Piston Diameter

[Alex170984]

I'm about to look like a complete cock in asking this, but nevermind...

I have recently bought some 0.5 oversize pistons

Is the overall piston diameter measured taking into account it's piston rings?

My existing pistons measure to 80.3mm, the new are 80.9, so that's 0.6 oversize

Can someone please correct me?

[ronin_ae86]

The bore is the diameter of the cylinder.
Allways the pistons are some 0.01mm smaller than the cylinder diameter.
Each piston has a different diameter on each surface of.
The smalest diameter of a piston placed at the side surface of the piston head.That happend because the piston head exposed on the hightest temperatures and has largest sweeling.

We measure the pistons at their skirt on the height where placed the pin holes but vertical of that holes.

That measures must be done with micrometer which can measure 0.01mm.

Most engine should have piston to cylindere clearance 0.010 to 0.050 mm.

In some extreme applications the clearance maybe exceeds the 0.050mm then when the engine is cold sounds the pistons .

The piston skirt has the bigest diameter because it lead and dont let the pistons to depart.
Thats why many racing pistons has coating on the skirt.

So first you should carrefully messure the pistons and after that you calculate how to boring and honing the cylinders.

Be carrefull if you talk about a 4AGE engine dont look the TOYOTA 4AGE engine repair manual about the piston to cylinder clearance they write about the axial clearance of the pistons not about the trust clearance.

The axial clearance is about the head of the pistons.

[oldeskewltoy]

Alex170984 Wrote:Is the overall piston diameter measured taking into account it's piston rings?

no

[jondee86]

I think that your old pistons wore down a bit. An 80.4 piston would be
fitted to an 80.5 bore, and when you bore the cylinder to the first oversize
of +0.5 you have an 80.9 piston in an 81.0 bore.

If you have a 4AGE the factory bore size would have been 81.0 so I am
guessing it is another engine ?

Cheers... jondee86

[Alex170984]

I've got an AE92 block.

So you are saying my 81.5 pistons are not actually correct

[Uzelac]

Stock are 81mm.
O/S .5 are 81.5mm
O/S 1 are 82mm

Those are most often sizes.

Some offer O/S .25 and some found 83mm and bigger.

[Alex170984]

Sorry I'm aware of what piston sizes are available.

What I don't understand is why my 0.5 oversize 4AGE piston I've been sold, is measuring to be only 80.9mm, which oversize by 0.5 is supposed to measure 81.5

[Project D]

Alex, like said ronin, mesure your pistons at the skirt !

[Alex170984]

Oh okay sorry.

I'll post a picture up later too.

[Alex170984]

Yes i've been a penis