The first few seconds after a rebuilt engine fires are some of the most important in its life. Assembly lube protects the bearings and cam for a short time, but the oil galleries, filter and lifters are still empty. Priming the lubrication system before the first start fills those passages so oil pressure comes up immediately instead of after several seconds of dry running.
Why Priming Matters
- Bearings and crankshaft: a few seconds of low oil pressure can scuff new bearings before they ever see a full oil film.
- Camshaft and lifters: hydraulic lifters need to fill with oil, and flat-tappet cams are especially sensitive during the first minutes of operation.
- Oil pump: a dry pump may take longer to pull oil from the pan, particularly if the pickup has an air leak.
Common Priming Methods
Drive the pump with a priming tool. On many engines with a distributor-driven oil pump, the distributor is removed and a priming shaft is used with a drill to turn the pump. Run it until oil pressure registers and oil appears at the rocker arms.
Use a pressure pre-oiler. A pressurized oil canister connected to an oil gallery port pushes oil through the system without turning the pump. This works for engines where the pump cannot be driven separately.
Pack the pump and crank with ignition disabled. For engines with a crank-driven or cam-driven pump, pack the pump with petroleum jelly at assembly (if the instructions allow), pre-fill the oil filter, then disable ignition and fuel and crank the engine in short bursts until oil pressure appears.
Tips for a Complete Prime
- Rotate the crankshaft slowly by hand while priming so oil reaches every lifter bore and bearing journal.
- Confirm oil is reaching the top of the engine — rocker arms or cam journals — before you consider the job done.
- Fill the oil filter before installing it, where the mounting position allows.
- Check the oil level after priming; the filter and galleries hold oil that has left the pan.
After Startup
Watch oil pressure immediately. If pressure does not come up within a few seconds, shut the engine off and find the cause before restarting. For flat-tappet camshafts, follow the cam break-in procedure right away.
Evergreen Rebuild Solutions
Evergreen engine rebuild kits and oil pumps are identified by engine application. Use the Evergreen eCatalog to find the right kit or pump, and follow the installation instructions supplied with the parts. Browse Evergreen engine rebuild kits.
