By Frank Warner July 2000, amended a number of times.
The sensor part of this unit can fail without warning but if a second sensor is fitted then by simply changing a connection you can continue with your trip. The second hall effect sensor is cheap and light (10 grams, add 20 for wires, connectors, silastic & cable ties), but not easy to fit. . If you do not know what a dividing head is, then I would advise against doing this yourself (you must have good workshop knowledge).
There is an article on repairing the Ignition Impulse Sending Unit by David A. Braun (Flash) that has trouble shooting information. Similar information can be found in the Haynes manual.
The unit as a whole is available from BMW, and the same unit is used in all R80 and R100 models - yes with the same advance curve!
The advance springs are available from Moto Bins in the UK.
The sensor was available in Australia from Jaycar part no ZD 1900 (Siemens
part No HKZ101) about $40 (AUD). They are having trouble finding more of these.
Other possible sources are from cars 79-85 VW, 78-83 Audi, or 79-82 Porsch. Take the old part with you when you go to the import car parts place, or cheaper yet, junk yard. Or for USA available from Newark Electronics as part #96F1986 for around $14.
Tech info available from Honeywell part No 2AV54 Search on www.honeywell.com/sensing/
This same sensor is used in the K model bikes and in the R11 oil heads! Makes the parts inventory easy.
However the airhead uses one sensor, the other models use two sensors.
Basic Parts, assembly order
Link to picture of disassembled unit. (82k)
For the purpose of this discussion, "top" refers to the end of the can with the lid and the two Philips head screws and "bottom" refers to the end which mates with the camshaft. The unit itself is pretty hardy. But there are two caveats involved in the disassembly/reassembly procedure. First, use a scratch-awl and mark things to simplify reassembly. There are plenty of asymmetries, and marks remove the puzzle aspect of reassembly. Second, none of the parts inside are available from BMW, be careful not to damage or lose them.
Read through the entire procedure before starting. The names used here correspond to the names in the drawing above. The hall effect device could be called a hall effect trigger and other things, but is simply called a sensor from here on!
With the sensor can on the bike, remove the two philips head screws and the top cover. You are now looking at a bearing retainer. Mark the retainer to indicate how it relates to the "slot" in which the plastic strain relief for the sensor wires resides. Remove the two flat screws and then remove the retainer. You are now looking at a large snap-ring. You should carefully mark where the ends of this ring reside and make a mental note that it goes in the bottom groove. The marks you have made so far simply establish the top cover screws position, so are only cosmetic. You don't need snap-ring pliers for this. You can re-install the screws and easily pop it out with your fingers or a screwdriver. Look down into the can and notice the three "tabs" into which the three flat screws from outside the can go. Mark one tab and the can to simplify reassembly. This mark is important! You may be able to establish this position using the position of the sensor wires, but don't count on it. Get it right. Remove the three screws. There is a little plastic tit that sticks out at the bottom of the plastic strain relief stripe, remove it, it will come all the way out. Once it is out, the strain relief will slip in the slot with a little effort, but don't move the strain relief yet.
Now remove the can from the bike, as you need to access the bottom side of the can. Two allen screws hold the unit to the timing chain cover. Removing the electrical connector has a little trick to it. The connector is held in a positive lock with a thin wire spring clip. You can take a small flat screwdriver and carefully push the open ends of the clip to make it slip out of its groove. That will allow the plug to be pulled apart. As soon as you get the plug apart, snap the clip back into its groove. That way it won't get lost. For reassembly, there is no need to fiddle with the clip. The connector simply plugs together. PS I have 'lost' the clip for over 8 years, and it does not come apart under vibrations, including corrugations (washboard USA). I have the clip at home, in a box of stupid parts that are not that useful.
Mark the shaft to drive dog so you can put it on correctly (this should not matter, but you never know). There is a "spring" wound around in a groove in the drive dog. Carefully pry one end of this loose from the groove and work it off the drive dog. Now you can see the pin that holds the drive dog to the drive shaft. A bench vise that opens far enough to contain the can is a Good Thing. Open the vise and note that you can put the tangs of the drive dog atop one jaw. As you carefully close the vise, note that the top of the drive shaft sticks out above the top of the can. You want the top of drive shaft to rest on top of the other jaw of the vise, with the vise clamping the can ONLY. Line the slot in the bottom of the can with the pin up other wises the pin will only come out till it hits the can. You want the vise merely snug, not tight. Using your punch and hammer, take a couple of whacks and knock the pin out. Take the rig out of the vise. Everything that holds the assembly to the can is now loose. Wiggle, fiddle, pull, and poke until you manage to slip the guts out, don't forget the wire and strain relief. PAY ATTENTION. There are stacks of washers on either side of the bottom of the can where the shaft goes through. Note the orientation and order of both stacks.
Use a jeweller's screwdriver to carefully disengage the outboard end of the flyweight springs over the tops of their posts. DO NOT STRESS THE SPRINGS.
