Michael Pardee wrote:
> "Ricky Wang" <RickyWang@has.none> wrote in message
> news:jJqSg.5123$TV3.3285@newssvr21.news.prodigy.co m...
>> A near mirror finishes are too expensive for the average car owner
>> could afford. Unless the car manufacturer requires a near mirror
>> finish, don't bother with it.
>>
> My retired ex-partner has done some milling for me in his garage, and the
> output of the milling machine can be described as "near mirror finish." If a
> milling machine isn't producing that sort of output, it's because the head
> hasn't been dressed lately. That's the sort of neglect that can weaken the
> head gasket seal as combustion gasses insinuate their way through the gaps.
>
> Actually, I don't think debris produces the milling marks. The cutter head
> is an abrasive disk spun at high speed that is scanned across the surface in
> the plane of the disk The edge of the disk cuts a flat groove at a preset
> thickness, then is moved laterally to cut an identical groove beside that,
> and so on. Milling marks appear if the wheel edge is not true.
>
> Mike
>
>
the point for both of you is that a /lot/ of head shops out there simply
use the same cutter on an alloy head that they use for cast iron. the
best case result is a grooved head that is a /long/ way from smooth.
and worst case is the gouging i'm warning you about - i've seen it many
times guys, so beware.

and the biggest point in all this is that for most repair shops that use
these kinds of milling services, they never get to see the consequences
so they never learn any different. most cars are high mileage when the
head goes the first time. if it goes a second, the car gets sold or
junked. for my personal vehicle, i want the repair to last at least as
long as the original - that's 140,141 miles. that's never going to
happen on a grooved head because gas channels along the groove base.
it's slow at first due to gasket sealant, but that sealant erodes, and
then you get leakage again.

unless you have access to a shop that can produce a bona-fide high
quality near-mirror finish, milling a head that is not warped is simply
"monkey see, monkey do".