False Bent Valve Diagnosis After 1JZ VVTi Cam Installation - Carbon Debris Causing Temporary Valve Leak

Engineadvanced✓ OP Confirmed

Problem

After installing 272 cams on a freshly rebuilt 1JZ VVTi head (ported, polished, new guides, new valves, seals, shimless buckets, valve job), the builder incorrectly set the crank at TDC and bolted cams down at the dot marks instead of setting the crank at 60 BTDC. After correcting the timing, a leak down test showed cylinder #6 leaking audibly out the exhaust. However, after pulling the head and retesting with cams removed, #6 sealed perfectly while other cylinders showed minor leaks, giving inconsistent and confusing results.

Cylinder #6 failed leak down test with audible air escaping from exhaustValve lash on #6 measured approximately 0.001-0.002 inch off from previous measurementsCrank would not rotate with light force when cams were incorrectly timed at TDCInconsistent leak down results - #6 leaked with cams installed but sealed with cams removed

Root Cause

Loose carbon debris from the piston tops was dislodged when the valves contacted or scraped the valve relief pockets during the incorrect cam timing installation. This carbon temporarily pinned the #6 exhaust valve slightly open during the initial leak down test. The valves were not actually bent - they came close to the bend threshold but did not exceed it, thanks to sufficient valve relief depth in the pistons.

Confidence

Moderate confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted October 2020 on SupraForums.com