PISTONS
(more photos to follow at a later date on this section)

sizeing pistons
Pistons will need to be measured to find out what their diameter is.
The quoted diameter is a guide only and they can vary by as much as a few thousandths of an inch.

So first we measure each piston accurately to determine its actual size.

We then write the size on the smallest, and then write the variation in size on the top of each of the others, this will be crucial when it comes to fitting them in the bores at a later date.
Number each piston too, so we know which one goes in which bore.

Piston to bore clearance
The important thing with regards to the width of the piston, is that we get the correct piston to bore clearance in the block. (see also the block section with regards to taper/ovality at this point!)
This is the amount smaller than the bore that the piston is.
It needs to be indivdually set for each piston.
The actual amount of clearance is application specific and can vary from about .0005" on a modern N/A engine with cast pistons right up to .005" on a turbo engine with forged pistons!

Piston rings
On the piston you will typically find 3 grooves, these are where the piston rings sit.
The first check that we need to do with these grooves is that there is the correct amount of height to the groove for the ring to sit in snugly without being too tight (refer to manufacturer for actual clearances required as its appication specific)
To measure this we place the ring in the grove and then check with a feeler gauge to see the clearance.

This isnt something you can adjust yourself, if its wrong you need to refer back to the person you bought the pistons and rings from, but you should check it just in case.

Its particuarly important in the case of using secondhand pistons and over time during hard use the ring lands can "close up" and become too tight.

The second thing to check with regards to the piston rings is that the "ring gap" is correct.
The ring gap is the space between the two ends that stop it making a full circle when its installed in the bore (without the piston)
This is checked by installing the ring into the bore and then using a set of feeler gauges to ascertain the gap.
EVERY ring must be checked in the bore to which its going to be isntalled, so its essential that you keep track of which rings are for which cylinder
Typically the top ring will have the largest gap, but check with your supplier what the required gaps are for each ring.