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Wannabe question

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Post  J.Toney March 16th 2019, 9:48 pm

Machinists: Whats your accepted range for tolerance and when is someone splitting hairs? Example, deck clearance. Customer requests .010 on a NIB iron block, nothing fancy. You have all rotating/reciprocating pieces and are doing the meat and potatoes (I assume, I'm no machinist, and a hobby assembler) for your industry.
Upon mockup, customer finds the 4 corners range
.008-.015 #1 bank front & rear holes
.011-.018 #2 bank front & rear holes

Measurements by assembler done with mag bridge and indicator over wristpin area on flat portion of the piston. rock in either direction is minimal, ~.003.

For funsies, they back it up using 1 piston/rod assembly on all 4 corners. Results within .001 of first setup.

Am I overthinking it? Am I measuring wrong? Am I wrong for thinking to take it back and ask for it to be "correct"?

I'm not on a witch-hunt or trying to throw anyone under a bus. And maybe this is an unspoken thing that I shouldn't bother asking, but gonna anyhow. Feel free to PM if that would be better.

If you made it this far and have input to share, THANKS!!

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Post  BBFTorino March 17th 2019, 1:34 am

There could be slight differences in the pistons themselves. They need to put the pistons and rods in the holes that they are respectively going to be used in, and then measure again!! My guess is that their findings will differ slightly.


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Post  Lem Evans March 17th 2019, 11:10 am

.007" from front to rear wouldn't suit me.
The .003" side to side I could live with.

Lem Evans

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Post  Dave De March 19th 2019, 10:14 pm

If the machine shop cant locate the crank centerline on the block when they are cutting the deck you might want to find another shop to machine your block. Shops that need your rods and pistons to square the deck shouldn't be into performance machining.
I know this is a strong statement but when you consider that some of them only pick up the plane of the deck and adjust it based upon squareness from a corner mock up. There is a high amount of variation possible with this method.
When the crank centerline is registered the squareness will be a few thousandths based upon a small number of tolerance stackups. And you can shuffle the pistons/rods to get that reduced.
Dave De
Dave De

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Post  IDT-572 March 22nd 2019, 4:20 pm

Time for a come to Jesus meeting with the BlackSmith Er I mean Machinest

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