crank polishing question

[robmog]

how much metal can i expect to lose on a polishing job?
my crank is well with in spec.
a local machine shop said .0004".
does that sound right?
bob

[Porschekid962]

.0004 would be 4 ten thousandths of an inch. An incredibly small number, are you sure they did not say four thou? Either way that is pretty darned small as for pricing on things like this a fabulous tool is the search option, if you look up machine shops you will most likely recieve a plethora of posts talking about porsche specific machine shops throughout the U.S. of A all with websites and many detailing specific jobs and prices.

[robmog]

oops, i meant .004".
but my question is if that is about right for a polishing.
i know i can ship it out, but its heavy and i fear it could get dropped and damaged in the process.
if i keep it local i could avoid the worries.
thanks for the reply

[cgarr]

The Typical amount should be around .0002, but you have to take material off to achieve the correct surface finish, if it takes .004 you are going to be out of spec.

[robmog]

I guess I was right the first time. Thanks

[BoxxerSix]

Also can depend on the type of machine they're using, and how well the surface condition of the crank is to start. A high quality tape polishing machine usually yields a more consistent and smoother finish than a belt type polisher. Belt type polishers can sometimes "dome" the bearing surface a tiny bit in that the tend to remove more material from the outside areas of the bearing surface than the center, but in the end it's really up to the person using the machine and doing the polishing.

2-3 tens is typically what is removed in the polishing process on a good condition bearing surface.