Using oversized pistons and boring the cylinders is a common practice when increasing engine displacement or rebuilding engines with worn-out cylinders. Many enthusiasts, however, assume oversized pistons are simply larger versions of the standard-sized equipment. That’s not always true.
Thanks to the generous tech pages on the United Engine and Machine Co. Incorporated‘s webpage, here are a few fine points to consider when talking about pistons.
Take piston-ring grooves, for example. There are differences in what is called the root-groove diameter, and “compensated ring groove” is a term you’ll soon get to know more about.
A compensated ring groove is where the root-groove diameter is expanded in proportion with the oversize piston. UEM, which makes Silv-O-Lite and KB Performance pistons, states: “For years manufacturers would supply the standard root-groove diameter for all oversizes. A .060-inch oversize piston would have the standard root-groove diameter.”
A compensated ring groove means that any oversized piston has its root groove moved out in proportion so there isn’t excessive distance between the back of the ring and the leading surface of the ring groove. This adjustment helps assure proper ring loading, reduces blow-by and helps oil control.
“By compensating the ring grooves,” says UEM, “it cuts down the space between the back of the groove and the piston ring. Less space cuts down on unburnt fuel stored in this area. Additionally, compensated ring grooves make the ring lands stronger, which helps rings to seat sooner and allow the top rim of the piston to run cooler.”
All KB pistons are supplied with compensated ring grooves.
For more information on piston technology or United Engine and Machine Co. Incorporated, visit them at kb-silvolite.com