How to measure a barrel?

John D · Post by **John D** » Mon Jul 26, 2004 10:02 pm

Sounds silly, but years ago I had a pair of model 20 barrels rebored to + 20. They subsequently got mixed up with other spare barrels. Years later i am restoring the bike and need to identify the rebored barrels. How can I do this easily myself?

Eric · Post by **Eric** » Tue Jul 27, 2004 1:00 am

If they were never used and all of your other barrels have been used it should be easy to see the honing marks over the complete bore. If a berrel has been used there will be some evidence of the piston rings smoothing out the honing marks. Otherwise what measuring equipment do you have?

John D · Post by **John D** » Tue Jul 27, 2004 9:29 pm

They did get used for a short period. i'm pretty sure I know the ones from what you said. I'm gathering measuring tools as I've also just purchaseda lathe. So, what would I need to measure, how and with what? Thankyou for your help so far.

lawrence · Post by **lawrence** » Tue Jul 27, 2004 10:13 pm

Most engineers will measure them free of charge (in the hope of some business!) and I have usually found they will tell you if they do not need reboring. I think they use a dial gauge.

Lawrence [}:)]

Colin F · Post by **Colin F** » Tue Jul 27, 2004 11:22 pm

A vernier caliper would measure the bore. Even one of the cheap ones would be accurate enough [:D]
They have internal measuring lugs (normally on the top). Put these inside the bore and open up the calipers until you have found the maximum diameter.
Check the standard bore, Model 20 is about 66mm or 2.598" [8D]
You should be able to work out the oversize of all you barrels with a little bit of maths [;)]