How do I know what size piston rings I need?

Measure and record both the axial height and radial width of the oil ring assembly while off the piston. Using either a set of calipers or a micrometer is sufficient. After recording those measurements, perform the same axial height and radial width measurements of your compression ring(s).

What happens if piston rings are too big?

Piston rings will expand when warm and you will set that end gap to take into account the thermal expansion and aim for best sealing once that engine is warm. Now, if the gap is too big, the engine will have too much crankcase pressure, have a ton of blow-by, burn oil, and lack proper cylinder sealant.

Can you use oversized rings on a standard piston?

Oversize rings are for oversize pistons. They will not work on STD pistons.

How big should a piston ring gap be?

Most piston ring manufacturers recommend a minimum end gap of . 004 inches times the bore diameter for the top piston compression ring. So for a 4 inch bore, the standard end gap would be . 016 inches.

How big is a.020 piston ring size?

An .020 piston ring goes on an .020 larger piston in an .020 larger bore. If a bore has wear it is possible to put in larger rings to compensate for wear, to some small extent. These are called “File-Fit” rings.

When do you need a larger piston ring?

To accommodate a larger piston a larger ring is required. So if the piston is .010 larger, the associated ring for it must be equally larger. There are exceptions to the rules but usually all cylinders are overbored by the same amount. Typically every cylinder is bored because it incresases displacement, and possibly piston weight. Not always.

Which is larger a.010 or.020 ring?

The .010, 020, etc are overbore sizes for the pistons, they are that much larger diameter than a standard piston.  To accommodate a larger piston a larger ring is required.  So if the piston is .010 larger, the associated ring for it must be equally larger.

What do you need to know about oversize pistons?

You will need standard size rings for standard pistons, if your engine has been rebuilt with oversize pistons they will be stamped on top .010, .030 or whatever oversize they are. If the cylinders are worn and tapered up to .010 there is an old trick, use .010 oversize piston rings and file to fit the lower part of the bore.