I'm fitting an aftermarket injection system to the old Rover which uses a
lambda sensor. The cast iron exhaust manifold has provision for this (for
US versions fitted with a cat.) but isn't drilled and tapped on UK ones. I
don't have the required tap, and maybe not the tapping size drill either.
Is it easy enough to do - I do have a pillar drill - or is it best left to
*Succeed, in spite of management *
Dave Plowman email@example.com London SW
Drill with a sharp HSS bit. Tap carefully; back off and cut again if there
is any sign of binding. Cast iron does not need lubrication, but, if you
have coolant on your machine, flood cooling does help.
So buy the necessary drill and tap. You might only need a taper tap,
as you can stick the whole length of the tap through into the
manifold. Buy the drill, as drills are cheap and exact tapping drill
sizes are a good aid to getting a good thread. If it's some archaic
Rover thread, try a model engineering supplier like Chronos. Ideally a
thread in CI will be something coarse pitch like Whitworth, UNC or the
rare metric coarse series, but I guess you're stuck with whatever the
It's usual to tap in a back-and-forth motion, but this is just to
break the swarf up and if the CI is doing that anyway, you might not
Use some cutting fluid too. It's not essential on cast iron (the free
graphite lubricates), but it doesn't hurt when doing awkward bits by
hand. A drop of engine oil will do (and you have some confidence
there's no lambda-unfriendly additives in there).
Cast iron is relatively easily drillable and tappable, but IIRC you need
a very hard steel bit, done slow with a lot of lubrication as cast iron
will shatter, not flow, if peak stresses are exceeded.
In other words, do it in very easy stages..
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