Classic Bike (UK) - - WORKSHOP RICK’S FIXES -

Adrian Player says: “My lad has re­cently com­pleted a Honda CG125M en­gine re­build, but on start­ing oil poured out of the crank­case breather. We tried drain­ing and re­fill­ing slightly un­der level, but it hap­pened again. It looks like the crank­case is be­ing pres­surised; when we re­moved the oil filler plug, the en­gine ran smoother and seemed quite happy.

“We didn’t find any prob­lems in the top end but some­one on an in­ter­net fo­rum had a sim­i­lar prob­lem due to in­cor­rect crank­case cen­tre gas­ket – could that be it?”

A bit off my usual beat this one, but it is pos­si­ble. In my Honda shop days I only stocked gen­uine gas­kets, pat­tern items were no­to­ri­ous for holes not prop­erly punched through – or even miss­ing al­to­gether.

It seems the CG breather comes off a cham­ber above the gear­box, whose only en­try is a small hole above the clutch – hard to see how oil can get in there in any quan­tity. I’d look un­der the clutch cover first, block that hole and blow through the breather pipe to see if it’s vent­ing any­where that it shouldn’t be.

ABOVE: Gas­kets may have all the right holes, but not nec­es­sar­ily all in the right places…

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