On Thu, 8 Jan 1998 10:52:24 -0700 mgb.roadster@juno.com (Larry A Hoy)
writes:
>I have a "spare" set of front brake rotors for my MGB, I have
>considered drilling them for ventilation purposes. The rotors are
>from a 1976 B roadster and my car is a 1969 B roadster.
>
>Are these rotors the same? I think so.
Yes
SNIP
>What is the minimum thickness specs? My "spares" measure .290"
The minimum rotor thickness, per factory manuals is .300". You don't have
any spares:, you now have two very large, very heavy paperweights. Sorry
>Do you drill then turn, or turn then drill?
If you insist on having it done, drill the rotors first, then slightly
camfer each hole, then turn them.
>The rotors look OK so do you drill and just put them on (and forget
>turning).
No, see above.
You will also have to make sure the machinist who drills the rotors does
not make the hole pattern too close, or the holes too large, or the
pattern symetrical. Any or all of the above WILL lead to cracking of the
rotors, starting at the stress raisers, the holes. Also, the drilling
removes mass from the rotors which is as important to cooling of the
brakes as airflow (possibley more so), So the net gain in cooling is
marginal. What you gain in airflow cooling is nearly offset by the
cooling due to the mass of the rotors.
By the time you pay a competent machinist to do all that is required,
plus assuring the rotors stay balanced, you'll find you have spent as
much or more than buying a set of new cross-drilled rotors.
With out some method of getting cooling air to the drilled rotors, the
effect would probalby be nil
A much better solution, and much less expensive, would be to fabricate
air ducts to direct a cooling stream of air onto the undrilled rotors.
Much more effective than plaine drilled rotors and a lot less expensive.
Not to mention a greatly reduced probability of a rotor cracking!
Rick Morrison
72 MGBGT
74 Midget
>TIA
>
>Larry Hoy (MGB.Roadster@juno.com)
>Denver, CO USA
>1969 MGB Roadster
>1987 Jaguar XJ6 Vanden Plas
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