The most important differences are found in the sprockets and drums: Vortex Flats uses the familiar needle bearing sprockets and drum designed by SMC about 24 years ago.   Vortex Threads uses a sealed, deep-groove ball bearing and has a screw-in connection with the drum. It was designed by SMC in 2013.

 

 

AGGRESSOR 2 Disc Engine Clutch Instructions

 

Vortex Threads One Disc Engine Clutch Instructions
Vortex Flats One Disc Engine Clutch Instructions

Vortex Threads Two Disc Engine Clutch Instructions
Vortex Flats Two Disc Engine Clutch Instructions

Vortex Threads Three Disc Engine Clutch Instructions
Vortex Flats Three Disc Engine Clutch Instructions

Although a two-disc clutch will get the job done, a three-disc clutch will operate at a much lower temperature. The wear rate of friction materials varies exponentially with temperature i.e. a three-disc clutch has about 50 percent more heat capacity than the two-disc clutch but possibly 100 percent more longevity. Consider too that the three-disc clutch costs only 8 percent more.

The added weight affects acceleration by less than .0003 second.

If the clutch engages/disengages several times per lap (an oval with short straights or a road course), then the disc clutch is well worth the money. Discs have a uniform temperature distribution and consequently have a uniform engagement rpm. The shoes in a rim clutch develop hot spots that cause the clutch to have a different engagement rpm every corner, every lap.

But, if the track is wide open and the clutch is used only at the start, then almost any clutch will do.

Save yourself some grief and stick to OEM parts. One sure way to go slower is to use a copycat sprocket. For example, Bully sprockets are wider than SMC sprockets and consequently cause a lot of unnecessary drag.

Get some new dowel pins from either SMC or Buller. The old ones are probably corroded and consequently a bit oversize. If you look closely at the pin holes in the two levers you will see big differences. The original lever has a punched hole that is large and rough. The hole in the SMC lever is drilled and reamed to a closer tolerance.

The Tomar lever plate has a slot width of only 0.175 inch and a pin groove diameter of 0.156 inch. The SMC roller levers have a thickness of 0.250 inch and a 0.250 pin diameter. It would take a lot of machine work on the Tomar lever plate to make all the parts fit, but it is possible.

There is no minimum thickness. (New discs are .125 inch thick.) SMC clutches are not sensitive to air gap. A lot of perfectly good discs are discarded because they look worn out. APPEARANCE IS NOT A CRITERIA. Heat and pressure will eventually change the frictional properties of the disc. How well did the discs perform on the race track? That determines when to replace.

If you start to notice the engagement RPM being lower and lower over time, then change the springs. Make sure the pivot pins and hole in the weights are kept clean.

Vortex clutches have torsion springs connected to the levers instead of compression springs connected to a pressure plate.  This allows extremely efficient and precise control of the levers which causes Vortex clutches to lockup in a shorter distance.

1956  Rim Clutches

Sometime called a shoe clutch, this first-generation kart clutch was noted for its simplicity and consequential low cost.  The friction material had a curved shape that rubbed against a drum.  In the late 1970’s springs were added to improve acceleration characteristics but the rim clutch still suffered from rapidly changing temperature gradients that caused irregular engagement speeds.

1978  Disc Clutches

Gilbert Horstman introduced the second-generation kart clutches which included a flat friction surface that minimized temperature variations and allowed the clutch engagement speed to be much more predictable.  It was mechanically more complex and subsequently more costly.

1995  Soft-start Disc Clutches

Third-generation kart clutches connect springs directly to the levers.  There is no pressure plate.  This simplified clamping mechanism engages the engine without “bogging”.  Patented in 1995, 2001, 2003 and 2015 by Thomas Fehring.

• The screw-in connection is much stronger than the older design. This is especially beneficial to the drum half of the connection.  Aluminum drums can easily stand up to big engines.
• The ball bearing has a thrust capacity. It prevents the sprocket from wobbling on the crankshaft which wastes energy and accelerates wear between the drum and clutch discs.
• The ball bearing fits sprockets of all sizes (including #35-9T) and pitches (#35, #25, #219 and #428).
• The bearing has seals that exclude dirt and retain grease.
• Fewer parts. There are no thrust washers, machine screws or external retaining rings.

When the flag drops and you stomp the right pedal, the acceleration from a hard hitting clutch feels awesome. Your head snaps backward, the wheels spin and you saw the steering wheel back and forth to keep the kart in the groove. Wow, that’s fast! Or was it?

Let me give you an engineer’s perspective.

Engine Dynamics

Your tachometer indicates only the average rotational speed of the engine. But if you had a sensor that could measure instantaneous rotational speed, you would see that the crankshaft is turning fastest during the expansion stroke, slows down a bit for the exhaust stroke, slows down more for the intake stroke and then really slows down for the compression stroke. Pushing out burned gases, drawing air into the cylinder and compressing the air requires work. That is why the engine slows down during three strokes. Only the expansion stroke after the spark plug fires produces energy and increases rpm. The average rotational speed for the whole cycle may be 4000 rpm but the instantaneous rotational speeds for the individual strokes might be 4095, 4020, 3990 and 3895 rpm.While the piston, connecting rod, crankshaft, flywheel and clutch are moving, they possess energy or the potential to do work. The amount of energy varies with their speed.An engine that is not running has zero energy. It is necessary to get energy from an outside source (muscles or batteries) to get the cycle started. At idle speed the engine can just barely run by itself because the expansion stroke adds energy at the same rate as the other three strokes consume energy.

At higher speeds, the expansion stroke adds energy faster than the other three strokes consume energy hence there is a surplus of energy that can be used to move the kart and driver down the road.

Clutch Dynamics

The throttle determines how much energy the engine produces, but it is the clutch that determines how much energy gets to the axle and when it happens. Like the exhaust, intake and compression strokes, the clutch subtracts energy from the system. But unlike those strokes, the clutch does not extract energy with every turn of the crank. There are times when the engine produces a surplus of energy and times when it does not. The purpose of the clutch is to react to the engine’s energy level and siphon energy at the appropriate time and rate.

Clutch action is a function of rpm. It engages the engine at high rpm and disengages at low rpm. When the engine is turning slowly as in starting and idle, no extra energy is available.

The clutch senses this low speed, disconnects from the engine and takes zero energy from the reservoir in order to prevent the engine from stalling. When the engine is turning at high rpm, there is an excess of energy and the clutch senses the high speed and consequently connects itself to the engine which takes energy from the reservoir to move the kart.

Pulling Hard versus Hitting Hard

The “hard hit” clutch accelerates abruptly at first. It throws your head back but then acceleration tapers off quickly. The clutch is very popular because it has been around a long time and is fun to drive. And if every driver has one it is neither an advantage nor disadvantage.

The “hard hit” clutch takes energy from the reservoir as quickly as possible. But the aggressive nature of such a clutch also makes it slow to realize that it is stealing energy necessary to power the exhaust, intake and compression strokes. After the initial impact, the engine slows down a few hundred rpm because it just lost much of the energy needed to keep running. The engine needs time to recover but the clutch does not get the message immediately. It continues to drain energy and in extreme cases causes the engine to quit.

The “hard hit” clutch has another problem – it spins tires. Spinning tires look impressive and feel good but accelerate the axle not the kart. Instead of moving the kart forward, the energy from the engine is propelling stones and dirt backward and heating the tires. Now if your opponent’s tires slip less or not at all, then your loss is his gain. His engine moves the kart forward, your engine throws stones backward.

In contrast, the “hard pull” clutch accelerates at a constant rate. It feels much smoother and
perhaps a little less fun to drive. This clutch has not been around very long. A technical problem had to be solved to make such a clutch possible and for a long time we did not even know that a problem existed. Computer data acquisition systems provided evidence – hysteresis. Part of the solution was a faster reacting mechanism.

The “hard pull” clutch takes energy from the reservoir at a steady rate. It extracts surplus energy from the energy reservoir and nothing more. There is always adequate energy to drive the exhaust, intake and compression strokes. The engine does not bog down because the clutch is a very cooperative partner. The acceleration may be a bit less but it lasts a lot longer.

The “hard hit” and “hard pull” clutches are just like the hare and tortoise story. One jumps out quickly then takes a nap while the other starts off slowly but advances persistently and eventually wins.

