Quote:
Originally Posted by dataway
Back in the day didn't they sometimes knurl valve guides to snug them up?
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Sure did, but that's a bit different. The guides would be knurled to raise the material at the "peaks" in between the indentations, effectively closing up the clearance. Then a hone or reamer gets run through the guide to get it to the exact size needed. Since the valve stem is only riding on the raised areas and the low areas fill up with oil, the load bearing capacity goes down. Knurling was a low-cost/budget way to restore guides but isn't a good long-term solution.
A valve sliding up and down inside a guide isn't quite the same thing as a main cap that's holding a spinning crankshaft in place in a main saddle that's also flexing.
I had a friend who had pistons in a Chevy 396 knurled too. The shop honed the cylinders and put new rings in and that left the cylinders a little oversize and he was cheap and didn't want to buy new pistons or pay for an overbore. That always made me cringe - knurling a piston would induce all kinds of little stress risers in it which could lead to cracks and again, only the high spots in between the indentations are taking up clearance and providing a load bearing surface, but he beat on that engine for a couple years and it never gave him any problems...