Stan Bradbury's Speedway Training Notes
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STARTING TECHNIQUES AND CLUTCHES
In general this is very dependent upon the machine, the rider and the starting area surface conditions. Experience allows many riders to read these conditions and avoid any big "wheelies" which tend to damage the frame, and sometimes, the rider. The type of engine also determines what throttle opening is best. Two valve Jawa's tend to perform better with plenty of revs. available, while 4 valve Weslakes have torque available from very low revs which is also true, to a lesser extent for the 4 valve SOHC Jawa's and Godden's. From that point on, it is a matter of choosing where to sit, how far, to lean forward, tire pressure, gear ratio and position of rear wheel in its slots. While this may sound complicated, it is not really so. It is simply that if you have a high or low gear ratio to suit the track, or a high or low tire pressure or a wheel back or forward of centre, you must make mental adjustments to compensate for these factors which can effect your starting ability. Other factors which can affect starts are: make and type of tire, clutch condition and adjustment. In Europe riders tend to set the clutch spring tension on the verge of slipping and de-glaze the plates frequently to ensure consistent performance. On a "tacky" track the rider of average weight would require a clutch which would not slip. A light-weight rider on a European track with lots of loose top dressing would spin the rear wheel before his clutch would slip hence light spring pressure. It is a good idea to put your hand on the clutch immediately after coming to a stop in the pits after a race, to see if it is hot and has been slipping.
In more recent times, modified clutches specially designed to work well under European-type starting conditions have been developed. These are such that, on a groomed starting area, when the clutch lever is released, the clutch will slip slightly maintaining engine revs, the rear wheel will spin (because the clutch is still transmitting enough torque) and the front wheel win lift one or two inches off the ground. This combination seems to provide the best start under the conditions mentioned. On a tacky track however, the clutch would slip to excess and overheat. The clutch would also tend to slip on tacky parts of the track and would probably result in a burned-out clutch. Where the starting areas are not groomed (raked or graded) it is a matter of reading the surface to decide if it is "slick" or tacky and react accordingly. The clutch should be set so that little or no slip will occur if the start and/or the track, is tacky and even if the start and the track is slick with perhaps only tacky spots coming out of the turns. Barring external damage due to falls etc., the clutch should be reasonably indestructible, particularly if it is well maintained and not abused.
Maintenance of the clutch consists mainly of a light smear of high melting point grease on the clutch centre bearing on the early Jawa clutches and occasionally de-glazing of the plates. A piece of sandpaper (not emery paper) on a flat, level surface will do fine (a piece of plate glass makes a cheap surface plate), upon which the plates should be lightly rubbed this way and that until the plate is consistently resurfaced. This can also be done on a flat concrete or flagstone surface. I repeat, just a smear of grease on the clutch centre race is sufficient as any excess will be flung onto the back friction plate and will cause some slip to occur. Later Jawa and NEB clutches have sealed ball races.
Clutch levers, cables, push rods, adjusters and fulcrums should all be inspected and maintained. The cable needs no lubrication if it is nylon lined. If it is not, it is a good idea to occasionally disconnect it, form a funnel around the handlebar end of the cable using plasticine or similar, then fill the funnel with light oil and let it seep through to the clutch end of the cable. The same treatment can be applied to your throttle cable if it is not nylon lined. This ensures that the cable is well lubricated and is not going to rust from one week to the next if your bike got wet on a trailer. On no account put any oil on nylon lined cables as this win cause the nylon to deteriorate and make the cable bind or stick.
The clutch push-rod assembly usually consists of three pieces. A short piece of 6 mm carbon steel rod at the clutch end, a 6 mm ball bearing and-a longer piece of 6 mm carbon steel rod from the ball to the adjusting screw in the centre of the fulcrum-arm on the outside of the countershaft assembly. It is important that these parts are coated with grease, particularly where the long rod goes against the fulcrum-arm adjusting screw. Many riders pack the cavity around this point with grease then trap a piece of foam rubber between the fulcrum-arm and its support to retain the grease and to keep much of the dust and grit out of the cavity. If you allow these parts to run dry, they will heat up and loose their hardness and will have to be replaced if they are too far gone to salvage. If they can be repaired, grind off the rough ends of the rod and adjusting screw and heat the re-ground ends up to a dull red then quench in cold water. This will re-harden the ends to resist the rapid wear that would otherwise take place. If too much metal has been lost, it may be necessary to replace the 6 mm ball bearing with a 1/4" ball or a 1/4 x 1/4" roller or even a 1/4 x 3/8" long roller. If you can not get hold of the proper parts to renew the push-rod assembly, you can always make one up using 1/4" carbon steel drill rod and a 1/4" ball bearing but the ends of the rod will have to be heat-treated as mentioned earlier. If the adjusting screw is beyond repair, it will have to be replaced with either the genuine article or a home-made copy, if you have a good workshop available. Some clutches use a "mushroom" on the end of the short push-rod which goes against the inside of the clutch spring plate. This is to reduce wear by providing a larger surface area, ensuring that the spring pressure-plate moves out evenly, particularly on those clutches built up of light alloy parts. The later Jawa's went to a thicker short push rod with built-in mushroom. In order to save unnecessary wear and tear on your clutch, only withdraw it for as little time as is absolutely necessary. Don't sit at the start waiting for someone who is on the two minute time allowance, with your clutch withdrawn. Tip the bike over onto its footrest and then you can release the clutch lever while your rear wheel revolves clear of the ground. If your carburetor floods in this position, you can always ride slowly round the track providing that you don't allow the engine to idle too slowly and stall or oil up the spark plug.
