Gear change control hand grip clutch lever, decompression lever

Gear change control

This bike needs a complete new set of cables, many of which seem to have been replaced with naked Bowden cable cobbled together with solderless nipples. The gear change also has a problem in that although it does shift the gears, it wont stay in any gear you select but always slips back to second. I suspected that the control detents or fixed positions were damaged so the hand grip is going to have to come off for inspection. This grip is complex since it includes the clutch cable lever, decompression cable terminus and lever as well as the gear cable itself. Luckily as a two-speed bike there is only one gearshift cable. I took some general views before dismantling.

Views of the fixed section including decompression lever and its terminus.

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Views of the movable section, note gear indications molded into the metal and bracket for mounting the clutch lever. I will paint the numbers to make the markings more visible.

Note slot at rear into which the teeth of the fixed section should fit. 

The hand grip slips off once the clamp screw is released. The hand grip is in 2 sections; an inboard fixed section attached to the bars and a rotating section attached to the cable that can slip within the fixed section to move the cable. A window through the fixed section shows a gear indicator on the rotating section beneath to show the gear selected. The clutch is attached to the movable section and the decompression system to the fixed part.  In my case when the grip came off the handlebars the two sections simply separated. The gear change cable can only be removed by levering the grip flange away from the control

I cleaned the sections in the sonicator and then took some views of the fixed section (including decompression lever and cable terminus) so I had a record of how the various components were attached.

Decompression lever. Note the small hole to the left of the lever attachment screw. At first this appeared to be empty, but inspection showed that in fact there is a small spring inside this. Note teeth on this section (top left)

The movable section has gear indicators etched into it. Teeth on the fixed section mesh into the slot at the rear in this photograph where they engage with a flange on the clutch lever which holds the bike in the gear selected when the clutch is released

Indicator section- is there something missing from the slot seen here at the rear of the  body section to engage with the teeth on the fixed section.

Removing the clamp screw allows the decompression cable terminal to be removed.

Decompression terminal shares its mounting screw with the bar clamping screw.

Removing the smaller screw releases the decompression lever and its washer. The fixed section is then clear- there is a row of pits which look like detents for a ball bearing perhaps under pressure from the spring I found internally but I cant see how this is supposed to go together.

Fixed section; Decomp lever removed. Note the row of pits that serve as detents giving a positive indication of gear selection.

Clearly I need to find out more about how this should work before trying to reassemble it.

So its official! I really am missing a spring, ball and grub screw. I think this system allows some form of positive feel so that the rider has a sense of when a gear is selected when the clutch is in and the toothed section thus disengaged. I'm guessing its not essential, a bit like frets on a guitar vs a violin, but obviously it helps and it ought to be there. Luckily these parts are still available so I ordered the spring and screw from UK and the ball from Germany with my usual order. I do still  have the spring from my control but I'm thinking its probably broken as it seems v short.

I received the grub screw, it turned out to be an  M5 0.8 thread. It was clear that this could never have fitted into my control as the hole was only 3mm in diameter and unthreaded. I think that at some point the design was changed and the grub screw was omitted. The hole was then left blind to retain the spring and ball. However, the grub screw presumably would allow spring pressure to be adjusted which seems a useful feature. Accordingly I drilled the hole through from the top at 4mm and than tapped it to M5x0.8. This should allow all the components to be introduced from the top and then pressed into position using the grub screw to compress the spring. They will however fall out when the control is disassembled which probably explains why they are missing in my control.

I inserted the spring and ball after the control was assembled and positioned on the handlebar. To my delight, this did indeed restore the positive feel to gear change when the clutch lever was in.

Unfortunately the ball soon worked loose and fell out. If using a ball retained this way then the boring of the socket requires careful control of depth and size. I think the threaded section needs to be flat bottomed so probably bored using a flat ended mill, the opening at the base needs to be smaller to prevent the ball from falling through. Fortunately there is a far simpler solution in the sprung ball detent pins are available in grub screw format, the smallest is M6. I ordered 5 "Sprung plunger, steet, standard spring" no. GN615-M6-K from Zoro UK and got 5 for around £3. Having failed in the attempt to use an integral ball above,  I simply enlarged the bore of the hole and tapped it all the way through at M6. The sprung ball screw could then be inserted and its position adjusted when the gearchange was in position to make sure the detent pits were functioning (I did need to redefine these using a 5mm drill as they'd become worn into a track.)

