Flail mower shaking the tractor? One missing hammer can start the whole dance

October 13, 2026
Agri-Can News
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One missing hammer isn't “just one hammer”

There are two kinds of vibrations we enjoy on the farm: the phone buzzing to say the parts have arrived, and… well, mostly just that one.

When a flail mower starts shaking the tractor like it is auditioning for a dance competition, it is time to stop and find out why.

With the season winding down, a few minutes of inspection now could save a much bigger repair job next spring.

Under the mower, hammer flails spin with the rotor at high speed. If one is missing, cracked or much more worn than the others, the rotor can become unbalanced.

Vibration may also point to other issues, such as worn bearings or a damaged rotor shaft.

The right move is to shut the machine down and check the manufacturer's instructions.

Several manuals, including McConnel/Twose documentation, call for replacing worn or missing flails in diametrically opposite pairs to maintain rotor balance. They also specify replacing the mounting hardware as required when fitting new flails. my.mcconnel.com

In other words, replacing only one hammer because “the other one still looks fine” is not always a bargain.

Same mounting hole. Very different hammer.

Here is a detail worth knowing: two hammers can share a 16.5 mm bore, a 40 mm mounting width and a 110 mm working radius — yet be quite different.

Agri-Can's standard 6061900 hammer weighs approximately 832 g, while the 6061700 Heavy-Duty weighs about 1,305 g.

Both appear in applications involving Kuhn, Maschio, Kverneland and other equipment, but nearly half a kilogram of difference per hammer is a very good reason not to mix versions randomly on a rotor. Agri-Can

Before ordering a heavier replacement, verify the exact machine model, mounting measurements, weight, the complete rotor configuration and the manufacturer's recommendations.

Heavier does not automatically mean better for your machine.

Small bolt. Big consequences.

One of the easiest mistakes is ordering “an M16 bolt” without checking the rest.

For example, Agri-Can carries the J1891003E kit with M16 × 90 mm bolts and a 2.00 mm thread pitch, and the F20110093RE kit with M16 × 95 mm bolts and a 1.50 mm thread pitch.

Same nominal diameter, different pitch and length. They are not universal substitutes. Agri-Can

Check the locking nuts, spacers and mounting tabs while you are there.

Follow the fastener specifications and tightening torque in your mower manual.

A spinning rotor is no place to experiment with the workshop's “assorted bolts” drawer.

The end-of-season check

Before storage, look over the hammers and knives, mounting hardware, belts, bearings and any signs of cracks or excess play.

Remove built-up debris, grease the specified points and make a list of the parts you need while the numbers are still readable.

Safety first: stop the engine, disengage the PTO, remove the key, wait for the rotor to stop completely and lower or securely support the machine before inspecting it. Never reach into a moving mower.

The best time to fix it? Before it disappears into the back of the shed.

In October, there is still time to measure carefully, identify the correct hammer and replace a handful of bolts.

Come spring, we would much rather see the mower working than serving as a mechanical puzzle at 7 a.m.

At Agri-Can, our job stays the same: finding you the right part at the best possible value, backed by strong and reliable partners around the world.

Because the mower is supposed to beat up the vegetation. Not the entire tractor.

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Heavy-duty flail hammer blade 120mm X 110mm X 40mm. Hole: 16.5mm - Weight: 1305g

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