B31 & small BSA bikes

[muskrat]

Well done Bob. Think how many people learnt to ride on one of those.
Cheers

[Bikergrandad]

Hi to all.  Here is one of my bikes I just sold 1957 c12 lovely bike.
               I am just finishing my b31 I will send in a photo. Bob.

[Brian]

Well its not a B31 but this might be of interest, it is a 350c BSA but from 1929, a L29 model.

I'll add a pic of when I bought it and where I am up to with it now. I have a veteran to finish first and then I will restore it.

[KiwiGF]

hi brian, the president of the nz bsaoc has an L27 and may be able to help you if you get stuck.....I can see you have the front guard sorted and I know sourcing one of those caused him much grief!

[Brian]

I searched for a flat tank OHV for years but could never find one I could afford, then I came across this one and it was reasonably close so I bought it.

Both guards are repo, the front one made to suit and the rear a plain blade that I fitted and then made the rack, brackets etc.

The hardest thing to source and then get to fit was the exhaust pipe, its a strange shaped thing but I managed to find one close and then spend hours cutting and shutting it to make it fit.

I have a veteran (1910) Triumph to finish and then I will start on it.

[jachenbach]

Love the pictures. I've always thought BSA singles were beautiful, especially the pre-units. A B33 would be real nice to have, after I get an A10 on the road. Well, I guess I should get  on with the Daytona, Trident and Commando first. So many projects, so little time...............

[olev]

Hey Brian,
Have a look at page 30 in the latest OBA.
It looks like Harry Hinton tore the mudguards off your old beesa and went racing??
cheers

[Rocket Racer]

hi wilko, the project bike came with the xs650 piston and the cylinder has already been bored to match, its been looked at by a local "expert" and there are pros and cons, the yamaha piston is lighter with a shorter skirt and has nice narrow rings, but it has valve cut outs in the wrong place, it looks like it wont need a spacer under the barrel to reduce the compression unlike the triumph piston. Its oem yamaha so hopefully of known good quality.

Its worth a go I think, and as its slightly smaller diameter than the triumph piston the barrel can be rebored later to suit the triumph piston if it doesnt work out.

Given your building a nice light rigid, overboring it isnt really necessary. The swingarm b31's are typically overbored by overweight riders to compensate for the heavy "frame" which better suits the 500/650 and struggles with the stock 350.

Tough little suckers the B series. A stock B31 or B33 (std cams) will run at full throttle all day without complaint. The rigid 350 is a very pretty bike!
Eat less pies and keep it a 350

[muskrat]

I agree RR.
At the races I was often asked "Why so much alloy?" as they were looking at my beer in hand and belly to match.
Cheers

[KiwiGF]

hi Tim, the yam piston makes it about 390cc so its going to be near enough a 400 like those with a triumph piston.......Ive got it built to the point of being able to check the head to piston clearance and there is no need for a spacer under the barrel. It should be all together by next Feb and yes i does look pretty 

The head is away getting the inlet bored to suit the over size 389 carb.

I have the rear hub back with a new sprocket fitted which was a major job for the engineer who does not want to see another rigid style hub any tine soon 

For the reason Muscrat provided I'm not over doing the making it light thing, but it will have alloy guards as they look neat (the oem type steel ones will stay on the shelf).....and I will hopefully eventually figure out how to make tubular mudguard stays that look right!

edit.....added some pics including the yam piston at TDC

[Bikergrandad]

Hi to all. I have just finished the B31 1954. Last week now waiting for a dry day to check the brakes.
             But most probably be March next year, so I will spray soon with ACF-50 on the chrome & wiring
              To keep out the Moisture, out it is very good. Bob.

[muskrat]

Very nice work Bob.
The reflection in the tank chrome doesn't do you justice LOL.
Cheers

[muskrat]

G'day all.
Thought I'd resurrect this topic.
I was asked by a mate about cams for his 49 ZB31 in a later s/a frame. It's got the T140 piston mod. He's after a bit more bottom/mid range. His thoughts were 65-2454 (B34 scrambles 50btdc-80abdc 0.415") inlet and 65-2450 ex (70bbdc-45atdc 0.380").
I've not had much to do with singles and didn't know there were so many cams to choose from.
Any thoughts?
Cheers
ps lucky bugga's also got a ABSAF600 Goldie.

[Rocket Racer]

G'day all.
Thought I'd resurrect this topic.
I was asked by a mate about cams for his 49 ZB31 in a later s/a frame. It's got the T140 piston mod. He's after a bit more bottom/mid range. His thoughts were 65-2454 (B34 scrambles 50btdc-80abdc 0.415") inlet and 65-2450 ex (70bbdc-45atdc 0.380").
I've not had much to do with singles and didn't know there were so many cams to choose from.
Any thoughts?
Cheers
ps lucky bugga's also got a ABSAF600 Goldie.

Muskie,
 trying very hard to bite my tongue on your thread: the goldie book by eddie dow recomends the goldie touring cams for more sparkle. Anything else and you have to watch for coil bind on the higher lift cams.
Personally I'd say the best thing he can do is to sleeve it back to std 350 and put its stock cams in it. The ZB31 is a sweet light flexible and bullet proof wee bike. All a 410 piston and hot cams will do is turn it into a half arsed goldie  .  and he already has one 
All the cams will do is rob the bottom end and give it top end. A stock zb31 (or zb31) can be ridden full throttle all day and the motor will never complain. Tougher than superman although the magnetos its Krytonite.
Great wee bikes. My ZB33 will be with me until I drop. stock cams, stock valves and carb, versatile as.
If he's a big lad and wants more bottom end a B33 motor is probably the go, but please avoid stuffing it up with "go fast" bits. A B33 is sod all faster than a B31. Dont overgear, those bikes can work hard within their original parameters.
Cheers
Tim

[Tomcat]

Great topic, keep it up please guys. That pic of the broken bridge is a pearla Scotty!