Compression Test
A cranking compression test reveals the mechanical health of the rings, valves, and head gasket. Always perform on a warmed-up engine with all spark plugs removed and the throttle held wide open. Fully-charged battery, ignition disabled, fuel pump unplugged.
Typical Acceptable Ranges (cranking, all plugs out, WOT)
| Engine Type | Healthy Reading | Minimum |
|---|---|---|
| Stock low-comp OHV (8.0–8.5:1) | 120–150 psi | 100 psi |
| Stock OHV (8.5–9.5:1) | 140–175 psi | 120 psi |
| Stock high-comp (9.5–10.5:1) | 165–195 psi | 140 psi |
| Performance / built (10.5:1+) | 180–220 psi | 160 psi |