Crankshaft Polishing

Luke · Post by **Luke** » Thu Nov 11, 2004 11:17 am

Is there any easy way to tell if a mark on a crank journal can be polished out or if it needs grinding?

MdR · Post by **MdR** » Thu Nov 11, 2004 1:45 pm

It's not accurate nor technical but on a VW crank I've worked on the theory that if you can feel it rather than see it then it'll need re-grinding.
I run (what's left of) my fingernail along the mark to see if it catchs.

domo1977 · Post by **domo1977** » Thu Nov 11, 2004 1:51 pm

Hi Luke

I did the first couple of years of my apprenticeship at a company that made new crankshafts, so I should know, but I struggle to remember!
We only used polishing to 'super finish' cranks that were going in top spec engines, things like Judd V10s and Metro 6R4s, didn't bother with the Maestro Diesel ones! The crank had to have a pretty good 'ground' finish to start with, the polishing would just improve what was there, removing any micro sratches from grinding and any dullness to provide a super shiney low friction surface. Think the maximum amount of material we ever removed using this process was 0.002mm, so naff all!!

I dont know if crank re-finishers use a corser grit or anything to remove bigger marks, but I suspect that you would only polish a crank (as opposed to re-grind) if it measured within original tolerance and had only the lightest of marks or looked dull/oil stained after years of service.

I'll stop waffling on now! hope that helps your crank selection for your new engine!

Dom

Luke · Post by **Luke** » Thu Nov 11, 2004 1:54 pm

thanks guys, I'll let my fingernails grow a bit and then test it out!

Airhead · Post by **Airhead** » Thu Nov 11, 2004 6:04 pm

Should you file and polish your fingernails first though?

Lightweight_911 · Post by **Lightweight_911** » Thu Nov 11, 2004 6:18 pm

When considering buying a used crank it's also worth checking the 'roundness'/ovality of the journals (using a micrometer) & the overall straightness of the crank (not easy for the 'layman' to do !).

Luke · Post by **Luke** » Thu Nov 11, 2004 6:29 pm

thanks guys I've manganged, in the course of a day, to secure a Std/std magnaflux, and polished crank c/w with reconditioned rods. So it looks like I won't be needing to polish anything!

Oh the wonders of the internet!

MdR · Post by **MdR** » Fri Nov 12, 2004 8:58 am

Result!
And you kept your manicure intact. Cubist will be please