Rebuilding the motor 1: building an engine stand.

There are probably an infinite number of ways of building a suitable stand for the motor but here's what I did. I ordered 25mm steel box section with a 2mm wall plus 25 and 30 mm flat steel bar 8mm thick. In addition I have 20mm od steel tubing with 2.5mm wall and 15mm steel round bar. Here are my initial sketches. The stand consists of an "H" shaped base. To this is fixed a vertical mounting upright bearing a hollow tube to accept the pin from the swivel mount. The motor itself is mounted on a 90 deg bracket attached to a swivel mount that slips into the mounting tube.

The design can be adapted, I think I might make the base a little wider and the upright a little shorter if remaking as this will improve stability. However, this is as always a record of what I actually did so here it is warts and all... and its not intended to be an advert for my welding. I am of the low skill welder category; any weld you walk away from is a good weld for me! Basically if I start with two bits of metal and stick them together then that's fine. I will say though that this 2-8mm steels are easier to weld than thin car body panel steel.

Components of base, assemble 2x20 and 1x 35 lengths of box section to form an H. Make upright from 25cm length of box. Grinding the end to accept 15cm length of 20mm tube. Weld this to the upright and fix to the H as below. Note weld nut inserted as clamp. 

Swivel mount, fix a 20cm length of 15mm round bar to centre of a 10cm length of 30mm flat bar using screw and weld

Assemble engine mount using motor to ensure fit. In my case this resulted in 10 and 18cm lengths of 25mm flat bar. Grind ends to fit with crankcase

Building the stand:

Basic components, 25mm box (2 or 2.5mm) and 25mm steel bar (8mm)

Engine Mounting Bracket:
Cut two convenient lengths of 25mm flat bar and drill 8mm holes on the centre line 1.5cm from one end of each. You may (will) need to grind the end profile of both to remove wickedly sharp corners and ensure that the bars can fit against the crankcase profile

Vertical section of mounting bracket ground to fit with the crankcase.

Slip M8 bolts through these holes to hold the bars loosely to the motor

Attach the two bars loosely and swivel them to form a 90 degree junction, mark and cut to length.

Align the bars to form a 90 deg junction, scribe and cut. Refit the bars and weld together to form a mounting bracket.

Bracket welded together, this ensures it will fit!

Swivel Mount,
The bracket needs to be able to swivel so to make the swivel mount cut a 10cm length of 30mm flat bar and a 20mm length of 15mm round bar. It is possible simply to weld the two together, but I wanted to strengthen the join so I drilled a 6mm hole through the 30mm bar 3cm from one end on the centre line. I then drilled and tapped the round bar to M6 and fitted the 2 bars together with a screw. I had intended to use a countersunk screw but didn't have any so I used a button headed screw and welded that into place before grinding it back flat to the bar surface.

30mm bar screwed and welded to 15mm round bar; screw head and weld ground flat

...and welding in the other side of the round bar to form the swivel joint.

Front side of bars welded together

Finally the mounting bracket was welded to the swivel joint along the centre line of the 30mm bar below the position of the swivel (round bar) so that the weight of the motor would hang vertically from the joint.

Welding the motor mounting bracket to the swivel joint

Base,

Meanwhile construct a base for the stand from 25mm box section. Cut two 20cm lengths for the sides and one 35cm length to join them in an "H" shape and weld together

Base Upright and Swivel Tube,
Cut a 15cm length of 20mm round tube (15mm ID) and drill an 8mm hole, 3cm from one end.

Run a nut up on an M8 bolt

Drop that into the hole

Weld on the nut making sure that the bolt isn't welded in too!

M8 nut welded to tube

Make the upright by cutting a 30 cm length of bar and filing the end to accept the profile of the 20mm round tube. If making this again I wouldn't make this quite so high, 20 cm would have been fine.

Upright profile filed to accept swivel tube

Weld the pre-prepared tube onto the top of the upright

Swivel tube welded to upright

Weld the upright to the base

Upright welded to the base, I straddled the side to centre join of the "H" to try and strengthen it.

