Tuesday, 2 June 2020

QR50 - Assembling the Transmission

Now that we have the engine back together, we can look at the transmission.

The QR50 has an automatic (centrifugal) clutch, with a chain drive to a reduction gear set up at the rear wheel - it is single speed, and the transmission acts as a single sided swinging arm. The wheel is mounted on a single sided axle, running in a sealed ball bearing in the inner case (that forms half of the crankcase) and a plain bearing in the outer cover. We can see it fitted to the bear case here: 

First we need to set up the drive chain tensioner and rubbing strips. It's a good idea to use some Loctite 243 in here to ensure we don't have a bolt come loose:

Here's the complete assembly:

I've mounted the clutch drum. This has the engine sprocket welded behind it - I have fitted the drive chain and the intermediate sprocket, which drives the rear axle. the chain is pretty loose and I think we may need a new one

Here's a close up of the tensioner. As you can see there is not much travel left - the upper path is the slack side of the chain as this engine runs backwards, by which I mean it rotates in the opposite direction to the wheels.

Here's the crankshaft taper and it's woodruff key:

Here's the clutch and final drive pinion in position. You can see the two pawls which are driven by the kickstart:

The case needs etch primer and a lick of stain matt black:

These are both U-Pol paints

Here's the kickstart quadrant and it's spring in position in the outer case:

The outer case has a couple of neat features. You see that cast slot linking the interior to the screw hole - that's the drain. there is another similar arrangement for the level plug:

Here's the drain plug from the outside:

Outer cover fully assembled with Threebond 1215 used for sealing. Unfortunately, it appears that the kickstart relies upon a fibre gasket for the proper axial clearance - the kickstart does not return with the case screws tight. It all has to come apart again to have the OEM gasket fitted, which does the trick. I fitted it with 1215 one side and grease the other, so it will come off easily next time - and maybe preserve the gasket for re-use.

This is the brake cable bracket:

I've fitted the rear wheel and centre stand to have a look-see; I've also assembled the rear brake.

I can see now that the centre stand is misshapen - possibly bent, or the wrong stand. It needs to come forward 10 - 15° or so which will stabilise the bike and allow the spring to work to retain the stand in the up position. I think I will also straighten that kickstart...

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