What is it? Make, model, year.

[Jantar]

The attached photo is of a bike that belonged to a mate's father in the 1950s. My mate wants to buy one just like it, but the question is: What is it?

My guess is a BSA, possibly a B31, but the lack of suspension and the sprung seat suggests it could be earlier.

Any ideas?

[bugjuice]

bikes have sure come a long way..

[Fishy]

Maybe a Norton 16H? Indiana Jones style bike!.

[MSTRS:Me]

Distinctive looks of a BSA, but not a B31. Note - pictured bike is a sidevalve. Where's Motu when you need him??

[MSTRS:Me]

On a second look, is that a Matchless 'M' on the tank?

[Ixion]

BSA M20 or M21 - M21 I think.

Here's an earlier one . This on is late 40's , OP's was early 50's I'd guess

[Motu]

Never far away when in need laddie...

That's an M20,or M21...500cc & 600cc respectively.Same running gear as the B31/33.I'd say 1950 as it has telescopic forks and a rigid frame,earlier ones were girder,then in 51 came the plunger frame.But the ''M'' bikes were Military and were kinda out of phase.The M20/21 ran into the 60s as a sidecar hauler.

I had a girder fork M20,1948 I think,but never ran it as that - I got the motor together first,then when a big end went in my B31/33 I couldn't resist and slotted it in place - there it stayed until I stripped the bike down and sold off the parts.The bike is actualy a 1954 A10,the 650 Goldflash,but the 650 threw a rod and I couldn't be bothered rebuilding it when I had a shed full of B31s,so out of a wreck swing arm B31 for the plates and oil pump kink I made my A10 into a B31...it was a flash bike sometimes as everything was chrome...but you can't tell that eh?

[Zebedee]

On a second look, ...

I'm no expert when it comes to these things, but ... http://www.vintagebike.co.uk/Bike%20...ess%201946.htm

[Jantar]

Many thanks Motu. It looks like you're right on. The bike in question ended up in the Clutha River when the owner failed to take a bend only a few Kms downstream from ScumDog territory. The bike itself was never recovered.

[Motu]

How about a story on my M20 motor,you won't find many people who have gone indepth with these.

I stripped the motor down and the big end seemed reasonable,so it was a go to put it together.I replaced the mains,ball races are cheap,two on the drive side,and the M20 had double timing side bearings too,unlike the B series OHV valve motors,this thing was heavy duty alright.But that made the motor wider,and required some persuasion to fit in the frame.

The piston was the big issue,as it had none,and the bore was 80 thou over and rooted.So I rang John Gurney who had a shop on the Nth Shore,and I knew he had bought a couple of containers in of old stock from a bike shop in England.I asked if he had an M20 piston - ''What oversize?'' he said.I nearly fell over! I hadn't expected to find a piston on my first phone call.He had a 20 thou and a 60 thou over,so I took the brand new 20 over piston.The barrel had to be double sleeved to get back to this size.I had to get new valve guides made as well,they were flogged out in the barrel and ended up very big in OD.The valves were salvagable,and faces and seats just needed a clean up.

There were no gaskets available,but these motors used very few.The biggest problem was a head gasket - I made some myself out of sheet aluminium,but it wasn't too successful...so I asked my mother if she could help.I don't think many bikers would go to their mother for help fixing their bike eh? She worked all her life in engineering shops and I told her I wanted some sheet copper,the best she could get me was some 1/8 plate.So I made a head gasket out of that,and used it for most of the time I ran the bike.Later I had some proper gaskets made,a couple in solid,and a couple copper asbestos - of course soon as I had them made Bill Russell cleaned out his shop and I picked up half a doz full gasket sets.He always denied he had any BSA single parts.

I fitted it into the frame and made the exhaust pipe - 1 3/4 pipe,I made it out of segments...there are 17 welds in the pipe,and I thought it looked better and more purposefull than a smooth curve.I ran several carbs - 626 Concentric,28mm Mikuni,even a small SU once,but the old Type 6 worked best,although the float chamber got in the way.On a B31 it is on the inside,but with an M20 the mag/dyno gets in the way,so it sits outside.The genuine M20 carb has the body horizontal to clear the mag,but I've never seen one.

It was a fun bike,a welcome change from the go fast stuff,and I rode all over the country on it,although only as far south as Nelson.A real solid hack I took some time in killing....I loved it,plenty of good memories....

[TLDV8]

Maybe a Norton 16H? Indiana Jones style bike!.

I'm still kicking myself for not picking a 16H up when they were still resonably priced..the last one i saw was around $8000

[Edbear]

Had a B31 as my first bike. Loved the sound through the gutted Dunstall megaphone, but it wasn't too fast or reliable and I sold it for $250! (I think in '76?) Last one I saw for sale was $4500!!! Damn!:slap:

[m99dws]

My Father-in-law has a BSA 350 Goldstar which, although is a bugger to start, goes really well!

[Motu]

A Goldstar was always a dream,I had several opportunaties to get one (kick my self for not getting that Goldstar scrambler!) but the price was too high,always has been no matter what era you want to talk about.But you can make a B31 go half as good,and that's a bit of fun.

[Paul in NZ]

Lot's of M20's out there giving good service to their owners.

The poms made vast amounts of the things for WW2 and the British army used them for DR work well after the war. Like 'Army' Indians, you could still purchase brand new ones well into the 60's from 'stores' and even today some specialists have brand new parts purchased from the british govt.

They are (by all accounts) a tough old beast and revered in british bike circles. Personally, I'd love one for plonk plonk plonking about the neighbourhood but then I like Moto Guzzis so that accounts for bugger all..

They do come up for sale in the UK fairly regularly (ie they are not at all uncommon) and while there was a civilian version, the vast majority of M20's were civilianised ex WD machines. With a great shortage of personal transport after the war, both dealers and individuals would buy anything that moved and press it into service as family transport. Hence the whole giant sidecar thing and a role ideal for an old flathead 500cc single.

Unfortunately, prices have risen for these beasts. There are effectively 3 markets for them, the everyday rider market, the classic toy market and the ex military machine market all desire these excellent bikes. Demand outstrips supplies and the days of the cheap old M20 has gone!

Interestingly, the Matchless 350 was probably a much better military bike as it had telescopic forks and a OHV engine. It was apparently much sought after by the DR's. However, the army was not convinced by all this tricky overhead valve and suspension stuff and specified sidevalves after the war for a standard issue contract which Triumph won with the 500cc twin, the TRW... A bastardised speed twiin with rigid frame that was used long after swing arms became the norm...