The swivel mount can then slip into the tube

Assembled stand- I did get a bit of a bend in the swivel bracket but it should work fine.

The motor then bolts to the stand using 2 x 55mm M8 bolts fitting washers against the crankcase

Motor mounted to stand. It can be swivelled around the swivel pin to any desired orientation and fixed in that position using an M8 bolt tightened through the weld nut. It will probably help if some location hollows are drilled into the swivel bar as well as tapering the bolt end so that the bolt can grip the swivel pin better.

The motor can be swivelled and secured in any position using an M8 bolt through the weld nut to clamp the swivel pin inside. It would probably help to drill some location points into the bar and shape the end of the bolt to help it locate and grip better.

Testing the motor

Oil Change

Having refitted the motor and before attempting to start it I set about changing the oil. Draining the oil is a lot less messy if you insert a hose joiner as a spigot into the drain hole. The oil then drains clear if the motor and frame.

Using a hose joiner as drain spigot

I could then try starting the motor,  it did run but only at full throttle and wouldn't run on. In fact it soon stopped running completely! 

There was also a tremendous vibration when it did run. I had wanted to replace the points and reset the timing as these were original anyway so I removed the flywheel again. To my surprise the Woodruff key had actually sheared and this had allowed the flywheel to shake around, generating the vibration and ruining any attempt at accurate timing. I think this came about because I hadn't fully torqued up the flywheel nut. This needs to be tightened to 21 ftlb (28Nm). I hadn't thought this would matter for a short test run and although my nut was tight, it wasn't at full torque- Big mistake! This shaking had actually sheared the key and also chewed up the taper on the crank and its matching partner  inside the flywheel. New flywheels are no longer made and the taper is part of the crankshaft which is available only at vast cost.

Damage to end of crankshaft, taper is now scored.

I was therefore forced to try and rectify this damage as best I could and  I approached this first by removing obvious burrs on the crank taper with a fine file, and then  using coarse and fine valve grinding compound in sequence; applying it to the magneto internal taper and then rotating it on the shaft. It helps  to remove the back plate while you do this. Luckily this returned the tapers to a close fit and although it didn't remove the scoring damage, it did give a considerable improvement.

I then set about removing and renewing the contact breakers (points) and started by taking several pictures of the setup before it was disturbed.

General view of old cb in position.

Close up

The moving point is retained on a pivot pin which is part of the base plate fixed point. The moving points are held onto this pin by a split clip and washer. Remove the split clip with small snipe nosed pliers and lift off the tiny washer. In my case this was very worn where the clip had been positioned.

Remove the tiny washer- note the wear marks where the clip had rested against it.

I then removed the base plate retaining screw so that both points could be removed as its then easier to get at the connections to the moving point.

removing the contact breakers by removing the base plate retaining screw so that the points can be lifted off complete.

Unscrew the nut on the rear of the moving points and remove the black wire connection. You can then lift the moving points off the spindle on which they move.

Black wire contact to the moving points removed, note the loosened nut replaced on the bolt. Note  also the two nylon insulation sleeve washers that sandwich the mounting bracket and ensure that there is no electrical connection between the mounting bracket (base plate) and moving points via the bolt or spring.

Note that this connection is to the moving point only, there is no electrical contact between the retaining bolt and the  the base plate through which it is screwed, or via the spring and the bracket. This is achieved by a number of insulating washers and plastic sleeves which isolate the bolt from the bracket through which it passes. These must be refitted correctly.

Moving point fixing bolt, washer press on the spring of the moving point, the nylon sleeve washers remain attached to the mounting bracket.

