B34-2 Rebuild

[Goldnrust]

Hi guys. I've recently bought myself a B34-2 project bike. I've been lurking in the forum for a while, reading other helpful posts and so I thought I might do a bit of a blog as I bring my bike back to life.

Hopefully you'll be able to help me with some tips along the way and also maybe someone else might find it useful to learn from my mistakes along the way!

I'm new to bikes of this era. The oldest bike I've owned or ridden is my '72 Suzuki, but having enjoyed how much more raw and simple that experience was compared to the more modern bikes I've owned, I thought I might like to take that a step further and try an old British single out. I was looking at post war bikes, but then the more research I did, the more I was fascinated with the idea of a 'really' old bike.

I had been looking at bigger, more powerful bikes but when I saw this little B2 come up in need of some love and attention, the heart said 'this is the one'. I liked that it had all the antiquated features I thought would be interesting to experience, like the girder forks, rigid frame and hand change, and with an OHV engine in a much more affordable package than many other bikes with that feature set. It seemed a good way to dip my toe in the water!

The bike clearly needs a lot of work. Initial thoughts of doing a bit of recommissioning and getting out on the road, have predictably instead turned to a full rebuild. I'm not doing a concourse restoration, more of an oily rag rebuild. I want it to be mechanically spot on, but cosmetically will leave the patina and age on the components. This bike has either had quite a few parts swapped about, or it's been assembled from parts, and with no providence I don't think there's any reason to get too hung up on originality. I will try to keep it feeling 'period correct' though.

Attached are a couple of pictures of the bike as it was delivered to me, and yes I did finally get round to cutting the lawn shortly after!

The exhaust is obviously not standard, but stylistically I don't mind it, so it can stay for now. The tank I believe should have been the nickel plated type, with the green inlays? The green it is currently is poorly brush painted, so definitely not original. I'm crossing my fingers for old patinated nickel left under that paint!

The front wheel is wrong, its got a WM2 rim with the wrong spoke lengths as the rim is offset in the forks, or the whole front wheel is from a different bike? I don't mind the wider front rim, but having the front wider than the back could make for strange handling I'm sure. I'll cross that bridge later.

Before worrying about any of that though, my initial concerns are with the frame, engine and gearbox...

[courtney]

This is the one Andy Tiernan had for sale a few months ago, isn't it? I was tempted by this at the time as I'd been looking for one for a while, but found one in the end elsewhere. I remember the bungee cord kickstart return too! I'll be interested to see how you get on.

Despite having one, I've very limited knowledge of them, but if I can help with sending pictures of anything you're not sure of let me know. I've also got a memory stick with pictures of the restoration of mine before I bought it, so there might be something on there that could help too. I've not actually looked yet and the bike is away getting checked over by someone currently.

I don't do facebook, but some of the groups on there can be quite helpful as well as this forum.

I've had a couple of rides on mine and loved it. What area are you? I'm Chichester.

All the best!

[MGI]

Who designed that engine?

[Y13 Alan G]

Best of luck with the rebuild/restoration. By the way BSA used nickle plating up to 1929 and by 1930 bikes were a mixture of nickle and chrome plating (BSA never wasted anything and used up old nickle plate stock) but by 1931 and thereafter all bright parts were chrome plated.

[Goldnrust]

Yes, thats the one @courtney. It's nice to know I wasn't the only one silly enough to be interested in buying it! haha. Thank you for the offer of pictures to help, I may well have to take you up on that at some point. I'm not a Facebook person either, I'd much rather use a forum.

Obviously I'm yet to do anything more than sit on mine and imagine a ride, but I'm excited to see what it's all about!

Can't help you there @MGI! Maybe someone with more BSA knowledge knows? I do know this engine is a bit old fashioned even for the time by still using total loss oiling. Does make it nice and simple though!

That's interesting to know @Y13 Alan G. I had read online about the nickel tanks, but didn't know about the switch to chrome. Shame really, nickel plating has something subtle different about it to chrome that just looks nice.

It was a couple of months ago now that I got the bike, and as I eluded to in the first post I have made a start. It only took one evening pull it all to pieces, but as I did I could see that the rear end of the frame and centre stand were all a bit twisted.

Thankfully, as the rear frame sections are all bolt on it's not as big a deal as a welded together frame might be. With the help of a laser level and a whole lot of measuring, I'm pretty confident I've managed to tweak the frame back into line.

What I did discover is that my bike is fitted with the wrong 'back stays' as the parts manual calls them, or seat stays as I'd call it from my mountain biking days. The B2 should have a piece of flat bar joining the two, whereas mine is tubular. Hopefully the dimensions of what is fitted to mine are similar enough as to not change the geometry of the frame! 

