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Obviously before we start and more to the point, before you start modifying your designed and engineered motor bike, I take no responsibility for any damage or harm caused by you following these instructions. Nor do i take any responsibility for any personal harm to yourself or others if you have followed these instructions and things go wrong!
That said I have had no problems with any of these modifications and would not expect you to have either. You need to be able to operate hand tools and a 4" angle grinder and electric drill is about as technical as we go. REMEMBER: "These machines have no brain, please use your own". ALWAYS WEAR PROTECTIVE SAFETY GLASSES OR GOGGLES WHEN USING ELECTRICAL HAND TOOLS.
Sorry, but this modification is only tested on the later Chang Jiang with external distributor fitted to the front left side of the engine block. Although I'm sure that you could fit it to the earlier type using only the black box and a modified rotor.
This is what the finished product looks like!........no different from the original right?? Exactly!
I have noted a lot of interest recently on the Chang Jiang web boards relating to electronic ignition systems and there availability for the beloved Chang. Around 2 months ago I also was looking for a garage project to do and had wanted to improve on the standard contact breaker ignition system of the Chang. I read a few articles from the Internet and also read my trusted Haynes Service and Repair manual for BMW 2-Valve Twins 1970 - 1996. I saw how the ignition system was fitted to the later BMW's and started to think that if i could get my hands on one of those little black boxes (Amplifier), then all I would need was to fit a trigger system to the distributor in place of the contact breakers and bingo! The only problem to all of this was the cost, now don't get me wrong, I love my bike but I also have a wife and I also love a bargain more! BMW were quoting around USD$200.00 for the amplifier box alone and then there would be the hassle of trying to fit a trigger system to the distributor, the correct connection of all the bits..........
I felt that a trip to the car breaker yard was in order so off I went with my trusty Chang distributor in my hand. I asked them if I could look through their boxes of old distributors in hope that I might find the holly grail and indeed I did. It came in the form of a distributor from a Mitsubishi Colt or Scorpion (as they are called here in Australia) it was basically a four cylinder car with an electronic ignition system. The real trick here is that this design of electronic ignition has both the trigger unit and the amplifier all in the one little box which fits directly in to the distributor. There are only two wires coming out of the distributor both going to the ignition coil, the trigger wire (Blue) went to the coil negative terminal and the other wire (Black & White) went to the coil positive terminal. The system gets it power from the ignition switch wire also going to the ignition coil positive terminal. So simple! Try to get the short wiring loom which goes with the distributor if you can. I paid my USD$29.00 for the whole distributor and USD$21.00 for a pair of electronic ignition coils from a Magna and hurried off back to my garage.
It was going to be a long holiday weekend so i had plenty of time, I started by taking a couple of pictures of the complete distributor (above) to allow later referencing if required. I then removed the electronic module from the distributor base plate and put it to one side away from harms way. I then removed the base plate screws and released the base plate from the distributor body. Then by removing the centre screw from the distributor shaft i was able to pull out the 4 pole rotor together with the drive mechanism which locates on to the mechanical advance weights and also allows the rotor to be driven by the distributor main shaft. It's one of those horrible things to put in to words on paper but you will know what I mean once you have a distributor in your hands. The rest of the distributor from the car breakers yard is redundant apart from the odd screw which may come in handy on re-assembly in to the Chang's distributor.
So you should now have the following things on your work bench;
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The electronic module with wiring & two locating screws.
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The 4 pole rotor and top shaft from the car distributor.
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The Chang Jiang Distributor (complete at this stage).
Next you need to remove the Chang distributor base plate and breaker assembly. Turn over the base plate and using the 4" angle grinder, carefully grind off the breakers mounting post and adjusting screw by removing only enough of these items to allow the post and screw to be tapped out of the base plate. Then remove the centre screw in the distributor shaft which will allow the cam lobes to be pulled free from the mechanical weights, this is principally the same as what you just did to the Car distributor to remove the electronic rotor.
Now this is where your commitment starts to finishing this project, as the next step is one of no return! Using a suitable vice on a bench, mount the Chang Jiang cam lobes in to the vice with the rectangle drive plate facing upwards. The rectangle plate is what we now want to remove from the cam lobe and keep for re-use, but it has been factory fitted and was never intended to be removed. Using the 4" grinder carefully grind away the part of the cam shaft which protrudes through the rectangular drive plate until the grinder disc is flush with the drive plate. Don't grind away any of the drive plate! Then gently tap out the cam lobe shaft and throw the cam lobe part in the bin. You just destroyed it!
