Write in/get opinion
Holistic medicine and the workshop: an unlikely mix? Well, isn’t the concept of treating the body as a whole, rather than concentrating on specific symptoms, a bit like looking into why the big-end keeps going instead of just doggedly replacing bearing shells? There’s always a bigger picture. Take Tony’s Rex Acme; three weeks before the Banbury Run, he ran low on oil and it seized. “Where can I get a piston in a hurry?” he asked.
Well, you can’t. I use Triumph pistons, but they need modification and a special smallend bush. So instead I suggested that he cleaned up the original piston, freed the rings, got the smeared alloy off the bore and put it back together.
But Tony’s local engineer reckoned the piston was scrap, a rebore was needed and he should strip and check the bottom end. Hmmm, makes me sound a right cowboy… But then again, just as few doctors will accept alternatives to prescribed medication, a reborer inevitably advocates a rebore. That’s OK unless parts are scarce, then you have to take a wider view. If Tony re-used the piston, it might rattle and smoke more but that’s all – and at least it would be back together for the run.
As for the bottom end, with total-loss oiling there’s no pump to pick up debris and inject it into the bearings – and if the supply stops, the splash system will starve the piston, first causing it to seize while there is still just enough oil left for the bearings.
Tony brought the bike round and we flushed out the crankcase with petrol; very little debris came out and the bearings felt fine. Although Tony had managed to clean up the original piston, I machined him up a Triumph one anyway.
Thing is, the Rex could easily have been awaiting parts for the rest of the summer; instead, after a 12-hour day (and a bit of alternative medicine) it’s back up running and ready for Banbury.
‘THE ENGINEER SAID THE PISTON WAS SCRAP, A REBORE WAS NEEDED’
Gordon Dale has bought a 1962 Triumph TRW, the 500cc side-valve twin supplied to the armed forces. He asks if there’s any way to trace the military history of the bike. I had a word with my mate Will about this, he used to be into military re-enactment and still has a khaki M20 in the garage. Will said that the Beverley Museum of Army Transport are the first port of call and he also advises Gordon to join the Military Vehicle Trust (www. mvt.org.uk) who have quite a bit of expertise and information at their disposal. The Vintage Motorcycle Club library (01283 540557 vmcc. net) hold factory records for Triumph and also have military despatch cards detailing batch orders and machine numbers, so they may be able to provide information on when the bike was manufactured and supplied. The charge for a record search with the VMCC is a very reasonable £10 for nonmembers and free to club members
GETTING THE NEEDLE
A bit of feedback from Malcolm Ross, who has sorted his Triumph Speed Twin carburettor problem (last month’s Fixes). He says: “I think your comment about float height and carbs built up from mismatched parts makes you a psychic!”
It would save a lot of time in the workshop if I was… but no such luck, Malcolm! Anyway, apparently when he got the bike, the carburetter had an incorrect, 7° float chamber – Amal supplied various angles to suit carbs with a downdraft. A new, vertical chamber was obtained from Burlen Fuel systems and came with one of their ethanol-resistant plastic floats and a new needle. Malcolm was a bit puzzled to discover that the new needle had two clip notches instead of one, as on the original needle, but by measuring up he worked out which one to use.
When I suggested that the bike’s excessively rich running could be due to incorrect float height, Malcolm took a closer look and this time noticed that alongside the two grooves on the new needle were stamped tiny letters ‘C’ and ‘P’. These turn out to represent the two materials used for floats: copper and plastic. Measuring the needle from the copper float had led Malcolm to use the ‘C’ groove. Changing to ‘P’ for the lighter plastic float led to a huge improvement. Thanks for letting us know, Malcolm.
Jethro Bell writes in from Royston, Herts, to ask if he can fit a twinleading-shoe front brake to his 1955 Triumph T110. As he says: “I don’t expect it to be like my Fireblade but the standard brake is very poor!”
Triumphs of this period had a
half-width hub with a big alloy brake plate fitted with an air scoop. This brake plate has an anchor which extends upward and is secured to the fork with a heavy P-clip. The easiest TLS brake to replace it with is probably a 1968-70 Triumph/bsa type, but this is anchored with a peg on the fork lower and also has spindle clamps, rather than the push-through axle of the T110. I think the solution would be to change the forks (or at least the fork bottoms) for the 1957-on type; these are clamp-fitting and have a locating peg for the brake plate. You’d need to make sure the peg position is the correct height – they differ for 7in and 8in brakes – and that the axle is the correct length to suit the fork width (again, there are two, but these hubs will take eitherlength spindle. Unfortunately it’s likely to be a costly business.
A cheaper alternative might be to contact Ian Campbell at Classic Brake Services in the Peak District (07811 356619). Ian often finds cargrade linings have been fitted to motorcycle shoes and they are too hard. It’s also possible the contact area is poor due to drum wear or previous skimming; he can machine linings from the correct material to suit the drum, which can make a dramatic difference. Obviously modern brakes are much more effective, but if they are completely hopeless it’s more likely to be an actual fault than just poor design.
Is this freed-off, previously-seized piston fit only for the bin? Maybe not, reckons Rick
With a bit of intelligence, TRW’S military history might be traceable
Alternative grooves on new needles can lead to errors
Peg on the fork leg anchors Triumph TLS brakes