MAINTENANCE

REAR CUTTING UNIT CHAIN TENSION

A chain drive is located on the left side of the rear cutting unit. It maybe helpful to remove the Chain Shield (A) prior to adjusting the chain tension.

Adjust the tension of the chain by loosening the 4 bolts (B) on the rear cutting unit countershaft housing. Rotate the countershaft housing (C) about the pivot line created by the fixed bolts. The slots on the countershaft housing will slide over the remaining two bolts. Rotate the countershaft housing until proper chain tension is achieved. Tighten bolts.

Proper tension is achieved when the chain is slightly loose, but does not deflect more than 1/2" when pressed in the middle of the span between the two sprockets.

BED KNIFE REPLACEMENT

 

 

Reels and bed knife are sharp. Wear

 

DANGER

 

gloves to avoid cutting fingers on

 

 

 

 

sharp edges. Wear safety glasses

 

 

to protect eyes.

 

 

 

When the bed knife becomes damaged or too worn to keep sharp, it must be replaced. Follow the procedure below.

1.The backbar (A), bed knife (B) and fasteners (C,D) have been assembled at the factory under tension. To ease replacement and prevent misalignment of compo- nents, you may wish to clamp the leading edge of the backbar in two or three places before removing the old fasteners.

2.Remove the old shoulder nuts (C) and flat head screws

(D). If shoulder nuts are badly rusted or corroded, they may have to be cut off and screws driven out to be removed.

3.Clean the bottom surface of the backbar for maximum metal contact with the new bed bar.

4.Fasten the new bed knife to the bottom of the backbar in the position shown (bent edge up). Shoulder of shoulder nuts (C) must be seated firmly in the backbar and screws (D) must be flush with the bottom of the bed knife.

5.Torque shoulder nuts 35 to 40 ft-lbs.

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68OM-06/03

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National Mower 68 SR, 68 DL owner manual Rear Cutting Unit Chain Tension, BED Knife Replacement
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68 SR, 68 DL specifications

The National Mower 68 DL and 68 SR are two outstanding models in the world of lawn care, engineered for efficiency and ease of use. Both mowers offer a range of features tailored to meet the needs of both residential and commercial users, making them popular choices among landscapers and homeowners alike.

The National Mower 68 DL is designed with durability and performance in mind. It features a robust steel deck that enhances longevity while providing a clean and even cut. Equipped with a powerful engine, the 68 DL delivers high torque and swift acceleration, enabling users to tackle even the toughest grass and rough terrain effortlessly. The mower's advanced cutting system ensures that grass is cut finely and evenly, reducing the need for additional clean-up.

On the other hand, the National Mower 68 SR offers a self-propelled option, allowing users to move with ease across various landscapes. This model incorporates hydrostatic transmission technology, which provides smooth, variable speed control. This feature is particularly beneficial for those who demand precision in their mowing tasks, as it allow for adjustments on the fly, catering to changing terrain conditions.

Both models come with adjustable cutting height options, offering users the flexibility to choose their desired grass length. The easy-to-use lever enables quick and simple adjustments without needing tools, making the mowing process more efficient. Additionally, both the 68 DL and 68 SR are designed with ergonomics in mind, featuring comfortable handles and intuitive controls that minimize operator fatigue.

Safety is another critical consideration in the design of the National Mower 68 series. Both models come equipped with protective shields and safety switches to prevent accidental starts, ensuring that users can operate the machines with confidence.

For convenience, the mowers also feature large, easy-roll wheels that enhance maneuverability. The inclusion of a bagging system offers an option for collection of grass clippings, contributing to a cleaner lawn appearance post-mowing.

In summary, the National Mower 68 DL and 68 SR combine advanced engineering with user-friendly features that prioritize performance and safety. They are exceptional choices for anyone looking to maintain a pristine lawn with minimal effort, making yard work a more enjoyable task. Whether for home use or professional landscaping, these mowers stand out in their class, delivering reliable performance time after time.
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