Stripping the motor 3. Stripping crankcse and transmission.and rebuild

First step was removing the brake shoes. Usually not difficult but this time very difficult. The shoes pivot on a stud at one side and the other side is held under tension by a sping. The spring was missing in my case and the pivot pin badly rusted. You can see the split pin and washer here but the split pin would not come out!

These brake shoes lacked the spring but luckily I had one present on the other motor.

Eventually I broke the split pin and filed it flush so that I could remove the washer.

... and eventually the shoes... they needed tappingcapart with screwdrivers of increasing thickness until the shoe could be eased off the pivot stud.

First shoe off

Followed by the second. The remains of the split pin within the pivot stud would still not move and eventually had to be drilled out, bu I left that task until I had separated the cases to improve access.

The next step is to remove the brake actuating lever but before doing so I used a punch to mark against the position of the split in the brake arm splines.

Brake arm and spring

Punch mark against split in arm

Once the arm was removed (tap a screwdriver as a wedge into the split in the arm to open up the splines) the wire spring could be lifted out.

and the actuating shaft could be withdrawn. All were cleaned and stored.

Withdrawing the brake actuating shaft.

 

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 I could then remove the 8 crosshead bolts that secure the rhs crankcase. Note 2 are longer than the others shown here adjacent to the holes that require them. You'll need an impact driver to shift them. Note that this case contains a large oil seal and naked bearing.  In my case the bearing was rough and noisy. The oil seal looked fine but I'll change it anyway.

The rhs case could then be removed by tapping with a rubber mallet. The cover was removed to expose the reduction gearing and chains beneath.

Reduction gearing and chains as revealed

The uppermost sprocket and chain is the final drive chain and sprocket.  These just lifted out but sadly forgot to take picture. This photo shows sprocket and chain safely stowed in a bag. 

This left the next chain its sprocket and the sprocket on the secondary drive shaft

Chain and its sprockets, including the final drive shaft, could then be lifted out and stored. Confusingly this is also termed a final drive chain and its identical to the first. It also comes out with the smaller sprocket which is called the secondary drive sprocket.

Final drive chain and shaft, secondary drive sprocket below.

This leaves the primary drive chain still in place. This runs from a small drive sprocket behind, and part of, the clutch drum to a larger primary drive sprocket. There are 2 versions of this large sprocket, the earlier features 2 damping rings... mine didn't.

Final drive chain looping driven sprocket and the smaller sprocket under the clutch unit.

The last chain (primary drive... different from the other 2, can't be removed until the clutch body has been removed. The clutch being retained by a castellated nut and locking tab washer.

The first step is to knock back the tab.

And then use the special honda tool. To remove the 14mm castellated nut. I held the clutch body with clutch pliers and used an impact tool to remove the nut using the honda tool.

Honda clutch tool in place

impact wrench to loosen nut

Castellated nut and tab washer.

The clutch and the primary drive chain beneath could then be lifted out with its large primary drive sprocket.

Components of the clutch separated out, centre still in his drum, chain, castellated nut and washer.

Turning the clutch unit over revealed that the teeth on the driving sprocket were badly hooked. I will need a new drum and for completeness I'll also change the chain. I ordered both new and was v pleased to get a nos clutch drum.

The clutch centre just lifts out of the drum. On its rear face is the starter mechanism consisting of the three ball bearings in the triangular plate. These balls move under centripetal force, to allow the pedals to turn the motor at low speed and disengage at higher revs. This mechanism is not attached and simply lifts out.

Note that the friction material on the centre doesn't look particularly worn

 I couldnt find any wear limits anywhere, and other fb users assured me that this amount of shoe thickness was normal. I decided not to renew the centre but I will check its operation in view of the siezure which was obvious when I collected the bike.

I lifted out the clutch shaft bush and the washer beneath to store them for safe keeping.

I then moved on to remove the crankshaft.

The alternator cover is held by 2 screws, I'd already replaced these with Allen caps so they were easily removed.

The cover came of to reveal a pretty rusty alternator/magneto rotor

The centre nut was removed with an impact driver and the washer beneath removed for storage.

The rotor was removed with a puller

To reveal the sorry state of the coils etc beneath. At some stage this bike has clearly been in a lot of water as there are signs of corrosion on all steel parts and a pile of white oxide dust n the alternator itself.

Similarly the inside of the rotor didn't look great. I set about cleaning  everything up.