Replacing the points is pretty much the reverse and its necessary then to set the gap when the points are on the top of the cam or tdc. This can only be done when the flywheel is refitted and its damned awkward. In fact the centre of the cam coincided with one of the flywheel webs in my case and this correspondence cannot be changed. Fortunately the points are open over a wide area and I was able to set them  at tdc. My manual suggests that they should be set to 12 thou with the timing set to 2.5mm btdc. These settings  served me well 40 years ago so I have stuck to them: I'm told that with modern fuels and synthetic oils (which can be used at 30:1 instead of 20:1) its advisable to set the gap more narrowly to 8 thou and the timing to 2.1mm btdc although some needle changes may also be necessary in the carb.  I'm using mineral oil and I'm going to try and at least get it going with standard settings before experimenting with new oil ratios or ignition settings.

I refitted the flywheel with a new key. This time I also used Loctite retaining compound on the taper. I didn't want to use this because of the difficulties it will cause in stripping once more but I couldn't risk shearing another key or causing yet more damage to the tapers. I refitted the flywheel and torqued up the nut before leaving it for 24hrs for the Loctitite to cure.

Flywheel refitted and torqued.

I use a spark plug hole dial gauge to determine the timing position. This screws into the plug hole and allows me to determined tdc and 2.5 mm btdc quite accurately.

You can then slacken the two magneto back-plate retaining screws and rotate the plate slightly such that the points are just about to open when the motor is a  2.5 mm btdc. I use a timing box from "the magneto guy" which connects across the points with crocodile clips and indicates exactly when the points begin to open. This connection is awkward, one clip can just go to earth anywhere but the clip that attaches to the moving point is awkward and tends to pop off as you adjust. When I rebuild this motor I will insert an insulated fly lead that emerges from the magneto but connects to the moving point and allows a timing box connection when necessary. In the absence of this lead, adjustment is a fiddly and awkward process,  its hard to move the magneto back-plate without also moving the flywheel and thus the motor a little. It would be good to have a locking system to fix the motor in the desired position whilst you move the back plate.  However I persevered and by checking, adjusting and rechecking I found that I could obtain an opening point of 2.5 mm btdc- but this used all of the adjustment in the back plate slots. I don't think it will be possible to set this at 2.1 mm even if I were to try and do so.

Its not possible to time the motor dynamically but I can at least check it while it runs. I set the motor to tdc and then marked across the flywheel to a convenient datum on the crankcase. Marking both with white paint. I was able then to rotate the motor to 2.5 mm btdc (remembering the the motor rotates anticlockwise) and made a second mark there. When setting these positions it's important to turn the motor in its normal direction. Ie as this motor turns anticlockwise, you need to rotate it clockwise (backwards) past the point you want to mark and then back to the desired position in an anticlockwise (forwards)  direction to take up any backlash in the shafts and gears. I could check the timing as I peddled the bike using a neon timing light connected in series with the spark plug.

Timing marks indicated on the flywheel. Note the white spot datum on the crankcase. The two marks are righthand TDC and lefthandside 2.5mm BTDC. As shown above the motor is set to top dead centre (remember it rotates anticlockwise so has already passed the left hand mark which is before tdc.)

It would be nice to report now that having renewed the points and reset the gap and the timing, and  having fixed iall in place with Loctite, that the motor now runs well. Sadly that is not the case;  it doesn't want to run at all! It will start and run for a short while at full throttle and then stop. After a few of these cycles the motor stopped running completely even in this unsatisfactory manner. 

Removing the spark plug showed that it was very wet and it seemed likely that the motor was being fed too much petrol. I have re examined the carburettor  and found that the float chamber was overflowing, presumably because the float needle was not cutting off the flow of fuel completely. I cured this by regrinding the needle into the valve in the chamber lid with fine valve grinding paste. Although this stopped the overflow, it failed to affect any improvement in running. The fact that the motor did run for a short burst at full throttle indicates to me that the ignition timing is at least in a functional condition. The timing can now be checked dynamically and this shows its still firing about the correct position. I am wondering if I actually have two problems; firstly a leaking float valve and generally worn carburettor giving a vastly over rich mixture, and secondly a blocked or defective fuel tap/filter that reduces fuel flow such that the small quantity in the float chamber isn't being refilled fast enough to keep up with use at full throttle. I have therefore decided to renew both components and bought new items from Krippl in Germany . They are marginally cheaper there but I expect prices will soon rise significantly courtesy of Brexit!

