Distorted reason

‘Even if I buy a pre-war bike, I automatically assume somebody does the parts’

 Do we take the supply of reproduction parts like these Czechoslovakian manufactured flat-tank BSA bits too much for granted these days?

Do we take the supply of reproduction parts like these Czechoslovakian manufactured flat-tank BSA bits too much for granted these days?

Restorer John Wyatt tells me that classic Japanese restorers are turning to more modern bikes than the usual 1970s/’80s staples – less due to changing tastes than gradual exhaustion of the new-old-stock parts supply. For British bikes, a huge range of reproduction parts – which even extends as far as the 1920s items below – has filled this void. But with long production runs and many parts common to all, British bikes are relatively much easier to cater for. The thing is, while suppliers are now making reproductions of highdemand parts, reproduction is only viable for the most popular models. Others, no less deserving of preservation, do not provide the demand to justify remanufacture expense. A disgruntled reader wrote in recently, fed up with poor-quality pattern parts, in particular a pair of Honda CB175 downpipes with a different bend sweep and diameter to the originals. From my days behind the parts counter, I remember the CB175 having a onepiece pipe/silencer either side – but nobody wanted to pay genuine prices, so we sold similar pattern downpipes intended for use with universal silencers. Nobody cared about originality then, the priority was getting the bike through its next MoT – and even today not every restorer is prepared to pay new prices for old bike parts. Manufacturing replicas is expensive – typically if you make a batch of a dozen you will only get your money back after you sell the eighth; if you only sell seven, tough. So you need to be very confident of sales before contracting to make parts. Do we expect too much from suppliers? Even if I buy a pre-war bike, I automatically assume ‘somebody does the parts’ and have the nerve to feel a bit put-out if there’s an item that they can’t supply. For unusual models, you probably have to either put up with what’s available or have it made yourself. There are companies who will copy an exhaust pipe, for example – the catch is that it will cost three times the price of pattern pipes...

 

The Big Fix

Braking Bad

Single-leading-shoe system under-performing? There’s a knack to sorting it...

 Later-style floating brake shoe is an improvement on the earlier design.

Later-style floating brake shoe is an improvement on the earlier design.

Martin Collyer asks how to improve the very poor front brake on his 1961 Triumph Trophy and, while Triumph’s early ’60s front brakes are not the best, there is an essential adjustment. With a single-leading-shoe brake, a doublesided cam opens the shoes, pincer style, at one end and they locate on a pivot at the other. Thus only one end of each shoe is pressed out onto the drum surface – one ‘leads’ (confronting the direction of drum travel), the other ‘trails’ (following the drum rotation), with the leading shoe biting more strongly. By 1968 Triumph were using a twin-leadingshoe brake in which the cam and pivot were replaced by two single-sided cams that presented the shoes in a sort of figure ‘69’, giving two leading edges and greatly increased power. But with the singleleading- shoe design, since the pivot end of the shoe is not actively forced outward, it doesn’t do very much work and on old shoes the lining material is usually less worn at the pivot end, tapering toward the cam end. This uneven wear has actually compensated for the uneven lift, so the brake is probably most efficient when part-worn. But the shoes need to operate concentrically within the drum to avoid spongy action, and for that reason the shoe pivot is a floating fit in the brake plate, secured in place by a domed nut on the outside. By slackening this nut, spinning the wheel and then applying the brake and retightening the nut, the shoes are forced out by the cam and will brace their other end on the pivot, which, being free to move, can settle in the optimum position. Ignorance of this adjustment is usually the reason for a hopeless front brake. The brake will need to bed in again, so don’t always expect instant improvement. Around the early ’60s Triumph changed the design of the shoes; instead of the shoe casting hugging the pivot, it had a flat rather than notched end that allows the shoe some servo effect at the pivot end. Today’s replacements are usually of this improved type.

