dlwharleyman

Have a 97 Jeep Grand Cherokee Limited, 5.2L 318 V8. When I tore it down I noticed that each piston is stamped with a letter (A - D). I then noticed that the block mounting surface for the oil pan is also stamped with a letter (A - D) for each cylinder. In the OEM service manual there is mention about the letters and the min/max size for the pistons and cylinders. Although the original owner and the second owner, my friend, say the engine has never been overhauled, here's my cylinder breakdown:

1. cylinder D piston B
2. cylinder B piston D
3. cylinder A piston Blank - This is one of two that broke. The used piston I got is a C
4. cylinder B piston B - This is the other that broke. The used piston I got is a D
5. cylinder B piston B
6. cylinder B piston blank
7. cylinder B piston B
8. cylinder B piston blank

A retired factory worker said they would take the rough cast block and do a "gang" bore and then a "Piston fitter" would do a final bore (?) and fit the pistons. Never heard of such a thing. So how do others tackle this miss-mash of pistons and cylinders during overhaul?

dave1123

"Gang Bore?" Oh, yeah. My friend took a tour of GM's Tonawanda, NY engine plant and he saw a machine the bores all 8 cylinders at once! It also machined the deck surfaces at the same time. The head bolts and oil pan bolts are also gang drilled and threaded. On the bottom of the block, there are 2 3/4" dowel holes and everything is machined by different equipment in respect to the position of those holes.

All you have to do in the rebuild is check the piston fit with a feeler gauge to make sure it's within tolerance. If it's too tight, you hone it a little. If it's too loose, you get a larger piston. I've seen street engines run for years with one piston .020" oversized. Oversized pistons are matched for weight to normal ones.

Just as an aside, My first car was a '37 Dodge. When I was messing with it, I noticed the engine number said, in part, 39 B10. I checked with sources at the time and was told it was a '39 engine and factory bored .010 oversized. Not the original motor? Oh, well, time to hot rod it!