Iv had a look at the bike today, I can see that i have B barrels front and top! its not clear what pistons i need, if im reading it correctly is the ones with no makings? is that right?

It should be but if its been replated before who knows,if you need to get it replated then you need to send off the pistons you are going to use so they can bore it to match the pistons.

well i hope not!

Can you tell if its been plated before?.

but thanks for the piston info ill start making some calls!!

The platers are suppose to stamp the barrel each time its plated but Langcourts dont so it hard to know.You can measure the bore to see what size it is,the bore might be the right size but has it got the right pistons,so measure them as well

Safest really to buy the new pistons, and send them away with the barrels. No excuses for getting it wrong then.
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MC21SP Plaything
BMW F800GS Bumblebee
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I seriously doubt you've got a '21 that hasn't had either cylinder plated.

My '28 front barrel (the one that lunched itself) had been done twice, the top's been done once, the barrel that's fitted now has been done before (and it's a bit dodgy i.e. it's had a gentle seize) etc.

Don't forget to tell the platers what clearance you want, read Matt's thoughts here, second request down.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread