FORWARD

The Horstman Axle Clutch is engineered solely for organized kart racing with 2-cycle engines up to 150 cc. It should not be used for any other type of vehicle or purpose. The following instructions have been prepared to help you get the best performance and value from the clutch.

Model AX-4046 is for use with any gear ratio from 4.00:1 to 5.60:1

OIL FILL

The Horstman Axle Clutch must have oil in it at all times. Before using the clutch, add 4 ounces of Horstman Clutch Oil. Four ounces will bring the oil level to slightly over half full. Oil filling and draining can be done with the clutch mounted on the axle. To add oil, remove any two adjacent steel plugs (P/N 111100) near the top of the clutch. Insert the bottle through the hole in the aluminum bolt (P/N 111200) and squeeze gently until 4 ounces of oil are in the clutch.

The reason for removing two steel plugs is so that air can escape when the oil is going into the clutch. Replace the two steel plugs when finished. Caution: Do not overfill. (See Fig. 1)

INSTALLATION

Do not force the clutch onto the axle. Remove any burrs or nicks from the axle and file the key until the clutch slides easily. A light coat of anti-seize compound on the bore of the clutch hub will help prevent fretting corrosion between the clutch and the axle. The clutch is held in place by two locking collars, one on each side. The clutch works in either direction of rotation, so the only concern when mounting the clutch is having easy access to the spring adjusting screws. Therefore, mount the clutch with the aluminum bolts (P/N 111200) facing away from the closest tire.

THEORY OF OPERATION

The Horstman Axle Clutch uses centrifugal force to transmit the engine=s torque to the rear wheels. Spring pressure in the clutch can be adjusted to counteract the centrifugal force until the engine reaches its powerband. Then the clutch hooks up and stays hooked up until the engine drops below its powerband.

Since the clutch is mounted to the axle, the gear ratio determines the clutch RPM in relation to engine RPM. Notice in the example below that at 9500 engine RPM the clutch RPM varies considerably with different gear ratios.

The faster the clutch RPM, the greater the centrifugal force, therefore the stronger the spring pressure necessary to counteract the centrifugal force. This is why we have strong springs (color black) for gear ratios 4.00:1 to 4.89:1 and weak springs (color yellow) for gear ratios from 4.90:1 to 5.60:1.

STALL SPEED

Stall speed is the RPM that the clutch hooks up solid. Stall speed is commonly called clutch slip in kart racing. Adjusting the clutch for more slip is actually raising the stall speed. Adjusting the clutch for less slip is lowering the stall speed.

PRE-SETTING STALL SPEED

Before going onto the racetrack, it is wise to have the stall speed set as close to race ready as possible. The reasons are obvious: first, you save time, and second, you reduce the risk of having the clutch overslipping so much that subsequent heat build up destroys the clutch discs. Stall speed can be set with the clutch mounted on the axle.

HOW TO USE THE ASTALL SPEED CHART@

1. Match the gear ratio you are going to use with the closest ratio on the chart.
2. Use the springs recommended.
3. Adjust the springs to the Agage measurement@ recommended.

This should give you a stall speed of 9500 RPM +/- 100, which is a good pre-track starting point.

Note: The Model AX-4056 come from the factory with the black springs installed, therefore, if you are going to run a gear ratio above 4.90:1, it will be necessary to switch to the yellow springs. Refer to the HOW TO INSTALL SPRINGS section for instructions.

*Disclaimer: The stall speed chart are intended as a guide only. Due to great differences in engine power curves, the only accurate clutch adjustments are made by track testing with the aid of a tachometer.

GAGE MEASUREMENT

Gage measurement is the distances from the top of the aluminum bolt (P/N 111200) to the underside of the gage tool (P/N 114500).  (See Fig. 2)

HOW TO PRE-SET STALL SPEED

Stall speed can be set with the clutch mounted on the axle.

Tools Required:

• 3/16" allen wrench (supplied with clutch)
• 5/32" allen wrench (supplied with clutch)
• Horstman Gage Tool (P/N 114500 supplied with clutch)
• Dial calipers or feeler gages

1. Rotate clutch until the number 1 appears at the top of the clutch.
2. With the 3/16" allen wrench, remove the steel plug (P/N 111100) from the aluminum hex bolt (P/N 111200) that is located directly below the number.  (See Fig. 3)
3. Insert the gage tool into the hole in the aluminum hex bolt.
4. Take the gage measurement.  (See Fig. 2)
5. Refer to stall speed chart for recommended gage measurement and compare it to the measurement that you just took.
6. With the 5/32" allen wrench, turn the adjusting screw (P/N 111400) until the gage measurement recommended on the chart. Note: turning the adjustment screw clockwise decreases the gage measurement, and turning the adjustment screw counter clockwise increases the gage measurement.
7. Replace the steel plug.
8. Rotate the clutch until the number 2 appears at the top and repeat steps 2 through 7.
9. Rotate the clutch until the number 3 appears at the top and repeat steps 2 through 7.
10. Rotate the clutch until the number 4 appears at the top and repeat steps 2 through 7.
11. Rotate the clutch until the number 5 appears at the top and repeat steps 2 through 7.
12. Rotate the clutch until the number 6 appears at the top and repeat steps 2 through 7.

If you have followed the instructions properly, all six adjustment screws are now the same height. This enables the six compression springs that are connected to the adjustment screws to exert equal force. This is a must for top performance and consistency.