I replaced the carburettor, fuel tap and filter but obtained no difference in running suggesting that my old components were probably serviceable. I'm now having to contemplate a more serious problem with this motor- in fact after the last run  I noticed exhaust fumes emerging from behind the flywheel. Stripping off the flywheel showed there was now a lot of oil around the crankshaft and over the coils on the back plate. Turning the motor over allowed me to test around the crank with a hanging tissue. This showed distinct puffs of compression emerging from the crank and implied that the seal here has broken. This would allow the gases to exit the crankcase rather than enter the cylinder and confirmed the suspected breathing problem. 

This is a new problem, I hadn't seen it before. Its possible its of my own making, resulting either from running the motor at the wrong timing or using Bradex easy start. Alternatively it may simply have been a weak seal that gave as soon as the motor ran at anything like full throttle. There is now no alternative but to strip the motor and replace all seals and gaskets since if one is weak the chances are that all are in poor condition. I will renew the bearings and some of the bushes whilst I'm inside the cases as it seems daft not to renew them whilst it's stripped.

Speedo drive

When I got this bike the speedo was disconnected and stripping the front wheel showed that the drive unit needed restoration. The biggest problem being that the drive dogs were worn or absent. I was able to restore these by welding on tabs but this was at best a temporary repair and in the long run I'd always expected to fit a new drive. I eventually ordered one and fitted it. I had expected it to fit immediately but I was surprised in that the new drive teeth only barely contacted the hub even when the axle was tight. 

New speedo drive in position, drive dogs barely enter the driving slots in the hub.

I had initially attributed this to an error in reassembling the hub: you will recall that it's not really possible to control how much of each bearing cone screws into the central tube and thus how much of each protrudes on each side. I had tried to adjust my refit to suit my old speedo drive and hadn't realised that the speedo is itself adjustable to fit the bearing cone. This was because my original, being severely worn, had already been adjusted to the maximum and all adjustment washers had therefore been removed! For this knowledge I thank the Fb NSU group. 

The new speedo drive comes with three spacer washers internally below the white foam disc.

Speeedo drive adjusting washers beneath the foam seal. One washer removed, 2 left in situ.

Removing one washer allowed the drive to fit nicely against the bearing cone and yet still mesh the drive teeth with the hub slots. This looks fine now but I will see how it beds down in use and possibly remove another later.

Dogs fit better into driving slots

Rear Wheel Removal and Renovation

Removing rear drive chain, wheel and sprockets

To remove the rear wheel you need to remove the drive chain. No problem as it's like a bicycle chain with a split link. This should be fitted with the closed side facing direction of chain movement. In my case it was yet something else wrong with my bike. Anyway force the open end backwards with the flat of a screwdriver, withdraw the link. This chain was worn so will be replaced. 

The exhaust is also likely to get in the way so I removed that too. A single bolt holds the hanger inside the rear fork. 

Gearbox sprocket looked worn. It needs a puller to remove it. I'm told a conventional 3 legged puller will do it, but it didn't in my hands. I had to buy the actual tool

I also removed the pedals, not strictly necessary but will make more room.

I unscrewed the nut on the gearbox sprocket, jamming it with the wooden handle of a wire brush to prevent it turning. 

... And removed the nut and washer before using the puller.

The puller screws onto the sprocket and is tightened to remove it. But this tool was a bit of a disappointment.  Firstly, If you just tighten it up as supplied then the end of the push screw is so 

wide that it overlaps the threads on the sprocket shaft and will damage them as its tightened. It would have been easy to taper the end to avoid this as I did on the grindstone.



