I don't know what it is about the BSA B25, but I love 'em, warts and all! The first B25 Starfire was introduced in 1968, an illogical prefix as it was an update on the C25, itself an evolution of the C15. The C25 was much more short-lived than the C15, the former lasting only from 1967 to 1968, whilst the C15 was initially introduced as the Star well back in the midst of time (1958).
The model actually goes back further than this, to pretty horrible things like the C10. The Star was bad enough and set the pace for future models. Designed as a very basic commuter, if the engine was ever used in anger the main bearings disintegrated in short order, and not much later the top end would give up the ghost. If you really wanted to pay a lot of money for a really terrible motorcycle you could buy a 1962 C15SS, laughably called the Sport Star, which, in typical British manner featured a tuned engine with the same crank as the C15!
The chassis on the C15 models was most certainly in the commuter camp, pretty horrendous things used to happen if you tried to do more than 50mph. It wasn't until the C25 Barracuda became available in 1967 that a decent set of forks and proper TLS brake were fitted to the 250 singles (although it is not a difficult job to fit these later items to earlier machines). The C25 featured lots of minor mods to its engine as well as a beefed up gearbox, the latter almost as famous as the crank for giving trouble in the C15 range.
The C25 was a reasonable bike up to about 60mph, beyond that its single cylinder OHV motor churned out enough vibes to make the contact breakers fall apart, but often not before they had had a chance to alter the timing sufficiently to burn a hole in the piston. The main bearings managed about 20,000 miles under mild use, less than half that when the throttle was wound on relentlessly. I have put 75mph on the clock of one of these beasts and lived to tell the tale! Handling was okay if you were young enough to take the stiff suspension.
Whilst I would consider spending a hundred notes on a C25, it's the B25 that really gets my blood flowing. The B25 was named after the successful trials bike, the 441cc B44, sharing with it many components as well as 12 volt electrics, albeit of a fairly basic kind. In fact, I have found the electrical system gives more problems than the engine on these bikes.
I actually had one bike catch fire when vibes caused the main ignition wiring to fall apart, short out on the frame, ignite some surface petrol which quickly spread to the GRP petrol tank (later bikes have a much safer steel tank, which should be fitted to earlier bikes as soon as possible). One moment I was happily thumping down the road, the next I had a fireball between my knees. I sort of stepped off the machine, watching in anguish as it rolled off the road, cartwheeling down a slope, bits falling off. There was nothing left worth lugging home.
The vibes really do get inside the electrical components. Even the alternator has been known to fall apart! Lights blow with tiresome regularity and the joker who fitted an ammeter in the headlamp must have been out of his mind.....it takes less than a 1000 miles to have the needle flicking back and forth madly. The rider is left sitting there wondering whether it's just the ammeter that's on the way out or if the whole electrical system is about to burn out. It makes the GS Suzuki series look like they have first class electrical systems!
My next machine was fitted with clip-ons and a full race Gander and Gray tuning kit. Top speed increased from a gut churning 85mph to an eyeball popping 105mph. With not much more than 300lbs to shift it was easily the fastest, nastiest 250 in my area. Engine life of this machine deserves a whole article to itself. I never got away with more than 4500 miles before a full, and I mean full, engine rebuild was needed. It once only lasted 2500 miles before the crankshaft started rumbling.
But it was fun, at the time I felt the ease with which the motor could be stripped fully justified its finicky nature. I only tired of the machine when the gearbox locked solid at 80mph! I was spat off the machine and scraped off the tarmac by the local ambulance crew. The bike was another write off with little left that could be salvaged. I went off motorcycles for a couple of years after that but was soon pulled back by a 1969 example in prime, low mileage condition. I just could not resist the sleek lines of the shining Starfire.
Even with the B25, the main bearings are dubious, you'd be a very lucky man to do more than 30,000 miles without replacing them. They rumble quite obviously when on the way out, getting noisier as the revs increase. Vibration also goes wild when the mains are worn, but as a good bike also vibrates fiercely at some revs you will need to have some experience of the breed to suss out a decent 'un.
Although my machine was low mileage it soon started rumbling. This wasn't down to throttle abuse but the fact that the oil had not been changed. Judging by its consistency it had been there since new. The B25 has a Japanese like need for 1000 mile oil changes, the neglect of such even more violent and nasty in its manifestation than on small Hondas and the like. Oil leaks were also present on new bikes, let alone the ancient hacks that these machines have become. The crankcase covers are especially noticeable in the way they allow large quantities of oil out of the engine.
