Exploding flywheels / flying clutches... Myth or Reality?

[Ted Hamilton]

Throughout my racing career with kart-type vehicles, I've heard stories of OEM flywheels exploding at higher RPMs (every anecdote claims a different number) and clutches without 3rd bearing support flying off and whinging into the stands...

So what's the reality? How many of you have experienced personally, or as a direct spectator to the incident, an exploding flywheel IN A RACING SITUATION (not Dyno), or a rapidly departing clutch?

Just curious what the actual numbers are, or if this is largely a karting myth... (FWIW, I think billet flywheels and 3rd bearing supports are great, but I've always been a bit skeptical of the claimed neccesity...)

~Ted
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Owner, www.hamiltonhelmets.com // UAS Racer #76 // Karting for karting's sake...keep it fun!

[John Matthews]

I wasn't there when it happened but I worked with Mike Clements for about 2 years and he exploded plenty of them. He was also one of the first ones to build billet flywheels for the flathead.

There was at least one incident where a spectator was killed at a kart track from flywheel shrapnel so I would say it's not a myth but a deadly serious reality. The amount of kinetic energy in a kart flywheel or clutch is truly amazing, I'm sure one of our math wizards can explain it better than me but it's like a bomb when one of these things shatters at speed.

Of course the reason this is being asked now is that sprint tracks are trying to get clone classes going and insurance companies are requiring them to run billet flywheels, disappointing many who thought they were going to get a racing engine for $129.99 from Harbor Freight. Well, anyone on this forum can go over to the clone forum on 4cycle.com

http://karting.4cycle.com/forumdisplay.php?f=120

and see for themselves what the dirt oval crowd has to say about the issue. For me, I wouldn't even think about running in a class that allowed stock cast iron flywheels from China on an ungoverned engine. All it takes is a casting flaw, or someone to hit it with a hammer while removing it to cause a problem. The potential consequences are just too high for me. When someone gets injured or killed by something nobody could foresee that's an accident, when someone could have prevented it that's negligence.

Billet flywheels and third bearing supports are safety equipment just like gloves and helmets. Requiring them should be expected of all clubs and organizations, the risk of not using them just isn't worth the cost savings of going without.

JMHO,
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John Matthews
Heartbeat Power, LLC.

[Rob Kozakowski]

I can remember seeing clutches flying off of KT100's back in the mid-80's...at VERY high rates of speed. Watching a clutch go flying past a bunch of karts going into a corner, then launching off into the air at the end of the track is a sight that has stuck in my memory for a long time. Fortunately, I never saw them launched into a spectator area, but with the momentum they had, it was rare that people would find them deep in the bushes where they would eventually come to a rest.

I believe that the third bearing support has likely saved a number of people from serious injury over the years.

[Jim McMahon]

is it not feasble to shroud them in some way? Probably a cheaper option than a replacement flywheel.
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[Greg Wright]

Flying clutches, yep seen that!!
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[Bruce Peck]

I started in karting in the mid 70's when most were running Macs. No third bearing supports at that time. I was racing at my local track (Whiteland IN) with a Mac 91B1 and a Hartman clutch. As I came off the first turn the engine rev'ed very high as if I had thrown a chain. Turns out the crank broke clean. At that time there was a small set of bleachers just outside of that turn. A couple of us walked over in that direction trying to figure out where it had gone. A guy in the bleachers said he saw it fly off and sail toward the corn field beyond the track property. It didn't go too close to the bleachers but he said if had broken earlier in the turn it could have gone right into the bleachers - the height of flight was correct for that. This was a night race so my buddies and I walked up and down the rows of corn with flashlights and found the clutch maybe 30 or 40 rows out. It flew quite a distance. I'd hate to think of the result if it had hit someone in the bleachers.

[Max Wood]

I've seen a couple yamaha pipe clutches come off - both using 3rd bearings.

[Gordon Duax]

I lost a clutch off a Mc 91A in the days before 3rd bearings.
Never did find it, once it hit the ground at 10k, it sped off down the strait, then off the track, never to be seen again.
Spent a day trying to find it, all I found as a snake.....

[Greg Wright]

[Bruce Peck]

[B Thomas]

About 5 years ago at Quincy one hit the fence at the end of the long straight right in front of where my Dad was standing . Chain link fence sure can flex and dent .

Also saw the aftermath of a Kolher powered garden tractor puller flywheel explosion . It basically destroyed the frame and itwas 3/8 plate steel .
Brian
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[Jeff Campbell]

two stroke engine clutches can really roll fast if they hit the ground at high rpm ... a 4" diameter drum is about 1 foot in circumference, spinning at 15,000rpm = 170mph. Yes, they generally hit the ground and pass your kart with ease. I spun off an adapter shaft on one of the BM-130 engines on my dual vintage C-Open at New Castle last year at the end of the main straight, the clutch didn't' go far with the adapter shaft still on it, but the motoplat flywheel took off like a rocket, and nobody could find it.

Jeff
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[Ted Hamilton]

re: little faith in wise old men, well, I do, but these are the same old men that spread snake oil on tires and huff treatment fumes all week to prep for a race, and mandate neck collars but allow 250# karts...

I'm just trying to sort out the legitimate dangers from the rumors.

On our ungoverned but unmodified Tecumseh H35's and H60's, we welded a 1/4" band of 2" wide steel around the shrouds, front, top, and back. Never had an issue though, but the steel was cheap and I think it would have done the job at the speeds we turned 'em.

Thanks for the stories...
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Owner, www.hamiltonhelmets.com // UAS Racer #76 // Karting for karting's sake...keep it fun!

[John Matthews]

Back when the clones first started getting popular we looked at building a Kevlar blanket type of scatter shield like drag racers use that could go around a stock flywheel shroud. We concluded that the price would be too high and product liability would be a nightmare.

ARC sells their billet clone flywheel for $100 which I think is a pretty fair price especially since they also sell the yellow BSP clone. I know money is tight and gas prices keep going up but if you can't afford $100 maybe karting isn't the sport for you.

Rules committees sure aren't perfect but I do believe that safety and competition is enhanced when tracks run straight from a national rulebook rather than making up their own rules. I think these are volunteer positions anyway so there might be a place for anyone who thinks they can do it better

Cheers,
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John Matthews
Heartbeat Power, LLC.