1275 HEAD

Mini Magazine - - Mini Tech -

Q I’m hop­ing to fit a 1275 12G940 head to my 998 Mini. It’s an A-plus en­gine from 1985 with flat top pis­tons, so high com­pres­sion. I know you usu­ally have to pocket the block to clear the valves, but I also re­mem­ber read­ing some­thing about ma­chin­ing the head to sort the prob­lem in­stead. Is this pos­si­ble, and who might be able to do this? Rick

A Some say that you can not fit a 1275 (12G940) head to a 998 en­gine with­out hav­ing to ma­chine cut-outs in the block to clear the ex­haust valves - not at all so. By care­fully re-cut­ting the ex­haust valve seats deeper into the head, suf­fi­cient clear­ance can be ac­crued to cope with up to 0.340-inch valve lift. That’s enough to clear for a rea­son­able fast road spec cam. With the ex­haust valve typ­i­cally around 0.290-inch down from the head face on 1275 head, they need sink­ing in to give around 0.360-inch. Re­duc­ing the valve seat-to­face mar­gin on the valve to around 0.050-inch is the first move, then the rest is gained by re-cut­ting the ex­haust seat deeper us­ing a three-an­gle seat cut­ter to get the rest. And con­trary to what many think, sink­ing the ex­haust valve so much deeper in the head does not re­duce flow. Ex­actly the op­po­site oc­curs; the air flow is im­proved, es­pe­cially at lowto-mid valve lift. Make sure you use a 1275 head gas­ket too. Any de­cent au­to­mo­tive en­gi­neer­ing com­pany that re­con­di­tions or mod­i­fies heads can do this for you.

A 1275 head can suc­cess­fully be mod­i­fied to suit a 998 block.

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