PUB popped down to Popham for their Motorcycle Megameet, instead of visiting Brackley’s Festival of Motorcycling which was scheduled for the same weekend. In the workshop her efforts expose some of the repercussions of grinding/lapping in of tapers…
PUB popped down to Popham for their Motorcycle Megameet. In the workshop her efforts expose some of the repercussions of grinding/lapping in of tapers…
The Bill Lacey meeting at Evenley (Northamptonshire) always brings out a lot of interesting classic machinery, but PUB also noticed a modern Chinese 125 ‘HPS’ (they wanted to call it Hipster, but that name is taken elsewhere). Readers may have read that the FB Mondial name is resurrected again, and as PUB has one of the old Grand Prix Mondials from their heyday of winning World Championships (prior to the major Italian factories withdrawing from GP racing in 1957) this piqued her interest. The model is not another Yamaha YBR clone, but features a Piaggio designed dohc engine with the full fat 15bhp that learners are permitted (claims vary between 10 & 11kW), rather than the more common 11bhp of the clones. Apparently the current Count Boselli is one of the team responsible for the re-introduction of the name, of which the FB prefix stands for ‘Fratelli Boselli’.
Mistake of the month came when B44 Clive mentioned that he had to collect some parts from the same repairer to whom AJS Mary had sent her Rex-Acme engine and gearbox, it provided an opportunity for PUB to join him and collect it for her.
The box of parts contained a rebuilt Villiers engine and Albion gearbox, plus a surprising array of various rusty/oily bits. Some of these turned out to be items that had been replaced (which was good), but others were items not touched (not so good). In the latter category were the scruffy kickstart and spring, but more significantly the former didn’t fit the very distressed kickstart shaft. Admittedly that was how it had been before, but it wasn’t how PUB was prepared to reassemble the bike. Ideally the shaft would have been properly repaired by metal spraying and machining back to standard, but that would have meant dismantling a very expensive rebuild, and spending lots more. The shaft ought to be hard, but was no longer so due to former owners’ machinations with welders etc. That being the case PUB took her lead from Odgie, that much can be achieved with a welder and angle grinder – although she does not have Odgie’s skill with either.
Adding metal was a slow process as only a little weld could be applied at a time before it was necessary to cool the shaft down (with wet rags) to prevent anything inside the box getting hot. As she is not very good, a few extra spots had to be applied later, when the cutting down process revealed dips or slag. Actually PUB does not use an angle grinder very much, being a bit too likely to accidentally remove too much metal, so more laboriously filed most of the excess off.
Once the kickstart would go on to the shaft a small way it was possible to see where it stuck (either by polish marks, or engineer’s blue if required) and slowly take off the high spots (latterly with a small Swiss file) until it went on with a snug fit. The kickstart was expected to be held by a bicycle type cotter pin, with mating flat on the shaft, however previous owner appears to have drilled straight through as part of their fix, leaving a semi-circular groove instead. Fortunately, the attention to the shaft meant that this groove no longer quite lined up, so that a tapered pin
would tighten up in much the same way as the normal tapered cotter. Knocking up and threading a suitable pin did not take long on the lathe. The refitted kickstart appears to be sound enough, especially as it only has to spin a vintage 250cc twostroke.
An extra little job was to make a new clutch lever pivot pin. The rebuilders had refitted the old one, which was quite serviceable, but very sloppy. As neither the lever nor the casting has an excess of metal, neither was drilled/reamed oversize, but instead a new pin was turned and threaded to suit the worn diameters. There is now much less slop and ‘lost motion’, which is satisfying if not terribly important.
The engine, too, did not entirely meet PUB’s standards, low as they might be (re-using sound old parts and even bearings being normal). In particular, the mainshaft taper was rough from corrosion although now blasted clean. Its mating flywheel and sprocket remained in their dirty and unfitted state – possibly because the repairers had noted that the engine plate studs cannot be inserted with both magneto and drive-side flywheels fitted. Mary had sent it to them with those studs and two of the four engine plates still in
place, which explained why only two of the required four engine plates were present. The taper could have been left for later, but there are fewer tools and facilities at Mary’s place, so it seemed better to tackle it at home.
The only option now (rather than whilst it was apart) was to lap in the taper. However, there are snags with doing this, often though it is recommended (usually for magneto sprocket tapers). For a typical taper, the sprocket alignment will shift by 6 thous or so to take up 1 thous of extra taper clearance. However, one thous of actual metal removal produces 4 thous clearance (2 thous each side of the shaft and another 2 each side of the hole), and so potentially 24 thous misalignment. Grinding in tapers should be done only as much as is necessary, especially one as shallow as this A series Villiers looked.
Furthermore the minimal clearance between flywheel boss and crankcase suggested that this would not be the first time for this engine, and that the boss would have to be cut back first, to generate enough clearance to accommodate the above effect. The flywheel was too big to go in the lathe directly, and making up a mandrel to mount it on too much trouble, so some more laborious filing reduced the boss – its thread providing some guide to keeping things square. Next, and reflecting the need to remove the least metal, PUB used a small stone to clean up the shaft alone, since the surface inside of the flywheel looked fairly good. Again the use of engineer’s blue kept this shaft stoning process from going awry. Then some fine grinding paste was applied, and the usual grinding-in process undertaken.
