FOREWORD

This clutch is engineered specifically for use with Yamaha KT 100S kart engine in Jr and Sr Sportsman Can Muffler Classes. Follow the instructions in this manual for maintenance. This is a dry "direct drive" lock-up style clutch. This clutch is designed solely for organized kart racing and must not be used for play or industrial use.

Attention! - Dry clutches perform very well with low maintenance up to 8000 rpm stall speed. As you increase the stall speed above 8000 rpm the clutch maintenance will also increase. If you operate the clutch above 8000 you may need to service the clutch every race weekend.

APPLICATION

Junior classes with .600" restrictor and can muffler
Junior and Senior Sportsman classes with can muffler
Jr Formula Y

SPECIAL TOOLS REQUIRED

1. One 1 1/8" deep socket (available at most auto parts stores)
2. Clutch Spanner Wrench (Horstman P/N 330036)
3. Clutch Puller (Horstman P/N 304400)
4. Valve Lapping Compound (Available at most auto parts stores)
5. 5/16" Allen Wrench ("L" handle or socket style)
6. 9/64" Allen Wrench ("T" handle or "L" handle)
7. Torque Wrench

LAPPING CRANK TAPER

Before installing the Clutch it is wise to lap the tapered portion of the crankshaft and the tapered portion of the Clutch Hub. Lapping will produce a more precise fit. Place a small amount of coarse lapping compound onto the taper of the crank. Slide the Drive Hub assembly of the Clutch onto the crank and rotate it by hand until the two surfaces are 100% seated. Then wipe off the lapping compound with a clean rag.

INSTALLATION

1. Install Spacer (Item No. 1) onto crankshaft. Be sure the radius side of the spacer faces toward the engine. (See Fig. 1)
2. Apply a light coat of oil to the crankshaft.
3. Slide the Drum onto the crankshaft.
4. Insert the Woodruff Key.
5. Slide the Drive Hub assembly onto the crankshaft. Be sure the keyway in the Hub is aligned with the Woodruff Key. Rotate the Friction Disks to allow the outer lugs to fall into the channels of the Drum.
6. Install the Starter Nut (Item No. 12). Tighten to 350 inch pounds. NOTE: The Horstman Spanner Wrench (P/N 330036) is helpful in holding the clutch when tightening the Starter Nut.
7. Check end play. (See Fig. 2)
8. Check spring height (See Fig. 3)

END PLAY

When the Clutch is tightened securely to the shaft you should be able to spin the Drum freely. If the Drum does not spin freely, remove the Clutch and replace the Spacer with a new Spacer of appropriate width available from your Authorized Horstman Dealer. A temporary solution would be to grind some material off of the original Spacer. The recommended minimum clearance is .005" and the maximum is .015". (See Fig 2) If you have over .015" clearance the Clutch may not be properly seated all the way onto the shaft, or you may be using the wrong sized Spacer.

STARTING ENGINE & ENTERING TRACK

The Clutch is designed to permit easy starting with a battery operated Gun Starter. The Gun Starter should have a 5/16" hex drive. When starting the engine be sure to keep the brake engaged in order to prevent any sudden acceleration.

STALL SPEED

Proper stall speed adjustment will enable your motor to operate within its most efficient power band, which should provide the fastest lap time. A tachometer is needed to help you set the stall speed range for optimum performance.

CLUTCH ADJUSTMENT

The basic engagement speed of the clutch is predetermined by Levers that pivot in response to centrifugal force. The pivoting of the Levers is restrained by the six Compression Springs. A variety of stall speeds can be obtained simply by adjusting the spring tension.

FOR HIGHER STALL SPEEDS

Increase the preload on the six Compression Springs by turning the Spring Retainers clockwise.

1. Use caution as the clutch may be hot.
2. Insert a 9/64" allen wrench into each retainer and turn wrench clockwise 1/8 of a turn. NOTE: 1/8 turn of adjustment clockwise should raise the stall speed about 200 RPM's. Try to adjust all six retainers an equal amount.

