Disc Mower Maintenance

Disc mowers spin fast and hit rocks, fence wire and dirt, so a few minutes of attention before each day of cutting saves expensive repairs. This guide covers the routine checks and the jobs that belong in a shop.

Key points

Do a walk-around with the engine off and the key out before every cutting day.
Replace blades in sets and use the exact hardware the manual specifies.
Check cutterbar oil level and condition, and treat milky or metallic oil as a warning.
Never clear a plug or reach under shields while anything is running.
Leave shear bolts and slip clutches as designed.

What should you check before every cutting day?

Shut the tractor off, take the key out and make sure the PTO is disengaged before you walk around the mower. Look at the blades, the blade bolts or retainers, the shields and curtains, and the driveline. A loose or missing part on a disc spinning at high speed can throw debris a long way.

Then grease every fitting the manual shows, using the grease type the manufacturer specifies. Check the oil level in the cutterbar and gearbox where the design has a sight plug or dipstick.

Keep a simple log in a notebook or on your phone: date, hours or acres cut, what you greased, what you replaced. A short record tells you when a cutterbar is due for a closer look and helps if you ever sell the mower.

Blades present, undamaged and securely attached
Guards, shields and rubber curtains intact
Driveline shield turns freely, shaft slides and guards are not cracked
Hydraulic hoses free of rubs and weeping
Tires and hitch pins in good condition

How do you know when to change disc mower blades?

Many disc mowers use small flip or swing blades held on by a bolt or a quick-change retainer. Blades are consumables. They get nicked on rocks, worn thin by soil and rounded by use. A blade with a visible crack, a chunk missing or a worn retaining hole should be replaced, not turned around.

Always replace blades in sets so the discs stay balanced. A single heavy blade and a light one on the same disc can create vibration that hurts bearings. Use the blade, bolt and retainer parts the manual specifies, and do not substitute bolts from a hardware bin.

What is the right way to check cutterbar oil?

The cutterbar is the heart of a disc mower, and it runs in an oil bath. Check the level when the machine is sitting level and cool, using the plug or sight glass in the manual. Milky oil points to water. Metal flakes or glitter in the oil point to wear. Either one means the machine needs a closer look.

Use only the lubricant and the fill amount the manufacturer lists for your model. Overfilling can push oil past seals, and underfilling can run gears dry. If you find fresh oil on the ground, find the source before the next cutting.

How do you handle a hit rock or a plugged cutterbar?

Stop, disengage the PTO, shut off the engine, remove the key and wait for everything to stop turning. Never reach into a cutterbar or clear a plug while the engine is running. Disc mowers can keep rotating for a while after the drive is shut off.

After a hard strike, inspect the blades, the discs and the mounting hardware. Look for bent or cracked disc plates and loose bolts. If the cutterbar feels rough or noisy when turned by hand afterward, have a qualified mechanic open it up rather than running it and hoping.

Do not work under a raised mower unless it is solidly supported with blocking or locked as the manual describes. A hydraulic cylinder or a lift linkage is not a safe support by itself.

What about drivelines, shear protection and shields?

The driveline carries the PTO power from the tractor to the mower. Keep the shield intact and the shaft greased at the points the manual shows. Check that the shaft is the right length for your tractor so it does not bottom out on turns or lift.

Some mowers have a shear bolt, a slip clutch or another protective device. These are there to protect the gearbox, and you should leave them as designed. Replace a shear bolt with the exact bolt specified. Never swap in a stronger bolt or lock a clutch, because that moves the damage to a much more expensive part.

How should you store a disc mower for the winter?

Wash off packed crop and dirt, which hold moisture against steel and hide cracks. Inspect the blades and discs once it is clean, and order replacement parts in the off season when you have time and the dealer is not rushed.

Grease the fittings, lower the mower onto blocking or its stands according to the manual, and store it under cover if you can. Release tension on belts or springs if the manual calls for it. Fix hydraulic leaks and have a mechanic handle any gearbox work now, rather than during your first cutting window next year.

When to get help: Call a qualified mechanic or the dealer service department for any cutterbar teardown, gearbox noise, bent disc or hydraulic leak. Follow the manufacturer's manual for fluids and procedures, and ask your extension office about local hay equipment clinics.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

More in Hay, Forage & Livestock Equipment

← Mower Conditioner Buying Guide Sickle Bar Mower Basics →