I used a brass wheel on rusty metal and sprayed the electrics liberally with contact cleaner.

Things did improve, but obviously I have no idea whether they'll work yet.

It was now time to remove the crankcase itself. This is secured by a number of crosshead screws, there are 3 inside the transmission case.

Two were easily removed with the impact wrench but the third was recessed and needed a spanner on the screwdriver shaft to get it turning.

That screw was longer than the other 2

There is also 1 screw outside the alternator region in the side of the case.

This also turned out to be a longer screw.

The cases would still not separate but on searching I found 3 more screws between the fins on the base of the motor, transmission side.

This is a total of 7 screws in 2 lengths. The heads were a little damaged and I will try to replace them with Allen screws but they do need to be quite low so button heads are probably needed inside the cases.

Having removed the screws a few taps with a rubber mallet saw the cases start to separate.

It was a little awkward but they did separate eventually. Here looking inside at the pedal engage/disengage lever  or pawl locking lever.

The crankshaft also lifted out of the cases

Everything seems dirty although there is no play in the conrod or big end. I'm not sure about the main bearings, they seem smooth but I'll clean and refill everything before making up my mind. I think I can remove them with a bearing separator but I'm not sure how to press the replacements on without losing balance in the crank and of course, upsetting the end float on the crank. There's some guidance in checking the crank runout (crank true-ness) in the manual, but nothing setting the correct on end float

One thing that does concern me though is that an alternator rotor is usually driven by a Woodruff key slotted into the crankshaft thus also setting timing. This shaft doesn't seem to have a key or keyway, and instead a small metal peg seems to be fitted. This is pretty worn so I'd like to check this arrangement before reassembling.... This checks out and the crank should have a 3x4 knock pin rather than a key, however the pin in this one is damaged and needs to be changed.

I tried to remove the pin which was predictably impossible as there was insufficient material left to grip. I had intended to send it away for spark erosion but was informed that this wasnt a situation in which spark erosion could help, and was advised to drill it out. 

Pin as seem on disassembly... damaged end with little material to grasp.

This was very tricky as clamping the shaft was very difficult but I eventually drilled through with a 2mm cobalt bit and then removed the rest with a 3mm flat end mill.

Pin removed and the socket milled out

Ive ordered a range of knock pins... 3mm in dufferent lengths in case my modified socket is now deeper, and 4mm in width in case its too wide... If I need to use those, then they would need modification to fit into the rotor groove.

Note... this proved not to be possible as new pins were at best a loose fit in the crankshaft.

I washed and degreased all the cases, there were clear indicators of damage in the right crankcase which explains  the aluminium fragments  I found inside. At least one of these was tooth-marked indicating it had got trapped between gears and might explain the jamming and why the bike couldnt be wheeled. Damage appears around the socket for the rhs main bearing where the flange is damaged, and the case itself shows some cracking around this recess. The cam chain and oil guide were however in the way.

The oil guide is a press fit into the case and pulls out

The case could then be cleaned and damage around the main bearing recess was clear, but not I think terminal.

The flange around the rhs main bearing socket was broken.

There was cracking around this recess in the case

These cracks do not penetrate the case metal and the motor itself wasn't leaking oil when I obtained it. I'm not sure what could have caused this damage, but I suspect that the camchain had jumped off its sprocket and became trapped between the crank and the side of the case on the right side. If this happened, then its likely the tensioner failed, and I did find that the plastic stop which limits its movement was missing which might have allowed excessive slack to occur?

I will replace the tensioner, it's spring and the missing bump stop. The oil guide is also twisted. I don't know whether this is correct, but I will replace all these parts to be safe.

Although it does seem to be oiltight, I'm not sure whether the case is strong enough to reuse. A replacement is expensive and I would need to swap over the rear axle which is currently pressed into my existing case. I'm not sure how this axle mounts as there are other components involved. I'd rather avoid this procedure if possible.

I also cleaned and photographed the crank and piston for orientation purposes. Note direction of the arrow on the piston crown.

I also found that 
The free pawl lever seems to work by moving a spring loaded plunger in the final drive shaft. This can be pushed in and out of engagement with the final drive sprocket on that shaft to lock or free the pedals from the drive.

I removed the lever... it seems to simply pull out

... and photographed the oil seal in the mounting recess. I will fit a new seal.

