I have been drooling over pictures of classic bikes for years now and the other day I finally bought a bsa b31.
Its a 1948 rigid frame b31 350cc. the bike is complete but it is a non runner and has been sitting outside for years with no sparkplug in it. i have been told that it is a b31 engine but has a b32 crank, does this sound feasable? nothing is siezed up exept the carb slide. so i dont rekon it will need much work. i was wondering if anyone could give me some advice please. i would like to know how to start the engine once i have repaired it. i know about the obvious kickstart but i was told that the timing advance lever on the handlebars has to be set correctly. so how do i know if i have the various levers in the correct place? i was also told that if the advance/retard lever is in the wrong place i might be catapaulted through the shed roof by a backfire, is this true? i would also like to know if the bike is likely to withstand a 3 hr motorway journey every so often, not regularly, just every 2 weeks or so. any help would be great. thank you
Hallo Once you have the bike sorted it should have no real problem on the motorway but I don't think you will enjoy it much. My B31 seems to go forever at speeds of 50-55 mph and will pull 60mph apparantly without problem but it starts to vibrate a bit so I tend not to hold that speed for too long unless I'm in a hurry. I've seen over 70 on the speedo but things are getting a bit hectic by then so you would probably be limited to around 60 on the motorway..being hasseled by lorries etc, not my idea of fun! As to starting, I retard the ignition by around half of the advance/retard lever's travel and from cold fully close the choke, tickle the carb and it starts first or second kick. Retarding the ignition seems to be pretty important for staring without a kick back. I've also set the tickover a little high to rule out stalling when stopped at lights and then retard the ignition to get a nice slow tickover. Hope this helps and have fun.
I had a b31 1947. sold it about 4 years ago. Motor was gone through by expert racing in Hobart Indiana. The bike ran good as all experts motors do. However, I think your expectations of going 65 to 70 on freeways is a little high. Mine was all stock and yeas it would go 50 but man was it ever working. Lots of people with B31's I know just put around on them they really lack power. The 500's and 600 thumpers run pretty good. Yes I know some people really can hot rod a b31 I've seen it too so I know they can be made to go better. Get it running and try it out. P.S. ride it around the block first before you head to the on ramp.
Maxwell; By B32 crank do you mean the flywheels or the whole bottom end ie cases and flywheels? I am not sure that the YB32 bottem was much different from the YB31 unless it was a B32 GS (Gold Star)type that would have different flywheels. From my experience the B31 is very happy if it is not spinning too quickly. The real joy is that pulls very well so that you do not need to keep shifting down as you cruise along at modest speeds but at 70 MPH it would really be out of breath very quickly.
The engine parts that wear out are all easy to find.
Without frequent roadside repairs there is no fun in riding!
Hi Maxwell I have a plunger 1954 model with a sprung saddle fitted after the original seat kept catapulting me skywards over the bumps! Much more comfortable. I was out yesterday with a few mates (BMW R80, Yamaha 600 and Panther 600) and only really had problems keeping up on the hills although our speed on the main roads was no more that 60mph - nice sunday cruising. We covered over 160 miles including forest tracks, A-roads and some interesting steep downhill gravel/stones tracks which had the plunger protesting and me cursing. These are not sporty machines but seem to take pretty much anything in their stride without too much complaining. Remember they were made over 50 years ago as practical affordable transport for getting to work on and I don't think it was expected that they would be used much on motorways especially not those of 50 years later! You can get practically everything you will need quite easily to get the bike up and running. I use C&D Autos in Birmingham although there are lots of other sources. Why not head down to Netley Marsh or Beaulieu on 16-19 September, you'll find lots to keep you amused there. I'm coming over from Germany to lighten my wallet
Maxwell, I've a 1947 rigid B31 that I've just finished restoring. I'd advise:-
50mph is about the most that the bike will comfortably run at
Starting is easy if you have set the timing accurately - start at say half retarded - air valve closed - no throttle (or it will spit back)
Be sure that you know whether cable slack = retarded or advanced - the magneto changes from year to year - mine is anticlock from the driven end (clock from the points end) with advance/retard on the rear of the magneto - hence slack = retarded
Good previous advice - set up to idle a bit fast (for reliability at the lights) - and retard back for an even steady tickover
