I have these KB Claimer Hypereutectic pistons and the spec sheet here: https://www.uempistons.com/installation ... lation.pdf says to measure the pistons in a spot where the coating is present but that the coating must be removed to properly measure them. Obviously I'm not going to remove the coating, so I did my best to measure the bottom edge of the skirt that is not coated.
At this point I come up with 3.9987 or so. The recommended bore size on the piston box is 4.0010. The measurement on the skirt I get is like 4.0004, the location is only slightly above the uncoated tips where I am getting my original measurement.
If I have a bore of 4.001, that would mean they set you up with a clearance of .0023 out of the box based upon my measure of the uncoated skirt tips and only .0006 clearance to the coating. The spec sheet gives a range of .0015 to .0020 for mild applications. So if I shot for the middle of that range, I would literally have an interference fit with the bore to the coating. Is that right?
As it is, I have a 4.0015 bore and getting the pistons to slide in feels like an interference fit. Can I calculate piston to wall clearance based upon where I'm measuring these things from? I.e. with my bore I have .0028 clearance.
Seems a little wide but they are super tight at the coating.
Thoughts?
Measuring KB pistons with coated skirts.
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Measuring KB pistons with coated skirts.
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Re: Measuring KB pistons with coated skirts.
Right or wrong, when I use coatings I measure the piston in the same spot as I would a uncoated piston.
If I need to ask my machinist t increase the bore size to get the p-w clearance I desire, I do so.
I use Swaintech, and they have always given solid technical advice.
If I need to ask my machinist t increase the bore size to get the p-w clearance I desire, I do so.
I use Swaintech, and they have always given solid technical advice.
He who is in me is greater than he who is in the world.
Re: Measuring KB pistons with coated skirts.
KB is now using Line to Line coatings but I don't know if these pistons are that. I'm working with a piston that has the coating for a jr. dragster as a test for these little cars. The instructions from line to line talk about having a slightly tight fit on a DRY cylinder. The APC coating is supposed to wear to the proper fit during break in, hold oil and minimize wear after that. I know this is not apples to apples but calling those guys might help your situation. They were very good with info when I was setting this up.
Speedbump
"If it was easy, everybody would do it."
"If it was easy, everybody would do it."
Re: Measuring KB pistons with coated skirts.
Sicne the piston is barrel-shaped, I don't think you can trust any measurement taken at the bottom of the skirt.
Re: Measuring KB pistons with coated skirts.
If they have the Line2Line coating on them the piston size will be engraved on the underside of the piston.