AJS 18 IN CHAINS
Once you’ve got your old bike’s engine running perfectly, the next step is to transfer all that impetus to the rear wheel. A quick getaway and a quiet ride start with smooth transmission. Neil Cairns rebuilds the drive train on a typical British single…
Once you’ve got your old bike’s engine running perfectly, the next step is to transfer all that impetus to the rear wheel. A quick getaway and a quiet ride start with smooth transmission. Neil Cairns rebuilds the drive train on a typical British single…
Wrefitted it and pulled the chain up as tight as I could (remember, it was a rigid frame). I could not afford new bits on apprentice’s pay. To this day I still automatically look at rear sprockets on bikes.
It’s now 2020 and I have new gearbox and rear sprockets, and new chains on my bench ready to fit to my 1952 AJS 18S solo. I’ve owned this bike for a decade and it’s done a the chain jumping the rear sprocket. It was so worn that the worn chain simply jumped the hooked teeth unless you were gentle on the clutch.
Being a bit of an engineering twit back then, I removed the sprocket and took it to work to file the teeth deeper. A toolmaker pointed out I was actually reducing its diameter and making things worse. So I hen I was a teenager in the early 1960s, my first road-legal motorcycle was a 1946 BSA 250cc C11 with a rigid rear end and a dynamo that did not work. It was a wreck, but to me manna from heaven. If I tried to do a fast getaway to impress my mates, all I got when I dropped the clutch was a loud rasping noise and no go. It was
lot of miles as my main machine. It ate its last chain very quickly, which points to foolishly putting a new chain on worn sprockets – and this proved to be true.
On my Hinckley Bonneville, fitting new sprockets and the rear chain is very easy, but the AJS requires a great deal of stripping down. The first thing was to clean the bike as much as possible. Anything near ‘open’ rear chains gets well and truly covered in oily-greasy muck. This is good for preservation but bad for fingernails. The rear part of the mudguard has to be removed, then the rear chain (I should have left this in place, I found out later). The speedometer cable needs disconnecting along with the brake rod, and the brake drum torque arm’s stud must be removed from the swinging arm. Only then can the wheel be pulled out. Lots of bits to undo, unlike the G12 that has a QD rear wheel.
Once the wheel was on the floor, comparing the new and old sprockets confirmed that ten years of all-round use had done its bit. The sprocket is part and parcel of the rear brake drum. When I needed a new rear sprocket on my 1961 Panther M120, I had the old one machined off the rear drum and pressed on the new one in my vice. I then drilled three holes on the joint, fitting peined-over dowels for security. Hands up those who have never heard of peining? It is what the ball-pein round bit of your hammer is for, basically riveting.
The AJS drum is held on to the spool by five bolts which are locked inside the drum by nuts, themselves locked by tab-washers. The washers had obviously been used before so, once I had it apart, I made five new ones from some 22swg sheet steel from my stock (actually a side of an old twin-tub washing machine. Never throw things away as they come handy eventually).
The ‘spool’ is the centre of the wheel. I rebuilt this very wheel some years ago with new spokes and a stainless steel rim with a kit from an advert in RC, putting the wheel in the vice to true it up. I needed to re-tighten the spoke nuts after about a month.
Fitting the new sprocket / drum was easy, and bending over the newly made tab-washers was done with a handy set of mole-grips. The new brake drum required a good clean as it had preservative on it. The wheel was then put back into the swinging arm loose, as it will be required when I come to undoing the gearbox sprocket’s big nut (yes, I’ve done this before).
Next came the removal of the primary drive to get access to that gearbox sprocket. It was a filthy job as everything was covered in thick, black muddy greasy road dirt. It all looked in excellent condition, not surprising as the previous owner had given me some receipts for new clutch bits and chains. A large box-spanner I purchased in 1979 for the Panther once again became useful. It fitted the big nut that locked the sprocket to the gearbox shaft. The tab washers on the clutch basket nut and the gearbox sprocket nut looked like new and were reusable as there were extra unused tabs.
This was when I found I needed to refit the chain, so I could lock up the rear wheel to be able to undo that big nut. The sprocket itself was not going to play fair, so I attacked it with a strong puller. I won. Note the oil tank’s vent pipe discharging onto the chain.
Reassembling the primary drive was straightforward, apart from having to clean everything. While it was in bits I fitted a new chain, which I’d originally bought as a spare for the G12 so it was one link too long. I ground off the rivet head and pressed it out, to shorten the new chain. The photo actually shows the original chain that I fitted first, with the spring-links the wrong way around. The clip’s open end should face away from the direction of running. The new chain only has one link, fitted correctly.
I then had to re-adjust the free play on the new chains. The primary chain is done by the gearbox adjuster under the oil tank: easy. The rear chain is done by turning the snail-cam adjusters for the wheel axle with a really big spanner. And although the dynamo drive chain is actually driving an Alton alternator, it too required a small adjustment. Oddly enough, its locking clamp has the only A/F headed nut on the bike, ½” across the flats, an American confection, nothing to do with the thread. I wonder why?
Fitting the outer cover to the rear of the primary chain-case requires a bit of care, as it uses a fiddly rubber seal. The rubber seal I used was a late one with a lip between the two faces, with a T-shaped cross-
section. I took some time over this to try to get an oil-tight joint, not something these AMC bikes (and Nortons) are famous for. It is a bad design because all the ‘clamping’ is only done at the rear edge where the screw joins the two ends of the alloy strap. I hate using sealants and even with silicon I’ve never successfully sealed my other 18S chain-case. This time I filled it up with oil and – so far – no leaks. It will wait until I’ve left, and then leak onto the garage floor…
The final thing was to start the bike. It is usually a first or second kick machine as long as you set the timing to fully retarded, the choke lever to closed and flood the carburettor. Not this time, alas. I kicked and kicked for ages, just getting the odd ‘woooof’ from the exhaust. At least it was trying. When I cleaned the AJS I had used ‘MuckOff’ which works well. Too well in fact as it had diluted the Vaseline in the magneto HT wire Bakelite slip-ring connector.
AMC in their wisdom fitted the magneto in front of the engine, and even though it has a splash-guard the front wheel can sometimes deluge it and swamp the spark. So I seal it with Vaseline as I’ve been doing to my bikes since the dawn of time. I unscrewed it and dried it all out, refitting with fresh Vaseline. The engine burst into life at the next kick and sat there ticking over as if nothing had happened.
Back when I had that BSA C11 I would have done this job in a day. 58 years later it took me two whole days, and my knees are sore. I’ve some kneeling pads somewhere. Somewhere…