It's also clear that the clutch lever is worn. When released the lever has 2 flanges which interlock with the teeth on the selector unit. Although mine did do this the effect was marginal because the lever was worn away forming a hook-like recess.

I was able to repair this section using the low temp aluminium brazing rods advertised for aluminium repair on ebay. Using a gas torch I could build up the missing material and then form it to shape by grinding and filing. The result was a definite improvement and now interlocked more positively, however I don't know how well it will last in use.

I could now reassemble the unit.

I replaced the grips on the controls. These were new Magura grips and they were very tight. They're not quite like the originals though and I did prefer the more linear design molding. I found that fixing was greatly assisted by putting the controls in the freezer for 4 hours. I could then soak the grips in hot water with a little washing up liquid and push them onto the chilled grips.

New grips on the controls

The rear light

The rear light is a simple unit secured to the rear mudguard by two cheese head slotted screws. One of these seems to enter a weld nut whereas the second has a loose nut that detaches when the screw is removed. I'm not sure whether both should actually be welded but the loose nut was obvious when the light unit was removed- rattling. Once both these are removed the light will detach from the mudguard. Its in two sections; a rubber base that adapts to the curve of the mudguard and a metal body that houses the bulb holder and reflector. There is a thin rubber gasket between the two. These lights are no longer available although there is a more modern replacement that doesn't look too bad. I wanted to keep mine though so I took it apart to see if it could be renovated.

Removing the rear light. Two sections visible

Rubber base units surprisingly are still available. I opted to repaint mine in body colour Dove grey, but I may change it for a new part in the future.

The thin rubber gasket was in poor condition- dried out. These are now unobtainable. Mine has hardened and worn uneven, but its not broken so I will try to restore it with some rubber grease and siliconiser.

Looking inside the light unit the source of the rattling was obvious, not only was the free mounting nut shaking around, the bulb was also detached.

The bulb holder is removed by unscrewing the slotted screw at the top

Its not that complex and was in good condition although the copper contacts were bent out of position and wouldn't hold the bulb until bent back. The bulb appeared OK but twisted into two parts when trying to refit it! I ordered another. This is the low profile bulb

The rear reflector is held in place by a spring wire clip. This just squeezes together and lifts up to release the reflector. you have to remove the bulb holder though to get it out.

My reflector has become whitened and no longer as translucent as it used to be. This is due to discolouration of the inner plastic covering only. The reflector itself isn't affected. I will see if I can restore this but since replacements are not available, if I cannot restore transparency I will just cut the opaque plastic away as it seems to be separate anyway.

I cleaned and prepared the light unit before respraying this in aluminium effect engine paint. Finally I reassembled the unit and inserted a new bulb. I will test and assess it once I get the bike working and the electrics connected. I do anticipate needing to run a separate earth wire to the motor. 

The magneto

The magneto ignition system has always mystified me. So I was quite concerned to discover that I had no spark. Eventually I summoned up the courage to start to examine the problem. I removed the flywheel using some flywheel clamps to prevent rotation whilst I unscrewed the central nut.

 I could then remove the flywheel using a puller.

The key in the taper fit to the crankshaft fell out when the flywheel was removed and has clearly been damaged and will need to be renewed. Its a 3mm thick key and they are readily available. I took several views of the back plate and it's components before removing it from the crankcase.

Contact points

Bosch coil (black covered) is soldered to the press fit capacitor inserted in the base plate.

I could then remove the base plate of the Magneto by loosening the two screws (one top and one bottom) to remove it from the crank case itself.

Once I'd removed it I was able to check for spark using a pencil battery (see on) but this failed to produce any spark whatsoever. Using a meter I was able to measure the resistance between the HT lead (without the cap) and earth (base plate) and also the lighting output lead and earth; both of these should pass through the coils and so give me a measure of coil integrity. The lighting coil had a resistance of 1.1 Ohm and I can confirm that when spinning the Magneto by hand I could detect and AC voltage output on this wire. The HT coil gave a resistance of 6.7 kilo ohm which I believe is about right.

