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About oldjohn

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  1. If an engine has been idling for some time, or you've just completed a long downhill run with the throttle closed, then a little fuel can collect in the crankcase and you may find that the engine will hesitate very briefly upon reopening the throttle. A quick blip with the clutch disengaged should be all you need to keep this from happening. But if it stutters or four-strokes for more than a moment it's an indication that the engine is running rich so if the air filter and so on is in good shape you may need to adjust the jetting. Always jet from each end and work your way towards the middle, ie. do the pilot jet and air screw first, then the main, then finally the needle/needle jet.
  2. The wooden stand is such a simple thing but the first time you use it you wonder why you didn't do it years ago. Having the case lie flat and stable when assembling the gearbox or when fitting seals and bearings makes the work so much more pleasant. When I'm disassembling an engine I stuff a couple of oil absorbent pads into the opening of the stand to catch any oil that drops when the shafts are pulled out - it helps prevent making a mess on the bench.
  3. Thanks Peter. It was modified to take a 72mm stroke crank and a different barrel among other things - not a trials motor obviously but the tools work on any Bul engine. John
  4. There seemed to be some interest in some recent posts I made about Bul clutch upgrades, so I thought I might post a few engine related pics that might be of interest too. These are just simple homemade bits that make life easier if you do lots of Bul engines. First off we have what looks like four bits of 2 x 4 screwed together, and that's exactly what it is. Hardly high tech but very very useful for assembling and disassembling Bul engines. The shafts hang down into the opening so the engine lies flat and stable on the bench. Much nicer than having it wobble around on timbers and worth spending 10 minutes to make. Next is the tool I use to push the crank out of the case. This is nothing more than a piece of 10mm aluminium with a large hole in the centre and drilled so it can be attached to the case in place of the seal housing with some long 6mm bolts. Once it's in place the crank can be pushed out gently with a plain old 3 leg puller. I hate beating on crankshafts and/or wedging cases and this thing makes disassembly an easy and gentle process. Don't be tempted to use a seal housing to do this - it's way too fragile. When it comes to reassembly, again, I hate to beat on things. So I welded a nut that fits the end of the crank to a piece of threaded rod and drilled a hole through a short piece of square tube to act as the beam of this puller. If you make one for each end of the crank you can gently assemble both sides easily and centre the crank in the cases accurately. Last one is a homemade clutch holding tool. The clutch hub nut needs to be tight, and tools made from old clutch plates just aren't strong enough. I made this from a piece of steel tube that I hammered into shape and finished off with a die grinder. High rpms tend to loosen the nut and wear the spline in the hub, but with this you can really torque it up tightly.
  5. If the clutch isn't slipping or dragging with the oil you're using now then realistically there's nothing to gain by changing to something else. I only tested maybe a dozen different oils so it's quite likely that there are others that are as good or better than the Castrol Power 1. Having said that, all the non-friction-modified oils had very similar torque capacities so probably the best approach - as you said - is to pick one that doesn't get too thick when it's cold or too thin when hot.
  6. The only one I tested was 5w 40. Other grades may work just as well but I liked that this one had little drag when cold yet still had more holding power than ATF.
  7. Oils specifically designed for motorcycle engine/clutch/gearbox use were the best. Castrol Power 1 Racing 4T for example had around 15% more torque capacity than any of the ATFs - not a massive improvement I know but it all helps and might be the difference between a clutch that slips and one that doesn't. The same oil can be used in the gearbox.
  8. Nothing could be further from the truth - you can easily double the torque holding capacity of a Bultaco clutch with the right parts and oil (hint: don't use ATF). The clutch cover with the welded attachment is part of a testing fixture I made to test different plate combinations and oils. Some would hold well over 500lb/ft of torque. The reason for all this clutch work is the 75hp LSR bike that's shown semi-finished below. That engine has destroyed a set of Barnetts in less than an hour, while the Honda plates with thin steels and an appropriate oil hold up much longer. Of course you don't need all this capacity with a Sherpa, but a better clutch allows the use of lower spring pressure without slipping, and that makes the bike more pleasant to ride.
  9. OK, to file the tabs properly you need a simple fixture like this one. It's made from 12 x 32 flat and will make the tabs a consistent width. Note how the small piece on the underside is only welded to one side; this allows the tool to be squeezed together when you hold it in the vise, holding the clutch plate in position. The lower edge of the tab rests on the large cross-piece, the small cross-piece supports the opposing tab and locates the plate laterally so you don't have to position the plate manually. You just drop the plate in, squeeze it in the vise and start filing. The vertical piece on the top is just a guide or fence to prevent you from filing a notch into the OD of the plate. It takes about five minutes to file a plate but usually you also have to dress a few high spots off the OD so the plate slips in easily. I've done quite a few sets like this, mainly used with thin 1.2mm steel plates that I get laser-cut locally. The thin steels let you use more plates which helps with high-output engines. My apologies for the terrible phone photos - hope you can see what I mean.