I had a look inside the chaincase on my new bike yesterday... well, it's new to me. The machine is a 1952 BSA M33 500cc ohv single. The engine sprocket looks well used, but the teeth are not hooked. The cush drive centre nut looks like it's been off and on many times with a chisel. SRM in Wales make a better replacement with a hex head so you can torque them up properly. The chain looks almost new and the chainwheel has had a new set of teeth cleverly fitted on from a much newer bike sprocket. It looks like just an interference fit from the outside, but may be welded on the inside. Both chain and sprocket have a logo on that looks like a rising sun... so it's not a Renolds chain.... The chainwheel has been welded up where the clutch plate tangs have worn grooves. It looks grooved again, but the action is good. The pressure plate has some corrosion but is solid and the centre nut has been welded up. This case should have oil in it, but it didn't when I got the bike and I wont put oil in it yet either. These pressed steel cases leak easily unless you get to flat the faces properly, then seal up with a cork gasket and sealant. I took the chain off and cleaned it with parrafin, then soaked it in sae 90 gear oil, before refitting. So, I'll just spray lube on the chain regularly for now. Then all back together and ready for a run. What a lovely looking engine and it's a real thumper, fires every power pole in top gear. So, off we go today from the Viang, out through Chiang Saen on the mountain road 1129 to Chiang Khong and up to the viewpoint past Huai Yen. The 1129 is not in the best condition and the potholes were quite a test for the old suspension, which did very well, just the odd clonking here and there. I quite like the sprung saddle with independant left and right buttock springing. I took the 4007 river road back which was much nicer, past Rai Saeng Arun and then joined the 1129 again at Bahn Saeo. I stopped a little further on to make sure I could still see the giant Buddha statue in the cornfield across the river in Laos. One of the biggest old Buddha statues in the area and one of many old unrestored temple sites from the ancient city of Suvannakhomkham. Unfortunately the Laos government does nothing to look after these sites and appears only to be interested in building casinos in the area now. Top marks to those of you who have noticed the non standard jap carburettor, which actually works quite well. The electrical system is not ideal as the bike should have a Lucas magdyno, but is fitted with a Wico magneto from a boat. This provides a good spark, but there is no charging system for the battery, so I have fitted a small lead on the battery, tucked under the tank, to plug into a charger when I get home. The battery has enough charge to power brake light and horn for day trips. I put a bulb horn on the bars as a back up for now and I'll fit a magdyno and charging system at some stage in the future. This bike was one of about 30 BSAs brought in to Thailand over the years by a certain gentleman in Mae Sai and would have been sent to Burma under a government military contract soon after independence. The non matching mudguards are as standard, as is apparently the lack of speedo drive from the gearbox which is unusual. I haven't quite worked that out yet. There is an Indian speedo in the cowl, but where the drive unit should be, the hole is blanked off and that looks original. Anyway, a very enjoyable day out, thumping through the Lanna countryside. These are great bikes for the roads up here. Max speed is about 70 kph which is quite enough for country roads, 23 bhp and about 150 kgs. Easy to start with a valve lifter, unburstable bottom end, simple and reliable. Spares are pretty easy to find on the internet. I have friend in England who has one with over 100k miles on it, it's been overland through Russia and on to Kathmandu. There are quite a few of these machines up here around Chiang Mai, so if you get the chance to buy one that's in reasonable condition and you like a bit of spannering, they're a good bet and will only appreciate in value.
My limited experience on a chug around the lake from outside Viang Yanok on your M33 was unforgettable Ian. She's a beauty for sure.
Another fine old beast in the stable! (The bike Ian, the bike!!!) Looks very tidy for its age. Hadn't even heard of the model till you got one.
BSA started the line with the rigid framed M series M20, built from 1937 to 1955, thousands of which were supplied to the British Army. This was a 500cc sidevalve engine. The engine was also enlarged to 600cc as the M21, between 1937 and 1963. These were supplied with various special parts to the AA in UK. Between 1947 and 1957 BSA put the B33 overhead valve engine in the M20 frame, mostly for civilian use and it was called the M33. The B33 had come from the B31 350cc ohv engine which ran from 1945 to 1959. The M and the B series ran concurrently for many years. So, the ohv M33 used the same frame as the sv M20 and M21. The B33 then ran from 1947 to 1960. Yes, complicated....... The plunger frame was introduced on the B range in 1949 and on the M range in 1951. The rigid frame was discontinued in 1954 on the B range and 1960 on the M range. David, things are starting to quieten down again at the hotel, so I'll be wanting to take a trip up to Mae Salong soon, with you guys. The colour is nowhere near original and I don't like it that much, but it's a good paint job and I'm not taking the bike off the road to repaint yet.... too much fun riding it. Ian
