How to Adjust a Reel Mower Bed Knife for a Clean Cut

This page primarily discusses bed-knife adjustments for a USA Clipper and a Mascot Reel mower. However, aside from the actual adjustment mechanism, the principles apply to most reel mowers.

The bed knife and rotating reel must remain correctly aligned across the entire cutting width. An improperly adjusted mower can leave grass uncut, become unnecessarily difficult to push, or accelerate cutting-edge wear.

What the Bed Knife Does

The bed knife provides the stationary cutting edge against which the rotating reel cuts the grass.

Think of the reel and bed knife as two parts of a single cutting system rather than as separate blades.

Symptoms of Incorrect Adjustment

A mower requiring adjustment may:

Leave strips of uncut grass.

Cut paper on one side but not the other.

Become unusually difficult to push or become totally locked up out of the box.

Produce excessive cutting-system resistance.

Show uneven cutting performance across the reel.

Start With a Clean Mower

Don't attempt precision adjustment while grass, mud, or debris is packed around the cutting surfaces.

Be careful around sharp edges and wear protective mechanic gloves to prevent cuts.

Clean and inspect the reel and bed knife first.

Perform a Cutting Test

Check multiple positions across the bed knife using strips of newspaper.

A mower that cuts at the left but not the right requires a different diagnosis than one that fails across its entire width.

Make Small Adjustments

Reel mower adjustment is a precision operation. Make small, even adjustments on both sides. (Review Video on Adjusting and Maintaining.) Both the Clipper and Mascot Mowers use identical adjustments. Other mowers with different adjustment mechanisms will differ, and you will need to study which adjustment moves the blade closer or farther away.

It is very easy to lose track of clockwise and counterclockwise adjustments, or of the number of adjustments per side. Especially with the reel assembly on its back, lying on a bench. Those adjustments will need to be in reverse.

Both the Clipper and Mascot Mowers use the adjustable trunnions and take a 9/16” open-end wrench. To bring the blade closer, you would turn the trunnion clockwise. To move it further away, you would adjust counterclockwise.

Having one side adjusted at a different distance can cause uneven wear on the reel and lead to a condition called coning. Meaning the reel cylinder cones, becoming smaller on one end.

Use a tape measure or caliper to measure the distance along the adjustment trunnions on each side of the mower to ensure they are equally adjusted at the same distance.

Small changes can make a significant difference.

Avoid aggressively tightening the bed knife simply because the mower isn't cutting.

If the mower locks up, it is adjusted too tight; loosen the bed knife evenly on both sides until the reel turns freely. Then proceed to adjust until the reel is just touching the bed knife. Proper adjustments will produce a faint clicking or swishing sound as the mower cuts.

If the cutting surfaces are dull, excessive tightening isn't a substitute for sharpening.

Toro similarly notes that excessive reel-to-bed-knife contact can increase wear and power requirements.

Know When Adjustment Isn't Enough

If proper adjustment cannot produce a clean cut, the reel and bed knife may need honing, grinding, replacement, or professional servicing.

This information is provided for general educational purposes. Always follow the mower manufacturer's instructions and observe appropriate equipment, blade, towing, and operating safety practices.