Ask the Mechanic

Making the Cut

(Steve Thompson)

READER: I have a John Deere platform on my combine and an older John Deere sickle mower. I have always heard that when the grass begins to hang up between the guards and the sections, that the guards could be worn out. On my sickle mower, I see that there is a plate on the guard that has serrated edges. The dealership says they may need replacing?

STEVE: The most important thing about clean cutting with a sickle-type cutter is the clearance between the hold-down clips and the sections. This clearance is critical. The sickle can't clean if the grass is not cleanly clipped rather than bending and jamming between the sections and the guards. Some grasses are extremely hard to cut, and some are easily clipped off. The wear plates between the sickle and the bar, the sections themselves, the hold-down clips, the shims under the wear plates and the ledger plates (if equipped) all work together to make a clean cut. Most sickle mowers have a replaceable shear plate (held on by one rivet) that fits on the top cutting surface of the guard (see photo accompanying this article). The section should run closely enough to the wear plate to make an easy shear cut. Just like scissors, the blades must mesh very closely together for an easy cut no matter how sharp the blades are on the scissors. A quick feel of the shear plate should make a snag/sharp feel on your fingertips. If they are worn out, they will feel smooth to the touch. The serrated ledger plate helps hold the grass for a clean shear action.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email, and be sure to include your phone number.


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