understand gearbox selection

‘I have to admit I enjoy scrutinising parts books to see what’s changed year by year’

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Let’s face it; we’re all optimists. If we weren’t, then we wouldn’t be absorbed by obsolete old motorbikes that should have long since been recycled into household appliances or new cars. But one aspect of my own overoptimism in rebuilding old nails is that when I estimate the time a build will take, I only ever consider the actual jobs that need to be done. Okay, I do factor in an allowance for the unexpected – welding or machining work, for instance – but I completely overlook research. When assembling any bike from bits, it’s likely they will not all be the right bits. This is not the preserve of a manual, which assumes the bike was complete when you pulled it apart. No, you need parts books. I admit I enjoy scrutinising them year by year to see what changed and, using a bit of detective work, why. Recently I had a problem with a front hub that was too wide for the forks. Oh no, I panicked, was it the wrong wheel? Going through the parts books I learned that they’re the same for all years – as are the spindles and spacers. Panic over and a closer look revealed slightly squashed-in forks. It was an easy fix but the research took much longer. Now I realise that’s where internet forums can come in very useful. Yes there’s a fair amount of duff information on the internet, but when it comes to a simple question like “How wide are your front forks?” it’s a winner. But I still love doing it the hard way.

 

Top Tip

lathe chuck vice

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I rescued this old lathe chuck from a scrap pile. It’s way too big for any machine of mine and the fitting makes it specific to a long obsolete lathe but that doesn’t make it ready for the melting pot. It makes a very good vice for circular objects. This one has three large studs in the back that I locate into three holes drilled in the bench top. I use it for splitting and assembling crankshafts mainly.

On most I work on, the big-end pin is a taper fit in the flywheels. With the nuts loosened and one flywheel securely gripped in the chuck, a smart blow from a copper hammer to the other wheel will break the taper easily. One man’s scrap...

 
Turn a conical spacer to seat Norton ES2 fork springs in the seal retainer

Turn a conical spacer to seat Norton ES2 fork springs in the seal retainer

Comfortable springing

Evgeny Perekatov is rebuilding a late-model Norton ES2 in Israel and has a query about the forks. “I’ve ordered the correct external springs from RGM,” he says. “But I have a problem with the seal holders. They are cone-shaped inside and although there is a washer to seat the spring it just looks like part of an old steering bearing. I wonder if my fork is a mixture of Norton and AJS parts.” Certainly in the latter days of the AMC empire there was some fusion of the AJS/ Matchless and Norton ranges, but I think Evgeny’s problem is simpler. Firstly I’m sure his bike should have internal springs, concealed within the stanchion; the only short Norton Roadholders to have external springs being the Manx and the G15 hybrids. It’s popular to fit external springs on cafe racers but these tend to use Manx-type aluminium seal holders (or more correctly ‘retainers’, since the seal is in the alloy fork slider). I’ve seen the cone Evgeny mentions in the retainers and it would make seating an external spring difficult. But, looking in my Norton box, I found an old pair of flat-bottomed retainers from a 1964 Atlas, so I wonder if the late holders were designed (with the G15 in mind) to take either internal or external springs. My suggestion is to turn a conical spacer on a lathe to mate with the cone in the retainer to present a flat base for the spring.

Breaking the engagement

Gearbox rebuilds are an area that many shy away from, perhaps partly because their workings are not so clear as other assemblies or maybe because the gears can all look muddlingly similar lying on the bench. But that didn’t stop Nick Howarth replacing a damaged first-gear pinion on his 250 MZ. Trouble is now the bike seems to jump in and out of third, as though the clutch is intermittently slipping. “But if a gear is jumping out,” he asks. “Would it be able to jump back in like this?” I’d say yes, Nick. The dogs on gears are carefully profiled to draw them into engagement while remaining easy to change. If engagement is only partial, the profile might try to draw in the gear but if unable to do so fully, it will slip out again. Two possible causes spring to mind; either Nick might have overlooked or misplaced a thrust washer in the assembly, allowing excess end float somewhere, or he may not have got the selector indexing right. This is the relationship between pedal and selector camplate: the movement required isn’t always the same for each gear and indexing the gearbox – usually by means of markings – ensures that the selector fork movement, dictated by the camplate groove, is matched to the relevant gear set. Either way I think it’s going to have to come apart again.

Scott Sunday discovered these Commando forks in a field. Perfect for a US-based Norley project?

Scott Sunday discovered these Commando forks in a field. Perfect for a US-based Norley project?

Condensing the argument

When a magneto fails, the condenser is often blamed; probably because back when everything had coil ignition with points, changing points and condensers was a service item – and condensers were cheap, accordingly. But there’s a problem with magnetos; the condenser is inaccessible, sealed inside the armature. Phil Harris got in touch through www.rickparkington. co.uk to say that the Bosch magneto on his veteran Douglas is putting out a bit of a ‘light show from the points’ and, suspecting the condenser. He asks whether he could wire in an external replacement using an ignition cut-out, whose carbon brush is the only way to tap into the low tension circuit, spinning at half engine speed, from outside. It’s a clever idea but I don’t think it would work. Steve Marks from The Magneto Guys agrees: “The hit-and-miss contact of a carbon brush is fine for a cutout or a high-tension spark but too unreliable for a condenser connection. The mica condensers in vintage Bosch magnetos are excellent and very seldom fail; I don’t recall ever having to replace one, even though some are 100 years old. But there’s always a first time.” Admittedly the arcing points do suggest this might be it, but I wonder if it could simply be that the internal connection has fractured. A mica condenser may be almost everlasting but soldered connections are definitely mortal.

Lucky find

Talking of Norton forks (p90), how’s this for a find? Scott Sunday found these forks (left) in a field in Oklahoma and bought them from the farmer for $10. “They say ‘Norton and Lockheed.’ I’m thinking of using them on a Norley project; what are they off?”, he asks. They’re Commando forks, Scott. If you’re using a Featherbed frame they will fit – but you’ll need Featherbed yokes. They’re a bit longer than Dominator legs but I have Commando forks on my Norvin and they work fine.

 

How To

understand gearbox selection

Nick’s MZ problem (left) may be due to selector indexing. A Rudge-Whitworth gearbox shows an exaggerated view of the issue

1. The Rudge gearbox is unusual in that the camplate’s position, relative to the selector forks, is adjustable by means of its threaded pivot bush.

1. The Rudge gearbox is unusual in that the camplate’s position, relative to the selector forks, is adjustable by means of its threaded pivot bush.

2. In first gear (camplate removed for view) all looks well. The two gears bottom left are snuggled together, while the two gears top right (fourth) are well separated.

2. In first gear (camplate removed for view) all looks well. The two gears bottom left are snuggled together, while the two gears top right (fourth) are well separated.

3. But with the camplate in place, there’s a problem. The first-gear pinions are fully home before the selector forks have reached the end of the track. This will affect fourth gear.

3. But with the camplate in place, there’s a problem. The first-gear pinions are fully home before the selector forks have reached the end of the track. This will affect fourth gear.

4. With the camplate set to fourth and removed, the top right pair (fourth) are not engaged. The top and bottom engagement must be evened out by adjusting the bush.

4. With the camplate set to fourth and removed, the top right pair (fourth) are not engaged. The top and bottom engagement must be evened out by adjusting the bush.

In