FOR LOWER STALL SPEEDS

Use low tension springs or decrease the preload of the Compression Springs by turning the Spring Retainers counter-clockwise while following steps 1 & 2. Re-enter the race track and determine if you now have the desired stall speed. If not, return to the pits and repeat adjusting procedure.

ADJUSTMENT LIMITS (See Fig. 3)

The clutch is designed to work within adjustment limits. Do not exceed the limits or damage to clutch will occur.

Minimum: .270" Maximum: .340"

HELPFUL TIPS

1. Never check stall speed by engaging the brake while revving the motor. This puts excessive stress on the clutch components.
2. When racing in wet conditions lower the stall speed 300 to 500 RPM's to help prevent overheating.
3. Oil or grease bushing in drum before each track session.
4. Optional springs are available to raise or lower stall speed.

CLUTCH REMOVAL

1. Remove Starter Nut. NOTE: Spanner Wrench (P/N 330036) is helpful in holding the Clutch.
2. Thread optional Clutch Puller (P/N 304400) into Drive Hub and tighten until Drive Hub comes off Crank.
3. Remove Woodruff Key.
4. Remove Drum.
5. Remove Spacer.

DISASSEMBLING CLUTCH

1. Remove Jam Nut (Item No. 11) use 1 1/8" socket.
This Nut is Left Hand Threaded. Turn clockwise to remove.
2. Remove Coned Washer (Item No. 10).
3. Remove Lever Support (Item No. 7).
4. Remove Friction Disc (Item No. 5).
5. Remove Springs from Lever Support. Pressure Plate, Levers and Dowel Pins can now be removed.

MAINTENANCE AND REPAIR

The HDC-3 CLUTCH subject to heat and wear due to friction from high slip conditions. The Clutch must be properly maintained for optimum performance. Remove Clutch and inspect all components after each racing event.

1. Spacer

Look for cracks or excessive wear. Replace if necessary.

2. Drum

Inspect Bushing for excessive wear. Replace bushing if bore size is above.568. Oiling the chain before each track session will increase the life of the sprocket. Replace drum when teeth are worn to a sharp point. Chain adjustment should have at least 12mm of free play. An over tight chain or chipped chain causes immediate sprocket wear. Inspect slots in steel drum where friction disk lugs nest. When worn beyond .080" replace drum. (See fig. 4)

3. Friction Disk

The friction disk has a hard steel core with special friction material bonded to the surface. Replace when glazed or worn below .120" thick.

4. Pressure Plate

The pressure plate is precision ground on the surface that engages the Friction Disk. This surface should be checked periodically for warpage or a glazed condition. Replace if necessary. Also, check studs for cracks or loosening.

5. Drive Hub

Check for wear in the triangular area that comes in contact with the Pressure Plate. Check for cracks in keyway.

6. Levers

The pivot hole in the Lever is subject to stress due to frictional loading from centrifugal force. This causes the pivot hole to eventually elongate. Inspect the Levers for elongation of pivot hole whenever you rebuild the Clutch. Replace when severely elongated.

7. Dowel Pins

Replace after every five races.

8. Springs

Check for breakage and minimum free length of .470". Replace if necessary.

9. Spring Retainer

Replace every six races.

ASSEMBLING CLUTCH

1. Clean parts with disc brake cleaner. Disk brake cleaner comes in an aerosol spray can and is available at most automotive parts stores. Do not use gasoline!
2. Slide Dowel Pins into Levers.
3. Insert Pressure Plate into Drive Hub.
4. Place each Spring over a corresponding pressure plate stud. Screw a Spring Retainer clockwise on each stud, but do not tighten yet.
5. Install The Friction Disk.
6. Place the Lever Support assembly over the Drive Hub making sure you align the triangular drive lug with the recessed portion of the Lever Support.
7. Install Coned Washer.
8. Install the Jam Nut and torque to 550 inch pounds. Note: The Jam Nut is left hand threaded.
9. Now adjust the Spring Retainers to .320".
10. The Clutch is now ready to be installed onto the crankshaft. See the installation section of this manual.

FIGURES

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PARTS LIST

Note: HDC-3 clutches use one piece levers not shown in above diagram.

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Manual # 333339, rev 1, February 1999