Sump bolts

[Zetomagneto]

I often make up drilling/ tapping guides similar to A G . On a sump flange I drilled a plate on the pillar drill with 3 holes which corresponds to the bolt centres , drilled the centre hole with in my case, the Timesert drill then bolted the plate to the crankcase with the 2 outer bolts and then drilled the hole into the crankcase. Then remove the drilling jig, back to the pillar drill to tap the centre hole with the Timesert tap, bolted back to the crankcase then tap.The hole is bound to be square in all planes and you have no trouble starting the tap.
Sounds a bit long winded but works well .