Sprung seats (rider and pillion) are easily available - as are all other parts - I use Draganfly plus C&D Autos
When I got my bike I just ran it and performance was more than I had expected except it kept throwing the inlet valve cap, although the performace didn't seem to suffer, just rattled like hell. After this had happened a couple of times I thought new valve springs might help and took the head off. Holes around the piston crown suggested taking the barrel off might be a good idea and revealed thet the top piston ring had escaped (lots of pitting on the piston crown as well). Basically the piston was shagged, rebore long overdue, small end bush definitely buggered, valves and guides 'orrible. And it was still going better than I had expected from a 50 year old 350! New piston, rebore, oversized valve guides, new valves, small end bush, lead free inserts etc. cost me another 200 or so quid and gave peace of mind. What I'm trying to say is, even if it runs OK I would suggest stripping it down (a pleasant weekend in the shed with a couple of beers and catching up on the "Archers") to see if there are any horrors lurking inside. The engine is quite simple to work on-even I can manage most stuff myself- so don't be afraid to have a look. Running in afterwards resulted in the piston seizing a couple of times, due to running at constant speed on an A-road, and I still haven't got the carb correctly set up but it now runs sweetly, fist kick starter and I know that at leat the top end isn't going to blow up up on me. I have to say that, although I have only had the bike for a year, it is definitely my favorite as far as the "grin factor" goes. As I write the bike is in the garage, on a trailer, ready to be towed to London on Thursday for a 1000+ mile tour around England. I know I should ride it there from Germany but my old arse would protest at the time in the saddle and I wouldn't be able to bring so much Marmite back with me in the saddle bags as in the car boot.
Just grabbed another beer and realised I had just been babbling on and not answering your post! Ther is no kill switch as such unless someone has fitted an earth wire to the magneto! On the left handlebar under the advance/retard lever there should be a small lever which opens the exhaust valve resulting in loss of compression and the engine dies. If the engine isn't running, and depending on the position of the pistion, this can be difficult to operate if you are trying to fight the valve spring, but when running it is easy to operate. Take off the exhaust rocker cover and see how it works, adjustment is easy but important if you want to avoid a burnt exhaust valve. As far as customisation goes..it's your bike, do whatever pleases you! I'm looking for a piece of sheepskin for my saddle to make it more comfortable on long haüls, it will probably look like **** but then that's my problem!
yea thanks for the advice, i will probably take it to bits to check the piston, i think there are also gaskets that need changing as well, and seals. thats a picture of the bike in its present condition ha ha.
did you notice much of an increase in performance once you changed the piston? i mean in power and stuff
Looks like you ahve some "cosmetic" work to do at least but as long as it runs, what the hell! My bike runs better after the top end work was done but I still have to get the carb tuned properly, she's running too rich and slogs a bit on full throttle. I set it up rich for running in and haven't gotten around to sorting it out..too damn lazy really as with the 276 carb I have to take the tank off to get at the slide/needle etc. It looks like you havee all the important bits on the bike so I would personally check the mechanics first and ride it until the weather gets too cold for comfort and think about making it pretty during the winter months. Keep us posted as to how it progresses.
Max, to be honest if your looking for more than 60mph and reliable motorway transport buy another bike B31's are plodders. The B33's were not alot faster (and its a simple matter of fitting a B33 barrel, Piston and Head if you want the extra cc), you can also fit different cams (Scrambles are the best for road work) and get someone like Phil Pearson to flow the head, put a bigger carb on it etc. Trouble is it will suffer, its an old bike and unless you are Graham Ham its not for blasting up and down motorways on.
I just purchased a 54' B31, and i was wondering if anyone knew the specs and part number for the original carburettor that was on this model. I see it was discussed earlier as an AMAL 276, but does anyone have any further information of this carburettor? thanks for the help.
also, know anything about a Pacco Mikcarb??? thanks.
The fitting of Gold Star touring cams will lift your cruising speed to 60 odd mph. When I start my BB31, Flood carb. put the timing on advance, bring to TDC. Release the compression (using decomp. lever) Then Kick Starts first time every time, even after several weeks rest.