‘AS BIKES HAVE BECOME MORE SOPHISTICATED, PROBLEMS ARE MORE PREDICTABLE’
Have you noticed there tend to be more British ‘fixes’ here than for Japanese or European bikes? ‘That’s unreliable British bikes for you,’ you may say... but maybe there’s more to it. Glenn Curtis asked why his wife’s Yamaha XV535 starts and ticks over fine but misfires up to about 45mph, pulling cleanly thereafter. New coils and leads haven’t helped. With a Triumph, I’d start looking if the slide cutaway or needle setting was wrong; parts on Amal carbs are so interchangeable that often a worn part is replaced with something that fits... but isn’t the correct part. But less is interchangeable on Japanese bikes. No, Glen’s problem was bound to be ignition and my guess was a ‘sticky’ electronic advance. I confidently rang Marcus Rex at ignition specialists Rex’s Speedshop for confirmation. “No,” said Marcus, “It won’t be that. Their only ignition issue causes the rear cylinder to cut. And coil problems would generally be worse at high revs, not better. I’d say it’s a carb fault.” It seems that as bikes have grown more sophisticated and faultfree, such problems are so predictable that someone like Marcus could almost diagnose the fault just by knowing the bike model. When it comes to British bikes, as you fix one problem they’re busy thinking up another. But now that the classic scene means modern bikes are expected to outlast their design lives, there’s more likelihood that the unpredictable will occur. At that point nobody will know what’s wrong and a new learning will begin. I wonder if Glen’s problem is due to the ethanol content of the fuel attacking rubber components in the carbs...
Oh dear, this is getting to be Rick’s monthly moan... after complaining about stainless spokes, now it’s powder coating. It’s a good, tough finish but too often it gets put in the wrong places; here on the sprocket mounting face of a rear wheel, where it makes the sprocket difficult to fit and will go on to compress in service until the sprockets bolts become loose and it all starts to chatter.
Electrical earths and threaded holes are other common victims. Before sending things for paint, check what should be masked and tell the coater what you need. It’s a lot easier than getting it off again after!
Rattly ariel Red Hunter
Martin Bailey from Durham emailed to ask about a nasty noise from the cylinder of his 1947 Ariel NH350. The bike had a top end rebuild 500 miles ago and everything seems fine apart from the noise, which Martin describes as a metallic, dry-sounding rattle that, fortunately, doesn’t seem to be getting any worse. He suspected the magneto drive chain, but the tension seems to be correct – and he doesn’t think it’s the small end bush as this was carefully reamed to require firm thumb pressure when fitting the gudgeon pin. The piston would be my prime suspect. Being essentially an aluminium bell, it makes quite a racket if it gets a chance to rattle about in the bore, and even just a partial seizure – or tightening up – can lead to enough metal erosion to give it the space. But I also think the small end sounds too tight. The pin can be a tight fit in the piston; the idea being that, from cold, the harderwearing bush takes the load of movement, giving time for oil to get around before the pin moves in the soft piston. But if it’s tight in the rod, it may have seized – and while a small end seizure can damage the piston, this may not make itself obvious to the rider. It’s also true that handreaming a small end is a difficult job to get right; it is very easy to end up with a tapered hole, meaning that the pin is only a tight fit at one end, and once the tight spot wears the pin will be loose. I think it’s worth lifting the head and barrel to see what’s happening.
Pete Harry has bought a Laverda that would originally have had black-chromed exhaust pipes, but is fitted with bare steel ones. Having tried various exhaust paints with little success, he wonders whether ceramic coating would work and where he could get it done. I had a word with colleague Alan Seeley about this subject and he said it seems to be a very effective solution. It stays on very effectively and is a durable finish, although it is possible to scratch it if you really make a go at it. Al suggested Pete tries Zircotec in Abingdon, Oxfordshire (01235 564050) who are ceramic coating specialists. I was a bit concerned that the finish might only be suitable with brand new pipes, but apparently not so. Hopefully they will be able to sort out Pete’s problem.
The real seal deal
Bit of bad news for Keith Hett with the crank seal problem on his Suzuki T500 ( July issue). Neale Didcock emailed to say that, unfortunately, on the T500 the centre main bearing is fed with oil from the gearbox, with a seal either side of the bearing to keep the oil out of the crankcase; so if gearbox oil is getting into the engine, it means a crankcase split to fix it. Neale recommends replacing all four crank seals at the same time, as they tend to harden if the bike has been laid up. He says the two centre oil seals are both the same; the outer two are different, but all are conventional types and still readily available.
Mick Addison emailed, assuming that I had, by now, completed the Project Royal Enfield and could advise him on how I set up the temperamental gearbox selector. Ha! I’m afraid everything is done in real time here and the gearbox assembly is a pleasure that still awaits me... Last time I built it, Judy said it was brilliant... for about a week, then went downhill again. I should really be saving this for the project feature, but Martin Hitchcock gave me a useful tip. He said sometimes the range of movement allowed by the slotted plate is inadequate due to wear and tear elsewhere in the box. His solution being to take a spare selector plate and (after making sure it is stamped 4 or 5, which indicates whether you have a four or five-speed gearbox) file out the slot to provide more movement. Then, by superimposing the standard one on top, scissor-fashion, you can work out where the stop needs to be at the two extremes and file it out accordingly. I know it’s confusing, but I’ll show you what it all means when I’ve actually done it me-self!
Malcolm Ross complains that he can’t get the alternator clearance right on his 1953 Triumph Speed Twin. The stator is fitted into the primary chaincase outer, the rotor is on the crank and although the outer case is dowelled to the inner, which is bolted to the crankcase, the rotor is not central and rubs the stator. On later models the stator is mounted on a ring inside the case, which is easier to deal with; fitting it to the outer cover always seemed a bad idea to me – although that’s how it is on many Japanese bikes, including the project CB400/4. The answer lies in the dowels which keep everything in place, and I wonder if Malcolm’s problem is simply that he has a mismatched pair of cases. If so, I’d recommend removing the dowels and seeing if he can sort the clearance (through the inspection cover) without them. If so, he may either be able to weld up the dowel holes and have them re-machined or, as a more home-brewed fix, while he has the cases secured in the right place, ream out a couple of the screw holes to take dowel bolts – these are screws made up with slightly oversize shanks to be a snug fit in the reamed holes. It’s an easy job on the lathe and is a trick often found on crankcase bolts.