‘Often the ability to think around a problem using your ingenuity is your only weapon’
Although I make parts on a lathe and a mill, I am a mechanic not an engineer. Training gives engineers a work discipline that provides both accuracy and consistency. While I’m proud of what I make, I admit I struggle to make two the same and some of my home-grown methods have drawn criticism from proper engineers. “But then,” I say, “if it works, how can it be the wrong way to do it?” This month I got my answer (sort of). My mate and bespoke leather worker Gez Cater was telling me how he had achieved his first wheel build. To ensure it would be true after rebuild, he took the old Sunbeam’s wheel over to his piano. Pinging the spokes one by one with a spanner, he identified the note from the piano’s keys and labelled each accordingly. Then, after replacing the wheel rim, he tightened the spokes to match their original notes, like tuning the strings of a guitar. He reasoned that, with each spoke back to its original tension, the wheel must resume its original truth. “B... but... that’s not how you do it!” I found myself stammering, staggered by how he had made a relatively simple job so incredibly complicated. But, just like me, Gez derives a stubborn satisfaction from exercising his ingenuity; it steers him away from seeking out and following approved methods. And, after all, it worked. Old bikes are able to find many more ways to go wrong than any text book could ever unravel. Often the ability to think around a problem using your ingenuity is your only weapon. Perhaps that’s why good engineers are often no more mechanics than I am an engineer.
your tube talk
Talking of crushed inner tubes (Fixes August) Nick Hayman emails from the USA to say he and his mates only ever carry 21in tubes on their Baja Desert excursions as all that matters there is they fit any wheel size and hold air. Meanwhile Indian specialist Calvin Jones sent this pic of a tube he pulled out of an old wheel.
He says: ‘It tells its own tale of depression-torn America. Of 20 repairs, only two are proprietary patches; the rest our hero made hmself! I have been known to re-use vintage tubes on my own bikes, but I draw the line at this; trouble is I can’t bring myself to throw it away...’
Laurence Watts in Australia emailed my blog site (rickparkington.co.uk) to say he has just restored a Triumph T100A with various racing mods and wonders why the engine prefix has been overstamped and a letter C has been added (see above). ‘Could the engine have been pulled from the line for racing?’ he wonders. According to the factory records held in the VMCC library (01283 540557) the bike is a standard, early Tiger 100A despatched to a Melbourne dealer in October 1959, so any tuning must have happened in Australia, and the ‘C’ added then. But the overstamping is what fascinates me. It’s not unusual for humble Thunderbirds and Speed Twins to be re-stamped as Bonnevilles and Tigers, but here the prefix is the same – just done again, harder. Triumph’s engine and frame numbers match, but I wondered when they stamped? It’s unlikely to be before the two are bolted together, otherwise there’d be long assembly delays trying to find the matched pairs. Hughie Hancox told me that the frame number was added last of all – but how can that be, if the frame is already painted? Doing the engine number last seems more likely. Look at the picture. See how the ‘T100A’ is very regular (both times) while the subsequent numerals are a bit wobbly? This suggests to me that the model code was a single stamp – faster on the production line than fumbling to stamp five digits – and has simply been done twice because the first was too faint. The actual number looks to have been stamped by another hand, seemingly confirming that this was done some time after the prefix. It makes sense to stamp the prefix first, to confirm the engine spec – compression ratio, cams etc. The individual number could easily be left until the end of the production line. Funny how, of all the people who made Triumphs, the one I’d like to speak to right now is the one that stamped those engine numbers; but then it’s often the simplest questions that are the most difficult to answer...
will my bonnie lump go in whole?
Ken Adams asks whether, once he’s rebuilt his 1970 Bonnie engine, he can fit it into the frame in one piece, as he’d prefer to assemble everything on the bench to ensure it’s oil-tight. To be honest, I’m not sure; it’s certainly going to be a squeeze, although the 1970 models have detachable front engine mountings, making it easier than my ’68 Trophy. I think I’d fit it with the rocker boxes off – these are not difficult to seal, anyway. The pushrod tubes are the big one, and you seal these when you fit the head. Once Ken’s stripped the engine, I’d suggest reassembling it with no internals and trying to replace it in the frame from various angles, which is a lot easier than doing it with the full weight. If he finds a way, he can write it in his workshop manual... and let the rest of us know the secret!
sitting below the plimsoll line
I’m pleased to say my internet blog seems to drawing queries from owners of pre-war bikes, for which information anywhere is a bit short. Latest question comes from Ernie Garvey, who says that, after a rebuild and carb overhaul, the bike is running very rich on its AMAC carburettor and he thinks it’s because the fuel level is almost over the top of the float. He has tried adjusting the level by fitting washers under the needle clip, but to no avail. I think the float is too heavy. Sometimes the brass float develops a tiny leak and slowly fills with petrol until eventually, of course, it won’t float at all – and therefore doesn’t cut off the fuel, leading to flooding. You’ll know a problem is developing if you hear a swishing noise inside the float when you shake it; the leak is usually so tiny that nothing actually drips out. But here the float is still buoyant, it’s just sitting too low in the water like an overloaded freighter. I suspect the float has been repaired in the past and the extra weight of solder is causing the problem, so I suspect the float will need to be replaced. AMAC floats are not exactly common, so I would recommend using one for a separate-float-chamber Amal, which are made new from ethanol-resistant nylon, although personally I would search around for a secondhand original. These, like the AMAC, are made from copper, making them easier to modify to suit the AMAC needle – although beware using too much solder!
Paul Rigby emails to ask about tappet settings on his Triumph. It’s a 1981 Bonneville with an earlier 650cc TR6 engine, fitted with a Morgo 750cc conversion and twin-carb head. The settings for 750 and 650 are quite different and Paul asks which he should use? Unusually, the T140 had a larger inlet gap (eight thou) than exhaust (six); the 650 had conventional settings. I have never found a satisfactory answer regarding the strange 750 settings. Brian Valentine, son of Weslake’s Ron Valentine, once told me that it was to do with finetuning the horrible cam profiles of the 750 engine. John Nelson, former Factory Service Manager said it was designer Doug Hele’s idea, having been drawn from racing experience. Either way, it is more to do with cams than capacity, so assuming the engine still has 650 cams fitted, I would go with the 650 settings.