Kevin Mark Klughart

PhD, PE, JD, MIP, LLM

Patent Attorney / Engineer

 

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Lawn Mower

 

My neighbor recently purchased a new lawn mower and was kind enough to give me his old John Deere Sabre Model 15.538HS.  This unit was about 15 years old, but was still in relatively good shape.  The previous owner had complained that the mower drive train would slip when going up hills or in rough terrain.  Replacement of the drive belt (standard 95-inch A-belt) and adjustment of the drive belt tension fixed this.  When combined with new tires (10-inch on the rear wheels), the mower would spin the tires if necessary - no shortage of drive train power here!  Note that this unit can support 10-inch rear wheels if spacer washers are placed on the rear axels to move the tires out about 1/8-1/4 inch.

I proceeded to refurbish this mower with new tires, air filter, fuel filter, gas cap, mower mulching blades, blade bolts, drive belt (95-inch A-belt), deck belt (93-inch A-belt), idler pulleys, deck blade pulleys, headlights, deck height wheels, oil change, etc.  Most of the repair work occurred on the mower deck.  A parts outline is listed below for reference:

It was clear that most of the bearings on the mower deck moving parts were toast.  These included parts 16, 29, 33 (2).

However, after these changes the mower kept throwing belts on the mower deck.  I should mention that the mower deck belt would disengage ONLY at the most extreme lowest deck position, but not at higher deck positions.  This intermittent nature of the failure made it especially difficult to diagnose and correct.  After much frustration, it was determined that there were several problems with the mower deck:

First, the deck is reasonably sensitive to belt length.  Apparently, a 93-inch belt is optimal for the mower deck, whereas a 95-inch belt is optimal for the drive train.  A 92-inch belt is just a bit too short.

Secondly, the idler arm (20) vibrated due to wear in axle bushing (23).  This was solved by machining the idler axle bushing (23) true and fitting a 0.750 inch cylindrical sleeve to the idler arm (20), drilling out the idler arm to accept the cylindrical sleeve, and welding this sleeve to the idler arm.

Thirdly, one idler pulley (29) was incorrectly height mismatched to a deck drive pulley, requiring a new height bushing (30) to be fabricated.

Fourth, the belt guide (28) was too flimsy to adequately guide the mower belt.  I fashioned a quarter-circle cover with radial arc section to more positively guide the mower belt around this idler pulley.

Fifth, one idler pulley (16) needed an additional belt guide to prevent the mower deck belt from flying off when the mower deck was at its lowest position.  This took the form of a cylindrical spacer on top of the pulley axle tied to a right-angle piece of steel welded to this cylinder.  The right angle forces the belt DOWN and prevents the belt from binding on the upward tab of the idler arm at position (20) as shown above.  This may be a bit difficult to visualize, but it is essentially a mirror of the tab shown at position (20) above, with the tab angled DOWN instead of UP.

Sixth, the deck spacing wheels (44) needed to be replaced, but the sleeves on these wheels (43) were also worn and needed to be replaced with some accurately machined replacements.  The stamped metal original (43) sleeves only contributed to accelerated wear in the deck wheels.

After all this work, the mower operates better than new.  My only suggestion for anyone wanting to perform this repair is that I opted to buy replacement blade pulley assemblies (33) from an aftermarket supplier who indicated they were "compatible" with the John Deere original.  These were cast aluminum replacements instead of stamped steel and one of them cracked on first use.  While I was able to TIG weld it and turn it down to fit on the lathe, these parts are definitely inferior to the John Deere original.  If I had it to do over, I would have just replaced the bearings in the original assemblies or opted to machine out an entirely new assembly.

 

Contact Information:

Kevin Mark Klughart

Registered Patent Attorney, USPTO

3825 Leisure Lane, Denton, TX 76210-5589

tel: 800-353-1211 / 940-320-0580  -  fax 940-320-0581

Kevin@Klughart.com   email  -  web    www.Klughart.com

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