 

Top Tips

 Want to brush-paint a frame? This is good stuff, apparently

Want to brush-paint a frame? This is good stuff, apparently

Mick Addison got in touch to say he has found Teamac ‘Metalcote’ enamel (primarily designed for agricultural vehicles) very successful for frame painting. He has achieved a deep, run-free gloss and says although the paint initially seems quite soft, it hardens over time. My mate Gordon Geskell and his son Rod have come up with a clever way to drain a tank for the winter lay-up. They use a car fuel pump fitted with a long hose, like a sort of fluid vacuum cleaner. The pipe can be poked into every corner and will continue even when drawing mostly air. I also have to say thanks to Col Garland from Australia who has gone to the trouble of sending me a set of copper bolt soldering irons he bought from a local garage sale, so the shed now resembles some sort of Aztec temple. Assuming I don’t perish from copper poisoning, I’m set up for life! Thanks very much, Col. Er... thinking about it, next time could you keep an eye out for a decent-sized anvil for me?!

 These’ll help Rick solder on...

These’ll help Rick solder on...

 

Spoke speak

 Keyhole spoke holes make wheel-building a doddle – see ‘Spoke Speak’

Keyhole spoke holes make wheel-building a doddle – see ‘Spoke Speak’

Kevin Ellis emailed to ask my advice with building his BSA Bantam D1 rear wheel. Both of the spoke flanges have keyhole slots and Kevin wonders whether he would be best off fitting the inner spoke runs to each side first or fitting both inner and outer, one side at a time. Neither he nor Harry, his workshop terrier, can decide. The good thing about keyhole slots is it doesn’t matter too much. Instead of having to poke the internal spokes (the ones whose flattened heads lie on the outside of the spoke flange) through a forest of others, like some reverse version of Ker-Plunk, spokes can easily be inserted through the wheel rim and simply hooked into the flange. You could even put all the spokes into the rim first, with the nipples lightly screwed on, and go round buttoning them all into the hub from there. But I’d advise completing one side first, then turning it over. I told Kevin that Finbar is rubbish at wheel-building, too. He says the whistle from the spokes of a spinning wheel, that only dogs can hear, drives him nuts!

XS250? Don’t start...

Lyn Edwards emailed my blog (rickparkington.com) to ask if I could advise about a problem with a 1979 Yamaha XS250. When starting from cold, the engine won’t rev past 1200rpm regardless of throttle opening. When riding, it doesn’t run well below 3000rpm. New plugs, points, condensers, inlet rubbers, carb diaphragms, etc have made no difference. I passed my test on an XS250. They had a very poor reputation for starting that mine seemed to delight in; 30 seconds on the button followed by 25 kicks usually did it. If I was running late, dad would go out and begin the process while I ate my breakfast. I had another XS later as a hack, an ’81 model with electronic ignition which, significantly, didn’t suffer from the problem. Two things strike me about Lyn’s bike. First, it sounds like the problem is more difficult when cold than hot, suggesting that the choke may not be working correctly. The choke system on these carbs, from memory, is a plunger that opens or covers a separate fuel jet. I think there’s a rubber pad in the plunger, and if that is perishing it’s possible the jet is blocking and not supplying the extra fuel a cold engine demands. But, thinking back to the difference between my two bikes, I wonder whether the ignition advance is sticky. The mechanical bob-weight system seldom gets any lubrication, so if it was sticking at full retard on start-up, the engine certainly wouldn’t want to rev. If the weights are stuck by hardened old grease, it could be that the grease softens as the engine warms. Might be worth a look and a squirt of oil...

 

How To

Do a jig for drain-plug drilling

I needed to drill some drain plugs for lockwire. You can buy kits, but I needed it done now. Here’s how I made a jig...

  1.  The first step was to select a piece of flat bar of about the same thickness as the bolt head and drill a hole of the size that I needed for the wire.

1. The first step was to select a piece of flat bar of about the same thickness as the bolt head and drill a hole of the size that I needed for the wire.

  2.  Next I positioned a nut in the best position to align with the drilled hole and scored around it, centre-punching at the apex and drilling a small hole.

2. Next I positioned a nut in the best position to align with the drilled hole and scored around it, centre-punching at the apex and drilling a small hole.

  3.  Hacksawing along the scored lines to this apex hole produced the correct angle to match two sides of the hexagon. I then cut off the surplus bar.

3. Hacksawing along the scored lines to this apex hole produced the correct angle to match two sides of the hexagon. I then cut off the surplus bar.

  4.  With the bolt-head located into the jig and clamped into a machine vice, the drilled hole guides the fine bit neatly through the corner of the hexagon without skidding.

4. With the bolt-head located into the jig and clamped into a machine vice, the drilled hole guides the fine bit neatly through the corner of the hexagon without skidding.

