I just torn down a 97 Jeep Cherokee Limited 5.2L engine. I noticed that the top of the pistons are either blank or are stamped with a B, C or D. What does this mean? When I pulled the rods and pistons it appeared there was no rime or reason as to which rod goes to which cylinder and in what direction the pistons/rods face. Seems I saw a warning about not interchanging rods/pistons from side to side. I tried looking for casting number information, but didn't see anything. This is my first Jeep 5.2, so I'm not real familiar with identifying parts. Casting numbers I found on the engine parts:


Crankshaft 3751841


Block 53005798


Rods 53005798 (noticed different markings on each one)


Pistons 53008567 (inside piston), 43567, 39567, 11567, 42567, 37567, 33567, 54567 and 48567 (on outside of the pistons)

 

I believe, but am not sure, that the letter code has to do with production weight tolerances. If you were to "blueprint" the motor, you'd want all the same letter code. As in all production engines, they just used whatever was in the parts bin. I know guys in ProStock that were picky enough to want all the valve lifters the identical weight!

 

The cylinders are all slightly different sizes and the alphabet on the pistons are a code for the size. Kind of nice to know someone at Chrysler is making sure the pistons are fitting in the cylinders perfectly and not being too tight or loose.

 

If you notice closely, the rod bearing inserts are shorter on one side; that is not coming out to the extreme edge of the rod. This is to clear the fillet on the crank journal. That's why you shouldn't swap sides of the motor with the rods. Actually, if the pistons aren't marked for "front", I see no reason not to turn the whole assembly around to satisfy the bearing journal fillet. The only pistons I've seen that are "front" critical are high performance domed pistons that are notched for valve clearance.

 

On each side of the piston in the flat area around the wrist pin, one side has, 6 numbers. On the other side, each piston has an "F" on each side of the wrist pin. I noticed if you face the "F" forward on the pistons (left side) 1, 3, 5, and 7, The rod casting number faces forward. If you do the same thing on pistons 2, 4, 6, and 8, with the "F" facing forward, the rod casting numbers face the rear. So I guess "F" means forward or front. I need to do more research on the stamped letter on the top of the pistons. A repair manual refers to the letters A through E with different skirt sizes. The parts book only shows B, C and D.

 

Yeah, Chrysler was always picky about stuff like that.

Chevy small blocks are another thing altogether. We've taken used piston and rods out of a motor, didn't even measure them, and thrown them into another. It stayed together at 6 grand at the strip! 57 283.