Pistons

[bmh]

Can any one tell me what change occured to pistons in 53 that prevented their use in 48-52 motors? All my factory parts books read this way, A -48 part for 48-52 and a-53 part for 53-up. Yet all the aftermarket catologs read one piston 48-74? Also , and of real interest since I am doing an EL, all aftermarket pistons for 61 inch motrs are listed as 36-52, I didn't think pans and knucks ran the same pistons, do they? As always any help is appreciated.
Brian

[Rub]

Brian,
As i recall it has to do with the advent of the drain hole in the cylinder walls. The location of the oil ring on the early pistons makes them not compatible with the later cylinders. However the later piston works with either type. Using the early piston in a cylinder with a drain hole in the side will build a great top end oiler and mosquito fogger.
Robbie

[Rub]

Brian,
I seem to have missed the second part of your question. Knuckle and Pan engines have slightly different deck heights. So even though the stroke is the same the length of the assembled cylinder/crankcase is different. The piston pin location is different and using one type in both engines either results in higher or lower compression. Knuckle 61ci pistons are taller when assembled.
Robbie

[bmh]

Thanks, I knew they changed oil rings in 53 but didn't know they changed the groove location as well. I didn't see any reason why the later ring wouldn't work in an earlier motor and still don't see why the parts book says it won't.
I also didn't think pans and knucks ran the same pistons although I did run across a service bulliten last night that implies that at least early 48 motors used the same piston as a knuckle because it told me to re-lable my parts book with a new number for pistons in 48 motors. The reason I ask is I am doing an EL pan and I don't think the NOS pistons I have are going to work, I will need next size up. I was going to order some aftermarket pistons but every catolog I look at says 61" pistons 36-52. While they may fit a pan motor, would they function correctly and provide the correct compression ratio?
Brian