After rebuilding my engine from the crankcase up it did about 15000 miles with few serious problems, then needed a repeat dose of tender loving care. The B25 does seem to have been designed in a way that encourages all its bolts to come undone. Loctite works after a fashion, but the engine mounting bolts come undone regardless of how much of the stuff is spread on their threads - a daily chore is tightening up these bolts. Neglect leads to the engine jumping about, taking great chunks out of the crankcase mounting lugs.
Another vibration inspired problem is the petrol tank falling apart - the two halves are not welded very well, tending to gradually allow ever increasing amounts of petrol to seep through the seams. The first I knew about it was a wet crutch. Not wanting to have a repeat performance of the earlier's machine passable imitation of a fireball, I bought a new tank. It took only 7000 miles for the same thing to happen again. Feeling brave I pointed the welding torch in the direction of the old tank, which solved the problem.
By way of contrast, the chassis gives few problems, is still up their with the best in terms of chuckability and stability and hasn't even cracked up under the fierce vibes it receives. The engine growls out its 25 horses in no uncertain terms, revving all the way to 8500rpm with little reluctance or plodding along in top gear at 30mph with no hesitation. Once used to the vibes the Starfire really is a delight to ride on any road other than motorways.
The swinging arm has grease nipples which needed pumping full of the thickest grease available every time the engine oil is changed. Apart from that it's just a case of keeping the tyres in more than 3mm of tread. Bald tyres make the bike do really lurid speed wobbles and it is also dead easy to throw down the road in the wet in such a state of neglect! Tyre wear is over 15000 miles, fuel consumption in the 75 to 85mpg range and chains do about 10,000 miles. If it wasn't for the yearly engine rebuilds it would be an exceptionally cheap machine to run.
I now own three machines that are rideable, one of which is really immaculate, the other two are useful hacks. I've got the bits to make another six, but have no intention of doing so, they are just my ultra cheap source of spares. I've never paid more than a 100 notes for any one machine. They used to be ridiculously cheap, but even now it's possible to buy a very rough one for about a hundred quid.
I can't really explain why I like them so much. I'll be the first to admit that the engine is far from reliable, but I derive a huge kick from riding my machines, chatting with other BSA owners and, I guess, going against the grain. If any readers want to swap engine parts for chassis components I'll be very happy to hear from you (write via the UMG), as I have an excess of the latter, including some straight frames. I aim to have enough spares to keep going well into the next century!
Derrick Davies
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I bought a B25S Starfire (BSA not BSI as the lady in the insurance suggested, sweet young thing that she was). I travelled four hours up the motorway in a car I thought might break down any minute to see it. It was beautiful, the white paint gleamed, the chrome sparkled, the shape of the engine.......so, veiling my enthusiasm I started to go over the bike more carefully.
The forks shook about; slack headraces at the very least, but the bike was only £140 and then the nice man gave me £10 back towards petrol, which I thought rather generous.
Back home, I found I couldn't start it. Tried kicking it over, no good; it just lay on its side and grinned up at me. Seriously though, lunging on the kickstart either before compression or after did nothing. The seller had started it with ease but it took me ages. One of the perils of owning a highly tuned OHV single that BSA hadn't fully developed.
The sparkling chrome, however, was simply not there - the front rim was painted over rust and the rest was pitted quite badly. I consoled myself by patting the spare petrol tank and stripped the front end. Then I took a closer look and tried to work out what else I'd need to do. I knew it needed a new loom (excuse me whilst I wax lyrical about the simplicity of the wiring, no indicators, no block connectors, not a microcomputer in sight). I needed a new rear tyre as the old one had cracked sidewalls even though it had plenty of tread. Everyone called the front one a Slidemaster which wasn't very reassuring. I decided on new tubes and a Roadrunner which has behaved impeccably. Also, a new battery - I was told that batteries made in Britain were not available - and bulbs. The headraces were knackered and the fork bushes and seals had seen better days.
Once back in one lump I had a test ride and discovered it needed a new alternator. The new rotor had six magnets and was larger than before and the stator had nine coils, but the bike had only a two phase rectifier which may or may not burn out some of the coils. Still, it worked brilliantly, or so it seemed to me as I've always had 6V electrics in the past.
It came with a TLS front drum which led me to wonder why they ever fitted discs. Once set up properly it was ace. I bought a 12V coil, some nice drop bars and some Smoothrite for the frame.
