Hi folks, Although not purely Buick-related, it certainly relates. I have been rebuilding engines for 45 years. In the old days we would always have the machines knurl the piston skirts. Seemed to have several advantages. Since that is the thrust/wear surface, it expands the metal--often giving us .001, or so, expansion. This is usually needed w/ worn engines that don't yet require a boring. The knurl also seemed to hold oil, which was always a good thing. Seemed to sometimes return the concentricity to a piston that was a little "out." But it seems most machinists laugh at me, now, when I suggest it. Oh, I know we have great coatings that we didn't have in the past, of course. This may be part of the reason? Best, Ranger Aiken, SC
I remember hearing about it as an apprentice, but not since. Been out of the industry for 30 odd years wouldn't help either.
I doubt its done much if at all anymore. I read about it way back in the late 70's in a book about engine rebuilding, and THAT book was probably published in the 60's It may have been diesel technology... low rpm stuff. But with the piston choices today, and precision equipment to bore and hone, its outdated.
I thought knurling of pistons was used on the used pistons for when the budget rebuilder would over hone and use over sized rings, and you would have a motor that ran better than it was running to sell the car.... used car lot trick.. lucky to get 5000 miles out of the motor....
Knurling of valve guides, and piston skirts got a bad name in the 80's and 90's till it's become a lost art. In drag racing I've always liked knurling of the valve guides.
I worked for auto machine shop for many yrs, we knurled valve guides all the time, I still do, with my equipment at home, pistons.... was common yrs ago, but is a lost art, was ok for the time, saved few $$, and would last many many miles, as it was as strong as orig piston. actually (IMO) better then the coatings now days as they wear off very quickly, where as knural does last much longer, and does hold some oil, for better piston lubrication, ( less wear) to each their own, don't recommend, or knock it either way .
Piston knurling was a low-budget band-aid back in the 1950s. The only way it made sense was when labor was a lot less costly than parts, and the consumer was a lot less picky. For mainstream vehicles, the situation is reversed--parts cost less than labor, thanks to Corporate Criminals importing junk from the Third World (or worse...) I know a small-block Ford that got punched .020, the original pistons were knurled to take up the clearance, and they put .020-over rings on 'em. Knocked like a diesel for thousands and thousands of miles.
I actually have a piston knurler, a real nice K-Line one. The reason I originally bought it was to get the last bit of life out of stock eliminator pistons when the bore was max legal over size, but loose. If the ring lands are still good, it actually works. Now that they’ve made skirt coatings legal. That’s the route to go. We’ve knurled and coated though. Just use with care. The latest thing I’ve used it for was for demo derby engine builders. We knurl the brand new pistons for oil retention. I’ll have a special hone profile as well. These are often $6-$8K engines, and they need to be able to run with no water. This has really been a huge improvement. Same with two stroke one lung endurance racing snowmobiles, the knurled pistons last longer. It’s just one of this odd machines that really works in certain applications. Can get you out of a jam here and there. Say you sleeve a cracked block and the adjacent cylinders get a little out of round. You can hone them a couple thousandths and knurl the pistons. Some odd show car stuff or whatever. Tractor or impliment where pistons are no longer available. You can knurl the taper back into a skirt if needed too. I’d have never thought I’d have found a use for a knurler. I gave my last one away 30 years ago. As far as concentricity, pistons are cam ground, not concentric. You have to be careful to only knurl the thrust area on the piston or it can expand with heat and score. You’re spot on with the advantages though.
