4G93 CP pistons

[aapje]

I bought a slightly used set of pistons and rods from someone. They are CP 81mm pistons. (9:1). Just took all the measurements and the pistons are slightly smaller then my stock pistons :blink:

The piston to wall clearance is now about twice what it should be according to the specifcation sheet that came with the pistons. My block is still within spec (according to the engine manual). For me it's hard to believe that these pistons wouldn't even fit a stock block.

Is the piston to wall clearance the clearance between one side of the piston to the wall of do you have to multiply this value by 2? I suppose putting it back together like this would cause excessive oil usage and piston slap? Or can you get away with some extra clearance?

New pistons diameter is 80.85mm
My cylinders are:


Cil 4
T 81.021
C 81.018
B 81.018

Cil 3
T 81.010
C 81.015
B 81.000

Cil 2
T 81.010
C 81.006
B 81.012

Cil 1
T 81.016
C 81.003
B 81.011

The engine manual says my cylinders are within spec. (81.00 - 81.03mm)


The spec sheet says: piston to wall clearance = 0.089mm

My "worst" cylinder is number 4, that would mean a piston to wall clearance of 0.171mm which is about twice the clearance I need. It doesn't make sense to me that a piston for a stock bore size wouldn't even fit in a factory setting.

Any ideas?

 

[Ian91]

You could contact CP or a supplier and find out what the piston measurements should be, incase someone has machined them to suit something else.

Also maybe these pistons expand more than a factory piston would and the size is to account for that.

I have spoken to people who say their forged engine is rattly because the pistons do move in the bores more. Whether that is just a bad build or if it’s a forged engine thing, I don’t know.