⚠️ Safety Warning: Engine timing is critical to the mechanical integrity of your motorcycle. If the timing marks are misaligned even by one tooth, the valves can strike the piston, causing catastrophic engine failure. Always rotate the engine by hand at least two full revolutions after setting the timing to ensure there is no mechanical interference before attempting to start the engine.
Yamaha YZF-R125 & WR 125 Timing Marks Guide
Setting the timing correctly is essential during a top-end rebuild or valve clearance adjustment. This involves aligning marks on the crankshaft (flywheel) and the camshaft.
Flywheel / Crankshaft Timing
Access: Remove the timing plug on the left-hand engine cover.
The "T" Mark: Rotate the crankshaft until the "T" mark (Top Dead Center) on the flywheel aligns with the stationary pointer on the engine casing.
Note: There are other marks on the flywheel representing the ignition firing range; ignore these for mechanical timing. Use the bottom-most distinct mark for TDC.
Camshaft Timing
Alignment: The timing mark on the camshaft sprocket must align with the corresponding mark on the cylinder head (usually a notch at the 9 o'clock or 12 o'clock position depending on the generation).
Chain Tension: Ensure the cam chain is taut on the exhaust side (front of the engine) when checking these marks.
Balance Shaft Timing
If you have split the engine cases, you must also align the balance shaft gear marks. There are dots on the gears that must point toward each other to ensure the engine remains balanced and vibration-free.
Shop Timing Components
Cam Chains:
Yamaha R125 Cam Chains on eBay UK Timing Plug Tools:
Engine Timing Tool Kits on eBay UK
The bottom mark on the flywheel rotor in workshop the other marking above are the firing range of spark plug before TDC.
The bottom mark in above photo shows the timing mark to be aligned with the generator engine casing mark.
See video of this process below
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