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LongroofJosh 11-01-2004, 10:47 AM Hi guys, I am looking at a set of used pistons. They are std. However, the motor I need them for is a GM Goodwrench, and I suspect it may not be std bore. There are no measurement markings on the pistons such as .030, or .060, nothing like that, only a C with a line above and below. My question is this, what is the std bore on a 6.2. Thanks Fred482` 11-02-2004, 10:13 AM Standard pistons have four different bore sizes (marked "A, B, C, or D". The size difference is very slight ( 1/2 thousandth or metric equivelant) and was used to compensate for odd bore sizing at the factory. Also used to compensate for the difference in heat transfer from different areas of the block. Most after-market pistons have markings indicating the oversize (like you mentioned, .010, .020, .030, etc.). The "C" piston is the most often-used piston. Seems it fits most bores. I've seen the top of the block marked with the same "A, B, C, or D" as well. Usually, low on the block deck surface next to the bore. Don't know if the factory did it or someone did it when they worked on the engine and wanted to ensure the same size piston went back in the hole after a tear-down. Oversize pistons don't have the letter code mark. LongroofJosh 11-02-2004, 10:53 AM Thank you project 6.2L 11-03-2004, 09:19 PM According to a tech book of mine the standard cylinder bore for the 6.2L is 3.9789" to 3.9824" A=3.9789", D=3.9842" or visa-versa, B and C are somewhere in between(My guess anywayshttp://www.dieselplace.com/forum/smileys/smiley5.gif) LongroofJosh 11-04-2004, 11:33 AM When I mic'ed it, the two I checked only measured out to 3.970?? What gives?? grape 11-04-2004, 07:07 PM measure 1/2" up from bottom of piston on skirt. piston should be tapered. quantum mechanic 11-06-2004, 10:02 AM I just had my 6.5L apart to replace the #6 piston. The stock pistons where stamped STD on all of them. I bought a salvaged piston and rod for $35 and the piston top was marked "D" ( I didn't know they had an A-D. the D piston was a tight fit but with a little lubricant I was able to slide it past the widest part and when the rings neared the cylinder it moved freely up and down. http://www.dieselplace.com/forum/uploads/quantummechanic/2004-11-06_074043_pistoncrack.jpgEdited by: quantum mechanic | ||