Installing piston rings

Proper installation of piston rings is a critical step in engine assembly. The rings allow sealing of combustion pressure, they scrape the oil from the cylinder surface and also transfer heat from the piston into the cylinder wall. The ring set consists of a Top ring, a  Second (oil wiper) ring, and one Oil Control ring. The oil control ring set contains three pieces; a spacer and two scraper rings that regulate a film of oil that lubricates the cylinder wall.

Step 1) unpackage and carefully inspect each surface.

Step 2) carefully clean the rings with contact cleaner

Step 3) End gap: all Fuel Moto kits come with the ring end gap pre-set. There will be a white sticker stating so on the packaging. For reference rings are typically gapped as follows:

  • Top Ring = .0045 – .0050 per inch of bore
  • Second Ring = .0050 -.0055
  • Oil Rings – Actual gap = .015-.050

Step 4) Install rings on piston. Starting with the oil rings install each ring on piston using the following orientation. Important note: the dot or marking on each ring always faces up.

“TOP” refers to intake side of piston in the diagram below


Important Note: oil expander tabs face up as shown below


Before installing pistons in the cylinders be sure to thoroughly clean the cylinder bore, this is absolutely critical for proper ring seal. We prefer to start with contact cleaner and white cloth, followed with WD40 until there is no debris transfer on the on the white cloth. We then use a liberal coating of Redline assembly lube.