Pistons

[gasman]

Just a reminder to all who have bought new pistons, check the distance between the bottom of the piston and the crankcase when the piston is at BDC. Mine appeared ok but when the engine got hot I heard a slight tapping sound. When the better got me I stripped the barrels off again to find a lovely mark all the way round the crankcase. I have removed 40 thou from the bottom of each piston. Also while i'm at it I am converting to the 3/8 chain.

[Smokey_Paul]

Oh crumbs... I checked my pistons against the measurements that Clive gave me I hope I measured them ok..!!!

I did not see any marks with the engine stripped but then again it hasn't done any work yet...

Another worry.

[hendred]

Interesting - my Silk has new pistons and I get a tapping sound when the engine is hot.  What clearance should there be between the pistons and the crankcase - nothing in my manual about this?

Thanks.

[Smokey_Paul]

Clive has told me that the later bikes did not have this problem and you can clearly hear the tapping if you have this issue. My main engine noise when I went over it today was the primary chain and tightening that up made a massive difference.

I have had my screwdriver against the engine and my top end appears quite quiet especially at the lower end of the barrel.

I have a slight tapping at the top of the stroke but I guess this is usual engine noise especially with such a big piston other than that I need some good weather for a good ride

[Hendred]

That's good news.  I think I will look again at the ignition auto advance and retard; there is a bit of play in the slots in the alloy bob weights.  Does anybody know the correct springs for the unit?  I have ones from a Norton Commando fitted at present but there seem to be many different versions of the springs.  There was only one spring fitted when I acquired the bike!

[Smokey_Paul]

I will have a look to see if I am some spare.