Alternatively, you can ride back to the pits exist and stop your engine, if you know you have a pusher available there, then wait until the two minutes is nearly up, restart your engine and go to the starting line. This will also save both fuel and oil and many a rider has been leading a race after a delayed start, then run out of fuel and failed to finish. Don't forget, you only carry a small amount of fuel and a Speedway machine does only five or six miles per gallon. Any re-run races should mean that oil, and possibly some fuel should be added before going out in the re-run, particularly on the long track (1/2 mile) events.
There should be a little free play in the clutch cable (about 1/8") to make sure that there is no pressure on the clutch push-rod assembly once the clutch lever has been released. Also make sure that the handlebar lever is positioned so that it is able to move the inner cable for its maximum distance to ensure the clutch is fully withdrawn when that is the intention. Some riders give the fulcrum arm a tap with the heel of their right boot to fully disengage the clutch, if they are to spend more than a few seconds with the clutch withdrawn. On the starting line, most riders partially release the clutch lever until they can feel the clutch start to "drag" slightly. This will ensure the best start providing there is not too much delay which would cam rapid heating-up of the clutch. It is a good idea to carry a spare adjusting screw and nut for the fulcrum arm along with other clutch spares and certain spares for the rest of the machine, which need not be expensive. However, more about suggested emergency spares later in these notes.
Jawa 3 Spring Clutch Hubs
On old-style 3 spring Jawa clutches, drill and tap 3 more M6XI.0 stud holes in the hub so that if one stud breaks off, the hub can have 3 more studs screwed in place. This enables the hub to be repaired between races. Just carry 3 spare studs and if the 2 remaining unbroken studs will not unscrew out of the hub, just break them off and use the 3 new studs in the 3 new holes. Later the broken stud(s) can be drilled out and, by carrying 3 more spare studs, the problem can be resolved whenever it should re-occur. The hub is then interchangeable with any of the earlier 6 spring hubs. By having the outer cover machined to accept more pressure spring cups, your 3 spring clutch can be converted to a 6 spring and back again in a few minutes. Alternatively, 3-6 mm clearance holes drilled in the outer cover to match the 3 additional studs permits the rapid repair of the 3 spring clutch without the necessity of removing the 2 remaining studs. Using locknuts on the studs inside the clutch hub makes removal of the studs easy and also prevents the studs from coming loose during operation. This is preferable to the old method of "peening-over" or riveting the ends of the studs.
The clutch pegs on the older Jawa clutches were also "peened-over" in this manner. Breakages were not infrequent due to over-peening to a point of brittleness. When drilling out and replacing these broken clutch pegs, it is a good idea to install them with a non-setting thread locking solution such as "Locktite #22004 Medium Strength (Blue)". If the pegs are tightly installed, there should be no problem of the pegs working loose.
So now you know your clutch is in good condition, adjusted correctly as described in these notes and you know how to determine the condition of the starting area. You are now ready for some starts.
Usually, you can sit towards the front end of the saddle with your chin over the handlebars and your elbows pointed straight up. In this position, if there is grippy dirt in the start area, the throttle can be opened wide and the clutch lever dropped when the tapes go up. If the start area is tacky, move your weight further forward and again use lots of throttle so you spin off the start. If the start area is "spiny" (dry, hard, with loose grit or dust), sit further back and use less throttle.
It takes some experience to be able to "read" the start area and, until you gain more experience, it is wise to play it safe and sit well forward. This may give you a slow start due to wheel spin but it will avoid "looping" at the start (going over backwards) which is hard on both rider and machine.
It is wise to keep both feet on the ground until you leave the start area and, as you become more experienced, you can push forward with both feet while staying in the saddle. As you move forward, your feet can be allowed to trail behind you but clear of the ground. Be prepared to step off the machine if it "loops." It is also possible, on a start area that becomes progressively more tacky, to pull in the clutch lever and so prevent a loop when the front wheel lifts excessively. Some lifting on the start is normal and even desirable. On loose dirt, the front wheel can be 2" to 3" off the ground with the rear wheel spinning, the engine revs high and the rider positioned in the middle of the saddle with his feet off the ground and level with his rear wheel spindle. Unfortunately, this can only be achieved when the starting area is "groomed" or is accidentally in a satisfactory condition.
You now have the basic information to commence starting practice.
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