3.2 piston dimensions?

Quicksilver · 10-11-2012, 02:59 PM

Trying to determine the pin height and dimensions of the factory ring package for the 3.2.

Anyone know or have a resource to go to?

KTL · 10-11-2012, 03:06 PM

Compression distance is 32.8mm. Ring package is in Wayne' rebuild book which I don't have in front of me....

I just received a set of 3.2 Carrera pistons w/rings in the mail yesterday. I can measure whatever you like.

Quicksilver · 10-11-2012, 03:58 PM

What I found in the engine rebuild book under the Carrera's ring and groove dimensions was "N/A". What I'm looking at is what kind of room for the whole ring package there is. Width of the ring lands, etc... If there is room between the pin and the top of the piston it would be nice to put in a longer rod to help the upper end breathing. I would want to be sure that the ring lands don't get too small for reliability though.

KTL · 10-11-2012, 04:23 PM

Yeah I thought it might be N/A after I posted that. Sorry. I'll take some measurements of the pistons to give you an idea. Just gotta finish dinner and put the kids to sleep.

But I recall from visual memory that the pin is quite high in the skirt and there is a relief undercut in the "ring band" area of the piston to allow the pin to clear the bottom of the ring band.

You could also have your custom pistons cut for only one compression ring, no?

KTL · 10-12-2012, 06:51 AM

OK Wayne,

Ring package is 1.5mm top, 1.75mm middle and 3.5mm oil control ring.

The ring band thickness is 0.913" = 23.2mm and the piston pin relief/cutout in the ring band is 2mm. I should have meas'd the distance from the bottom of the oil control ring land to the bottom of the ring band, but I forgot to do that. I can get that tonight if you want.

The smushed shape of the piston dome definitely affects the underside of the dome, inside the piston. I meas'd from the pin boss down to the OD of the pin, pin dia., and distance from pin boss to the fattest/tallest region inside the piston and got me around 12.5mm of space between the pin OD and the piston. You'll need to measure a rod to see what the thickness of the pin end is from ID of pin bushing to the end of the rod.

Bottom line is that with stock pistons, it doesn't look to me like there's a lot of room inside the piston. However with custom pistons that have a raised dome/more area inside the piston, i'm sure you could move the pin up a bit if a thinner ring package (or only one compression ring) is spec'd for the piston.

You can also offset bore the piston pin a little bit on stock rods. This is easier to do on SC & earlier rods with the 22mm pin because the bushing is thicker. The 23mm pin makes for a tougher offset bushing because the bushing would seem like it becomes too thin. But with custom rods, you are spec-ing the shank length and that eliminates the thin pin bushing issue or thinning the pin support region at the end of the rod.