Stripping the motor 4.Motor and Transmission Reassembly

Having stripped the motor and reassembled the crankshaft into the crankcase and right side transmission case I'm going to reassemble the transmission. I had noticed that the primary drive chain is slack and the sprockets on the rear of the clutch hub had hooked teeth. I got a replacement chain as a DID 25H 64Link. For reasons I dont understand this chain is a smaller design than the other 2 transmission chains and it appears prone to stretching and has no tensioner to compensate. I'm replacing the clutch hub and it's integral sprocket as well. It seems sensible to change the clutch sleeve bearing and spacer washer as well. I'll check the camshaft sprocket teeth as well when I get around to refitting that.

New primary drive chain

Camchain on crankshaft... note wrong position of chain guide... see on... it should fit inside the loop of the cam chain.

Adding spacer washer

New clutch sleeve bearing

NOTE.... in this pic the cam chain is positioned wrongly... the oil flinger/chain guide should be positioned entirely within the loop of the camchain

Teeth on this clutch not hooked!

Insert the three clutch balls and their retaining frame

Clutch centre drops in and locates onto the balls

Assembling the clutch hub with the new chain and its driven sprocket... the primary driven sprocket. Note the 3 discs are uppermost. There is a central hub which has to be installed to centre it.

Then fit the final drive shaft assembly with the loose pawl and the secondary drive sprocket, looping the drive chain around the secondary drive sprocket in the centralising hub of the primary drive sprocket.

Make sure that the free pawl enters the final drive shaft. 

And that everything drops neatly into place.

Loop the chain around the final drive shaft's upper sprocket and the final 

driven sprocket. Note that the final driven sprocket has a recessed boss on one side and a chamfer on the other. The recessed boss goes downwards and engages with the top of the centralising hub of the primary drive sprocket to locate the sprocket. It's a fairly light fit and it's not firmly he'd here until the case is refitted and the rear wheel drive boss is inserted.

The clutch centre nut is refitted and torqued to 38nm. The castellated washer was peened over to retain it.

I also wanted to check the operation of the free pawl locking mechanism. The engine disengagement lever moves a rod up inside the final drive shaft. Provided the shaft cant move, this forces the free pawl against its spring and disengages it from the sprocket. This is shown in the pics below... As the case is open I had to push the shaft down manually to prevent the disengage lever from simply pushing the whole shaft upwards.

Lever in engaged position. Free pawl is slotted into the centre of the sprocket, engaging drive.

Lever in free position (disengaged) free pawl moved up and out of the slot on the sprocket. Note I had to apply hand pressure to stop the whole shaft from rising, this would normally be prevented by the other side of the case.

 CHECK NOW... check at this stage that the chain guide/oil flier is located within the loop of the camchain. 

Check again now before the chain and guide are fed through the slot for the chain in the transmission cover.

The case was then refitted with a new gasket. I didn't use sealing compound because I'm not certain that I won't be revisiting the interior soon... given my error with the chainguide this was just as well!

Piston and Barrel

I had bought a pattern piston but the assembly was the same as an original. There are 2 rings and a multipartite oil ring assembly that fits in the lowest groove. Rings are shown here after the oil ring was fitted (wavy ring between top and bottom slim guide rings... it doesn't matter which one goes on top.

The actual piston rings are different. One has an obvious silver edge and this is the top ring. The ring with the black edge goes in the second ring groove. Both rings are stamped with their size (in this case +050) on the UPPER side.

Silver (top ring) and black (2nd ring) note markings on their TOP sides.

I fitted the rings carefully and then inserted the gudgeon pin clip on one side only. Gudgeon pin clips are the work of the devil and you should always get a ring with the circlip plier eyes. If not then the stye with one-side tang will at least help you fit them with pliers. The absolute worst type are the simple wire snap rings. These are impossible to fit without pliers, but have no way to be safely gripped. Unfortunately these are the usual type supplied. Once they spring out of the plier's jaws they instantly migrate to another universe and you will not see them again. For this reason get spares and aways plug the mouth of the crankcase to stop them from falling inside.

I chill the pin itself and warm the piston with a heat gun just before fitting to make the fit easier. However, in this case the conrod small end eye was slightly burred on one side, and I had to remove the burr using a 13mm reamer... again plug the crankcase and keep any metal debris out!

Piston fitted by sliding the pin through

Blocking off crankcase and camchain slot to fit the pin clip

Fit the piston by inserting the pin towards and up against the pre-fitted clip. You then only have one side to swear at as you try to retrieve the pin snap rings, realise they are gone for good and postpone the job whilst you wait for more.

Note that the piston has an arrow on its crown which must point forwards. That is to say that with the motor in front of you and the camchain on the right, the triangle should point forwards.

The barrel is then oiled and fed down using fingers to compress the rings into the bore.

Piston inserted into barrel

I reassembled the head.... fitting new valves and springs. The valve seats weren't great, the inlet looked rescuable but the exhaust was more pitted. I ground both valves to fit their seats, inlet went well but a few pits remained in the exhaust. Ideally I would have had the seat recut, but I couldnt find any seat cutters small enough, or anyone who could do this for me.

