.001 to 005” on a 4” bend pretty easy and it isn’t much anyway. Funny that when I increased the size of my OT Harley the JE pistons called for .000” at the bottom of the skirt. We put them at .002”.
I recall hearing them referred to as "ribbon gauges", usually 8" or 10" long so they fit the full length of the bore. If you loaned them to somebody, they had to swear that they weren't going to use them to adjust valve lash so that they didn't get hammered up! When I worked at a GM dealership I never saw a tech use them when installing pistons. No, they are flat like a regular feeler blade. Just longer to fit the full length of the bore. https://www.grainger.com/product/WE...44ZE62?opr=PDPRRDSP&****ytics=dsrrItems_3R012 I've used them a few times but never with the pull gauge. The pull gauge was like a lighter duty spring scale used for weighing fish. It measured the drag on the gauge in ounces instead if pounds. I've never used the pull gauge. But with just the ribbon gauge it was amazing to me that, with a bit of practice, you could feel the difference of a .0005" change of piston to cylinder clearance.
That sounds a little scary, doesn't it? Wonder if that's due to being an air cooled engine. If they were fitted too loose do some bikes pick up a piston noise when they're at full operating temperature? Like the noise you sometimes hear on a cold-start of a SBC with forged pistons that are fitted slightly looser than cast. It's hard to not like the sound of a stock L79 Chevy with forged pistons, solid lifters and mufflers on a cold start up. For a few minutes at least, it's musical!
I finally got an up date. Hemi engine is a stock rebuild, was bored to .020 over. Consensus between owner, machine shop and Ross is that it probably overheated with out the owner realizing it. Shop ordered a torque plate and will bore to .030 over and new Ross pistons with skirt and top coatings will be used, probably at .005 clearance. Thanks to all who have posted, much appreciated.
Just throwing out for discussion, remember the old practice of knurling piston skirts to tighten up the clearance? I've been told, and it makes logical sense, that the knurling helps hold additional oil on the skirt. Which would seem to help with the scuffing issues. Not for the original post problems, but all this discussion on clearances has me thinking about it.
Feeler stock still comes in 12" length, McCarr has it. I think from .0005 to around .150 thick. Piston knurling was one method to expand piston size and some did it for oiling. There were some pretty neat tooling for making the knurl, didn't have to do full diameter of piston, could do in specific areas. Last I saw the tooling was in the 60's.
From the picture I'll go with this is not mainly a street motor. I would go with what piston manufacture recommend so now we have lack of lube bearing and rod side clearance
At one time people were using piston ****ons? Also i have heard of coating the skirts with some kinda slippery stuff. I believe they emprage them??? people that do aircraft coating do it!
Knurling will take up some clearance but isn’t good for lots of miles but for most people who never drive their cars it’s probably fine.
^^Exactly! Same with valve guides. We've evolved a lot since then. Engines last longer as a direct result of decades of racing and refinement. Materials. oils. coatings. etc. The Science is pretty cool. Babbit engines cut too tight used to be 'pulled through' also. Never happen today. Just took a peek at a 351W that had some crank damage. Journals on the high side. Housings on the low side. This thing had NO oil clearance when it was all said and done. BTW: CK10 is a Solid machine.
""At one time people were using piston ****ons?"" Yes, they stopped using them 20 years before I called a place 20 years ago looking for them for the Single cyl Garden tractor puller engine I was building; the guy had a good laugh. So I had the skirt coated with some slippery blue stuff and had the top ceramic coated, maybe 1998 or so.
I do not recall. I think that the feeler stock was thin or narrow enough to flex. The pull thingy was like a fish weight scale, aka a spring scale. The link below explains the process, I also have seen it in old car manuals. http://pautomotivemechanics.blogspot.com/2011/06/piston-measurement-and-clearance.html
We used to have a parts house with an excellent machine shop attached to it. The guy that ran it knew his stuff. My brother had the pistons for his 327 reconditioned there. They had the Perfect Circle logo embedded into the knurl. Real old timers would use 2 large flat files, a bench vise and a hammer. The "knurl" depth was controlled on how tight the vise was closed. Tap each file in turn until the skirt was covered.
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