Can the lobes of a good used camshaft be polished? not ground, but polished to smooth the lobe surface? along with rocker arm surface? no meterial removal, just a buff with a wheel and some compound.

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I imagine just polishing it would not hurt anything.

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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.

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I had a 280 with worn exhaust cam. Sanded it in shape when it got noisy (every year), started at 200k sold it at 500k. Not the neatest solution but the sanding took only 5 minutes with an electric sander and at the end the car still managed to run 125mls/h for long stretches (German autobahn)

Rob

Aaaah!

__________________
RIP: 80 300SD
RIP: 79 450SEL
2002 E430 4matic (212,000km)
2002 ML500 'sport'

____________________________
FACEBOOK: PANZER450

My local engine shop has a machine for polishing cams.

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- Jeff

I an not sure about the new cam, bur the older cams (M110) are surface hardened.
Once the surface is damaged it will wear again quickly. If you take the cam out the best is to replace it. A used but undamaged cam is the best option, not as good as a new cam with new followers, but much cheaper.

Rob

If it has, for example, a light coating of rust (the type that will pretty much wipe off), you want the surface polished, but aren't removing a significant amount. If it's damaged or badly rusted, it's probably scrap.

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