loose pistons?

[Classy67]

hey everyone!! got a problem with my '67 charger with 318 engine. i had a low compression cylinder (almost 0). i've noticed since spring that it seemed to lack power and developed a miss and didn't have the power it had last year. i pulled the heads on it tonight and it looks like it has a burned exhaust valve. when checking over the block i noticed that the pistons have a very slight amount of slop in them (sideways movement). is this normal? i wasn't going to rebuild the whole engine as it hasn't burned oil plus the additional expense of a total rebuild (4 times what the heads will run me). thanks for your replies in advance, keith

 

[67 coronet]

if they move easy,could indicate worn rings.good rings keep the piston very tight in the bore.

 

[Meep-Meep]

Most likely the rock or movement you see is normal. The piston fit to the bore is along a pretty narrow foot print and that is perpendicular to the pin. It may not seem right by the movement you get but it is. If the bore is smooth with some cross hatch evidence that means it has a lot of miles but you should be OK.

 

[440roadrunner]

As old as this car is, and without knowing the engine history, only speculation.

But if it's not using oil, things are probably fine.

It used to be "a thing" for a cheap rebuild on engines that "really should" have been bored, to knurl the pistons to take up some of the wear, re-ring the thing, and toss it back together. This won't last long, but you might have gotten another 20K out of the thing, and back when many folks "did their own" it was a way to get a little more out of a used car.

If pistons are worn/ loose enough, you get "piston slap." This is hard to describe, sort of a low pitched "num-num-num" while idling.

 

[RustyRatRod]

Normal. The fitment of the piston is critical nowhere except along a narrow line in the center of the skirt. Modern pistons are cam ground and actually elliptical in shape, so the actual measuring points are somewhat narrow. Movement at the crown is perfectly normal, regardless of ring type or condition.