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The thread on adapting a Miata tranny to a bike engine coupled with this from the Duratec lighter flywheel thread has me thinking.

Don't worry, the smoke you smell will go away once all the cobwebs are burnt off. It's like the grease that's built up on an old unused stove burner. If it bothers you just turn on the exhaust fan over the stove.



That's what I was thinking too. I know that I have heard of these smaller clutches in race engines, I just don't know which ones.

I have a complete set up to allow me to build a BEC using the traditional method with a chain drive connected to an diff, but were you aware the Harley and S&S type motors are dry sumped so I could turn it 90 degrees with no bad side effects and they have dyno plots very, very similar to a Miata engine?

That means I could ditch the tranny (it's separate) and figure out a way to connect the output shaft to a tranny (or longitudinal transaxle) and come up with a sturdier clutch and tranny package. Yes, I realize the car tranny is WAY heavier but clutches and trannies (whoops, now I've brought sex into the equation) don't seem to last long on BECs. (WOW! that's a picture I won't get out of my head any time soon!)

I happen to have a spare RX7 5 speed just sitting there begging to be used and abused.

I'm not quite ready to begin that build, but it's time is coming soon and it seems that once people mentally commit to a certain modus operandi it's de rigeur they begin a thread even if it will be ages before they begin - so why should I be any different?

At least there won't be any goats in this thread, although people here are all the time giving away previously loved goats on Freecycle. Also you don't have to answer all those questions like you do on Match.com or eHarmony.

So back on subject, what does anyone know about these smaller diameter clutch set ups? It would seem that they would be more durable than a motorcycle clutch for pulling all the extra weight and yet give less mass for the motorcycle engine to accelerate and therefore give more bike like characteristics to the engine. Not that the S&S engine is a real revver.

This would also solve the super high 1st gear issue on a bike tranny.

They are designed for racecars and are basically a lightswitch. Either on or off. Some people will tell you they're "not that bad on the street", which is pretty much another way of saying "they're a pain, but I don't want to openly admit just how bad of a decision it really is" and seem to be trying to convince themselves of it as much as anybody else. Some racers can measure the life of their clutch in full race seasons with a heavy V8 car, while others must measure the life of theirs in race weekends even with a light I4 car...and some will manage to toast theirs just getting the car onto the trailer. One key to longevity with them is that you want to slip the tires and not the clutch whenever possible. The reason for the shortened life on stock bike clutches is that while the wet-clutches used in bikes handle slipping like a champ, it's still trying to get 2x+ the weight it was designed for moving.

For any type of street use, you would probably would be better off adapting a more traditional lightweight aftermarket automotive flywheel and OEM style clutch to the engine/transmission...Especially if you already have an RX-7 trans, which utilizes a transmission mounted starter as standard.

I have an F3 clutch in my FF. I don't think it's very hard to use. It might be hard to use though I was told not to drive my car up onto the trailer anymore with it. So naturally enough I took it as a challenge and it seems to work.

I would not use it for races that have standing starts, but I did use it for hillclimbs so I guess I'm full of conflicting information tonite. I don't actually use it while driving on the course, so it really sees very little use. Perhaps it was used 10-20 times on a weekend with 2 days of driving. Mostly it would be babied each time. Starts on level ground and low speeds (idling) just around the paddock and pits. It didn't seem very hard, but you're really concentrating. If you stall it people for a hundred feet around you point and laugh.

When I put it on the trailer I tired hard to get the speed and momentum just right, coast up the ramp and a touch of clutch at the top to nudge the car on. It was %100 concentration.

A stock light aluminum flywheel would make sense. The car is lighter and you're willing to pay attention while you drive. You'll probably find you actually need to apply throttle to get going, not get started with inertia and then use throttle which is more normal. So timing is more critical, but not hard to do.

Yo Carguy-
I had a local shop build a "puck type" clutch for the MGB, with some very heavy springs. It was perfect for racing/autocross, quick take-up and essentially zero slippage. It was a PITA anywhere else, like in the paddock or loading on the trailer. As Driven said, it was essentially "On" or "Off". Not anything I'd recommend for street use, especially in any kind of stop and go urban traffic. (I know, none of us intend to use these cars in city traffic, but it do happen...) Anyhoo, point is, a more "streetable" clutch is the way to go. I wonder, however, if using a more OEM-type clutch with a much lighter flywheel is a good combo... Seems to me the light flywheel lets the engine rev quicker, and the "street" clutch would only have to slip more on take-off. Don't know, just sayin'...

A few years ago, my British car mechanic buddy JK was trying to order a bushing that went in the transmission of some ancient TR or Morgan or something. He wound up calling a supplier in England. During the course of the conversation, he referred to the part as a "Tranny bush". The right-proper-English guy on the other end said, "My good man, do you realize what you just asked me to procure for you?"

