Verify in this order: find true top dead center on the compression stroke for cylinder one, confirm the crankshaft index mark against it, check the camshaft and gear train marks against the manufacturer's diagram, and on mechanically governed engines verify injection pump timing at its own index. Then rotate the engine two full turns by hand and confirm every mark returns exactly. Marks that return mean the timing is correct; marks that drift or fail to meet mean the assembly gets opened again before the engine runs, not after.
How to confirm it
- Decide when verification is required
After any timing gear, camshaft, injection pump or cylinder head work, and whenever an engine runs correctly but with an unexplained loss of power, elevated fuel use or valve-to-piston contact noise. Verification after the work is a five-minute check; verification after a bent valve is an autopsy.
- Find true TDC on the compression stroke
There are two top dead centers per cycle. Use the one on compression, with number one valves closed: confirm with the rocker arms, or by the pulley mark together with the valve state. If the pulley or damper is suspect, use a piston stop tool to establish true TDC rather than trusting a stamped mark on a part that may have slipped.
- Read the crankshaft index mark
Flywheel rim marks, damper marks or gear cover pointers, per the service manual. Clean the marks first; a flywheel timing window caked with oil has caused more false readings than any mechanical error.
- Check camshaft and gear train marks
Match the cam gear, idler and crank gear marks against the diagram in the manual. Gear marks are set with the engine cold and at a stated crank position on some designs; follow the manual's sequence exactly rather than reassembling to the marks as they happen to fall.
- Verify injection pump timing on mechanical engines
Lock the pump at its stated index and confirm the drive gear and coupling marks. On electronic engines the equivalent check is the phasing procedure in the diagnostic tool, not a physical mark.
- Rotate two full turns and recheck every mark
Hand-rotate the engine through two full revolutions and confirm all marks return precisely. This catches a half-tooth installation error that the first assembly misses, and it costs nothing but the time to do it.
- Record what was found
Photograph the aligned marks and note the result with the job paperwork. The next technician, and the parts desk when gear trains are ordered, both work from that record.
What to do about it
All marks return after two revolutions: timing is verified. If symptoms persist, the fault is elsewhere — valve lash, injector condition or, on electronic engines, sensor phasing and calibration.
Cam or pump marks fail to meet: stop and re-open the front cover. One tooth of cam error is enough to cost real power, run hot and, on some engines, kiss valves to pistons. Never start an engine to see whether it matters.
Crank mark disagreeing with true TDC from a piston stop: the damper has slipped or been replaced wrongly. Replace or correct the damper; never re-stamp a timing mark to match reality.
Where gears, dampers, gaskets or a pump drive are needed, Guangzhou Shenyue Machinery Technology Co., Ltd. supplies engine timing and gear train parts from Guangzhou, with 3,000+ part types on the shelf and 100,000+ part numbers available to order, each line stated as genuine, OEM-quality or aftermarket.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Front cover and timing gasket set | Genuine; OEM-quality. Reuse is false economy once the cover is off. |
| Camshaft and crankshaft gears | Genuine; OEM-quality. Match tooth count and keyway to the engine build, not the model year. |
| Crankshaft damper and pulley | Genuine; OEM-quality. The timing reference lives here; a slipped damper corrupts every check. |
| Injection pump drive components | Genuine; OEM-quality. Confirm pump index and coupling orientation on installation. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
The engine runs fine, so why verify at all?
Because one tooth out of time hides in plain sight: it starts, it works, and it loses a few percent of power and efficiency forever, on an engine that now has an unexplained appetite for fuel. The verification takes less time than one tank of the extra fuel it costs.
Can I trust the marks on the pulley?
Only until the pulley or damper has been off the engine. Dampers slip on their hubs, and pulleys with sheared keys have sent more than one technician chasing a timing fault that lived in the reference mark itself. When in doubt, find true TDC with a piston stop.
Do electronic engines still need this?
Yes, though the marks matter less than the phasing procedure. The cam and crank sensors tell the ECU where the engine is, and a cam driven one tooth out confuses the sensor relationship exactly as it would a mechanical engine, just with different symptoms.