Have you ever wondered…
Friends call me Tom. I am a husband, father, grandfather, mechanical engineer, Air Force veteran, motorcyclist and racer.
Motor racing was one of my hobbies. It all started by accident in August, 1969 when three of my college buddies said, “Gather up some beer and a sleeping bag because we’re going away this weekend.” I was happy to go on vacation and did not bother to ask where or why. As we were heading north on I-71 out of Cincinnati, I figured we were headed to Woodstock. Wrong! We camped on the infield at the Mid-Ohio racetrack and watched a Can Am race. Bruce McClaren, Denny Hulme, Mark Donohue, Peter Revson and Jim Hall were racing unique cars with unlimited engines! That’s the day I got hooked on motor racing. Had we gone farther up the road, Jimi Hendrix might have hooked me on rock-n-roll instead.
A short time later I joined the Sports Car Club of America (SCCA) and started autocrossing. I converted to kart racer in 1978.
Although I was having fun on the kart tracks, I was frustrated in the pits because those old clutches were fragile and inconsistent. So I designed and built my own clutches from scratch with technology acquired from my engineering world. I’m not a great driver, but I started to win races. My friends quickly figured out where my sudden advantage came from and asked me to build clutches for them. Then it snowballed.
I started Structure Mechanics Corporation in 1983. Originally it was a consulting business that solved complex stress and vibration problems. I employed mechanical, civil and aerospace engineers to work on everything from surgical instruments to jet engines to spy satellites.
By 1989 clutch development was more fun than rocket science. I laid off the engineers and sold the office building. I kept the state-of-the-art aerospace experience, high-tech industry contacts and the computers. I purchased CNC machinery, patented four clutch designs, rented industrial space and focused on racing clutches.
- SMC clutches are used in North America, Europe, Asia, South America and Australia
- SMC is kart racing’s second oldest manufacturer of disc clutches. (Horstman Corp. is first.)
- SMC manufactured approximately 4,000 axle clutches. Most are used on road courses such as Daytona Motor Speedway and Mid-Ohio.
- SMC has produced tens of thousands of engine clutches. I’ve lost count.
- Sprockets and clutch discs designed by SMC in 1996 are now used by virtually all manufacturers of kart clutches.
I wish I had time to design a chassis but good clutch design consumes all of my working hours. I am still searching for the perfect clutch. SMC’s computers and dynamometers are always loaded with prototype clutches. Faster clutches are forthcoming. Bookmark this site.
This company is run by an engineer not an accountant. I measure success with trophies instead of dollars. I sell the best clutches not the most clutches. SMC’s longevity is a result of a large R&D budget and a single minded pursuit of maximum clutch performance.
If you are a past or present customer – Thank you for your business.
Everyone else – thanks for visiting this website.
Good luck to all.
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.
- 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.
SMC Vortex RED and Vortex BLACK Engine Clutch Applications
The most important differences are found in the sprockets and drums:
Vortex BLACK uses the familiar needle bearing sprockets and drum designed by SMC about 20 years ago.
Vortex RED uses a sealed, deep-groove ball bearing and has a screw-in connection with the drum. It was designed by SMC in 2013.
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 RED Technology
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.
Sprockets connect to chains. Gears connect to other gears. Drivers wear helmets.
Clutches should be set to the engine’s maximum torque rpm. If you don’t know the peak torque rpm, set the clutch to a low rpm. Acceleration will be lazy but you’ll do no damage. Adjust upward in small increments. If you don’t know the peak torque rpm and set the clutch too high you will have lazy acceleration and a fried clutch. The two biggest reasons why clutches overheat are wrong engagement rpm and bad sprockets.
Sprocket bearings must be clean and properly lubricated. Dirty or dry rollers skid rather than roll and cause drag on the clutch and generate heat. Chlorinated brake cleaner and Mobil 1 Synthetic Grease are recommended. Read FAQs Sprocket Bearing Lubrication (Update: this answer does not pertain to the new SMC Vortex RED Sprockets.)
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.
Axle clutch because big engines need big clutches.
It is extremely important to properly clean and lubricate the sprocket bearing. A bearing that is dirty or dry will waste horsepower because the tiny rollers inside the bearing skid rather than roll. That increase in friction causes a lot of heat that diminishes acceleration.
Clean the sprocket bearing with chlorinated brake cleaner. It’s convenient to use, inexpensive, an excellent solvent, dries quickly and it’s non-flammable.
