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Mower deck cutting problems and solutions
Deck Wheels Incorrectly Set
The deck wheels should be set evenly so that the pitch of the cutting blades will not be affected. If any difference is required for a better cut on some walk-behind mowers, the front height adjuster can be one position lower to assure that you are cutting with the front of the blade. If the deck is slightly lower in the rear you will tend to cut the grass at the rear of the mower. This causes the grass to be thrown to the rear wheels and causes a rough or irregular cut.
Deck Wheel Adjustment
The deck wheels on all lawn and garden tractors should be adjusted so that they will be 1/2" to 1" off the ground at all times. All cutting decks are floating so that they can cut evenly over the ground. The angle from front to rear is built into the assembly on lawn tractors. Check to be certain the distance from the bottom edge of the deck to the ground is the same on both sides of the deck. If it is not, adjust the links on the left side of the unit. The linkage is adjustable on garden tractors. After you have leveled the deck to the ground, you must adjust the linkage up 1/2" to 1" above the ground. Check to be certain the front of the deck is 1/4" to 3/8" lower in the front of the deck than from the rear of the deck. If it is not, adjust the two front links to obtain this distance. This is of most importance. You must keep in mind that if the deck is riding on the ground and you want to make a turn with the tractor the cutting deck still wants to travel straight if the wheels are on the ground and then as you turn the cutting deck will be dragged sideways. This then damages the wheels or the rollers. The deck doesn't turn because there is no differential on the rear axle assembly. This condition will also damage or bend the deck hangers or deck links. From then on till the problems are corrected the quality of cut is affected. When the wheels are set to run on the ground, the deck drive belt is also subjected to excessive load conditions. This causes the belt to become very tight and then loose repeatedly during the course of mowing and again this condition is magnified when making turns, causing premature wearing on the belt. Bent or uneven deck links can cause cutting problems. Deck links should move freely and not bind against the frame of the tractor or other component parts.
First of all, the blades must be the correct part number for the mower and original equipment style, according to the owner's manual. The blade part number is stamped and is found stamped into the back side of the blade. MTD blades are tempered and designed only to bend on impact and not to break. They are tested for this properly and upon impact with an object. Nothing can come off the mower. The only time a blade breaks is when it is bent and the person operating the mower chooses not to do anything about it. With the blade now vibrating it will crack at the mounting bolt holes. You may vision this as to when you take a piece of metal and bend it back and forth. Many times it will break in two pieces. This condition on a mower blade can easily be detected by looking at the crack. The first part of the crack will be rusting and the final stage of breaking will be shining and not rusted. The blade adapter will often show evidence as either being cracked or one of the mounting ears bent upward. Blades are designed to be high lift, therefore meaning that they are made with a raised area, behind the cutting tips which create a lifting action, pulling the grass up to the blade. The proper lift is more important to the cutting quality than even a sharp edge.
The blades must be run at full throttle position on the mower. To assure this, the engine should be checked and running at 3400 to 3600 RPM (Gas Kohler / Briggs). This should be checked with a tachometer by a qualified dealer. The blades running at the proper RPM develop a vacuum lift action. This is created by a combination of things, mainly a deck designed with baffles in the front and rear of the deck. The deck depth and controlled flow design helps to develop a deep vacuum action lifting the grass for cleaner, sharper cutting and efficient discharge of the grass out the side or to the rear for bagging. This then brings us to understand the importance of discharging the grass. To accomplish this most effectively a full baffled deck housing is needed. That is also why the most effective decks for mulching are designed like a donut. The depth is important because after the grass is cut it must rise into the dome of the housing and as it falls to the ground the grass is cut many more times by the inner angles and edges of a special mulching blade.
Most walk behind mowers are designed to be what we call three-in-one mowers, meaning that they will mulch, side-discharge and side or rear bag grass. Blades must be properly sharpened, following the original angle and then checked for balance. If the blades are dull and nicked on the cutting edge this will tend to tear the grass rather than cut it. Mulching blades are more critical and most often it would be better to replace the blade rather than trying to sharpen the varying angles and possibly lose effectivenes.If blades are in question, measure from a level surface to the blade tip, using a rule or tape measure.
All of our mower decks are equipped with a missile deflector to direct the flow of grass out the side of the deck at a safe angle and mowers should only be operated with the deflector in the down position. During our testing procedures we inject steel balls and nails under the deck while the mower is running so that we can determine the angle that these objects will be discharged. The regulated height that any item can come out is no higher than the knee. Decks should always have this deflector properly installed on the mower housing. If for some reason that this deflector is off the mower during the warranty servicing, a claim can be submitted for replacement. A mower without a deflector can project stones from the driveway and the nails that fell into the lawn when the roofer was installing the new roof and of course, no one would find them, but the lawn mower does find them when you least expect.
