Engine Vibration Analyzer
From an engine’s RPM, stroke and cylinder count this computes the characteristic frequencies that dominate its vibration and sound: the firing frequency, the 1X rotation order, the 0.5-order misfire signature, the harmonic series, and belt-driven accessory frequencies from pulley ratios — plus a diagnostic order guide.
ℹ This is a calculator, not a measurement. The frequencies are exact kinematics for ideal, evenly-firing geometry — you must verify your own inputs (stroke, cylinder count, true pulley diameters). The order → cause map is a common diagnostic convention, not a diagnosis: a real spectrum mixes orders, mount/structural resonances and driveline inputs. To actually measure engine vibration you need a calibrated accelerometer + vibration analyzer (ideally order-tracked to a tachometer); a microphone or this tool cannot give true mm/s velocity or g amplitude. No engine-specific part database is fabricated here.
Engine
Stick map of the key orders (0.5X, 1X, 2X, firing and its 2nd harmonic) on a linear-frequency axis — not a measured spectrum.
Order harmonic series
Diagnostic order guide (a guide, not a diagnosis)
How It Works
An engine repeats two kinds of event as it runs, and each shows up at its own frequency. The first is simply the crankshaft turning: it rotates RPM times a minute, so its fundamental — the 1X or first order — is fr = RPM ÷ 60 Hz. Anything tied to rotation (an out-of-balance crank, a damaged harmonic balancer, a bent driveshaft or wheel) puts energy here. The second is combustion. On a four-stroke each cylinder fires once every two crank revolutions, so the cylinders together produce cyl ÷ 2 power strokes per revolution and the firing frequency is (RPM ÷ 60) × (cyl ÷ 2). A two-stroke fires every cylinder every revolution, so its firing frequency is (RPM ÷ 60) × cyl. The firing frequency is therefore always a fixed order of rotation — 2X for an inline-four four-stroke, 4X for a V8, 6X for a V12, and so on.
Two more orders are worth watching. Because pistons accelerate twice per revolution, reciprocating engines carry an inherent second-order (2X) shake that is famously strong on inline-fours — it is why many four-cylinders buzz at idle. And on a four-stroke a single weak or dead cylinder fires only once every two revolutions, half as often as a healthy one, so a misfire characteristically appears at the 0.5 order (and its odd multiples 1.5X, 2.5X). Belt-driven accessories spin at their own rate set by pulley size: an accessory turns at f = fr × (crank-pulley diameter ÷ accessory-pulley diameter), so a smaller accessory pulley spins faster, and a worn alternator, A/C-compressor or power-steering-pump bearing peaks at that accessory frequency independently of any engine order.
Two honest cautions. First, these are exact kinematics for an idealised, evenly-firing engine — they tell you where peaks should land, not how big they are. You must confirm your own inputs: whether the engine is four- or two-stroke, the real cylinder count, and the true pulley diameters. Second, the order → cause table is a widely used diagnostic convention, not a diagnosis. A real machine mixes many orders with engine-mount and structural resonances and with road and driveline inputs, so a peak at a given frequency only nominates a suspect to investigate. Diesel and marine engines follow the same maths (use the four-stroke or two-stroke rule to match the engine) but often run uneven firing, large flywheels and propeller/shaft orders that add their own peaks. Crucially, to truly measure vibration you need a calibrated accelerometer and a vibration analyzer, ideally order-tracked to a tachometer — a microphone reveals only the frequency content of the airborne sound and cannot report calibrated mm/s velocity or g acceleration.