Free printableMaintenance and recordsTSP-MA-07
GY6 valve clearance check and record
The check the most experienced owners do first when one of these runs badly — recorded, without a target figure we cannot source.
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TSP-MA-07 · version v1.0 · September 2026. Opens in your browser's PDF viewer, where you can print directly.
The problem it solves
When one of these four-strokes starts running badly, the most experienced people on the forums check valve clearance before anything else — because the alloy heads let the valves and seats recede, closing the clearance until a valve is held slightly open. Owners instead reach for the carburettor, because that is what the internet suggests.
The mechanism is worth understanding because it explains the symptom. As the valve and its seat wear into a soft alloy head, the valve sits deeper, which pushes the stem further up and closes the gap at the rocker. Eventually there is no gap, the valve never fully closes, and compression leaks past it — worst when the engine is hot and everything has expanded.
That is why the classic presentation is an engine that starts and runs when cold and gets worse as it warms, or one that will not idle without the throttle cracked open.
What this sheet will not do is tell you what the clearance should be. Published figures for nominally identical engines disagree, and some are quoted in thousandths of an inch and others in hundredths of a millimetre in ways that do not convert to each other. Print one of those and somebody sets their valves to it. So the sheet records what you measured and what you set it to, against the figure from your own manual if you have one.
The mistakes this sheet exists to prevent
- Checking clearance on a warm engine. The specification and the procedure both assume stone cold.
- Checking at the wrong point in the cycle. It has to be at top dead centre on the compression stroke, with both valves closed.
- Taking a clearance figure off a forum. They disagree, and the units sometimes do not convert.
- Rebuilding the carburettor first, when zero clearance is the most commonly named cause of exactly this symptom.
- Adjusting until it feels right without recording what it was before, losing the wear rate.
Who it is for
- Anyone whose four-stroke starts then dies, or gets worse as it warms up
- Owners doing scheduled maintenance who want a record rather than a one-off
- Anyone about to buy a carburettor to fix a running problem
What is on it
- Why the clearance closes up on these engines, and what that does
- The conditions the check has to be done under
- A record of measured and set clearance over time, which gives you a wear rate
- An honest statement of why no target figure is printed
How to use it
- 01Engine stone cold. Not warm, not recently run.
- 02Rotate to top dead centre on the compression stroke, both valves closed and both rockers free.
- 03Record what you measured BEFORE adjusting anything. That number is the wear rate.
- 04Set to the figure in your own manual if you have one, and record which figure you used and where it came from.
Use it with the registry
Other sheets you may want
- GY6 starts then dies, or will not idleIt fires, runs for a few seconds and stops. Or it only idles with the throttle cracked open. Four causes account for most of it.
- Scooter compression test logOne reading tells you little. Four over a year tell you whether the engine is going backwards, and how fast.
- GY6 maintenance schedule and service logA service record you build yourself from what your machine actually needs, rather than from a schedule invented for a machine nobody can identify.
Free to print, copy, and share — including in forums, clubs and workshops. If you find a mistake on this sheet, tell us and it gets corrected. Quote TSP-MA-07 and the version so we know exactly which sheet you mean. All printables.