I'm still deciding whether my centre stand, which has had previous repairs and is rust damaged, is worth trying to save or whether I should keep my eyes open for a replacement.

[Goldnrust]

The gearbox was next. As was noticed in the first post, the kick start was being held up with a bungee cord, as the spring was missing.

In my naivety to boxes of this age, I took the box apart looking for a broken spring internally... only to realise that it uses an external spring! Haha, oh well. It gave me chance to check over the innards of the gearbox anyway, most f which look nice and healthy. The kickstart pinion doesn't look great though, possibly as a result, of the missing spring allowing the lever to catch the spinning gearbox at speed? Or maybe it's just normal wear. Either way, the kickstarter was engaging fine before I took the box apart, so I've just left it alone for now.

I found evidence of welding to the gearbox casing, maybe as a result of the same incident that cause the bend in the chain stays at the back of the frame and the need for a replacement back stay do we think? I also spotted another crack which had not been dealt with, so broke the welder out and sorted that out now.

I purchased a kickstart spring from Draganfly, which I knew wasn't quite the right one but the measurements sounded close to the original. Sadly it didn't fit right, so I had to do some modifications. Works fine on the bench, how long it lasts in regular use on the road, we will have to see!

The gearbox is now back together, filled with a fresh charge of Castrol D and ready to go back in the frame, but first I need to look at the engine...

[Steve.S]

A few random thoughts, which may or may not be helpful. It all depends on what you want to do with the B2.
I imagine the gearbox had split because the kickstart stop had become loose a few times over the last 90 years, and the motorcycle had probably fallen over onto the kickstart a few times. The stop does tend to come loose, so keep an eye on it. You should fit a rubber sleeve over it with a steel outer (like a silent bloc bush) otherwise the rubber will only last a few weeks.
I know it's too late now, but mainshaft and layshaft endfloat are critical for a good gearchange. If you ever dismantle the gearbox again, you might want to fit a sealed bearing to reduce oil leaks. One of the problems is that the layshaft is often slightly bent, which makes setting endfloat nearly impossible.
Your kickstart ratchet pinion is very badly worn. I've not seen a worse one, and you may find  that it either slips or jams in use, although the quadrant looks to be in quite good condition. I would try to find a new one as a matter of urgency.
Cam wear on B2's seem to be quite high, so it might be worth checking how far the valves open. I eventually found mine were only opening 1/8".
If you split the flywheels, note there are a pair of con rod thrust washers on the flywheels with chamfers on them. They can be drifted out through holes on the outer faces of the flywheels. They must be fitted with the chamfers in a certain position. The chamfers allow more oil into the big end. Oiling is splash only. There is no feed to the big end. It would be very worthwhile getting hold of a copy of Bruce Main Smiths green book of BSA's 1935 to 1940, in which he shows the position of the chamfers, and many other things.
You will probably find the unbushed little end is badly worn. Alpha Bearings can bore out the eye and fit a thin wall bush if required.
Your petrol tank with the raised ovals, is from a later machine. Yours would have had threaded oil and petrol filler holes and alloy caps. But as long as it doesn't leak.............
The original advance/retard would have been a twistgrip on the left handlebar. The bar would have been slotted to accommodate it.
Replica twist grips are available from Cornucopia in Germany, but they are made up of a lot of parts and are quite expensive. So you may want to fit a lever control for the time being. There would also have been a valve lifter fitted as part of the original clutch lever. These levers turn up on ebay every now and then, but again, they are prohibitively expensive.
I think your backstays may be from a Blue Star Junior, but as long as it all lines up...........
Carburettor settings, Main jet 75, needle jet .106, slide 4/4, needle position 2.
I set my pilgrim pump to 1 drop every 3 or 4 seconds.
Terry's valve springs are part no. VS 22.
The Maglita is a very wonderful instrument. Set points between 0.010" and 0.012" and see which is best for starting. If you're lucky it should produce about 2 Amps unregulated. Your headlamp switch should have an "off" position as a 2A charge on a long run may strain an AGM battery. They don't like it up 'em.
I set my maximum ignition advance to 35 degrees BTDC which seems to give good results. Spark plug gap 0.018" or 0.015 if it gives better starting. I highly recommend checking your valve timing figures against BSA's figures. After all, every little helps.
Finally, I believe the engine would have been designed by a fellow called Harold Briggs, who was BSA's Chief Designer in the '30's  before Val Page took over.
Let us know how you get on.