This is the final drive shaft and the free engine/locking pawl is visible projecting from the shaft above the larger sprocket. I'm not currently sure how the engine disengagement lever acts to move this pawl. The lower pic shows an earlier stage with the lever still in place.

Removing the clutch guide sleeve distance spacer to camchain timing sprocket still in position.

Clutch guide sleeve and timing sprocklet (camchain) spacer still in position.

I eventually ordered new parts.

Crank, camchain, camchain tensioner and spring plus the tensioner rebound rubber.

Dealing with the last part first, my manual was adamant that it existed, although I'd not found one on disassembly and had assumed it had been destroyed in the camchain debacle. However there seemed to be no possibility of mounting the new one and it seems to have been discontinued although there's no record of when. The tensioner has also been modified and I suspect this happened at the same time.

Tensioner rebound rubber... no obvious mounting hole... the hole below the axle is for the chain guide.

Parts manual featuring rebound rubber and old style tensioner

The tensioner itself is riveted into position so I ground off the rivet head

And pushed the rivet out releasing the tensioner arm.

Rivet in position

Head ground down

washer removed

Releasing the tensioner arm.

New honda rivets are not available but it's a simple 4mm aluminium rivet so I bought a selection of 45 mm.length. the removed rivet is 2.4cm long. The rule is rivet length = joint length plus 1.5 rivet diameters in this case 6mm so I need to cut the rivets to 30mm to use.

Refitting the chain tensioner marks the start of the motor rebuild. I lined the parts up to check. The teeth of the new tensioner wheel were obviously more distinct than on the old.

Old new tensioners compared

Peening the end of the rivet is very tricky since you need at least 3 hands. I got it started using a vice to hold a broad punch vertically. I could then hold the case horizontally with the rivet head engaged with the punch and then hammer the upper end until it gripped. As I had noticed during disassembly, the rivet grabs inside the spring washer rather than pressing down tightly on the tensioner. I have no idea if this is correct or not.

Tensioner peened onto rivet

Obviously you don't want it so tight that the arm cannot move, but likewise you don't really want the possibility of a twisting action either. I'll try and tap the washer down a little and peen again. I'd like a smooth pivot in a single plane rather than a lifting motion. (I managed to improve it but not to my complete satisfaction).

I also removed the small oil seal through which the engine disengagement lever passes..  checked I had the right seal.

And tapped the old one out with a suitable socket

New seal just popped into place and I restored the disengagement lever.

I tapped out the alternator oil seal from the outside with a socket and replaced it tapping it in from behind  the alternator case.

And checked from the alternator side that it had seated correctly 

I had acquired a new oil guide for the camchain athough the top washer was not fitted. I compared to the old

And then fitted the new top washer.

The guide just presses into  socket hole in the case

Oil guide ⁰ⁿrefitted, camchain tensioner peened over.

There are 2 mysterious O rings, one fitted to the rear axle

And the other to the rhs case.

It's not clear what these are for at this stage because they form a seal only later on against the brake lever on the case and the axle nut assembly on the axle.

I went on to assemble the crankcase with the new crankshaft. I worked red assembly lube into all the bearings and also the new oil seals. This remains in place if there is a delay between assembling and starting the motor.

 

Here is the centre case, this is held onto the rhs crankcase by 7 screws. I replaced the worn crossheads with Allen caps. There are 2 lengths of screw, 35 and 43 mm. The longer 2 go each side of the cylinder opening, one from inside the centrecase and the other from outside. Of the shorter ones fit 2 inside the crankcase and 3 outside at the bottom. 

I was able to assemble the crank into each side of the case without a puller. I fitted a new gasket which was sealed with Permatex before assembly and tightening the screws.

The crank emerges through the greased oilseal on the alternator side.

I could then start preparing the transmission cover. First levering out the old oilseal.

And tapping the large rear axle bearing underneath.

This was a pretty chunky beast!

New bearing acquired

I did notice what might be a small crack in the oil seal housing so I smeared this with some permatex in case it leaked.

And then tapped in the new seal. Note, the seal should be tapped in to be flush with the surface of the case, not all the way into the recess. I got this wrong and this runs the risk of oil leaks.  Writing now at some distance from the work described, I don't feel like revisiting the installation and removing the cover yet again. I will see if I can insert a second seal above the first

Finally I used the old bearing to tap in the new bearing.

All ready now to start assembling the transmission.