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Old 08-16-2012, 11:10 AM
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Yes this sounds about right. I had this same problem on my first shortblock build up recently. After doing investigation here is what I found: If you want perfection you have to pay for perfection (line hone block (or aftermarket block), deck the block, expensive aftermarket crank, quality aftermarket rods, quality pistons, quality measuring tools).

Here are some details...

There will be differences in deck height from each side of the block. GM made the blocks to be "close enough". If you want to make them exact, then you are going to have to get the block line honed. This is where they rebore the main bearing journals and caps for the crank. This puts the center of the crank exactly at the center of the block. If you do this, you also need to get oversized main bearings to accommodate for the removed material and you have to get a different sized timing gear set to accommodate as well.

Other factors that can contribute to this are:
-crank shaft throws are not indexed at exactly 90. This can be a problem with brand new factory cranks (not really that common though), or from reground cranks, or from cheap Chinese cranks (Eagle and Scat). Sometimes if they are not offset too much, you can get an offset regrind to bring them back on center.
-rods can stretch.
-rod bolts can stretch
-rod caps get elongated
-cheap pistons that do not have an precise compression height (wrist pin center to piston crown).

As an alternative to the line bore you can have the machine shop measure to the existing center of the crank to the deck. They will do this on all four corners (cylinder #1,2,7,8) and then deck the block so that all four corners are even. Generally it is noted that factory block corners are higher than the middle.

Also when you measure, try not to let the dial indicator go past its highest position. I usually try to make a slow pass, note where the high point is, then rotate back to the high point. Once at TDC I also use a straight edge and slip feeler gauges underneath to find the clearance. Also be sure to measure parallel to the crank (this is parallel to the wrist pin) and will eliminate any measurement errors due to the piston rocking in the bore.
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