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The Northstar Tuner
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2,759 Posts
Discussion Starter #1
I missed this question a few years back on a semi annual exam.
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The question read some thing like this.
On an 03 Escalade is the pistons OD bigger than the Cylinders ID?
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I got it wrong.
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The information is stated in the following area.

New Product Information
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The purpose of New Product Information is to highlight or indicate important product changes from the previous model year.

Changes may include one or more of the following items:

  • Torque values and/or fastener tightening strategies
  • Changed engine specifications
  • New sealants and/or adhesives
  • Disassembly and assembly procedure revisions
  • Engine mechanical diagnostic procedure revisions
  • New special tools required
  • A component comparison from the previous year
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Disassembly and Assembly Procedure Revisions
  • For certain applications, a spacer plate has been added between the flywheel and rear of the crankshaft. It is necessary to remove the spacer plate prior to removal and installation of the crankshaft rear oil seal and clutch pilot bearing.
  • The piston, pin, and connecting rod are to be serviced as an assembly.
  • Newer design pistons have a graphite coated piston skirt. The coated skirt outside diameter (OD) may be slightly larger than the cylinder bore inside diameter (ID) and the piston assembly may have a slight interference fit to the cylinder bore during initial installation.
 

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Registered
The Northstar Tuner
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2,759 Posts
Discussion Starter #2
The second test this year had a question about an 8.1L in a 2007 GMC Truck Sierra Classic. Is the piston OD bigger that the cylinder ID. I was not going to miss this one. We sure have come along way from the old TRW pistons that had .0066 clearance

GM info
The piston skirts are coated in order to create an interference fit into the cylinder bore.

Important: The coating on the piston allows for an interference fit between the cylinder and the bore. The piston diameter can NOT be measured accurately because the piston coating is not a consistent thickness. DO NOT measure the piston diameter.

To select the correct piston for installation, the cylinder bore must be measured. If the cylinder bore diameter is within service specifications, install the original piston/connecting rod assembly or a new, standard size piston/connecting rod assembly. A used piston/connecting rod assembly may be installed if, after cleaning and inspection, the piston is not damaged. If the cylinder bore is NOT within specifications, the cylinder must be resized to accept a new, oversized piston.


For proper piston fit, the engine block cylinder bores should not have excessive wear or taper.
 

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2006 STS V8 AWD, '95 Ford Ranger
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29,096 Posts
Two-stroke motorcycles are very critical for cylinder to piston clearance. I measured the clearance during a rebore operation by inserting the piston in the cylinder with a long feeler gauge at 90 degrees to the piston pin. Then I'd use a spring scale to measure how much force it took to withdraw the feeler gauge. I handled the piston and cylinder using gloves and/or shop towels to minimize heat transfer.
 

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Sedan de Ville, CTS
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4,764 Posts
Two-stroke motorcycles are very critical for cylinder to piston clearance. I measured the clearance during a rebore operation by inserting the piston in the cylinder with a long feeler gauge at 90 degrees to the piston pin. Then I'd use a spring scale to measure how much force it took to withdraw the feeler gauge. I handled the piston and cylinder using gloves and/or shop towels to minimize heat transfer.
When you worked on the cylinders, did you polish them to a mirror finish? My uncle had a H D dealership, and he used to remind me to make sure that the cylinders (at least on the 2 cycle) bikes had a mirror finish. Greater speed, less heat, I guess.

Just curious.
 
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