Deck Belt Guards Belt guards must be properly adjusted and kept in place. The belt guards (hex bolts) on the engine pulley and belt guards on the deck pulleys should have a minimum of 1/8" clearance. Belt guards which are rubbing the pulleys and/or belts can cause the belt to be subjected to excessive heat. The possibility of a belt rolling over is greatly increased when this type of condition exists. The engine pulley and the deck pulleys should be free of any nicks or dents and the pulley sheaves edges should be smooth and free of burs. It is also important to then understand that these belt guards are not only to keep the belt on the pulley, but that they are also needed so that the belts trap-out against them. When the belt is disengaged, the belts then are prevented from continuing to travel. Understanding this, it is then easy to understand the importance of the proper belt size and construction. All MTD belts are constructed according to engineered drawings for the proper performance, not by chance to size. To begin a repair on any mower the first thing to determine is, does it have the original type belts installed on it? If it does not, that is the place to start your repair (Messicks only sells OEM belts). The belts must be to the manufacturers specifications. The results of the wrong belt on a deck can cause poor cutting quality because the belt could be slipping on the blade spindle pulley and this can cause too slow of a blade speed. Grass in the spring has a high moisture content and sometimes it is just too wet. This too can affect the quality of cut. Grass should be relatively dry when cutting and a moderate ground speed selected. Use the transmission to select the speed. Do not change the throttle control from the full throttle position.
Following is a list of cutting problems, which may be encountered with twin blade mowers and possible solutions.
1. Uncut strip of grass. Only the tips of the blades cut so they must be sharp clear to the end. Sharpen the blades. Dull blades tear the grass rather than cut it.
2. Engine speed too slow. The engine should be operated at full throttle regulated by O.P.E.I on mowers where blade is fastened directly to crankshaft. On riding mowers the cutting blade shaft is driven through the use of a belt and pulleys, or a gear box, and may not rotate at the same speed as the engine.
3. Ground speed too fast. Use the transmission to select a slower ground speed.
4. Blades not even with each other.
A. There should be no more than 3/16 inch difference between the blades. Check for a bent blade or spindles; if not bent, the deck may be warped and should be replaced.
B. Check the blade alignment by measuring from the ground (or flat surface) to tip of blade, rotate blade and check each end.
5. Turning to the right leaves small uncut strips of grass at end of lawn. To prevent this, make left hand turns when mowing or go back and trim when finished.
6. Short blade. Blades are sometimes manufactured short or sharpened too much on twin-blade units, replace.
7. Uneven cut.
A. Air pressure should be equal on both front and rear tires.
B. The deck wheels should be set evenly so the pitch of the cutting deck from side to side will not be affected.
C. Deck links should move freely and not bind against the frame of the tractor or other component parts. Links must also be the correct length.
D. Brackets on lift shaft must be welded in line with each other. If they are not, the deck will be higher on one side than the other. If this is encountered the lift shaft should be replaced or an adjustable link which is now available can be used to correct the problem.
E. The pivot bar should move freely. If the bolts are too tight, hung up, damaged or bent, the tractor could be tilted to one side. Some units have an adjustable link to help level the deck.
F. The welded brackets on the stabilizer shaft should be straight and even. This can be checked by removing it from the unit and laying it on a flat surface.
G. Frame alignment is very important. If the entire tractor is leaning to one side it was probably out of position during the assembly process. This is usually noticed because the deck will hang higher on one side and will result in an uneven cut. This condition can be corrected as follows:
1) Loosen the 12 self-tapping screws which secure the right and left hand side frame panels to the rear hitch plate.
2) Push the frame of the tractor by hand until the tractor is level.
3) Tighten the self-tapping screws.
Following is a list of cutting deck problems and possible solutions.
1. Noticeable vibration. If a vibration is noticeable, a bent spindle can be detected by using a dial indicator.
2. Warped deck. If this is suspected, remove deck and place on a flat surface. Measure blade tip to surface of work bench at four points around the blade spindle mounting area.
3. Deck wheels out of adjustment. If cutting deck is equipped with wheels, make sure they are always adjusted from 1/4 to 1/2 inch off the ground after you determine the height of the grass is to be cut. If wheels are not on deck originally, wheels should not at any time be added.
4. Belt slippage. Belt slippage can cause uneven cut. The factory always recommends the use of original equipment manufacturer (OEM) V-belt only. They are of special construction involving the type of cord and cord location and fractional length. V-belts other than OEM generally will only provide temporary service. For best belt cutting performance, use only approved belts.
5. Strip or uneven cut. A strip or uneven cut caused by belt slippage can occur if the cutting deck has hit something and twisted the stabilizer links out of position. Links hanging from a stabilizer bar (whether front or rear mounted) must be in line. To check, remove the stabilizer bar and lay it on the work bench and see if it lies flat. If one link is twisted it can be brought back into alignment by placing it on a vise and twisting the other welded link back in line. If this cannot be done, replace stabilizer bar.
6. Deck not level.
A. On most riders and tractors the variance in the cutting deck can be brought into alignment with the adjustable deck links or an adjuster on the lift shaft handle assembly on the 600 Series riders prior to 1990.
B. For 1990 and 1991 38-inch decks only. If uneven cut is experienced, attach the rear stabilizer plate to the bottom hole in the links welded to the stabilizer shaft assembly. Reconnect the spring which was in lower hole to the stabilizer shaft assembly.
7. Belt fails to engage/disengage. The disengagement rod must be adjusted before operating the lawn tractor to be sure belt engages and disengages at the first notch of detent bracket.
8. Front axle pivot binds. Always make sure that the pivot bar to which the front axles are attached, pivots freely. Grease if necessary.
9. Uneven ride or difficult steering. Observe the brand name on the tires and make sure all tires (or at least the two front and two back pairs) are the same name and size. Some tires inflate differently when manufacturer is different, even though size shown on tire may be correct.