However, it was difficult to test the LT coils whilst they were still connected  so I unsoldered the ignition coil LT wire from the condenser  and unscrewed the two screws passing through the terminal horseshoe plates in order to remove the coil. Once it was removed I was able to test resistance etc more easily. First of all the to end horseshoe plates were continuous electrically with each other giving a value of 0 ohms resistance. Surprisingly, testing the low tension lead; the brown lead now unsoldered from the capacitor, I found no resistance between this lead and the end plates whatsoever. This is clearly not right since this wire  lead joins  to the coil and  so should have no direct connection to earth but only via the primary coil windings.  Hopefully this is my only problem. I also tested for continuity between the low tension coil and the high tension coils inside this unit. These should not actually be connected, but since both are  connected to the earth horseshoe plates they can be linked via these and so once again I obtained s value of 6.7 kilo  ohm. This is different from say a traditional battery powered points ignition system as in a car where the two coils can be tested separately. It  is obvious I was going to need to change this coil but it wasn't clear whether I should simply obtain new coil or send the whole Magneto away for reconditioning. The magnetism on the flywheel did appear better than I had suspected once the flywheel was removed from the Magneto core. However I placed it back on the core for storage.

Disconnecting the baseplate

Wear marks on crank taper. These were probably caused by failure in the Woodruff key which was clearly worn. Hopefully this will not be critical once the key is renewed.

Removing the backplate. 

Capacitor. This is a press fit and can be drifted out for replacement if required but capacitors can be fragile and I think this procedure would be risky. Luckily these rarely fail.

Removing the ignition coil- held on by only 2 screws

Pattern ignition coils of the Bosch format are around £15 from Mopedland. Its a direct fit replacement.

I was able to verify function using the spark test. Reconnect the cap and fit a spark plug. Rest the plug so its in contact with the base plate or something that's earthed to the base plate. Then flash a 1.5V pen-cell from the base plate and capacitor terminal. This should produce a weakish spark at the plug. My old coil didn't but I'm pleased to say that the new one does!

I held a pen cell in contact with the base plate, route the HT lead with plug in the cap such that the plug earths to the backplate. Then run a wire from the other terminal of the pen cell and flash that onto the capacitor connection to the ign coil. You should see a spark at the plug, although this is driven by only 1.5v so it will be weak.

For what its worth I present the following values from coils that worked.

Lighting coil: test between yellow  output lead and base plate earth  1-1.2 ohms

HT coil: measure  after removing the spark cap between end of HT lead and base plate earth  6.6 k-ohm. (My old coil which didn't work was 4.6 k-ohm).

LT coil: This can't be measured unless disconnected from the capacitor then test between the freed end lead and base plate earth, previous coil; 1.8 ohm. The new coil was lower at 1.2 ohm.

Capacitor 330 nfarad. 

Now refitted, had to adjust the position of the new coil. Adjustment is limited but as originally installed it fouled the magnets. I set it with a 7 thou gap top and bottom which equalised the space available. I also had to set the points gap to 12 thou at TDC, and set the timing. This last is very awkward because you can't access the rear plate easily to adjust it once the flywheel is on. However using a dial gauge through the plug hole and a Magneto boys magneto box I was able to set it to 2.3mm btdc. Although this was a full movement of the back plate. Once done I trimmed the HT lead both ends and attached it to coil and cap before testing for spark.... Yippee I got one!!! I then used some old 2 stroke mix and a temporary fuel tank to attempt to start... And yes I got firing!!! I can't run properly as my throttle cable is incorrect but the motor did at least run. So milestone achieved!!! I will replace the points plug HT lead and cap though as these are all very old. 

Since I fixed this magneto, I restored another using the old style, tape-wrapped coils. Unlike the bonded plastic ones above, this coil requires the HT lead be soldered into an eye mounting. I dismantled the old coil to see how this had been done. The inner wire from the HT lead was itself soldered into a narrow metal rube. This tube was then inserted and soldered into the eye. I'm guessing that this arrangement gives greater mechanical strength to the junction and also reduces the amount if solder (and therefore) heat needed to make the join. I was unsuccessful in finding a source of new metal sleeves for the inner wire, but I found a small roll pin could be opened out to allow the wire to enter. 

