|
Well, the general thought is that if you can catch any ridge/defect with your nail (particularly on the tips of the lobes), a cam is shot. defects across the cam are worse than ridges going around it. Divots, pits, chips, etc at the tip of the lobe will definitely and rather quickly turn into a flat lobe. This is a lubrication/corrosion failure, and with pits here the remaining area across the lobe has to take up even more pressure, and an oil film will be disturbed by the pits and might not form correctly. It's kind of like a pothole, and why small potholes turn into big ones between winter and spring. Cams are not chromed, they are case-hardened, and once you get past the case hardening, life expectancy of a lobe measures in the hundreds of miles. I had to send a cam back to a recycler over this issue recently - the cam was poorly stored.
The actual PSI at the point of contact of the lobe and follower when the valve is open is pretty mind-boggling; it's hard to believe that this actually works at all (and without a good oil/oil film, it won't).
I put in a used cam with a few ridges, but otherwise very good, about 12K miles ago, I didn't do anything to it but thoroughly coat everything in assembly lube. I looked at it recently and it's fine, it basically polished itself, but the ridges are still there - and I didn't buy new followers, which also had a few ridges of their own. Will this last another 100K miles? I don't know.
Any "polishing" you do might make you feel good but any serious polishing you do involving the removal of metal will thin the case hardening and will probably not be absolutely even across the plane of the lobe, creating an uneven pressure, and who knows what to the oil film. Of course, if you do any polishing with polishing compound, make sure that every speck is cleaned off before reinstallation.
Last edited by Strife; 10-16-2009 at 12:45 AM.
|