Do not use acetone or non-chlorinated brake cleaner. They pose a serious fire hazard.
Apply a small quantity of Mobil 1® Synthetic Grease to the needle rollers. This grease is typically used for wheel bearings on cars with disc brakes. It has a 350 degree temperature capacity, resists moisture and contaminants. It’s inexpensive and available at most auto parts stores.
Do not use Vaseline®. It is a skin lubricant not a metal lubricant and melts at only 165 degrees.
Not if you look closely. There are important differences.
First we have to talk about the bearing. The bearing is composed of rollers, a cage to align and separate the rollers and a hardened steel shell to hold everything together. The shell is the critical part because of the way it is manufactured. It starts as a flat piece of steel that is stretched into a cylindrical shape. After the cage and rollers are inserted the edges of the shell are bent for containment. Unfortunately it is impossible to bend steel into a perfect cylinder. Roller bearings are not round! See for yourself. Press a bearing out of a sprocket and measure its diameter in several different places. But there’s a solution. The shell is very thin and will conform to the shape of the much beefier sprocket. If the sprocket bore is round, the bearing becomes round also when pressed into place.
Small sprockets like the chains that connect them must be hard and strong. It is very difficult to cut sprockets from a hardened steel bar, therefore sprockets are machined from annealed (soft) steel then hardened. Steel becomes hard when it is heated to a high temperature (1500 degrees plus or minus according to the alloy) then dropped into a tank of water or oil. Heat treating solves one problem but creates another. Thermal shock from the rapid cooling causes steel to warp slightly. The sprocket bore is no longer round or straight. If a bearing is pressed into this sprocket, it will not be round and straight either. Furthermore, the interference fit between bearing and sprocket is inferior and the bearing will probably fall out during the race.
There are two solutions to this problem. One right. One wrong. The wrong solution is to machine the sprocket with a snap ring groove to contain the sprocket. Wrong because it does not solve the bore inaccuracy problem. The bearing stays in place but does not turn freely. The drag generates heat that wastes the engine’s power. The right solution is to re-cut the bearing bore after heat treatment. Simply hone the sprocket in the same way one would hone an engine’s cylinder. Most manufacturers skip this step to save money. Big mistake. For pistons and bearings alike, a precise geometric shape is the key to speed and acceleration.
Three indicators of racing quality sprockets:
- I. D. Finish – “Cross-hatching” on the sprocket’s inside diameter indicate it has been “blueprinted”.
- Uniform Inside Diameter – Measurements at all points should be within a few ten-thousandths of an inch.
- Width – 0.750 inch. Snap ring take up additional space. Anything wider is a “Fun Kart” sprocket.
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.
“James Crow wins first night out on the SMC Aggressor Clutch winning both heats and main in Jr3. I finished 2nd after starting 3rd with the Halbert Performance Clutches, SMC Aggressor Clutch setup. Was bad fast and jumped every one on the starts. I also had up to 5 people interested and sold 2 more at the track as I have to order them this week.”
Charles CochranApril 25, 2017
“Thanks so much!! Ordered the parts I need and even ordered an extra clutch for a spare. My son uses it to race Mini Snowmachine on a Polaris 120. He’s been kicking some butt up here in Alaska.(Vortex RED Engine Clutch, 2 Disc)UPDATE: April 25, 2017“Julien placed second for the season for his total points in the Mini Snowmachine 206 Class. That was his first year in that class.”
John LegardaAlaska, March 30, 2017
3rd Place (1st among USA schools)
Shell Eco-marathon Americas 2016
April 22-24, 2016“A big focus for the team this year was a highly efficient and reliable drivetrain. SMC’s Vortex Red clutch gave us the tuning capability to match our engine’s highly specific operating conditions, while providing consistent engagement characteristics and 100% reliability.”On to the next one…Best Regards,
Dorian CappsApril 28, 2016
Jr. Sprint Class Winner
May 9, 2015
San Diego, California
“My son Kaden and I wanted to thank you for making a great product and all your feed back.”
Note: Kaden was using a SMC Vortex RED 3 Disc Engine Clutch.
Ken McKownMay 9, 2015
Lonestar Kart Nationals
Payton Pierce qualified 8th. He finished 2nd in his first heat and won the feature by over a half lap! He raced the Outlaw Cage Modified class running a PSE modified Briggs Animal. Payton used a 3 disc Bully with SMC Roller Levers prepped by David Martin at Martinbuilt Clutches.