As soon as a reasonable contact area was visibly obtained, the process was stopped, without attempting to get through all the corrosion pits – which would be too much metal removed. Even so, the
alignmentin addition movedto any previousin excess figure.of 1/32 The inches, nicewell movenew corksthat sprocketin the clutchthe other plates way may a similar amount, so PUB can expect anything up to 1/10 inch primary drive misalignment (depending on how good it was previously). Hopefully the engine plate arrangement should allow spacer readjusting if necessary.
However, that is not the only repercussion of grinding in a taper. Another is that the shaft will move further through the hole, and it may even finish up standing proud. The nut then pulls up tight without clamping properly, and the taper will slip – something always to watch out for. Usually this is easily fixed with a washer that has a hole slightly larger than the end of the taper. In this case, however, it was not quite that easy. The shaft did indeed protrude, as expected, but a washer cannot be fitted because the retaining nut has a flange to make the flywheel self-extracting. Instead, the nut had to be modified in the lathe, to enlarge its existing counterbore sufficiently to clamp properly (PUB hopes) when it is finally assembled. Mary, bless her, hoped that a professional power unit rebuild would just leave a couple of mounting bolts to fit and do up and the Rex-Acme would be ready again. But it doesn’t work like that, does it dear reader?
The month has not been spent entirely in the garage fettling the above. Unfortunately the Popham Motorcycle Megameet clashed with Brackley’s Festival of Motorcycling, which PUB usually attends. Reports say that Brackley was bigger and better, but as she had never visited Popham she decided it was about time to go there instead, and it was a worthwhile visit. The autojumble made a very good first impression, with the first stand visited having lots of good stuff. However that one was exceptional, and subsequently PUB did not find any of the very obscure bits she is seeking. Morini Alan did recklessly state that if the price on a little Motom he spotted had been £500 he would have bought it. Imagine his chagrin when another one was indeed priced at £500 – and his ‘friends’ did not let him forget. No matter, as there were plenty of bikes to peruse, in the marquee and always outside helps. where Some the of sunthe more shone unusual– which bikes are illustrated in the accompanying photos. Unfortunately RealClassic does not yet have Harry Potter type holograms embedded in it, so the demonstration cutaway Wankel engine is not as instructive as at the event. Another trip took PUB in the opposite direction up to the Lincolnshire Fens,
where Maughan & Sons is hidden away – even more so as the normal approach road was closed. Whereas the VOC Spares Co. is the go-to place for Vincent spares, Maughan are machinists and manufacturers, as well as offering some rebuild services, and all dedicated to the marque. In particular they rebuild crankshafts, and the visit proved that PUB’s pre-war assembly was no problem, which will save her from attempting the task with inadequate facilities (such as press and grinding equipment). How lucky she is, to be able to get this kind of service for an obscure machine made in ‘a half forgotten corner of Hertfordshire’ as Bruce Main-Smith used to say.
It was impressive to see shelves of new parts, and lots of work in progress. The classic bike world is extremely lucky to have specialists such as these catering for its needs – but remember that they do have to earn a living. So parts cannot be overly cheap, or riders would still be breaking the bikes for parts as they used to, instead of rebuilding them. Hence there is a correlation between the price/value of bikes, and the spares availability. For the ‘big four’ as they were once known (BSA, Triumph, AMC, Norton), where volumes are higher, a good spares supply nevertheless demands that the bikes hold a decent price, whilst for the lower volume exotica both the spares, and thus the bikes, are inevitably more expensive. The upside is that with those prices supporting spares producers, the bikes themselves remain repairable and therefore useable.
Next problem: where will the petrol come from when the Government phases out fossil fuel vehicles? Actually the proposed 2040-2050 does not represent much of a threat for PUB, as she will be well past riding and probably long gone by then, but it might eventually impact prices…
Wartime German sidecar outfits front Popham’s autojumble, the visitors, and a sunny day
Italian Rumi two-stroke twins were also available in motorcycle form. These were rare in the UK, but even rarer is the Earles forked ‘Corsa’ model in front of the more usual standard model
Pretty little two-stroke twin scooters from Rumi were also excellent performers. The very rear-set pillion, and light aluminium chassis work resulted in a very light front end when carrying a heavy passenger – especially uphill
There were Norton rotaries at Popham, but the Hercules is somewhat rarer, and the Van Veen (with a Citroën engine according to proud owner) rarer still
Popham’s Wankel area provided this hand operated demo to explain the working principle. Unfortunately RealClassic does not contain ‘Harry Potter’ type video pictures
One repercussion of grinding in the taper was a need to cut back this flywheel boss, in order to maintain clearance to the crankcase. A very manual approach was taken – note the file
The Rex-Acme’s Albion gearbox returned with the kickstart not fitted, because it didn’t fit. Some welding and filing later, it magically did fit. With a specially made cotter pin the assembly is now complete, and hopefully will prove satisfactory
New pivot pin is stepped and fitted to the worn holes so as to take out most of the slop from this clutch operating lever
Pitted mainshaft on the vintage Villiers did not satisfy PUB, but grinding in the taper was not without its repercussions (see text)
Although the pivot pin for the Albion clutch lever remained serviceable it was very sloppy. Rather than attempt to bush the holes, a fitted pin was turned on the lathe
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