[Steve.S]

Just to clarify what I wrote about the headlamp switch, it should have a 'C' for charge position, so charging (if any) can be switched on or off.
Re the centre stand, these were notorious for rotting away. You will find that a C10 centre stand (29-4860) will fit, but you will have to drill the stand legs and fit 2 short pegs to act as stops. They often turn up on ebay, and are also available from dealers, but quite expensive.

[Goldnrust]

Thanks for all that information Steve, really helpful!

I'm more than happy to pull my gearbox apart again if it's going to result in a better change Since reading your post I've found service sheet 46 mentions a 0.004" clearance when fitting a new mainsheet or layshaft bush, is that correct?

I could see the kickstart pinion was really badly worn but, as I said, the bike seemed to kick over 'ok' before I took it apart. When I had looked online the part seemed hard to find in good condition and other people said they were using clearly damaged ones. Your post prompted me to have another look though, and I spotted a NOS one on eBay. So have just purchased that and will swap it in when investigating the end float.

The kickstart stop is definitely just a bare metal pin, so will look for something to pad that with!

Regarding the engine, I'm just on the disassembly and investigation stage, so again thank you for all the helpful pointers. What I do know so far is that the big end and little end both have play in them. There big end is just a tiny amount, the small end is more.

I have split the flywheels and I think the big end will be ok with just some new rollers, as I understand it it should have 1 row of 1/4" x 1/2" rollers, mine had 2 rows of 1/4" x 1/4" rollers currently and they are worn and measuring 0.2480-0.2485" diameter. I test fitted some new standard size rollers and it felt much better. The big end bearing surface inside the con rod doesn't look marvellous, but then it's 90 years old? I don't know if this light pitting/marking is disastrous or not. I can't feel it with a finger nail or anything and it feels smooth when assembled. I think it's worth a shot to just assemble it and see how it goes personally. Picture attached, happy to be corrected!

Thank you for the notes of the thrust washers, I can see mine have a reasonable step worn into them, so I should look into replacing them. There did appear to be quite a lot of side to side movement in the big end. It's interesting seeing how the oiling was made to work, it's quite familiar to me from 2 strokes really. Much more so than if I was used to modern 4 stroke oiling.

Thank you for the recommendation of someone who can help with bushing the small end. I'm also looking into whether I can find a just slightly oversize gudgeon pin, and ream out the little end eye and piston to suit? I do like to find ways to do these things myself if possible, and am planning on purchasing a lathe to expend my skills and help with this project.

The cams look 'ok' to me, I've seen wiped out cam lobes before, and this doesn't look like that. Do you know what the original valve lift should have been? I've got approx 0.200" at the cam.

The piston is a +60 Hepolite 7151. I'm not sure what, if any, the difference is between this and the 7150 I see more often suggested as fitting the B2?

Piston to bore clearance is good, the ring gaps are not! The top ring is badly filed and the ring gap is too tight, only 0.005", and the 2nd ring and oil scraper look like they are much older or just plain wrong as the ring gap is almost 0.060"!! New rings are in the post...

I notice the original piston in the parts book was not fitted with an oil scraper, just 2 compression rings. It it a good modernisation to run with the oil scraper ring? Or would it interfere with how the oil was designed to be burnt off in this total loss system, and should therefore be omitted?

That's a shame about the tank. I will probably find a way to pay homage to what the original paint scheme should have been, rather than stick with the all green then. In terms of getting out riding though, yes the tank is a good one. Bit dirty inside but not rusty and no leaks.

Looking in the parts book, I agree, the rear stays do closely resemble the B3 model. The rear end bolts up ok (now I've straightened the lower arms out!) so I'll run with it!

On the electrics front, given how useless I find the pair of 35w bulbs in my '60s Fiat when faced with any kind of oncoming traffic, I'd presumed that a single 12/18w headlamp bulb on this bike would make night riding exceedingly difficult! With that in mind, and given that the bike has a cheap modern replica headlight unit fitted (with just 3 switch positions, no 'C' option), I was planning to run in 'daylight' trim and not fit lights, at least to start with.

A brake light might be nice though, just to deal with modern traffic! Is it safe/possible to use the power generated from the Maglita without a battery? In this case just connecting it to a brake light circuit as and when it's needed? If not I'll just disconnect the charging system and sort a standalone brake light system with a little rechargeable battery pack.

I've got an ebay bargain £10 C11 centre stand in the post (29-4883 I believe), so I'll see if that can be modified to fit. 

