Timing Belt Tracking Off-Center on Idler Pulley - Aftermarket Pulley Replacement

Engineintermediate✓ OP Confirmed

Problem

After replacing all belts including the timing belt and tensioner, the timing belt was riding approximately 3mm off-center on the idler pulley/tensioner. Despite multiple attempts to realign the belt, it would return to the misaligned position every time the engine was started.

Timing belt sitting ~3mm off-center on idler pulleyBelt returning to misaligned position after every engine startUneven belt wear visible as a line along the tensioner edgeIdler pulley had slight lateral play

Root Cause

The aftermarket timing belt idler pulley was out of spec compared to the OEM part. The gap between the spring plate and bearing on the aftermarket pulley was approximately 3-4mm smaller than the original, causing the pulley to not protrude far enough and the belt to track off-center. Aftermarket idler pulleys are often poorly manufactured with potential issues including out-of-round bores, questionable staking, and inferior build quality compared to OEM.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted August 2025 on SupraForums.com