SMC highly recommends cleaning clutch discs mechanically NOT chemically. We have found that brake cleaner and other chemicals are inadequate for removing dirt and other fine particles packed into the tiny voids. A stainless steel utility brush aka plater’s brush with a wire diameter of .006 is ideal for removing the hard-to-get-at dirt. Try this yourself and see the difference with a magnifying glass. Better yet, put a piece of white paper under the disc while brushing it. Check out the dirt!

The friction material is very porous and consequently works very well as a dirt collector. Once the voids are filled and packed, the dirt starts to act as a lubricant (think tiny ball bearings) and causes the clutch to slip for a greater distance.

Clutches like tires get dirty quickly. It is important to clean clutch discs every race weekend if not every heat if you want maximum acceleration. 

Pictured above is a NEW clutch disc. The left side has not been brushed and the right side brushed with a stainless steel utility brush. Even a new friction disc benefits from a light brushing. 

Pictured above is a USED clutch disc. The left side has not been brushed and right side lightly brushed with a stainless steel utility brush.

Vortex’s patented mechanism accelerates faster.

Vortex torsion springs are connected directly to the levers.
(Not the pressure plate.)
This extremely efficient and precise control of levers causes
Vortex clutches to lockup in a shorter distance.

Pit side advantages:

• Vortex springs are naturally more accurate. Blueprinting is not required.
• RPM adjustments are simple. Just relocate spring ends into another hole.
• RPM adjustments are fast. There are no spring heights to set.
• RPM adjustments are precise. All six springs apply perfectly identical loads.
• There are no air gap limitations. You get more races between rebuilds.
• Maintenance and repairs are easy. Say ‘goodbye’ to your clutch re-builder.

Professional performance and heavy duty parts:

• • Vortex torsion springs for mechanical efficiency
  • SMC Roller Levers for mechanical efficiency
  • New anti-wobble sprockets
  • New lightweight drum
  • New 12 tab clutch disc
  • New high strength steel drive hub
  • Click here to see video on Vortex Technology

SMC Vortex Engine Clutch Applications

ENGINE	Vortex 1 Disc	Vortex 2 Disc	Vortex 3 Disc
Briggs Flat Head
Briggs Animal
Honda *use Silver Springs for Two Disc
Honda Clones *use Silver Springs for Two Disc
Briggs World Formula
Burris Yamaha
Four Stoke Open
Jackshaft

If you plot the engine’s torque vs. rpm curve and the clutch’s torque vs. rpm curve on the same graph, the two lines will cross. At that point the clutch and engine are in equilibrium. The equilibrium point defines the engagement rpm. At lower rpm the clutch slips because the engine produces more torque than the clutch can accommodate. At higher rpm the clutch is locked up because it can handle much more torque than the engine can produce. If you modify the engine by changing cam, jets, bore, stroke, valve position, fuel type et cetera, the shape of the engine’s torque vs. rpm curve will change. If you modify the clutch by changing spring position, the shape of the clutch’s torque vs. rpm curve will change. When either curve changes shape, the equilibrium point moves. The table is merely an estimate of where that point occurs for various combinations of engines and springs. See Spring Chart for Estimated Engagement RPM.

Spring Chart – Estimated Engagement RPM

The Vortex clutches are different from other clutches in many respects. One important difference is the clutch is built in two parts – the clutch assembly and the sprocket assembly.

The Vortex Threads and Vortex Flats use essentially the same clutch assembly. It consists of springs, levers, rollers, drive hub, discs and drive plates.

The difference is in the sprocket assembly. The Vortex Flats is built with an old fashion sprocket (flats and retaining ring) and spins on a needle bearing. The Vortex Threads is built with a high precision ball bearing and a screw-in sprocket.

The advantages of the Vortex Threads are:

• An extremely large (200-300%) improvement in disc and drum life (abrasive wear between disc tangs and drum slots)
• Stronger connection between the steel sprocket and aluminum drum (especially important for the more powerful engines)
• Ball bearings in all sizes including the 11 tooth sprockets (no bronze bushings)
• Sealed bearings that exclude dirt and retain grease (less maintenance)
• Fewer parts. There are no thrust washers, machine screws or external retaining rings.
• A small improvement in acceleration especially with 15 tooth sprockets and larger where the bearing can be centered exactly in line with the chain.

It is possible to retrofit a Vortex Threads sprocket assembly to a Vortex Flats clutch assembly with a simple change in mounting hardware.