New valves

Seats reground

There was a lot of discolouration on the cylinder head mating face. I assume this resulted from moisture pentrating between head and head gasket to some extent. To reflat the head I used immobilised emery paper (240 grit) on an engineers flat plate, surfacing the head in circular motions and lubricating the paper with oil. Head shown on the plate below...

Clean up and reflatted

Mating surface was much improved. I then cleaned up both head and valves and put both to clean in the sonicator as I don't want any grinding paste near the inside of the motor. I coukd then reassemble the head components starting with the valves and springs.

Using new springs

I slipped the valves into their guides with assembly lube  then crumpled some tissue into the combustion chamber. This supported the valves whilst the head was inverted and the springs installed.

Fit the spring seating washers

.. and the springs themselves

Compress by hand using the retaining washers to hold the springs down

I fitted the inlet first and then the exhaust... note that the heads of these valves are different, the exhaust is wider, and so the retaining washers are not interchangeable.

Both springs fitted

Valves in place and shut

Ensure both locating sleeves are positioned in the underside of the head. When I trued to thdn fit the head I discovered that the head gasket had been badly cut, and the location sleeve would not fit. I had to amend the stud hole with a punch. This permitted the head to be fitted.

Stud hole enlarged to admit locating sleeve.

I could then fit the head. I used a wire to pull the cam chain through the tunnel and settled the head onto the gasket, tapping it down to seat it onto the alignment sleeves. The oil flinger chain guide will be secured at its upper end when the camshaft is fitted.

The head was fixed by torquing the 4 x 6mm nuts and washers diagonally across the head. The long 6mm retaining screw was also fitted.

Assembling the camchain system requires that the valve timing be reset. This means that you need to set the motor in the tdc position. As this is indicated on the alternator rotor its necessary to fit the alternator and  torque the central but at this stage. You need to torque it now so that the tapers mate and the force of turning the motor does not rest solely on the alignment pin. Check that the rotor and crankshhaft turn as one with no relative movement between them.

I could then try to fit the camshaft. I'm not going to say this was easy... its a pretty awkward thing to do as there's not much slack in the chain. I found it was best to fit the camshaft pretty much anywhere with the central shaft out. I could then insert the centre shaft and rotate the motor to the T timing mark on the rotor. This showed which way and roughly by how many teeth,the camshaft needed to be rotated.  I could then remove the centre shaft again, push the camshaft down in the head, and ease the chain off the teeth on the right hand side where there was more space. I found I could lift and move 1 link and then work the chain around the sprocket without allowing the sprocket to move as well. Reinsert the centre shaft and check timing again at the T position. It took several attempts but I got there in the end.

Camshaft centre pulled out yo allow chain fitting and adjustment

Alternator rotor set at the "T" tdc mark

Sprocket timing holes horizontal across head

The central shaft coukd then be inserted properly. I fitted a new O ring at the exterior end and also skipped the 10mm steel  washer between the end of the camshaft and the head.

Central shaft pushed fully home, not the small pin fixing hole is at 90 deg to the screw slot so in this position the alignment was close. Note assembly lube used along the shaft.

Final lining up of the pin holes. There is a hole only in one side of the centre shaft so you may have to rotate it until the hole can be seen down the dowel hole in the head.

Camshaft retaining pin fitted

I usedcassembly lube to  grease the rockers... I had never dismantled ti's assembly so just greased it as best I could before fitting it into place with a new gasket.

Assembly lube on rockers in rocker housing.

There are 4 screws to hold the rocker housing but in my case the cross-heads were all worn so I replaced them with Allen caps.

Finally I could replace the tappet cover, again with a fresh gasket. I didn't use permatex on feather of these top-end gaskets as I suspect I'll be revisiting the cam timing at some point soon.

Tappet cover with decompression valve fitted

I had already cleaned the existing points so I rechecked the gap through the window. This was .12 mm which is in the correct range. I will return to this, and maybe fit new points as well, once I see if/how the motor runs.

Contact breaker points visible thru window in rotor

Brake actuating rod refitted and brake lever attached (lining up my mark with the split in the brake lever). Spring coukd then be hooked onto the arm.

Note that there is an O ring installed over the moulded boss in the transmission case. To be frank, I can't see any need for this at all, but it does sit inside the brake arm return spring and so possibly has a centralising role? In any event it was missing from both the bikes I dismantled so I don't think it's necessary. However, I did refit one here.... its just visible inside the brake return spring.

Finally I tidied the mounting pin holes in the brakeshoes, applied some copperplate to the mounting pin and refitted the shoes. I fitted the washer and split pit to the mounting pin and then the spring between the shoes.

Note that the shoes fit only one way round with one atop the other to move smoothly.

Brake shoes refitted with spring and pivot pin washer/split pin. Note that in this pic the oil seal is still recessed too far into the case.

I attempted to insert the motor into the rear wheel but it wouldnt go. Investigation showed this was due to the brake shoes. They must be fitted the correct way round or they bind on one of the moulded ridges in the transmission cover so check each way to unsure full movement. This didn't eliminate the problem though and I still got a hard stop about 1.5 cm from closing the wheel. This turned out to be down to the new brake shoes I had bought. I found that brake shoe serviceable thickness in 2-4.5 mm. This shoe was over 5mm at the ends and on separation there were clear witness marks from the binding.

I changed the shoes for my part-worn pair and the motor mounted perfectly.