However, these pins are coated so I had to rub them down to bare metal using rolled up Emery paper.

Widening the slot allowed the wire from the HT core to slip in smoothly and ialso let the solder flow in well to hold it.

 

This then fitted nicely into the eye mounting on the coil. I did try to solder but the insulation resin seems to melt very easily so I crimped the eye onto the soldered roll pin and applied the minimum of solder just to the open end of the mounting eye.

The centre stand and crankcase mounting repair

The centre stand on this bike was wobbly which I had attributed this to the fact that the mounting bolts were loose. In fact I found that these were damaged and wouldn't screw up any tighter. The bolts themselves are 30mm M10 bolts with a 5mm M12 shoulder. The shoulder fits into the centre stand and the M10 section fits through lugs moulded into the bottom of the crankcase. Each bolt has two washers and is retained by an M10 nut.

I found the threads were damaged so I recut them using an M10 1.0 tap and die.

I cleaned up and examined the stand and crankcase lugs and found that both were damaged. (Wouldn't it be nice if I took something on this bike apart and found it was in good condition!) The LHS in particular was badly worn and the holes were distorted. One side of the stand was worn very thin.

LHS crankcase lug-hole worn oval

LHS stand lug- hole distorted and worn close to the side of the stand- I think I got this one just in time.

RHS crankcase lug

RHS centre stand lug- enlarged but still almost circular and there is a lot of metal remaining all round.

The stand is steel and so could be welded. I decided to fix this with repair washers fitted inside the metal and to the outside of the stand. I couldn't fit anything on the inside as this would obstruct the fit with the crankcase. On the RHS I  enlarged the bolt hole to 18mm with drill and reamer. At this size its a good fit for an M10 washer so I fitted two into the thickness in the metal and fixed them with spot welds on both sides.

Hole drilled and reamed to 18mm

This fits two stainless steel 10mm washers perfectly

Washers secured on both sides with weld.

On the LHS the hole was already, so distorted and the edges worn so thin that I didn't want to drill or ream here. In fact owing to the wear there wasn't really anything to drill into and the hole was already too large for my repair washer! I used a 10mm drill as a line marker, passing it through both lugs to position a 10mm washer on the outside of the RHS mount. I did this by eye, holding the drill such that the washers were at the same height and the drill passed horizontally between the two legs of the stand.  I could then clamp  the washer in position and secure it with weld. However the wear was so bad that the washer didn't cover all the damage. I filled in  below and behind the washer with extra weld to replace the missing metal.

All that was necessary now was to drill and ream the holes on both sides to accept the 12mm bolt shoulder. I had used stainless steel A2 washers for the infill. These are very hard and probably harder than actually required. This meant I had a difficult job to drill and ream them to 12mm but after many drill sharpenings I eventually succeeded. 

Centre stand lug, reamed out to 12mm and welds ground down.

Welded washers now accept the 12mm shoulder

I ground the weld down in both sides of the stand before degreasing and painting in blue Hammerite; this isn't quite a colour match but I wanted a durable finish.

Inside surface ground smooth

Painted in Hammerite.

The Motor Lugs

The motor lugs were distorted and would need lining. I ordered some 1/2" (12.75mm) brass tube specified as 10m id. This is thinner in the  wall than I would like, but its a bit of a compromise as I don't want to remove too much metal from the lugs themselves.  I enlarged the M10 holes (probably rather larger already!) using a drill bit passed through the narrowest first to line drill both holes.

Once the hole was enlarged close to 12.75mm I was able to pass an adjustable reamer through and line ream them both to accept the tubing as a tight fit.

In the meantime I cut two inserts from the tubing. The lugs are not actually the same thickness and I needed inserts of different lengths so I cut one 13.4mm and one 14.8mm. I cut these on the lathe partly to ensure the ends were square but also to chamfer the leading side for insertion. I suspect cutting them with a hacksaw would be perfectly adequate.

I pressed both linings into the lugs with hand pressure and secured them with Loctite bearing fit.
The linings had closed up a little in the insertion so I cleaned them with an M10 drill and checked that the bolts would fit.

The repaired stand could then be attached and jobs done.

Refitted to frame.