HeathCliff Engineering NewsEdition 9 Back Issues |
EditorialHi Chicklets, 1. Editorial With Edition 9, HeathCliff News enters a new era as the format is updated and we focus more on the Hesketh motorcycle. In particular, we will run a series of items on progress with development of the new 1200cc machine and Mick will prepare a feature Technical Topic on the bike starting with the sprag clutch in this issue and a detailed look at carburation in the next. This will also be a snapshot of the Master Class Mick plans to organise later in the year. Once in a while we’ll also include some off the wall stuff about the background to the Hesketh and other Hesketh related stuff. We’d also like to hear from you, our readers. In particular:- • First recollections of Hesketh ownership In preparation for the next Technical Topic you might also wish to let us have your carburation concerns. 2. Hesketh Works News Following the move to Turweston two new faces have joined us. Edward, of ‘new’ Cedos’ fame, is leading the machining of new parts and Derek, who has been blue printing Ducati engines for Baines Racing, is leading on engine assembly. New equipment in the workshop includes a large bead blaster so in future, EN10 and other engine rebuilds will include a clean up of all the unpolished castings. Progress with the V1200 is steady. The first batch of con rods has been machined and crankshafts are just beginning to appear. As machine time becomes available, smaller parts are being made and plated. Pistons, which have been a bit of a problem, are now on order and expected during February. New products available from stock include new brake and clutch lines which are stainless with a proper crimp – apparently; this is a new requirement for MOT tests. In terms of machines for sale, following a bit of a rush, we’re now down to just one V1000 in stock. This is to be remanufactured during the year and will be in the showroom next spring.
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Technical Topic ………... Sprag ClutchThis really should be headed the starter system but in common with other bikes it’s the sprag which is the word used when the system fails. So why do we need one? We need to start the bike somehow. Remember kick starts, push starts and now electric starts? There are other ways of starting an engine but are not used in the bike world. The progress to the normal electric start is not a completely market led luxury in big bikes, nor is it riders getting too old to jump up and down on a lever hoping the advance/retard behaves itself and does not throw you over the bars (if you do not understand this ask your Vincent / Velocette owning dad). The modern engine with the four valve heads and better design are more difficult to start because the efficiency of this valve arrangement at low valve lift gives a better actual compression to overcome. The other variation to complicate matters is the number of cylinders; the bigger the size and the fewer the number the worse it gets. 500cc single should therefore equal a 1000cc twin from a starting point of view (well not quite, this is only correct if it’s a flat twin). In fact, Vee twins are worse because of the unequal spacing. The electric starters we use on the big bikes require both a reduction system to allow them to turn fast and a means of disengagement for when the engine starts; this is where the sprag comes in. One of the recommendations from Ron Valentine who did a lot of the detail design on the engine was for a car type engagement onto a flywheel starter ring but this was rejected on the grounds of noise when it engaged. So just what is a sprag? The sprag clutch acts as a one-way rotating clutch to allow the starter motor to turn the crankshaft and thus turn the engine for starting. Once the engine is running of its own accord, the crankshaft will be turning faster than the starter motor, so the sprag clutch free wheels and the starter motor can be powered down. On the bike the centrifugal force keeps the parts clear of each other when running to stop noise and wear. So why does it fail? The sprag has a load limit over which the forces are so great that the pieces which provide the drive, break or go over-centre which then gives a free wheel in both directions with the symptoms that you can hear the starter going around but the engine does not turn over. The load will break the Sprag if the engine backfires or tries to run backwards. This might be caused by incorrect timing causing the engine to fire on the wrong side of top dead centre which can happen with a wasted spark system (fires both plugs at the same time). Due to the reduction gear when the drive is reversed its like running into a brick wall from the drive point of view and it usually proves too much. The only other failure occurs when the gap in which the Sprag runs wears and becomes large enough for the parts to rotate under a normal load. In the early days of testing I had one of the prototype bikes lock up at about 100 miles an hour which we discovered was due to an early type of Sprag that had failed and jammed solid. This had tried to drive the starter motor around at a very high speed which itself had exploded the starter shaft embedding all the windings in the case. We could only guess at what speed the starter attained before all the windings flew off but it definitely required a new one. Fortunately, on the Hesketh, it is a quick job to take the side cover off and mend or replace the sprag clutch unlike some modern engines which require a complete engine strip. Is there room for improvement? Like any mechanical system there are ways to improve its operation and there is a solution which has yet to be found. I would suggest that there are three main ways this could be achieved. • Option 1 - Increase the capacity of the Sprag clutch to be able
to take the load. All this is not exactly rocket science I know but you need to start somewhere.
I have two restrictions when bringing about improvements to the Hesketh, one I need to engineer solutions within the present design framework for cost and customer requirements, this I enjoy and find a challenge and over the years have found ways to improve parts well beyond the original expectations. The second restriction I find more frustrating and that is the cost, especially as limited numbers are involved. This makes it almost impossible to work with suppliers unless they are sympathetic or have a solution sitting on a shelf. I don’t have the volume or cash to be able to bring pressure on suppliers to find a solution as they know there is no profit in it for them. Some are sympathetic but not enough. Given the above what can the owner do? The majority of Hesketh and other bike owners will never come across any of the problems outlined above and do many miles without a problem. The development test bike is used regularly and has done more miles than most and has only suffered the problem twice. So averaged out that’s once every twelve and a half years. Non-Hesketh owners please note: that’s used regularly for just over twenty five years; mind you it wants a clean now and possibly a bit of paint to cover the road rash from falling off on the ice. Not bad for a museum piece. Sorry I digress; back to the few who discover the starter disconnected from the engine. Well, basically you must reduce the chance of the engine firing backwards. Balanced carburettors, correct ignition timing, a fully charged battery and a positive attitude when starting - get the motor turning before opening the throttle should do it. At present I am trying a different shaped sprag which so far is working well. Together with a special starter gear I have identified the cold starting current requirements for the bikes at 300A for the later computer ignition bikes used regularly and 350A for the standard V1000. I strongly recommend a battery maintainer for when the bike is not used over periods of say three weeks or more though this does depend to a large extent on the battery condition. The starting current can be reduced to 300A for a regularly used bike with the ampere-hour rating of the battery not making much difference as the primary use of the battery is for starting. Also sods law works on a Hesketh as much as anything else so carry a spare sprag and you will never need it. Mick
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New Products
Have you got droopy indicator stems? We now have two options on the height of the footrests with the lower ones being 50mm lower than standard. Fully tested for ground clearance and finished in chrome with an improved gear change pivot position and brake stop the set includes new brake pedal, gear link and footrest rubbers while stocks last at 20% off the normal price of £301.82 which is £240 a set including VAT. Twenty five year old brake lines? Time to ‘stop’ and have a change. We now have sets of stainless lines which are covered with a black sleeve and fully crimped as some MOT stations are requiring now for the Hesketh. There are two options on the rear line, one as standard and one which does away with the Hesketh pressure switch and replaces it with a single line and pressure bolt on the master cylinder. This aids fitting and replacing the fluid. The full set comes complete with washers, bolts and clutch line at £117.50 including VAT or the lines can be supplied separate. |
4. And Finally We hope you like the new format and agree that we are providing the sort of information you’d like to receive. If not, do let us know as we are only doing it for you and could be out riding our Hesketh’s.
The Web Editor |