Secondly the body of the puller has flats milled in it. They could have been milled to any size but the manufacturers chose 37.5 mm across the flats. I don't know about you but my spanners don't go that large- in fact neither did my adjustables and I had to buy a new extra large one to cope. Why couldn't this have been milled to a more convenient size??

Anyway, it did eventually work and once removed the old sprocket was clearly in need of changing!

Wear on old vs new sprocket

The oil seal behind was dirty and although it looked poor it didn't seem to be leaking. I have bought a new seal but I'll not change it now as I'm expecting to have to strip the motor down soon and change all seals and bearings.

Oil seal behind not looking good. I will clean this up for now. I'm expecting to replace all oil seals later when I do a rebuild

New sprocket installed

The rear mudguard is held by 2 stays that share their fork mounting with the rack carrier legs.

Remove the bolt to release all 4 struts.

Carrier is also held by a top nut and bolt.

Loosen the axle nut and tap the axle out towards the opposite side. Catch the spacer from the rhs which will drop out as the axle is removed towards the left. It's not necessary to release the chain adjusters but as I was expecting to change sprockets and chain so there was no point in preserving this setting. I slackened them off

Once removed the rear wheel can be finagled out. Remember to release the brake plate from its torque button on the inside of the lhs rear fork.

Torque button inside rear fork left

Stripping the hub

I took several views of both sides of the hub before dismantling the wheel.

Brake plate side (LHS)

Plain side (RHS)

Brake lever and spring

The rear wheel rim was in poor condition with flaking chrome shedding razor sharp shreds, most spokes are loose and all are rusty so this wheel will need rebuilding. 

Lifting chrome

Dismantling the rear brake

The brake arm is held on with a nut and spring washer, in this pic the axle is still present.

Removed

I've had problems aligning the brake arm on the front wheel because I forgot to mark its position. This time I remembered and used a centre punch to indicate the alignment of the arm and the shaft.

Using a centre punch to mark position of brake arm on actuating spindle.

The arm then levers off and the spring lifts out.

To remove the brake cover plate unscrew the 22mm nut, hold the back plate arm  to steady against the spanner.

When this nut is removed the brake cover plate will lift out of the hub, bringing with it the brake back plate.

Brake cover plate/back plate assembly

The brake shoes and anchor spring are mounted on the brake back plate, the cover lifts off

Rear view- shoes and spring

The spring can be levered out and then the shoes removed. Mine were in good condition so I just cleaned them with brake and clutch cleaner and will refit. These shoes are probably not the originals because they are bonded not riveted. Once the shoes are out, the actuating spindle pushes out, it didn't seem very worn but will need cleaning and re-greasing.

I set both the cover and back plates to de-grease and de-rust before I resprayed them with engine aluminium paint. I could then attack the hub.
Note that there is a shim above the bearing cone/plug and below the back plate- keep this safe.

Shim below brake back plate

Removing the bearings

As the front wheel, in this model quickly (and older models) the bearings are a three part system consisting of a threaded outer cone or plug against which the bearings run, these being pre-assembled into a cage for convenience of installation. The bearing cage is pushed by the plug up against an inner bearing shell pressed into the hub so that the bearings are held snugly and run in the shaped grooves on the plug/cone on one side and the shell on the other. To remove the bearings you need to unscrew the bearing cone/plugs. The manual calls for you to unscrew the right hand plug but there's no way to control which side will actually unscrew. I don't think it matters so use a 15mm spanner on the flats of each plug and unscrew. 

In my hands the rhs unscrewed completely and could be removed by pulling it out of the oil seal.

rhs bearing plug being removed. this leaves the oil seal and bearing cage in position. Note the shaped groove in the plug/cone in which the bearings run.

The oil seal itself can be levered out with a screwdriver.

oil seal removed

The manual then calls for the opposite side bearing cone/plug to be tapped out. Use a soft drift inserted from the opposite side and feel for the edge inside. 