Next you need to do the same with the rotor shaft from the car distributor, only this time it is the rotor shaft that you want to keep because this is the part that you will be fitting back in to the Chang distributor once all the carnage is finished. Before you start, first scribe a line around the top of the shaft to indicate where the 4 pole rotor is located on the shaft. Then gently tap off the 4 pole rotor from the shaft so that you do not damage it by heating and grinding etc. It is quite tight but does come off. Place the shaft in the vice again with the drive plate facing upwards use soft vice jaws or wrap something around the shaft to protect it from the vice jaws. Gently grind off the portion of the shaft which is protruding through the drive plate, once flush with the plate, tap off the drive plate and then continue to grind off the remaining part of the cam until you get to the shoulder that the drive plate was originally against. You may need to use the grinder all the way to this shoulder to remove the old drive plate, just don't grind any further than the shoulder. Then turn the shaft around in the vice so that the scribed line that you made to indicate the top of the 4 pole rotor is visible and cut along this line with a hacksaw to remove the original part of the shaft (the part above the 4 pole rotor) which located the rotor arm of the car distributor cap. (Don't get confused with the 4 pole rotor which is the part that triggers the spark).
You should now be left with a shaft from the car distributor which measures 35mm long (see picture below left), after cleaning away all traces of swarf and dust you should be able to fit the car distributor shaft in to the Chang distributor. This is where our luck really starts to head our way, the bore of both shafts is identical. Meaning that once in place the mechanical advance will continue to operate as before. However as you may have noticed there is now no way for the Chang distributor drive shaft to drive the car 4 pole rotor shaft as we have removed the drive plate. Also you will note that once the shaft is slid in to place and fully home on to the washers of the internal shaft of the Chang distributor, that the centre screw can not fit as the recessed hole is not deep enough in the new shaft (looking from the top). You will need to use a post drill with a 10mm drill bit to recess this hole further in to the shaft. You will need to drill in only 7mm which will allow the screw to be replaced and for a small amount of end float in the two parts. However before fitting the drive plate lets take the next step which is to remove 2 of the 4 pole lobes from the rotor.
Do this by holding the 4 pole rotor with one lobe upwards from the vice. Gently and carefully grind away the lobe taking great care not to go in too hard with the grinder as we must not overheat the lobe for fear of altering its magnetic properties. Then turn over the rotor in the vice to have the opposite lobe facing upwards to the one you just ground off. Allow the rotor to cool before repeating the same process. It does not matter which two lobes you remove, as long as they are 180 degrees apart, just take the time to look at each of the four to see if any looks better that the others and if so keep those ones!
Now replace the now 2 pole rotor on to the shaft and press home until fully home. The place where you cut off the protruding part of the shaft (top) should be dressed with a file and should be flush with the top of the 2 pole rotor once it has been refitted to the shaft.
Now back to fitting of the drive plate, You now need to take the original Chang drive plate and drill out the existing centre hole from it's current 12mm to 18mm this will allow it to then fit snugly over the base part of the 2 pole shaft from the car distributor which has an outer diameter of 18mm. You should find that the drive plate needs to be firmly tapped in to place due to the slight interference fit acquired. The drive plate must be 26mm from the top of the shaft, it must be square to the shaft and also run parallel to the 2 pole lobes. Once you have tested your alignment of the drive plate on to the shaft by re-fitting the shaft in to the Chang distributor and engaging the drive plate on to the bob weights to ensure that the shaft is fully down on the drive shaft and that the drive plate still allows the bob weights to freely move without rubbing on them, you are ready to get the drive plate tacked in to place with a MIG welder. You should have noticed that to get the drive plate on to the shaft required you to drive it on, therefore you only need to have two spots of weld applied to the upper sides of the shaft (see picture below right) and drive plate to ensure that it does not move, ever again. If you need to re-align the drive plate with the 2 pole lobe than use a 22mm spanner to hold the drive plate whilst using vice grips on the bottom of the shaft and rotate the two until correct alignment is achieved. Check that everything is still square to the shaft then have welded in place. (see pictures below).
