those dealers who advertise Starfires as such I would say only one thing, if you can find anyone willing to pay £500 to £600 for one of these machines please send me their telephone number. Most bikers I know would expect 5 bikes for £500.
Running the B25 is financially rewarding for scrooges, mine does 70-80mpg, uses no oil, whilst tyres last so long they sometimes perish (I am using Avon ribbed front and SM II rear). Most parts are cheap and readily available new or second hand. My complete engine rebuild after my con-rod broke cost £40.
Another good dodge, if you aren’t performance mad, is to use a lower compression piston (e.g. Fleetstar) as this makes the engine much more docile and pleasant for town use. All in all, I can’t say I love my B25 madly but it does everything I ask of it. I travel the A180 most days and it has only let me down once. It’s a working hack, plain and simple, but only after I’d eradicated the bugs. The only drawback is having people in Ford Fiascos overtaking as if I was standing still, but I have nearly finished my Ariel Huntmaster, so then the boot will be on the other foot (or words to that effect).
I suppose that if BSA had done their homework properly they could really have made the motorcycling world sit up and take notice, because the B25 could really have been a decent 250 at a time when the Japs had not completely taken over the world. But everything was let down by the poxy power unit - the bike handles really well unlike some of the Jap 250s that had a distinct hinged in the middle feel; the brakes are pretty decent, just drums but not without their uses and the later TLS was well up to the power.
Vibration is the main complaint. I have read many of the old road tests and not one of them mentioned how bad it was. Now I don’t notice the vibes very much except on a long run when it’s nice to stop for a rest - I suppose that it just goes to show that however bad something is you can get used to it and cease to notice it.
Some of this may read like a horror story but if you attend to the things mentioned you will be rewarded with total reliability.
Len Seeley