High Leakdown Test Numbers Despite Good Compression - Valve Reseating Fix

Engineadvanced✓ OP Confirmed

Problem

Engine showed 16-17% leakdown on cylinders despite good compression numbers (155-160 PSI across all cylinders). Leakage was audible at the rings, cylinder, and exhaust manifold. Removing and reinstalling cams did not change the leakdown numbers.

16-17% leakdown on cylinder #1 regardless of breaker bar position around TDCAir leaking through to adjacent cylinder and exhaust manifoldGood compression numbers (155-160 PSI) contradicting high leakdown percentageLeakdown numbers unchanged even after pulling cams

Root Cause

Valves were not seating properly, likely due to carbon buildup preventing the valves from fully closing against the seats. This allowed air to leak past during the leakdown test even though dynamic compression was acceptable.

Confidence

Moderate confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted November 2020 on SupraForums.com