 

Shock Tactics

Another question from Martin Collyer; he says he enjoyed the Fixes supplement but referring to the ‘timing by degree disc’ section, he asks how to lock the engine to undo a Triumph crank pinion or sprocket nut. The usual answer is to use the rear brake to lock the rear wheel with the bike in gear, but lost motion from all the various backlash in the drive train can reduce the chances of success – and not all rear brakes are that good. You can pass a broom handle through the spokes, resting on the swingarm but unless you get it close to the nipple where the spoke is supported by the rim, you’re likely to end up with bent spokes. You can wedge a hard nylon block under the chain where it encircles the clutch sprocket, but make sure you’re using the crush of the chain stretched over the block to halt the wheel, not just wedging the resulting lump against the casing, which can crack. Shocking free by hitting the spanner with a copper hammer is actually gentler than heaving, but best of all is to use a compressed air ‘rattle gun’. They’re cheap (if you already have a compressor and work so effectively that the compression of the engine is usually enough to hold the crank without any wedging.

Book look

Back in 1959 and 1961, Peter Edwards bought a couple of yearbooks that listed all the motorcycles and scooters for sale at the time. Long since lost, he would like to know what they were called so he can perhaps replace them. I remember books like this in the 1980s, but haven’t seen a 1950s equivalent, so I phoned avid motorcycle historian and former VMCC librarian Annice Collett. Annice thinks the books were probably the Daily Mail Motor, Motorcycle and Scooter Guide, which she suspects were on sale around the time of the annual motorcycle show. Shouldn’t be too hard to find, but Peter may need to shell out more than the three shillings and sixpence cover price to replace them...

Stumped by a sump

After an oil change and oil tank wash out, Dave White is suffering with wet-sumping on his 1972 Triumph Daytona. He says that although the oil still seems to be returning to the tank, the sump is filling after about a mile’s riding. “The oil pump seems clean with no dirt or sticky valves; am I missing something?” The ‘dry sump’ design of British engines means that oil is pumped to and from an oil tank. Wet sumping is when something prevents the pump from returning the oil, so the engine gradually fills up, until smoke and leaks appear from everywhere. This is usually a problem in the pump, luckily not the feed side (which is gravity-assisted), but the scavenge. If Dave is missing something, I reckon it has to be a speck of dirt in those pump valves. There are two ball valves in the base of the pump which have to close perfectly to draw the next charge of oil. Of course, it’s much easier just to suck back the aerated oil they have pumped than draw fresh against gravity from the sump,  and any sealing issue on this valve will cause problems. I once had a ball held off its seat by a tiny cleaning brush filament, no bigger than an eyelash. Something really small is easily missed and may also cause the sort of partial failure Dave is experiencing. The other possibility is a leak in the pick-up pipe in the sump, which will also encourage the pump to draw air rather than oil; but as this has happened soon after cleaning the system – which typically disturbs debris, not all of which can be removed – I’d remove the pump and have another look under a strong light. Also, try reseating the balls into the pump body by giving them a tap onto the seatings with a soft drift.

 

Rick's Patch

distorted reason

Rick finally unravels the mystery of why his Martinsyde has turned from sprinter to limper – it’s all down to pressure...

 Hard a-port: why the Martinsyde’s performance is all at sea

Hard a-port: why the Martinsyde’s performance is all at sea

Finally, I think I have worked out the cause of the Martinsyde’s disappointing performance, at its worst at the Ramsgate sprint where it coughed and spluttered off the mark, accelerating to a steady crawl by the chequered flag. Valve timing? Well, the performance has varied, generally deteriorating, without my making any alterations there and a check revealed it was fine. Suspecting a leaky valve, I removed them. But again they looked OK – and a grind brought no improvement. Filling the ports with spirit and leaving them on the bench for ten minutes confirmed that all valves were well sealed. So what could the problem be? Turning the reassembled engine over with the exhaust pipes off, I detected a very slight hiss, as from a leaky exhaust valve, even though it tested out fine on the bench. Injecting spirit into the exhaust port while fitted to the engine proved the point, the fluid dripping through the ‘closed’ valve. Bolting the port to the head causes just enough distortion to oval the valve seat. Beneath the port is a copper washer that seals it to the head; the action of compressing the washer seems to distort the casting, dammit! Like the man said, it’s the one you don’t see that gets you...

 
In