The re­bor­ing process is not com­plete un­til the high spots from the bor­ing bar have been smoothed

Practical Sportsbikes (UK) - - CONTENTS - Words and pic­tures: Alan See­ley

Tidy up lightly scored bar­rels or su­per-fin­ish a re­bore

Once a bar­rel has been re­bored, the next step is to hone the liner to make the sur­face more suit­able for the pis­ton rings to run against. That’s be­cause when a bar­rel is bored, it’s essen­tially sim­i­lar to cut­ting a thread and you’re left with a rough, he­li­cally cut sur­face. The fa­mil­iar cross-hatch­ing you see on a newly fin­ished or un­worn bar­rel is the re­sult of hon­ing.

The process cre­ates lots of lit­tle peaks and val­leys to hold a thin film of oil to help pre­vent the pis­ton rings seiz­ing in the bores. Not that it takes much to go from freshly bored to prop­erly honed. The hone should take no more than a cou­ple of thou­sandths of an inch off of the bored sur­face. Of­ten when bor­ing a bar­rel an en­gi­neer will take ac­count of the hon­ing process to come and un­der-bore slightly.

Pete O’dell of The Mo­tor­cy­cle Works took us through the var­i­ous ap­proaches to hon­ing to ex­plain how he gets it right every time.

That’s Peter O’dell in­sert­ing his tool

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