‘use a soldering bolt as a conductor to press heat into the work’
I probably shouldn’t tell you this, because I’m still looking out for them myself, but you know those old solid copper soldering bolts that you have to heat up on a gas ring? They are absolutely fantastic! Sure, an electric soldering iron is the obvious choice for wiring, but when it comes to soldering petrol tanks or (in my most recent case) Scott radiators, they are just not man enough unless you happen to have an enormous one. See, I’ve had little success with soldered tanks over the years; I soon found that my electric iron was too feeble but a gas flame too easily distorts the thin sheet metal, especially when you are trying to solder in something solid, like a brass tap boss. Getting the brass up to soldering temperature puts the surrounding sheet well into warp territory. With luck, it will more or less resume its shape under cooling, but solder is ‘hot short’ – it solidifies over a narrow temperature band – so while it sets, the steel is still shifting around. At best, you get leaks and at worst, a tank that looks like it’s been kicked around a football pitch a few times. A soldering bolt is the answer. Less warpingly aggressive than the gas flame, you can nonetheless play a flame onto the iron, using it as a middle man – literally a conductor – to press that heat into the work. Admittedly, it’s a bit of a threehanded job, but I’ve had more success with this method than any other. So I’m currently keeping an eye out for old copper bolts in different shapes and sizes... funny how the old ways are often the best!
Never mind your fancy multimeters, I’ve carried this bulb tester in my jacket pocket for years. Mine is a sturdy old BMC car panel light, but a twinwire pilot light socket will do, even the guts of an indicator; anything with two wires that will fit in your pocket. Beginning at the battery, you can run through, connector by connector, to find a lost power supply.
Meters can misleadingly record a voltage even when the actual current is inadequate, but the bulb tells you exactly what you are getting. Its brightness (or otherwise) will reveal poor connections or earths and it also doubles up as a handy inspection lamp after dark.
Now Jim Brough is rebuilding a Honda CB350 Four, but is a bit uncertain about timing up the ignition. He asks: ‘Does the timing mark relate to cylinders one and four or two and three, and is the 350 the same as the more familiar CB400/4?’ Well, looking at the parts lists, yes the numbers of the ignition components are the same for 400 and 350 (out of interest, the points plate pictured in the 400 Haynes manual is stamped 333, which is the parts model code for the CB350). I didn’t have to think about timing on the Project CB400, because it was fitted with a Boyer ignition but I think the points set-up is pretty simple, too. The advance unit is keyed to the crank, so it will only fit in one position. That should locate the 1 / 4 or 2 / 3 mark in the points plate window when the pistons of those cylinders are ready to fire. You don’t have to worry which of the two is on compression and which exhaust, because the coils, being double-ended, spark both cylinders at once anyway. Maybe not a universal rule, but I’ve often found that when a manual doesn’t seem very clear about something, it’s often because it is simpler than it looks.
Follow the sines
Simple question: if your ignition timing setting is, say, 38° before TDC, how do you convert that to millimetres of piston travel – or vice versa? Roger Dodgson was the enquirer, he’s trying to time up his Moto Rumi Tipo Sport. Now , I know this question and there are two things I can tell you about it. One: it is an ideal question to sort the wheat from the chaff of technical ‘experts’. Two: I don’t know the answer. I’ll get my coat... See, I’ve seen this question answered before, incorrectly and provoking a storm of abuse, but I have never made a note of the correct answer. The general blunder is to say: ‘simply divide the crankshaft stroke by 180 (representing crank degrees).’ But this doesn’t work, because the piston speed (and therefore movement relative to crank rotation) varies through the stroke. Briefly stationary at top and bottom, it accelerates to maximum speed halfway up before decelerating again. I lamely told Roger I was sure I had read the answer somewhere in an old copy of CB but couldn’t remember either the answer or in which issue. Luckily he found it in the CB archive. The answer was supplied by my friend and predecessor Mike Jackson in the April 1992 issue. Now, although Mike describes the solution as ‘schoolboy mathematics’, I think he must have gleaned a lot more from his lessons than I did – it’s a half-page of intimidating sine and cosine calculations, for goodness sake! There’s no room to reproduce the whole thing here, but if you need to know, look out at autojumbles or on the internet for a secondhand issue or contact us at the CB office for a photocopy. Well done, Roger... and well done Mike!
Patrick Fizgerald’s delight at acquiring a 1962 Bonneville was slightly deflated with the discovery of a nasty case of hacksaw surgery inside the crankcase. As he points out: ‘The cases are old and welding could cause problems; should I leave it as it is?’ The missing lugs originally housed ¼in cheese-headed screws which secured the crankcase mouths front and back. They’re concealed and fiddly to access, so it’s likely that they were either seized or someone broke them attempting to split the cases without noticing they were there. Old aluminium can be tricky to weld; typically oil will have soaked into the structure to a degree – that’s why, when you oven-heat a casing for bearing removal, the previously clean surface comes out besmirched with black oil stains that have oozed from within. Heating the aluminium to welding temperature can lead this oil to burn or even explode, causing irreparable damage. Distortion can also give trouble; the localised heat of welding warping the case so that it will no longer be oil-tight. However, Triumph casings of this period are not generally too porous and so long as the welder understands the distortion issue and takes steps to securely anchor the casing to a flat surface, it should be possible to perform a welded repair. Certainly if it were mine I would have a go at it, but alternatively, taking the discreet approach to valour, it’s worth knowing that on later models, Triumph deleted these screws, so it’s unlikely to do any harm just ignoring the problem. Patrick says he’s going to think about it...
Et Tu Brute?
Well, my engineer mate Bruce Hazelgrove really slapped my wrists for saying in my recent drill feature that metric drills increase in 0.5mm increments. Bruce pointed out that ‘proper’ drill sets increase by 0.1mm and the 7.8mm that I mentioned is a tapping size for 9mm, not simply an Imperial equivalent. He also made the point that a full drill set from a proper tool wholesaler isn’t really that much more expensive than a set bought from a DIY store – and it will give you a set for life, having every size you will ever need, manufactured in a good quality material. Fair enough. Point taken, Bruce.