Riding Mower Leaving a Strip in the Middle (Reasons and Solutions)

A lush, evenly cut lawn and a picturesque landscape make for a perfect Sunday morning. Obviously, nobody wants an unsightly strip of uncut grass in the middle of their lawn.

So evidently, your riding lawn mower leaving a strip in the middle of your lawn is a problem. Here’s some reason why it happens:

• Off Cut Deck
• Wrong Deck Rotation
• Unbalanced Blade
• Lack of Tire Pressure
• Deck Belt with Poor Fit

Do they sound ungodly? Well, they won’t once you have read this article to its full length. Read on to solve your Riding Mower Leaving a Strip in the Middle problem and ways to fix it.

5 Reasons Why Riding Mower Leaving a Strip in the Middle and the Solutions

Here’s why your riding lawn mower is leaving a strip in the middle:

1. Off-Cut Deck

Sometimes the punch cut in the deck of your mower may be off. The spindles may not be mounted with proper specifications.

To fix this you could try-

• Cutting the new metal spacer plates with the correct tolerances for a permanent fix.
• Check and adjust the deck, possibly recut the deck for a spindle position.
• Potentially look for a spare deck and see if that works- or double check mesurements with it.

Additionally…

• When setting front deck height on adjustables, the nuts on each side should be turned the same amount. If not, the deck can rotate or pivot to the left or right with respect to the front axle pivot point.

Related Post: A Complete Guide on Lawn Mower Blade – Everything You Need to Know!

2. Wrong Deck Rotation

Another issue may be that the front mount hangers of the fixed type are bent. Or the other type maladjusted. Or, if one side of the front of the deck is bent the deck can rotate around a point between the spindles and the front mount.

If it rotates in the wrong direction (a line between the spindles becomes more parallel to the front axle), the blade overlap will be lost. With some rear hangers, it will pivot instead of rotate.

The ‘new’ type of mount has a single front connection point on the centerline of the frame. There is usually less deck rotation problem on this type of mount because of the rear hangers used.

Rear hangers on the fixed and adjustable mounts can contribute to rotation if they are connected to the wrong side of the hanger mounts of the deck.

To fix this, do the following –

• The deck should be hung with (usually) the left spindle closer to the front axle than the right. Check deck rotation with respect to the frame.
• A simple measurement from the front axle pivot point to the right and left spindle will reveal lots. The bigger the difference between right and left the more the blades overlap.
• Deck rotation vs. tire size is apparent at the left front and right rear tires. Somewhat less than bright eyed and bushy tailed engineer, I guess.

3. Unbalanced Blade

One blade may be too short, or both a little shy of the OEM size. A bent or damaged blade can cause imbalance and vibration. Additionally, the blade mounting hardware (bolts, washers, and spacers) may cause the problem.

You should do the following to troubleshoot unbalanced mower blades:

• Remove the deck and scrape/remove the built-up grass.
• Check to see if the tips of the blades are at the same level to each other (parallel to each other) by pointing the blade tips against each other.
• Check to see if there is over lap of the blades. To do this, loosen the belt. Then position the blades perpendicular to the direction/path motion of the deck (or the center line of the tractor).
• Then view the blades to see if the tips or the cutting path over lap to each other.
• Sharpen the blades.
• Inspect pullies and mandrels.
• Re-install deck.
• Level the deck left to right and right to left. (position the outer blade tips to the outmost and measure the tip to ground)
• Level the deck front to back with the rear of the deck being no-more than 1/4″ higher.

4. Lack of Tire Pressure

Tire pressure is vital for an even cut. The uneven cut due to lack of tire pressure is usually lower on the side. It happens all the time in the Murray morwers.

Here’s how you can fix it:

• A flat tire happens usually over time. Pumping the tire solves the issue.
• Over time, small punctures or damage to the tire can cause air to escape gradually. Conduct a soap test to find the leaks.
• A defective valve can cause air leakage. Replace the valve stem using a valve stem tool.
• Inflate the tire to the recommended pressure and check for leaks.

5. Deck Belt with Poor Fit

The deck belt may wear out or stretch, resulting in a poor fit. It would likely be visibly worn or loose. Another cause of a poor fit could be incorrect deck belt routing.

The belt may not fit tightly if it is not properly threaded around the pulleys and idler arms. Deck belts must be properly tensioned in order to function properly. The belt will not fit tightly and may slip if the tension is too loose.

Factory belts could be stretched too much causing poor fit. This allows the pulleys to slip the belt instead of hold tight and turn. Moreover, a worn belt can slip resulting in lower rim speed on the blades.

Here’s how you can solve it –

• The best solution is to replace the belt with a new one, compatible with your mower.
• Examine the belt routing diagram in the owner’s manual to ensure you’ve threaded the belt through orderly. Check each pulley and idler to ensure that the belt is properly seated.
• Make sure the pulleys are securely fastened to their respective shafts with the appropriate tools.
• Replace any damaged components to ensure the belt fits properly and operates reliably.

Related Post: Reasons Craftsman Riding Mower Deck Belt Keeps Coming Off

Preventive Maintenance for Riding Mower Leaving a Strip in the Middle

A few things can make the mower properly function. Here’s a few things to keep in mind:

• The overlap and parallel of the multi-blade decks determine if you get those lines. With the level of the deck from right to left and front to rear makes the difference.
• Also, other factors will play in if you are going to get lines. Such as, the speed of the tractor, the height of the grass being cut, and the type of grass/weeds being cut.
• Take the time to make sure the deck is set up according to the manual.
• Perfectly level side-to-side should be ensured. This means the front tip of the blade is ¼ to 1/8″ lower than the rear tip of the blade when the blade is parallel to travel direction and the deck is in the transport position (as per the manual).
• The tire pressure should be as per the spec in the owner’s manual.
• Some mowers will be naturally bad. Such as some Toro zero turns with 50-inch decks. The lot may not be flat and other problems may exist.  
• The pad on the deck that the mandrel housing is bolted to is a critical surface and all 3 should be in good shape with no signs of damage.

Riding Mower Leaving a Strip in the Middle – FAQs

Related Posts:

• Fixing a stripped bolt on a lawn mower blade: Removal techniques
• Resolving the issue of a slow-spinning lawn mower blade
• Troubleshooting guide: Riding mower blades not engaging
• Achieving a superior cut: Blade positioning on a 3-blade mower deck
• Common causes and fixes for a mower losing power when blades are engaged