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VOC of North America


Tips and How-tos

Velocettes have many unique features that mean that a certain amount of specialist knowledge is necessary to work on them successfully. Even enthusiasts who have experience of other British marques find that unexpected problems crop up when they turn their hand to a Velocette. Ed, and/or myself (Geoff Blanthorn) even after many years’ experience, still come across new quirks, but have (we hope) learned most of the tricks!

Ed’s philosophy has always been to encourage owners to work on their own bikes. This gives them more confidence to deal with problems that might occur on the road, and gives them a greater appreciation of the finer points of the bikes (and their weak spots!). To this end he has always been happy, time permitting, to answer owners’ technical queries. If you have one, why not e-mail it to us, and we’ll try to answer it right here.

Meanwhile here are a few miscellaneous tips which have cropped up recently:

Converting a Viper to Venom spec: This is actually pretty simple provided you can find (and afford!) the parts. You need to replace the barrel, head and piston  and exhaust pipe. The balance factor is different, but don’t worry, the different weight of the piston does all that’s necessary. The engine sprocket should be changed from 21t to a 23t one (which reduces torque on the clutch) and to cope with the extra loads, the rear chain and sprockets should be changed. A larger carburettor is also required (we have new Amals or Mikunis) unless you are converting to MSS spec.

Harley pistons: A Harley-Davidson “74” piston can be fitted to a Venom/MSS with little difficulty. The main differences are that they are oversize (+.040" and more), the gudgeon pin is about 5mm higher and slightly smaller diameter, and the small end width is also slightly less.

The oversize is not a problem if you are at +.020" and need a rebore. The pin  height means that the compression ratio is reduced by a couple of points. Removing any compression plates fitted will help toward restoring the correct figure, but otherwise the cylinder base flange must be machined. Of course, with modern petrol, a lower compression ratio is not altogether a bad thing! The smaller pin diameter can be accommodated by rebushing the small end, and the rod small end boss can be machined to fit inside the piston, or (a little more difficult) the piston may be opened out by milling.

The Big MSS which we have used a Harley piston and “Iron MSS” flywheels (96mm stroke). With this set up, the higher pin position is an advantage, as the piston rises to the same position at the top of the stroke, and there is no need to use spacers under the barrel or increase the height of the motor.

Clutch cable free play: If your clutch cable suddenly develops rather more free play than normal, especially if you find after taking up the slack that you have lost full movement of the clutch lever, suspect that the gear box sleeve gear bearing has moved. If you are lucky, it’s just that the retaining ring has unscrewed itself. You’ll have to remove the clutch, of course, but then it’s easy to re-tighten the ring, and peen the aluminium of the gearbox end into the slots, using a square ended punch. If the thread is stripped, stand back and throw money at it!

Clutch tightens up after refitting to bike: We’ve found two different things here. The simple one is that you have forgotten to put the sleeve spacer on the sleeve gear, or that you have the wrong sized spacer. The second and more obscure reason is that the “frying pan” (thrust race spherical cup/clutch release lever) has worn to the extent that that spherical part of the release bearing protrudes through and fouls the sleeve gear bearing oil shim. Note that the frying pan should rest against the gearbox end, and the shims at the pivot end should be sufficient to make the lever parallel to the gearbox face at mid-stroke. Note also that when fitting the clutch, the sleeve gear nut must be fully tightened against the sleeve gear distance piece, and then secured with the locking tab.

Spark timing: If you don’t have a timing disc, you may wish to note that on 86mm stroke motors 36º is .4" (or 1cm) before TDC, and 38º is 7/16” before TDC. Click here for a free timing disc!

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