Above shows pole aligned with drive plate Above shows spot welds each side
Next you need to fit the new rotor shaft in to the Chang distributor, you will have to remove the 2 pole rotor to allow the Chang distributor base plate to be fitted over the top of the shaft. Then taking the Chang distributor base plate and fit it back in to the distributor only this time the base plate should be rotated 180 degrees to how it originally came off. This allows you to mount the black box on the lower side of the distributor when it has been re-fitted to the engine, which in turn allows the wiring of the black box to go out through the upper side of the distributor in the same way that the original contact breaker wire was. This looks better as you can see from the pictures. Also the black box needs to have a metal contact to act as a heat sink and by fitting the base 180 degrees aligns this perfectly. (See picture below).
With the base plate now in position and the distributor still in your hands at the work bench, place the black box on to the base place and align one of the rotor lobes with it, then carefully mark the mounting hole position ensuring that there is about a 0.5mm "air gap" between the rotor pole and the pick-up. This distance will be adjustable once the holes are drilled and tapped. Then remove the black box and carefully drill the centre of the marked holes using a 1/8" or 3.2mm drill bit. Then thread the hole using a 4mm x 0.7mm thread tap. You will need to go to your local electrical store and purchase a small tube of heat sink paste, which you need to apply to the bottom of the black box before screwing it in to its final place on the base plate. This paste assists with heat dissipation and without it you may overheat your ignition system and burn it out!
Next step is to re-fit your distributor to the engine, the best way to do this is to set the engine to TDC and then fit the distributor such that one of the 2 pole lobes is aligned with the black box pick-up. There is a large amount of adjustment on the Chang distributor by releasing the allen key clamp and allowing the distributor to rotate whilst leaving the fine adjuster set to the centre position and locked off by the 10mm nut. (see picture below)
OK assuming you were like me you won't be able to wait to try out the new modification right? OK you need to remove the original wire from the original Chang Jiang coil to the contact breakers. Then connect the 'C' terminal of the black box to the Coil negative terminal and the 'B' terminal to the coil positive terminal. There will now be two wires fitted to the coil positive terminal, the original one from the ignition switch and the other from the black box 'B' terminal.
WARNING!!
Electronic ignition systems put out very high voltages to the spark plugs (that's why you want it right?) these high currents can KILL you, so do not stand in pools of water holding the spark plug to see if you have got a spark....you may die! Always ensure that the HT leads are connected to a spark plug and that if the spark plug is not screwed in to the cylinder head that it is firmly earthed out on the engine. Failure to do so will damage the black box unit and possibly your health.
Next remove the left hand plug from the cylinder and lay on the head with the HT lead still attached, with the ignition switch turned on gently turn over the engine using the kick starter and observe the timing marks until the 6 mark comes round to the viewing hole in the engine casing. The spark should occur at the 6 degree mark before TDC. You WILL know when the trigger unit fires to the coil because you will hear the crack of the spark at the plug. Gradually rotate the distributor until the spark occurs at the 6 degree mark then lock off the 8mm allen key bolt. The timing is now set accurately enough to allow you to run the engine and get to a workshop with strobe timing light for final accurate setting.
Next replace the spark plug and start you machine!
If you have also purchased the high output ignition coils then remove the petrol tank, remove the original Chang Jiang ignition coil and mounting bracket and fit the two high output coils between the frame top tubes below the tank. I used some stainless steel "bandit" straps to fix the coils to the frame. You will need to purchase two new and longer HT leads than the standard Chang ones, I used carbon suppressed leads. You must connect the coils "low tension windings" in series which means that the ignition feed must go to the positive terminal of the first coil along with the feed wire from the black box trigger unit. Then the negative from that coil must connect to the positive of the second coil, the trigger wire from the black box trigger unit then connects to the negative terminal of the second coil. This will cause both coils to fire simultaneously when either one of the two poles passes the trigger unit in the distributor. The tank can then be replaced (ensure to fit the HT leads before fitting the tank as this can not be done with the tank in place).
That's about it guys and girls it is a bit long winded but you will get there if you follow them, also I can be contacted by sending an e-mail to: E-Mail Me should you have any further questions. Or you can post a question on the FORUM board on this Website. Also if you are not up to doing all the above yourself then drop me a line and we can talk about other options such as parts or a finished product sent to your home.
Happy riding folks!