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Dew cat tee bob
I've talked to several people, over the years, who had this machining done,and had this seal installed with good results,I'm not sure,but I think Syd's cycles have performed this service for their race customers, I'll e-mail Mad duc man,he worked for Syd's a few yrs ago, Capt Paul

By good results, do you mean a long lasting crank bearing? It would help to have xray vision in order to see what is going on in there! I notice many crank ends are pretty buggered by wear.. perhaps by dirty oil. It must be well lubricated as it is right at the output of the pump. Any type seal may have a problem working for long with a poor surface on the crank end. I recall thin wall sleeves are available for scored harmonic balancers on auto engines. Perhaps the same would work here (12mm ID). The sleeve would slide off when the bevel gear nut is unscrewed. An oversize bush would be needed in the timing cover....beats removing and disassembling the crank to cut with a lathe.

Scott

Some well known single restorers in the uk do the simple O ring mod ,I expect the o ring would wear faster than a proper garter seal and is just a bit of insurance in this low pressure application.