An e-clip and a snap-ring retain the shield. Remove these. Note that a pin locates the proper orientation of the shield with respect to the advance tube. Judiciously utilising your bench vise and punch set, punch the advance tube down out of the shield. Do not distort the shield. Do NOT lose the tiny locator pin (this pin has rolled out of the photo!). The advance tube that goes through the sensor plates can be removed from the sensor plates by removing the last snap-ring. The plastic wire cover has three clips to the centre spigot, remove it.
Now you measure up and mark out the centres of the two new holes required to mount the second hall effect sensor. Using the present location of the sensor mirror image the mounting holes, use the central hole as your reference where possible. I used a dividing head to mount the sensor plates. I then scribe a line using a stand with scriber on a flat bead that would extend through the original rivet centre and the central spigot centre to the new rivet centre. I then checked my work by rotation the sensor plate through 180 degrees and redraw the line. You should have two lines, in the middle of these is perfection. If you end up with one line why are you reading this? Repeat for the other rivet centre. Using a divider set to 40.8 mm from the centre of the original rivet mark the new rivet hole centres. You should have two new centres 22.5 mm apart. Check then drill these two holes out to 3.5 mm diameter through both sensor plates. The bottom sensor plate holes should be enlarged to enable the sensor rivets to be penned over, be careful not to damage the smaller holes in the top sensor plate. One of these larger holes is very close to a tab cut out, I drilled this to 4.8 mm. Mount the second hall effect unit, peen over the sensor rivets. Then make a three 1.4 mm holes in a line through the strain relief very close to but on top off the present wires and pass the new wires through it. Place a small cable tie over all the wires through two holes already in the sensor plate near the strain relief to ensure that they do not rub on the rotating shield.
If I was to do this again, I think I would make a jig to hold the sensor plates, with 4 holes in the jig; 2 holes to locate the original sensor rivets and the other 2 holes to dill through. This would make life simpler, especially with repeats. The jig would be a version of the can with less length, mounting for sensor plates inside and the 4 holes in the solid end.
Reassemble in the reverse order, take care! You will not be able to use the plastic wire cover as the second sensor occupies some if its space. Ensure the wires do not rub the shield or any other rotating part by careful placement. Do lubricate the shaft and bushings. The flyweights ride on a piece of teflon, so do NOT lubricate the surface on which they ride. Take care to remove all small bits of metal as these will find their way to the magnets within and change the timing.... Go across another bump in the road and the small bit of metal changes its location, changing the timing yet again... endless fun. Before you put the top cover and bearing retainer on recheck that the wires (and anything else) do not rub on any rotating parts.
Once assembled you can extend the second sensor wires to the same length as the original and place connectors on the end. Use heat shrink tubing to make a neat job, and cable tie the new wires to the original wires. Seal the new wires to the strain relief using silastic making the can water and dust tight.
|
Layout |
Wire Colours |
Function |
||
|
Sensor |
R80 G/S 81-86 |
GS 87 on |
|
|
|
|
Red |
Violet |
Green Yellow |
+ve Supply |
|
Green |
Violet White |
Blue |
Signal |
|
|
Black |
Violet Black |
Black |
Chassis |
|
Check the timing, then change sensors and recheck, note the difference between the two. Use the sensor with the most advance, leaving the retarded sensor as the spare so you can use it with out retiming. You may lose performance/economy but you will not damage the motor with retarded timing, at least not a great deal of retarding.
There is a metal cover near the bottom of the plastic strain relief on the can that gives access to lubricate the flyweights area. Try some oil first as it may work till you have time for a complete disassembly.
Follow the above disassembly procedure to get access to the flyweights assembly. Remove the e-clips from the flyweights one at a time and carefully remove the flyweights. Clean everything up nicely, paying particular attention to all shafts and bushings. The flyweights ride on a piece of teflon, so do NOT lubricate the surface on which they ride. Do lubricate the shaft and bushings. Reassemble in reverse order.
If your problem is a dead sensor replacing the hall sensor will require you to drill out the rivets in the old one. On the newer models the rivets are solid that may make drilling out difficult. Try centre punching the rivet before drilling. You may find removing the sensor plastic around the rivet until you can remove the sensor, leaving the two rivets behind then you can then hacksaw the rivets off. You can install the new one with pop-rivets, with nuts and bolts or use the rivets on your new unit. You're going to have to splice the wires from the new unit to the old harness. There is plenty of slack to accomplish this and still fit all the stuff inside the can without fouling anything if you are careful. Use heat-shrink tubing rather than electrical tape to insulate your solder joints.
Old units had the sensor plates screwed together, newer ones are a tight push fit. Old units had the sensor rivets hollow, newer ones are solid. There may be other variations!
Article on repairing the Ignition Impulse Sending Unit by David A. Braun - Flash - DoD #412 - BMWMOA #18854
Haynes Manual
Flash help start me off (together with the failure of my unit) on this path,
further prompted by carrying a spare around with me for two trips back and forth across the country.
The space and weight were a trouble, now the spare sensor is in the can taking no extra usable space and little weight.
Alpine Alex has had a go at correcting some of my mistakes! Don't know if I have got them all but...
in getting rid of some mistakes some others have probably crept in.
If you quote me I would like an acknowledgment. Dated 13 May 2002.
