The Diary of a 1948 BSA M21, or if you like... A Blogg!


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My second Classic motorcycle after my 1961 BSA A10 Golden Flash is the M21, described in the heading above. This bike has a 600cc single cylinder side valve engine as opposed to the 650cc parallel twin engine the Golden Flash has. I chose this particular bike because it is so very different from the Golden Flash. It is of a rigid frame construction with the earlier girder forks and not the more common, modern tubular forks. I purchased this with the intention of re-restoring it to the civilian color of black as when these bikes were decommissioned from the army they were often sold off to dealers who painted them this way.

A recent communication with the previous owner informs me that the bike was rescued and restored in 1997, so I was lucky that I had not had to do any heavy expensive work on her. The purchase of the bike was through a dealer near Swindon, Bill Little Motorcycles not far from where the bike had spent most of its life. The insignia is that of the now disbanded Royal Berkshire Regiment.




                                                                                                                          This is the bike that cried out for me to take her home! 

                                                                                                                                  Thanks to Bill Little for use of his Photograph





Take a look at a small clip of the M21 being started, my daughter will give a demonstration on how easy it is to start the bike. It is not so much as heavy kicking away but more of a gentle technique. 


I intend to record a diary of this bike during the year 2007 so that you can see just how very versatile these machines are. Starting with Sunday 14th January 07. We start off with our very own local rides to find as many 'Thorpes' in an alphabetical format. This progress can be seen on the ABC Thorpes page.

Friday 26th January

Well apart from the Magneto that has been troubling me, this was sent off to Independent Ignition Supplies last 5th December and I'm 'still' waiting! grrrrrrr. I currently have a spare magneto from an engine that I purchased on ebay, that also has the same problem in that the bike just will not restart while the engine is hot. It is a break down of the windings and condenser and the only remedy is to send off for an overhaul of the armature, more on this later.

I had noticed that the Carburetor is in need of some attention. As the bike had been standing for a while at the dealers, the petrol is very weepy around the joints so I have decided to take a look. I had offered to do a photographed report on how I get on with this for a friend who had never delved into the dark depths of the carb. I have never done this model so it will be a new learning experience for me too!




             This Link will take you to the Carburetor maintenance page.











A useful gadget that I had bought for the A10 Golden Flash has also been fitted to the 21 and that is a battery Status Monitor. Amazing little blighter as he shows just how much juice there is in the battery and also if the dynamo is chucking out plenty of little voltlettes. I would thoroughly recommend one of these as it don't take much for a dynamo, battery or regulator to be come messed up. 

Sunday 28th January

Went out today to an auto Jumble and picked up a Gearbox, not bad for 45 quid! It will come in handy sometime when wear sets in. I also got another gear lever as the one on the bike fouls the exhaust pipe and was not very secure giving a uncomfortable gear change. What an improvement such a stupid little thing can make! all for a couple of quid. I seem to have got some sort of magneto disease as I appear to be  picking them up to restore and hoard away.... still no sign of the one I sent away to be rewound. grrrrrr

Tuesday 30th January

Yippee! The magneto Armature arrived today, So off I go to the shed for some intensive fettling. 

This Link will take you to the Magneto Maintenance Page.

Sunday 12th February

The past weekend had seen the 2007 Dragon Rally in North Wales in which I just had to attend. It is the ultimate rally to be at in the UK and would be a fine start to the year if I went. Ticket was purchased some weeks ago and Thursday evening saw me nervously loading up the M21 ready for an early Friday morning start.

 This Link will take you to my Dragon Page.

Thursday 22nd February

Been quite busy the last few evenings, got bored being indoors so I had resigned myself to the freedom, peace and quiet of... the shed! The fettling shed as the sacred place is known, is situated at the bottom of the garden and built of shiplap paneling, my shed measures ten feet by 8 and is completely lined out with 2 inch polystyrene sheets for both warmth and to keep the place relatively cool in the summer. I have four power points, one in each corner and two five feet long fluorescent lights. The shed easily houses both of my bikes and there is room also for a work table lift of which one bike is parked on.

The last few evenings have seen a new front brake cable fitted with one of those Teflon coated inners from Venhills. What a difference it makes, I had also fitted this type of cable to the clutch and valve lifter. Eventually I will get round to fitting it also to the throttle and choke controls.

I also refitted the original gear shift lever. Soon after I purchased the M21 I had set it to how I like the A10 and expected the M21 to virtually shift the gears with exactly the same feel and smoothness as the A10, but I have come to realise just how very different the M21 in just about every aspect. The M21 is very... 'Agricultural' as someone had described it, but it is great fun to own and ride. I also had a good go at trying to fix an oil leak... (well it is a BSA!) that seemed to come from the valve lifter. I took it all apart and investigated. It seemed that the inner cam spindle was worn away and was wobbling within a housing that screws into the barrel block. My remedy was to put in an 'O' ring at the end and with a spring pushing the cam against the rubber ring, it should seal and stop oil flow.

Unfortunately this afternoon after another job I had just done... will come to that other job shortly... I find that on very close inspection to see if the leak is still there, I notice a minute bubbling with heated thinned oil oozing out. It seems that there is a small crack in the barrel just around the top of the valves access compartment. grrrrrrrr, well the spew is not so bad and will have to carry on until such time the barrels come off for overhaul. This is something that I am going to have to keep a close eye on. It could affect the valve guides or cause other problems, I am also watching that smoke whiff from out of the exhaust pipe.