ON TRACK TESTING

Assuming that you have completed the AHow to Set Stall Speed@ section of these instructions, track testing can be accomplished.

Go onto the track and observe performance when accelerating out of the tightest corner, because if the clutch works well there, it will work well on the other corners.

If the engine bogs, you need more clutch slip. If the engine is over-revving of the tight corner, it means the clutch is excessively slipping, therefore you need less clutch slip. The trick to winning performance is to set clutch slip at the lowest RPM that won=t bog the engine.

For more clutch slip: Dial clockwise ... 1/4 turn = 150 RPM. Adjust the six screws equally.
For less clutch slip: Dial counter clockwise ... 1/4 turn = 150 RPM. Adjust the six screws equally.
Gear ratio changes: Higher numerical ... dial counter clockwise 1/8 turn per one rear tooth. Example - from 18/85 to 1884.  Lower numerical ... dial clockwise 1/8 turn per one rear tooth. Example - from 18/85 to 18/84.
Pipe changes: Shorten flex ... dial clockwise 1/8 turn.  Lengthen flex ... dial counter clockwise 1/8 turn.
Air Density: Drop 5 points or more ... dial counter clockwise 1/8 turn.

Tuning Tips: Document the clutch setting and gear ratio for each track, so that the next time you go to the track you can dial the clutch slip ahead of time.

HOW TO INSTALL SPRINGS

Springs can be changed with the clutch mounted to the axle.

1. Rotate the clutch until the number 1 is at the top of the clutch.
2. Remove the aluminum bolt (P/N 111200) that is located below the number.  (See Fig. 4)
3. With a 5/32" allen wrench, remove the adjusting screw, the spring retainer, and the spring. (See Fig. 5) Note: The springs fit firmly in the clutch, therefore a piece of heavy-gauge wire with a small hook on the end is helpful in getting the springs out.
4. Install the new spring with the proper retainer and adjusting screw.
5. Refer to STALL SPEED CHART for proper adjustment.
6. Clean the aluminum bolt (P/N 111200) then coat the threads with silicone sealer and tighten to 180 inch pounds.  (See Fig. 6)
7. Rotate clutch until the number 2 is at the top of the clutch, and repeat steps 2 through 7.
8. Rotate clutch until the number 3 is at the top of the clutch, and repeat steps 2 through 7.
9. Rotate clutch until the number 4 is at the top of the clutch, and repeat steps 2 through 7.
10. Rotate clutch until the number 5 is at the top of the clutch, and repeat steps 2 through 7.
11. Rotate clutch until the number 6 is at the top of the clutch, and repeat steps 2 through 7.

MAINTENANCE

The following maintenance recommendations will help you obtain many trouble-free hours of clutch performance.

EVERY RACE: Check the oil lever, and add oil if needed. Check the (P/N 111100) and (P/N 111200) bolts for tightness, because if they become loose, oil will escape, which can cause major damage to the clutch.

EVERY THREE RACES: Change the oil. Use only Horstman DXL disc clutch oil.

EVERY YEAR OR 40 RACES: Remove the clutch from axle and disassemble, clean and inspect all parts for wear or damage. Inspect friction discs. If worn under .090 or glazed, replace them. Inspect floaters, if they are scored or worn, replace them. Check the seals, if brittle or damaged, replace them.

Warning: If you run the clutch without oil, the friction discs will burn or glaze, and the floaters may warp. Immediate disassembly of the clutch would be recommended for close inspection.

Top of Page

HOW TO DISASSEMBLE THE CLUTCH

1. Remove from axle.
2. Drain oil.
3. Remove sprocket.
4. Remove the six (P/N 113200) socket head cap screws.  (See Fig. 7)
5. Put on a sprocket or sprocket guard.  (See Fig. 8)
6. Tap the back side of the sprocket until the two case halves come apart.  (See Fig. 9)
7. Lay the clutch halves on a clean workbench and remove the axle hub, then the floaters and friction discs.
8. Finally, remove the pressure plate assembly.

Caution: Do not use solvents to clean the friction discs. Simply wiping them with a clean rag is adequate.

HOW TO REASSEMBLE THE CLUTCH

1. Lay main housing in front of you with cavity up.
2. Insert the six drive pins into the slots in the main housing.
3. Insert the pressure plate assembly into housing.
4. Insert the axle hub into the housing until it is completely through the bearing and seal.
5. Install a friction disc.
6. Install a floater plate.
7. Install a friction disc.
8. Install a floater plate.
9. Install a friction disc.
10. Install a floater plate.
11. Apply silicone sealant to the outer edge of the main housing.  (See Fig. 10)
12. Install sprocket housing ... be careful not to damage the seal.
13. Line up the holes in the sprocket housing with the holes in the main housing and install new (P/N 113200) socket head cap screws. Caution: It is mandatory that you use only grade 8 or better bolts, and they must be 1/4-20 x 1-3/4" long. Shorter bolts will not hold properly, and longer bolts will bottom out, causing damage to the clutch. The reason we recommend using new bolts is that these six bolts take all the force when the clutch engages.
14. Put 4 ounces of oil into the clutch.

FIGURES

Top of Page

PARTS LIST

* For improving performance on shorter tracks requiring a gear ratio above 5.00:1 thru 5.60:1

AXLE COMPLETE CLUTCHES

Top of Page

Manual # 110000, rev 1, November 1998