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squaring and trueing the deck Tolerance

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Old 03-14-2017, 12:02 PM   #1
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Default squaring and trueing the deck Tolerance

Machine shop trued and squared the deck, what is the standard tolerance they should be held to? Just measured piston to deck surface front to back we are getting .006 difference, was not expecting to see that much of a difference. The crank was also reground due to spun 1+2 rod bearings, two new rods installed. I'm guessing that's were the problem lies since the other cylinders are true and square. Thoughts ??

1+2= .008
3+4= .003
5+6= .002
7+8= .002
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Old 03-14-2017, 12:23 PM   #2
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That seems odd to be out that much up front. How are you checking the piston protrusion?

It's not hard to get it within +/-.002", but sometimes you're battling tolerances in the crank, rods, and even piston machining.
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Old 03-14-2017, 02:46 PM   #3
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Depth Mic, squaring up piston every 90 degree's till the piston is parallel to deck.
.006 seems like a lot for stack up tolerance piston, rods.
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Old 03-14-2017, 06:53 PM   #4
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Quote:
Originally Posted by Smo's04Gto View Post
Depth Mic, squaring up piston every 90 degree's till the piston is parallel to deck.
.006 seems like a lot for stack up tolerance piston, rods.
I agree but usually any difference from one end to the other is more linear. Going from .003" to .008" so abruptly isn't normal. I'd say the problem lies in whatever was done to repair the #1 and 2 rod journals.
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Old 03-15-2017, 09:45 AM   #5
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KCS, trying to get the details on the crank now. All I know at this point is all the rods and mains are .010 under.
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Old 03-15-2017, 09:59 AM   #6
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I replied in your YB thread too.

I think checking the piston position at BDC might answer some questions too. If the crank grinder was out a little more on that rod journal to fix the damage, then you may have a little more stroke just on those two cylinders. If it is in the rods and pistons, then stroke would be the same.
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Old 03-15-2017, 11:08 AM   #7
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Thanks for your input, great idea on checking stroke/crank swing without pulling it a part.

Quote from builder.

Cranks was magnafluxed and checked for cracks, none found. The Crank journals were ground .010 to clean up the spun bearing.

I have never seen an engine with all pistons sticking out of the hole exactly the same. These are normal variances that all blueprinted engines have
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Old 03-15-2017, 11:52 AM   #8
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Quote:
Originally Posted by Smo's04Gto View Post
Thanks for your input, great idea on checking stroke/crank swing without pulling it a part.

Quote from builder.

Cranks was magnafluxed and checked for cracks, none found. The Crank journals were ground .010 to clean up the spun bearing.

I have never seen an engine with all pistons sticking out of the hole exactly the same. These are normal variances that all blueprinted engines have
Man, that's kind of a shitty response. Like I said earlier, it's not hard to get within +/- .002" and any worse is than that is sloppy IMO. When it's almost dead nuts the same in all cylinders except for just those two, that should be a red flag that something was off. It's not something that is going to make or break the whole build, but it's a good indicator of their quality policies/customer service.
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