The other job that I had completed and took the bike out to test was that, I had fitted a new electronic regulator. The old mechanical one was not functioning correctly. I know this because of having recently fitted a electronic battery status monitor which I described further up the page. The dynamo had been overcharging and either the cut out was not... cutting out or the regulator was set too high. It is very difficult to set this mechanical wotsit without a moving coil volt meter showing one volt increments. A tool that I don't have. I had fitted an Alan Osbourn V-Reg II regulator on the A10 and the results were very reassuring, especially when riding in poor visibility and I need the lights on to be seen. I also feel reassured that the sensitive Gel type 6 volt battery is not going to be damaged in any way and indeed the correctly functioning Regulator should also give the Dynamo some protection from itself too.

In all I had found the last few evenings quite satisfying, maintaining a vintage motorcycle takes some devotion but the returns in pleasure it gives is all very much worth while.

Sunday 11th March

I have not been updating the blogg over the last week, although the bike has been out an about and kept quite busy! Last weekend saw Emma and self riding down to the BSAOC members meeting at Long Compton village hall. We had arrived early which gave Emma the chance to ride around the hall car park, she did quite well. Its always difficult for a newbie to co-ordinate the clutch and throttle and after many stalls she eventually took off! Not wanting to stop until I shouted 'clutch in'! She chose a wire fence in which to end the ride. Out with the polish for punishment!



She got the admiration from the members for riding the rigid frame all the way from Peterborough and gained the new name of 'Iron Butt Emma'! (P.S. Check for updates on the ABC Thorpes page!)

Sunday 25th March

Lovely out there today, late start as someone had nicked an hour off the day so didn't get out riding until late morning.

I was off to see a wind farm open day and arriving there I found I didn't want to pay 2 to Look at these whirling monsters that are clearly seen from the road. So saving the couple of quid for petrol I rode off to find some nice pleasant Fen droves and lanes to see if I could get closer to them.

The first picture here was along a track where not a soul or car was to be seen but I got nearer to these whirling towers...

I later on came across a bit of a wacky garden center that has all sorts of unusual artifacts and thought this vehicle would be an excellent background shot next to the M21...

I was soon riding aimlessly around the Fens, just riding through small and large villages that I had heard of so many times but never been to before. I stumbled across the tallest windmill in the UK. Never knew this...

The Fens is a lovely place to be in the Spring as Spalding is well known for its Tulips which will all be out in another week or two. Daffodils will have to do for now and they were everywhere...

I found this to be rather depressing, sadly a common sight although not so badly vandalised. This was the main freight line that ran from March to Spalding and closed on 1st Nov 1982...

Can be dangerous riding in the Fens as so many of the smaller roads are badly subsided, and with deep dykes either side of the road, it is not the place to be riding on dark nights with 6 volts...

Next week will see Lillian on the rigid frame Pillion and myself wizzing off to start the 2007 Round Britain Rally again! The first Landmark will be at Littleport near Ely in Cambridgeshire. There looks to be a few of us meeting up for a Grand start off. Pictures and reports to come then.... Watch this Space! ;-)

Tuesday 27th March

Well... this morning she was a right sod! Talk about taming a wild west horse! I got her started and noticed the magneto was shaking around, so out came the spanners, she stalled, would she restart? Nope! I kick and she kicks back, flood the carb and she gets real stroppy. This then becomes serious leg breaking stuff, the kick backs and clouds of white petrol/vapour even spitting out petrol across the path. Eventually she fires and off we go, the whole bike felt really old and stiff as if someone was holding us back, there even felts like a bit of clutch slip so I test this by opening her right up only for the throttle cable to snap! Duhhh! I got her back home no problem and out came the flash! Now she's a good girl, didn't give me any stick and gave a good ride into town and back. Dunno why I have been neglecting her just lately.

Sunday 1st April

The first of April is well known for Fools day and its true to some extent as we are about to embark on a six month long Round Britain Rally. You'll need to visit that new page to find out what its all about and the progress we make.

Friday 6th April Good Friday

Well today instead of riding out and about in this fine weather the day saw me taking off the cylinder head and barrel. For a few weeks now I have been painstakingly watching a very small crack and wondering if this was the culprit for a horrendous oil leak that has been covering my right boot on every ride out. The job of dismantling was easy and only took about half an hour. It involved mainly to remove the carburetor, valve lifter, head stay and spark plug and lead. 

I found that the cylinder head gasket had blown and needed replacing with a proper solid copper gasket rather than the cheapie asbestos and thin copper coated gasket. The gasket between the barrels and the crank case was a very thin 'brown wrapping' paper like and this could be the reason why the oil is being chucked out. I have yet to sand blast the barrels to thoroughly inspect them for any other cracks. I had noticed a brazed repair. More to come about this after closer inspection.


Monday 9th April Easter Monday

Not yet sand blasted the barrel and head, but I had given a good scrape and found that the crack is not nice! It does look like someone had been heavy handed in removing a valve guide. Both valves appear to be very new with no wear at all both measuring 8.77mm all along the stems and although the exhaust valve guide seems firm the inlet valve guide seems a little slack. I wont bother replacing these in view of damage. It may not be worth while spending money on this barrel as I do have a spare one in workshop but I would like to get the full use out of this one before throwing it away.



It had been fun making up a gasket to fit between the base of the barrel and the top of the crank case as you can see, I also feel that the thickness of the gasket paper that I used will be much better in keeping in the oil. You can see the poor copper cylinder head gasket, tomorrow I will get a sheet of copper from some model shop and begin making this one as I am told they are not obtainable. Well it will give me something to do.

Thursday 12th April

Today saw me reassembling the barrel and cylinder head and after cleaning the carb the bike was ready for a run. The compression felt really strong in comparison to how it felt before. At this stage I feel that the job had been worth while. A test run over to a friends reveals the leak once again from the crack, we decided to put in a breather pipe and once again still proves that the oil prefers to come oozing out of that crack.


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