School Fees

As luck would have it, I'm now in need of a new piston and rings for this bike as I have managed to destroy the last set along with the cylinder. During the past week i had the piston out of the bike trying to diagnose the cause of some pretty audible piston slap. The noise has been there since I rebuilt the engine and I was a little concerned that damage to the piston or cylinder might occur if I left it to carry on for much longer. With the parts out of the bike I measured them up and they were all within spec so back in they went.

I proceeded to start the bike up, let it warm up, gave it a quick rev and pssss..... DEAD. Why now ?

This is what happens when you re-use old wrist pin clips. The clip was actually embedded in the piston but i had removed it and filed down the burrs before this photo was taken. 

 

This is what also happens when you re-use old wrist pin clips. Those gouges are quite deep. I reckon a 1 mm oversize re-bore might just clean up the barrel.

In the mean time I've ordered a new piston and rings and with those "school fees" paid and a lesson learnt the hard way, I hereby vow never again to use an old wrist pin clip. Luckily I  have a good used cylinder that will be painted, honed and installed. 

I have subsequently learned that Expresses all have fairly loose piston to bore clearances, hence the noise I was hearing.