‘if a bodge does the job and won’t make a proper repair impossible, why is it a problem?’
Are you a bodger? It depends how you look at it. If the definition is something like ‘the pragmatic use of ingenuity to perform a temporary repair’, probably we are all bodgers sometimes. And besides, as technology progresses, the hightech repairs of yesteryear would arguably be considered bodges today. It depends on your resources, too; it’s easy for an engineer with access to a full machine shop to look down on the work of a bloke in his shed. Years ago, I remember being sat on my backside when, after showing off what I thought was a cleverly engineered repair, I was loftily told: ‘It’s a bodge, but it’ll probably work...’ But tempers inevitably rise when the workmanship on your latest purchase falls short of your expectations. I’ve seen some really nasty ‘repairs’ – the best was a front wheel spindle welded into the forks because its thread had stripped – and it has led me to wonder if there is a universal rule about where to draw the line of shame. Take the late John Masterman, who famously rode all over the world on an ancient and filthy 1928 Norton with a screw-jack holding the cylinder head down. Sounds shocking, but a) it worked and b) it didn’t make the original problem any worse. There’s the line; so long as your bodge does the job and won’t make a proper repair impossible in future, why is it a problem? Even that welded-in wheel turned out OK; the welding was so bad, it fell off with a blow from a chisel... sometimes it’s just as well the job has been bodged.
I’ve had this book since I was at school; well, I was borrowing it off my dad then, but the thing is I have been referring to it ever since. Initially, I was only really interested in the pictures, but since then it has made more sense every time I’ve read it. Written by Vincent-HRD co-designer Phil Irving for Motor Cycling magazine, it is still one of the best technical works around for explaining why things need to be as they are to make an engine go well. If you don’t have a copy on your bookshelves, you should start looking for one now.
getting your collar felt
I’ve been doing an internet blog since last year (rickparkington.co.uk) and talk of my mid-’20s BSA project collection drew a question from Mike Boniface. He’s building an early Model L side-valve 350 and asks how much crankshaft end float is to be expected; anticipating just a few thou, he found several millimetres and he wants to get it right before continuing. The lack of information for older bikes can be a bit intimidating; with parts hard to find and expensive to buy, nobody wants to learn by their mistakes. Today we’re spoilt for choice between factory manuals and a variety of outside publications – but in the 1920s most owners had few tools and limited knowledge, so the bikes were made very simple. You’d get a comprehensive owner’s handbook, but it had more to do with how to ride than tech specs, often casually suggesting setting the tappets to the thickness of a visiting card. Mostly the engines are forgiving enough to be selfexplanatory, but the crankshaft end float caught me out, too; my engine had as much as Mike’s and there was no obvious way to shim it to a more reasonable clearance. It seemed something was missing; there was, and again the answer was very simple. Outside the main bearing in the crankcase is a sort of cup into which the collar behind the crankshaft drive sprocket carrier nestles, but between the two there should be a thick felt washer – it is this that regulates the end float. It’s hardly precise and when first fitted the crank feels very tight, but it will soon compress, sealing in engine oil and leaving just enough float. If you can’t find a suitable felt washer, try Autohose (01782 542486) who supply thick felt in handy-sized slabs to cut yourself – ¼in thick should do it, just soak it in oil before fitting.
Paul Bittinger emails from the States to ask about a peculiar problem that spoiled a recent ride though the Blue Ridge Parkway on his 1974 Bonneville. Dropping downhill under engine braking, with the rev counter showing 3000- 4000rpm, the bike started making a sound Paul describes as a ‘tank tank tank’ noise. After pulling in the clutch and allowing the motor to idle, the noise continued for a short time before disappearing. But it started again as soon as Paul carried on his descent. At one point he tried revving through the noise, but the engine was flat and wouldn’t pull. Paul has had various suggestions, from a loose pushrod end to crankcase vacuum interfering with the working of the oil pump; “Compression and all settings check out OK and the noise certainly isn’t ‘pinging’,” he says. “What do you think?” This is a new one on me. In my experience loose pushrod ends make no noise and only cause problems if oil gets in and creates an hydraulic lock that closes up the tappet gap, so I don’t think that’s it. Crankcase vacuum? Running on a closed throttle certainly creates a vacuum in the cylinder (that beneficially brings up a bit of piston lube from the sump) but if it created excess crankcase vacuum, surely the result would be over- not under-oiling through wet sumping. Admittedly this can cause some power loss, but attended by very obvious clouds of smoke and leaks. Although Paul says the noise isn’t ‘pinging’ (‘pinking’ as we call it over here), the power loss and return of performance after a cool-off really sounds like preignition, where the engine gets so hot inside that the mixture ignites without waiting for the spark to occur. Pinking isn’t the only noise associated with preignition, there’s also ‘knocking’ which sounds more like what’s happening here. Pinking is the tinkling sound that occurs under acceleration and sounds like tiny pieces of gravel blowing through the exhaust; the kind of knocking Paul has experienced reminds me of the sort of ‘pung... pung... pung’ noise that you get from old two-strokes on overrun. On overrun with the throttle closed, the engine is fuelling via the pilot system. This has a tiny petrol jet and system of airways of its own. The jet can only pass a measured amount of fuel, but although closed, the suck from the engine is bound to draw a certain amount of extra air past the slide – especially if the carburettor is worn. My suggestion is that this will weaken the pilot mix; on a short descent it won’t matter, but on a long one maybe it’s enough to cause overheating – especially if the plug grade is on the soft (hot) side. I think I’d try a harder plug and check the carb slides and bodies for wear.
Rob Heatley is another reader who got in touch via my blog to ask advice about a primary chain tensioner problem on a 1978 Bonneville. Removing the plug that covers the adjuster, he was disturbed to find it brought with it the bit of the crankcase into which it fits; this subsequently turned out to be mostly chemical metal. “The only way I can think to repair it is to plug the area and create another way to tension the chain. Is it something you have come across?” asks Rob. Yes it is, Rob. Overtightening to stop a leak (that is probably from elsewhere anyway) puts a strain on this thin-walled lug, so it is often cracked or broken. I can’t think of an easy way to devise another tensioning method – short of avoiding it by fitting a belt-drive system. Obviously welding is the best solution, but that would really require an engine strip.
The only dodge I can think of is to fit one of the later-type adjusters fitted to the 1982 models. These use a threaded adapter that screws in place of the plug, enabling the chain to be adjusted without removal, then you can glue it in by whatever means works best. It’s worked for years on my Trophy, which has a crack in the crankcase here, and it’s an improvement in that it makes chain adjustment the work of a couple of minutes with no need to drain the oil first. But the problem in this instance is that, although there’s no need to remove the plug from its dodgy threads, it now takes the spring load of the tensioner which may prove too great for a chemical repair. If so, I fear welding may be the only solution.