Tapping this will then drive the opposite bearing cone out complete with oil seal, bearing cage and inner spacing tube. The spacing tube has to be separated from the bearing cone and there's no way other than gripping the spacer in a vice and unscrewing the cone, but take care not to flatten it.

a little clearer when de-greased.

Brake plate side (LHS) bearing cone separated from the inner spacer tube.

Note that there is a crushable internal spacer that fits inside the central tube not visible in this picture. This needs to be saved and refitted when the new bearing is assembled.

Removing the chain sprocket

The rear sprocket is held on by 6 special M5 1.2mm  shoulder bolts with a flat ground on their heads to accommodate the shape of the hub.
(I had lost a few and replaced those with 1mm M5 socket cap bolts but had to swap the spring washer for a shake proof and threadlock.)
Remove the 6 nuts; each has a spring washer beneath.

Unscrewing the sprocket nuts 9mm spanner

The sprocket then lifts off leaving the bolts in position. These bolts look like they won't come out unless the spokes are removed- in fact they will, so remove them now or they will drop out and get lost as the wheel is moved around. As with the engine sprocket, the chain sprocket was very badly worn and there was no alternative but to replace.

Comparing old and new sprockets- replacement is well overdue!

Removing inner shells

This leaves the two inner bearing shells in the hub which need to be removed to complete the strip. As in the case of the front wheel, tap each out from the opposite side using a soft drift.

Tapping evenly around the edge drives the shell out, here you can see the corrosion on the inner surface.

... and the new shells which are thankfully not corroded!

Hub reassembly

Clean out the hub cavity and drive the new shells in evenly.

I used the old shell to start them and then switched to a suitably sized socket once they were down flush with the hub. Don't continue with the old shell as a drift unless you grind it a little first because it will stick in the hub recess and be tricky to remove.

Once the shells are in you can assemble the bearing cones for both sides fitting new oil seals and bearing cages. First remove any old grease from the inner spacer and refill with fresh- don't forget the internal crush spacer. Work plenty of grease into the bearing cages and the oil seal lips.

Assemble the oil seals and bearing cages onto the bearing cones

screw the brake plate (flanged) bearing cone fully into the central spacer.

Insert the brake plate side assembly into the hub, pressing the oil seal in by hand.

Feed the rhs  assembly into the hub and thread it into the central spacer.

rhs assembly inserted into hub.

Tighten the two bearing cones against each other until there is no lateral play in the hub. If the bearings bind release the tension, rotate the wheel on the bearings a little and re-tighten to achieve free rotation with negligible lateral sliding motion. This should also push the brake side oil seal into position. Make sure its gone in flush by tapping with a suitably sized socket and ensure the opposite side is squarely seated as well.

Should add here that the wheel spindle wouldn't pass through the lhs bearing cone, I think due to a manufacturing defect. The first time I tapped it through it jammed and I had to dismantle the hub again. I reamed the plug with an adjustable reamer until the axle was a smooth sliding fit and then rebuilt the hub. This seemed to give me a better bearing seat too. 

Oil seal being pushed inwards as the bearing cones are tightened.

The hub is now complete so I was able to refit the repainted and reassembled brake back/cover plate assembly. Remember to grease the actuating spindle and apply a little copper grease to the feet of each shoe. Avoid using excess grease or contaminating the shoes.

Brake plate and cover plate assembly, shoes reinstalled. Unit repainted prior to refitting in the hub.

Remember to place the shim in position before  inserting the brake plates assembly.

In my case there was no way to rescue this wheel, the rims were badly corroded and all spokes rusty and loose. I ordered new rim and spoke set from Krippel in Germany.Now that the bearings are again smooth it should be possible the rebuild and true the wheel accurately. I therefore reassembled the hub  and took the  lot to  Wheelwise engineering near Horsham for the work to be done.

Very pleased with the rebuild although it took a long time. They were able to lace the spokes in a different pattern that gives more room for the heads of the sprocket securing bolts.

 RE laced spokes giving more room for sprocket bolts.