“My son Devin Dowell is 17. He has been racing dirt ovals with 2-Disc Vortexes for 2 years now in Stock Flathead & Stock Animal & Stock Clone Engine classes. Racing in the North Carolina King of the Clay series & several local tracks: Wood Leaf Speedway & Coleridge Speedway in North Carolina. We Find the 2-Disc Vortex to be a good consistent & reliable clutch in the classes we run. With the new Roller Levers from SMC, the Vortex Clutch also seems to work really smooth. We like the silver springs in the third hole on our 2-Disc Vortex in Stock Flathead & Stock Clone, and when we Race Stock Animal we like the black springs on the Vortex in the third hole seems to work really well. Just keep the clutch clean after each weekend of racing by blowing the dust off and wiping the basket clean. The only problem I see in Dirt Racing is about once a month the tabs on the weight levers rust a little bit and need to be sand blasted with the hub. But overall the clutch works real well from what I have seen in oval racing.”
“Good luck to everyone racing SMC clutches & products.”
Michael & Devin DowellWelcome, NC, August 2011
Indiana State Champion Open Class
“We recently purchased two of your new three disc clutches for our brand new wedge body twin F200 outlaw go kart,we just got these in time for the Indiana State Championship race held Sept 2nd-4th, 2011 in Crawdfordsville, at Ben Hur Speedway. We feel the new roller clutches were instrumental in us winning the State Championship Outlaw class for 2011. We may very well switch our other outlaw kart over to the same clutch soon for the Indoor Series at Duquoin Il for 2011/2012.”
Cecil GrubbWashington, IN, September 2011
2011 WKA Mid-Atlantic Series Junior Sportsman 1 Heavy Champion
“I have used your clutches on my son’s kart since he started racing four stroke racing. This year we upgraded to the new roller levers and won the WKA Mid-Atlantic Series Junior Sportsman 1 Heavy championship. Apart from the speed, I like how easy the clutch is to adjust and maintain.
Spencer, Bandit , GT Machines (Dave Koehler) and an SMC Roller Lever clutch were an unbeatable combination in 2011.”
Guy PattersonHarrisburg, PA, 2011
“Here are a pictures of my daughter Charlotte who won the pre-final and final at our last club race in Ottawa, Ontario Canada last weekend (Sept. 2011). We have been running the dragonskin clutch for 7 years and so does all the club members.
I bought a Vortex clutch (non roller style levers) a couple of years ago but could not fit it on either my kids kart due to it’s size and the way we had the seat positioned, would clear the engine or seat, so it sat in the trailer for 3 years. This year we became CRG dealers and Charlotte wanted to try one out. Bolted a new LO 206 Briggs and off to the track we went.
Engine break in fine. Start pouring it on and clutch fails. Stick another Draggonskin on, snap the key way……..out of clutches……Let’s try this thing that’s been bouncing around the trailer for a couple of year. To our amazement, we were faster just by bolting the Vortex on. After a half dozen races we realized this thing (the Vortex) is amazing, very little to maintain, easy to set up and change engagement, release and engagement are precise and consistent.
It’s been our little speed secret until last weekend when other racers noticed it at tech when Charlotte lined up for a tear-down. Awesome product, reliable, cheap to maintain and fast out of the box.
Daytona Road Racing Championships
Daytona Beach, FL
Junior Animal Sprint Heavy Champion
“Just a sincere “Thank You” to SMC for an incredible clutch. My son won Jr. Animal Sprint Heavy at Daytona yesterday with the new Roller Lever single disc Vortex. And the best part….we didn’t have to touch the clutch the whole week !!! Not one single adjustment was necessary !! This bulletproof clutch let us concentrate on his driving and the chassis. What an amazing piece !!! Thank You !!!“
Don DelaneyTuscaloosa, Alabama, December 28-30, 2011
Norwalk Karting Association, Norwalk, CT
2011 Sprint Senior Raptor Class Champion
2011 Nutemeg Kart Club – 2nd place points finish in Flat Kart Clones
“Aside from the fact that the Vortex clutch is extremely durable and almost indestructible, it is light and engages smoothly so it will not spin the rear tires. From a mechanic’s point of view it is the easiest clutch to rebuild and maintain. There is no need to measure spring heights for rpm engagement, the five adjusting holes make it a snap to set up. You can rebuild this clutch in virtually seconds. The rebuild kit comes with clutch discs, drive plates and screws to do the job. There is no need to send the clutch out. Even the beginner dad or mechanic can do it. This clutch powered my son to his 2011 Championship. I would not use anything else but Vortex!”