[Steve.S]

So glad you have managed to source a ratchet pinion. Let's hope it's the right one, as there are many of them and they all look much the same.
When you first posted, I was going to suggest you got it running and tried it out on the road, to see what was what and deal with each problem as it arose.
But, by then you had already stripped it down. So you have a big decision to make. If you go for a full restoration, it will cost many thousands of pounds.
For example, if you got the correct tank...and they do turn up on ebay, it will cost you about £1500 to have polished, leak tested, triple plated, painted and lined. Then you are committed to making the rest of the bike looking like the tank. I think the approach is to do the minimum. You say the kickstart works OK. So why not leave it? Should it fail in the future, you have a new part in stock. Again, regarding endfloat (0.004" sounds about right, but you can't get better than a service sheet), maybe all the gears select OK as it is.
The tank is not dissimilar to the correct one, so maybe you could spray the top of the tank silver and gold line it. You will get an idea of the layout from the parts book, which I assume you have?
I just use a bit of rubber tubing on the kickstart stop, encased in a steel outer, which you will be able to turn up on your new lathe! (If you decide to do the gearbox, you will be able to check the layshaft for straightness with a DTI gauge).
However, I feel that since the crankshaft is the heart of the engine I am prepared to bite the bullet and get it fully overhauled. After all, it will only be done once, and you'll never have to take the engine to pieces again. Alpha are superb engineers and are very familiar with this engine. They are quite quick, but it will cost a few hundred pounds. This would solve all your problems with little end wear, thrust washer wear, and big end uncertainties. Also, you won't have the difficulty in setting up the flywheels, unless you already have the equipment. The choice is entirely yours, but if you decide on repairs, a few thoughts:  I have never seen the wear you describe on the thrust washers. I doubt if you will ever find new ones. Perhaps you could source some hardened steel washers of the correct dimensions from Bearing Suppliers, and grind a chamfer on them, but they do need to be an interference fit on the flywheel 'lip', and not turn.
I also think it will be very difficult to source a gudgeon pin that is the correct fit in the little end, which may be oval. Also, I think you will find the finish of the bore is appalling, with deep grooves in it. Also, bear in mind the clearances are minute, but perhaps I'm being pessimistic?
As a matter of interest, the little end on my motorcycle is very badly worn. It rattles a bit, but I'm ignoring it for the time being. You haven't said how bad yours is.
I suppose your big end doesn't look too bad, but an engineering shop would bore it out and rebush it. When you try oversize rollers, make sure everything is completely oil free and dry. Then, gird your loins, close your eyes, and turn the con rod slowly through 360 degrees a few times, to see if you can feel even the very slightest tightening and freeing of the con rod as it  turns. If you can, then I'm afraid it won't last long. I have seen a few big ends with a double row of rollers. I think it may have been a modification.
I will post again later on, but briefly, I once had a NOS cam, and that gave 0.216" lift, so you're not far out.

[Goldnrust]

The part number for the kickstart pinion is correct on the eBay listing, so I'm crossing my fingers!

Riding it and finding the problems along the way, was indeed plan A. Things just escalated haha. I'm definitely not doing a big money originality focused rebuild. This is just a case of making it run right and be safe and then get out riding.

I'm measuring the little end bore as 0.629" sideways and 0.635" vertically, I've got standard figure of 0.6250-0.6255". But I'm not entirely trusting of my accuracy of internal measurements on small diameters like that, I haven't got the right internal micrometer. The standard pin feels 'ok' side to side, so I think my measurements are over reading, but it does have some vertical movement.

I have to admit, I was presuming that any vertical little end movement was going to mean imminent disaster, and was one of the main reasons I decided to fully strip the engine. You can see the amount of movement at the crank here, and its 90% in the little end https://www.youtube.com/shorts/8bnaCPTe85A

The standard pin diameter is 0.6245", which is ~15.8mm, so I've got a 16mm diameter pin coming in the post, with the intention to try reaming the little end round again to suit this new pin and opening up the piston to suit. For a £20 fix, it's worth a shot, and if that fails, then maybe sending away to have it fixed properly will be the right move.

I've rebuilt several 2 stroke cranks of the same flywheel and pin design, so whilst I'm 'new' to pre-war bikes, this kind of work is not entirely new to me. I'm not expecting the flywheel truing to be too torturous on this one, single cylinder is much easier than the 2 cylinder crank I did most recently and unlike that crank this one doesn't need to rev to 10,000 rpm!

The bore isn't great, but I've seen worse. At +60 already, it would be a case of getting it lined to repair any damage, so in the mean time I'm hoping a light hone and new set of rings will get me out riding. I'll take some pictures next time I'm out in the shed.

