Free printableMaintenance and recordsTSP-MA-08
Scooter compression test log
One reading tells you little. Four over a year tell you whether the engine is going backwards, and how fast.
Layout preview of page one. The PDF itself is typeset text, not an image.
Download — free, no email
2 pages. No account, no sign-up, no newsletter. Print it, copy it, hand it to somebody else.
TSP-MA-08 · version v1.0 · September 2026. Opens in your browser's PDF viewer, where you can print directly.
The problem it solves
A compression test gets done once, when something is already wrong, and the number is compared against a figure from the internet. That comparison is nearly worthless — gauges read differently, cranking speed varies, and the published figures for these engines come from very few sources.
Compression is the most informative single measurement you can take on an engine, and it is almost always used badly. The value is not in the absolute number. It is in the comparison — against the same engine six months ago, with the same gauge, cranked the same way.
The one comparison that does work absolutely is the wet test. Take a reading, squirt a small amount of oil into the cylinder, and take another. If the reading rises substantially, the oil has temporarily sealed worn rings. If it barely moves, the leak is somewhere the oil cannot seal — a valve, a head gasket, or a hole. That distinction needs no reference figure at all, which is why it is on this sheet and a target number is not.
Benchmarks do exist and are printed here with their single source named, because they are genuinely useful for the question "should this even start". They are one experienced author's figures, not a specification.
The mistakes this sheet exists to prevent
- Comparing your reading against a figure from a different gauge on a different engine.
- Testing with a flat battery, so the engine cranks slowly and the reading is low for reasons that have nothing to do with the engine.
- Testing with the throttle closed, which restricts the air the cylinder can draw.
- Doing the dry test only, and missing the wet test that separates rings from valves.
- Not writing the number down, so the next test has nothing to compare against.
Who it is for
- Anyone whose engine has lost power with no obvious cause
- Buyers checking an engine before committing
- Anyone who wants a baseline on a healthy engine, which is the best time to take one
What is on it
- How to take a reading that means something
- The wet test, and what the difference between wet and dry tells you
- Cranking benchmarks with their single source named
- A log so readings accumulate into a trend
How to use it
- 01Warm the engine if it will run, then test. A cold engine reads lower.
- 02Hold the throttle wide open and crank on a fully charged battery.
- 03Crank for the same number of compression strokes every time, and note how many.
- 04Do the wet test straight after the dry one, and record both.
Use it with the registry
Other sheets you may want
- GY6 valve clearance check and recordThe check the most experienced owners do first when one of these runs badly — recorded, without a target figure we cannot source.
- GY6 poor acceleration and no top speedIt runs, but it will not pull. The first question separates a transmission fault from an engine fault, and almost nobody asks it.
- Used Chinese scooter inspection checklistWhat to check before handing over money, in the order you can check it, including the paperwork problems specific to these machines.
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-08 and the version so we know exactly which sheet you mean. All printables.