Monday, 27 April 2020

QR50 - Closing up the crankcases

Having put the bearings in, all I have to do to close the crankcases and move on with the project is fit the crankshaft oil seals. These allow the crankshaft to pass through the cases but remain sealed, so that the crankcase compression upon which 2 stroke operation depends is as effective as the designer intended.

Identical seals fit into each crankcase - they also came from Simply Bearings:

You can often push them part way by hand, followed by a little help from a mallet and suitable drift. On the generator side, the seal goes a little way in - the recess locates the generator.

Before you go any further, if you have not done so already, is to dry fit the crankshaft to the cases. Make sure the cases fit together and the crankshaft is free to rotate when the cases are closed up.

Don't forget that the crankshaft needs to be the right way round! It will fit both ways, but this worm drives the oil pump. Oil the seals, bearings and this worm before you attempt to assemble the cases for the last time.

Next job is to seal the crankcases. I'm using some Threebond 1215 silicone gasket to seal the cases. It's grey, discrete and rated at 250°C. Ample for this application.

This is spread thinly over the sealing surfaces and around the bolt holes, followed by mating the cases together and pulling down the bolts.

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