4agze pistons and rods

[jimmy19650]

Just bought a new genuine set of 4agze pistons and rods. I opened a piston box and found a piston, gudgeon pin and circlips, as I expected.
I then tried to fit the gudgeon pin into the piston for curiosity, only to find it doesn't fit, yet the same gudgeon pin fits nicely into the connecting rod.

My question is then, is there an interference fit between the piston and gudgeon pin, which I find this difficult to understand because of the circlips. Or is the tolerance so small to compensate for expansion due to heat?

Another curiosity was on a new aftermarket forged connecting rod, the tolerence between the rod and gudgeon pin was also similar to the piston.

I haven't measured anything yet, and all the trial fitups were by hand, with a small amount of oil applied

[Nikkojoe]

If you read the manual you will find you need to heat them up (the pistons) to fit the gudgeon pins on the pistons as they are an interference fit. They are a non interference fit on the conrod so it can pivot.

The circlip is there so it doesn't slide out from all the movement going on (and the temperature differences).

[jimmy19650]

Thanks mate. Thats what I thought, just wanted it confirmed. Looks like I will have to get a manual.

[lo_rolla]

I'll re-do your small ends and fit the pistons for 50 bucks.