Spring Nationals of the
Midwest Chase’n Race’n ProKart Tour
P&R Photos Image Solutions
“I qualified 19th for the Pro Animal feature paying $1000 to win. In the 20 lap feature, I passed 18 karts with the help of only one caution to take the win. I was on a 2007 Phantom Icon racing everyone else on 2012 Tritons, Impulses, and other karts. I was using a two disc Vortex Roller Lever clutch. I ran Animal 340 and Animal 375 also that day. I won Animal 340 and placed 6th in Animal 375.”
“The clutch performs perfectly race after race. Running an eighteen tooth sprocket really works the clutch hard but the engagement was always smooth. Even after a bunch of caution laps it never overheated. It’s nice to know I don’t have to worry about the clutch chattering or slipping unlike others I have had in the past. After making the switch to a two disc Vortex Roller Lever clutch I won’t ever change again. It’s simple to work on and setting the engagement can easily be done at the track with common tools and no guess work. Thanks SMC for a great clutch to put my Faster Motors power down!”
Branden ZinserApril 2012
Purple Plate Novice Class
Mid Michigan High Bank Nationals
Owosso Kart Speedway
“We got everything you sent last week and got Nicholas’ kart back together and headed out Friday afternoon to give it to em. The new clutch gear helped a ton. Still having trouble with our tach, but I think I’m close based on how he’s running against the other karts.
We took second in both heats and won the feature! It was his fifth racing, in his life, never drove a kart before. 🙂 It’s an amazing feeling to watch your child grow and evolve on the track and hearing the crowd cheering for him (they’ve watch him go from getting lapped several times to a feature win in just over a month) was icing on the cake. I’m not sure who was more proud of that trophy, him or me.
Ever since the first time I spoke with Tom and bent his ear for a half hour asking questions and discussing children’s racing, everyone at SMC has been more than helpful and a pleasure to deal with. We have many years of racing ahead of us and I am sure that every kart we campaign in the future will be running a SMC clutch.”
Rikk KolaczAugust 31, 2012
2012 Carolina Maxxis Kart Series Winner
2012 Maxxis Nationals
Thunder Valley Motorplex, Neeses, SC October 12-14
JR1 Lite Champion
2012 King of the Rock points championships in both JR1 and JR2
18th annual Thanksgiving Thunder
Jr. Big Dog Championships
November 22nd-24th 2012
Georgia Karting Complex
Jr. Big Dog Purple Plate Winner
“We have been using the single disc Vortex clutches for 3 years now. In 2010 my son, Jeremy Steele started kart racing in the Chase’n Race’n kids class. We won 23 races that year at 4 different tracks and one points championship. The 2011 season we moved up to purple plate/JR1 and had another very good season winning 17 races, another points championship and picked up wins at tracks we had never been to.This year we have ventured out to bigger races picking up a Carolina Maxxis Series win, had VERY strong runs at the JR Maxx Daddy race and went on to win JR1 Lite at the 2012 Maxxis Nationals. Then we ended the season winning the 2012 King of the Rock points championships in both JR1 and JR2….that makes three leather jackets for the 2012 season!! Awesome, awesome clutch that is simple but VERY tough! I love the fact that I can rebuild it myself in just a few minutes and we are not without a clutch waiting for someone to rebuild it for us. Saves us time, money and the hassle of mailing clutches off. Looking at going to a 2-disk for next year as we try to repeat as National Champions!”
update: November 25th 2012
….add JR Big Dog Purple plate winner to the resume’! That is like the biggest karting event of the year with racers there from 26 different states! We brought home the trophy that stands near 5ft tall! SMC Clutches have once again put us in winners circle for a HUGE win!
2013 WKA Gold Cup National
103 Street Sports Complex
“We would like to thank everyone at SMC Clutches for their help in winning the Sportsman Pro Gas class at the first WKA Gold Cup National of the 2013 season in Jacksonville, Florida. Tom’s guidance and the new SMC Vortex Red Two Disc clutch helped propel my son, Matthew Miller, to victory in his Jim’s Racing Tires/R.A. Spooner Contracting/GT Machine powered Bandit Chassis. SMC Clutches has once again raised the bar and set the new standard with the new Vortex Red Kart Clutch.
Brian MillerPerry Hall, MD, March 8-10, 2013