After the test ride it seemed to be knocking and a strip revealed a 23 thou undersize regrind on the crank instead of 20 thou to suit the shells, so I had it taken down to 30 thou and fitted new shells. It needed loads of helicoils, too. A new gear lever and shaft completed the engine rebuild after a pattern part didn't work and the reclaimed BSA part was a little short. I painted the spare tank quickly, saving the old one for a decent respray, and took it for an MOT. Joy of joys, it passed and soon I was running in the new big end.
Eventually, I reached the magic 500 miles and eased open the throttle. Down the local bypass it was that fateful day, 60mph came up, then 80mph, then the ton and still it pulled. Seriously, though, it did do about 70mph and all on a 14 tooth gearbox sprocket (16 being stock). The wrecked and pot-holed roads showed just how these old Brits got their reputation for fine handling - it would hold its line over rough going but part of the reason for such accuracy was taut suspension that not even age and mileage had done much to diminish. Still, comfort apart, I was well happy with the way the bike held its line and could be flicked through the curves.
But afterwards a glance revealed oil all over the engine, so new oil seals were ordered and a plastic tube fitted to the gearbox breather. Another thrash and the top speed was down to a ring smashing 60mph flat out with a smoke trail to rival any two stroke - the exhaust valve guide had worked itself completely out of the head after the bottom lip had disintegrated. Luckily, OTJ supplied an oversize guide and I replaced the valves as the stems were both worn. The breather tube solved most of the oil leaks - perhaps I shouldn't have added STP to the gearbox.
Two days later, the gearbox refused to change out of fourth and I had to ride straight back from town cancelling my visit to the shops. The strip revealed a broken camplate spring, which I suppose must've been original and I had to fit Cords rings as OTJ didn't do ordinary +60 rings. These Cords do give excellent compression after a quick blast to bed them in, though a bit more expensive.
A local engineering firm charged £11 to ream the valve guide hole and it turned out it was oversize at the top. I also added a decompression plate under the cylinder to bring compression ratio down from 10:1 to about 9:1 as it was pinking on four star unless I added octane booster. Longer pushrods to match and I copied an idea from Classic Maniacs and turned the front, left-hand crankcase timing plug into a breather. I didn't go further and fit oversize valves and have the cam ground down to lower overlap and increase lift, but if anyone has I'd love to know how it performs.
The original design of the bike was quite good, let down by the usual lack of attention to detail and production quality. Even brand new these bikes were rumoured to self destruct rapidly, so the problems with my used and abused example are pretty common stuff, although all the engineering skills already exist to turn the B25 into a reliable device; indeed, the bike was uprated and updated in CCM form and many superior bits from this engine can be employed if you've got the money to spend!
Now, I can't say I've been completely faithful while all this has been going on. I've dreamt of a Morini 350, I've lusted after a YPVS and lately a CBX has seemed like a good idea. The B25's kickstart was becoming a bit lazy in returning so I ordered a new spring - as the suppliers are having some more made it didn't arrive in time for the rebuild, so rather than wait I put the bike back together. Sure enough, three kicks and it broke; temporary replacement, a bungee cord. Patience is a virtue.
Tips: A 100 link rear chain just fits with a 17 tooth gearbox sprocket (47 rear) and that's after using the chain for 400 miles - I'll have to prestretch the next one, but the bigger gearbox sprocket gives the bike a much better feel and a higher top speed - there's little point revving the balls off the engine as it either breaks or causes bodily harm from the vibes, when anyway it pumps out torque at reasonable revs. Why are Reynolds chains so difficult to buy, the other stuff isn't hardened?
Torque Seal secures the alternator rotor if used on a third of the shaft; too much and the puller damages the rotor. Using a Jubilee clip stops the puller slipping off and also makes a reasonable ring compressor. Don't reuse paper gaskets on oil filled cases unless you lust after major oil leaks. Silicone rubber makes for oil tight engines and Blue Hylomar stops petrol tank tap threads leaking. Pet Seal is good for temporary repairs to tanks. Oh, don't knife edge the bottom of the piston or the skirt doesn't get lubricated properly.
The bike has now cost about £650 including a metal petrol tank (as the painstakingly resprayed one leaked), so as cheap transport it has failed. But it handles beautifully, if rather firm in the springing, looks great in Hammerite blue and black, and only needs a front rim, a five plate clutch hub and a tacho to finish it off. Unless I find that CBX first.
Jim Marston