Thats promising about the cam! Thank you.

[Steve.S]

I think you are very much on the right track with all this. I think the fact that you can strip an engine so quickly and easily, and also realign the flywheels is a great advantage. (I can't). As I said, my little end has rather a lot of play, but the engine runs fine....at the moment. I feel that if you reassembled it as it is, in practice it will be OK, but otherwise, I think your idea is a good one. We know that little end and big end clearances should be tiny. Your figures show half a thou limit. Precision engineers should look away now and 0.009" wear is massive, but on the other hand, precision costs a great deal of money and time. Under the circumstances, I think your approach is the right one, but others will violently disagree, and I can see their point. I've just seen your video, and yes, there is quite a lot of movement, but I'm sure your bigger pin will reduce it.
Pistons are a little confusing. I hope this is not too much information, but I have 2 undated sheets from Hepolite. One shows the 7151 piston as 6:1 compression, and the other shows 5.2:1 compression. 7151 has a flat crown with a slight chamfer and a compression height of 1", and mine has 2 compression rings and 1 oil control ring. 7150 also has a compression height of 1", and is quoted as for a B26 SV.
2725 has a compression height of 1 3/16" and has a "cone" crown. 5338 is a half dome piston and 3653 is a full dome piston, perhaps for running on methanol? (Well, why not? although your little end won't last long!)
I'm using a 2725 with no oil control ring, but for some reason I don't understand, I had to skim 1/8" off the bottom to clear the crankcase.
I'm sure an oil control ring is a good idea, and will not interfere with the oiling, but I see your point.
I too can't see the difference between the 7150 and 7151.
I think your approach to bore and piston is spot on, but if there is a ridge at the top of the bore, you might want to scrape it back to prevent the top ring from breaking.
BTW, you might want to invest in Radco's book "The Vintage Motorcyclists Workshop", a mine of useful information.

Tank colour would have been Mid Brunswick Green BS 226, rather than the Apple Green of yours, with a gold pinstripe between the paint and Chrome (or Silver paint).
I would get a repro Lucas MT 110 rear lamp, then you could get an LED "Lightboard" from Paul Goff to fit inside, which incorporates a stop light.
I see you have no battery or carrier. I made my carrier. It's not too difficult. You will need a hooter to be legal, but you could use a bulb horn, but I think the regulations state it must sound a continuous note.
I also use a clip on rechargeable bicycle LED rear light.
The repro headlight shells are very similar to the originals, but yours would have had a flat lavatory frosted glass, rather than a domed glass.
I have some info on the Maglita, but I'm not sure if it can be run without a battery. I'll have a look. But lets see if the Maglita is producing a charge first, and go from there. If you get caught out in the rain, you will probably want to switch the headlight on.

[Steve.S]

Lucas state that the Maglita can be run without a battery, but caution that high speeds should be avoided due to the risk of blowing bulbs due to high voltage. But you can obviously measure this. Remember also, that when the engine is ticking over, the points of the centrifugal cutout will be open, so the bulb will go out.

[Goldnrust]

Thanks for all that info Steve. All interesting.

I was aware of the centrifugal cut out but didn't realise it wouldn't be engaged at idle. A fair point about being caught in the rain without lighting. I've got a reproduction MT110, it came with the bike, I was planning to modify it to use as my brake light.

I believe a bulb horn is fine as long as the bike was first used before 1973. https://www.gov.uk/guidance/mot-inspection-manual-for-motorcycles/7-audible-warning

Either way, plenty of time to mull that over and work out the electrical and legality bits and bobs. In the short term I've got rather more major mechanical issues to deal with! haha.

I think fitting the oil control ring is probably the right move, I think the main thing it might effect, if its limiting excess oil making it to the upper cylinder, is the amount of blue smoke if the pilgrim pump is set wrong? Time will tell.

Interesting about the different piston domes available. I'm sure the bike was designed to run on pretty poor quality fuel compared to a modern super unleaded (which I will be using for the lower ethanol content), so a mild bump in compression would do no harm I'm sure and gain a bit of performance. Still I'm getting ahead of myself, make do and mend what I have to get out and ride the bike has to be my first goal.

I have the 16mm gudgeon pin now, along with the appropriate reamer, I should get chance over the weekend to investigate the little end further, I will report back!

[Steve.S]

Should you ever decide to replace the ratchet gear, it's worth noting that the thin ring nut on the mainshaft with the 4 holes for a peg spanner is a left hand thread. I have a feeling that you probably already know this, but it might be useful for others.