Well, DAMMIT, Man! Are you gonna tell us some numbers or email addresses???? I mean, if you wanna go around clutching trannies, that's your bizness, but don't be hoarding all the good goats too!!!


JD Kemp

I know that most of the small diameter clutches are puck type and are race only. I've driven one and it's very difficult to get a heavier car going with one. What I was hoping was that there was a way to replace the puck clutch with a more normal clutch.

I'm calling a few circle track race shops that are in my area today and see what they have to say.

I said autocrosser but I'm guessing I need to explain further. I stay far, FAR away from SCCA in our area because you work or stand around for 10-12 hours to get 3 sub 30 second runs. BUT there are several car clubs in the area that hold much better autocrosses where you get much more seat time and they use longer courses so this is what I run and I do it all for fun.

I'm not worried about fitting in a certain class. Usually my son, son-in-law and I go and just compete against ourselves driving the same or similar cars (Miatae or S2000s). We've actually moved way up the standings and that's another way to see if we're progressing as a group.

With that limited use would the belt drive CVT like snowmobiles use work? It'd definitely be lighter and simpler to drive, although I have no idea where to find one down here in the land of it never snows.

This is going to be not much more than engine and enough frame to hold a body or 2. I'll also use it for scooting around on the property.

Gosh, great minds think alike. I left this page live after I abandoned the Whippet project.

http://kineticvehicles.com/whippet.html

It was quite a challenge, mostly because the S&S/H-D crankshaft can't handle any flywheel weight or precession busts the crank if you turn sharp, so it wasn't going to be much of an autocrosser until that was dealt with. My solution was an adapter with a third main bearing on the hub that carried the flywheel...it was an interesting job, casting the adapter, and was my first complex foundry pattern.

I made my adapter fit mid-80s Subaru transaxles, because they can be torn into and made into transmissions, FWD transaxles, or 4WD transaxles. I was planning to make a FWD trike next after the Whippet.

The main prob with the concept is the engines are so expensive. By the time you've got the most modest S&S engine to the start-and-run level of completion you're hitting $6k. The HDs are less expensive (at least at the introductory level) but here's a shocker: their crankshaft quality control went completely down the tubes when they went to a superpress for assembling the three piece crankshaft, like .030 runout and when I went back to the dealer with it, it was within spec. Apparently that's no problem for a two bearing crankshaft with a sprocket on the end, but for three bearings and a flywheel it called for a custom flange (with broached splines to match the crank) for each engine, with the center hole offset as needed and the flywheel mounting surface ground perpendicular to the actual axis of rotation. Grr.

If I were going to start fresh, I'd probably go with an automatic transmission, or else a rear transaxle a la front engine Porsche. But a belt drive CVT a la snowmobile would work if you balance the driving clutch for the offset crank.

PS--anybody want a stainless steel exhaust for a Harley-powered hot rod?

Sorry, I guess I was assuming more of a dual purpose street/autox toy for some reason.

Unless you're willing to pay for carbon, your only option for an organic clutch with an aluminum 'race' type cover would be one of the 8.5" units. This could be the closest thing to what you're looking for if you want to keep it a little more slipable, and while still quite agressive might provide sort of "Goldilocks effect" if you've been unhappy with other clutches. Going down to a 7.25" or 5.5" clutch will leave you with with only metallic options of varying agressiveness. Of course with such a light and low powered car, they might actually be a little easier to use in a car like this than your previous experience too. Of course the smaller the diameter, the more agressive it needs to be to handle the same amount of torque. Some of the decision would also probably depend on how much you are willing to spend on such a car and how much custom machining you can do, or have done. Also for an autox only toy I'd ditch the street transmissions, since you really only need 2 well chosen gears and don't want to waste time reducing the life of your clutch every time you shift.


Probably...I'm pretty sure that's what a lot of A-Mod guys are (or at least were) running, although I think theirs is generally still attached to the 2-stroke snomobile engine too. I'm sure UPS/Fed-Ex could help you with your locational deficiency.

Oh, it's definitely not a deficiency - except for the snowmobile parts and expertise part.

Jack it's interesting that you would say that an automatic might work. I'm building a grossly overpowered real autocross/street car and I'm using an auto in it to simplify things. Not having to source and all the clutch flywheel nonsense makes things easier, except for one tiny little thing - most automatics are computer controlled nowadays. Hmmm, I wonder if the old school kick down lever of the old Mopars might could be adapted to a more modern auto?

A torque converter on an auto might also make the BEC even easier to launch.

Now that you posted that pic I do remember you doing something like this before. I'm glad to hear about the flywheel issue BEFORE I did something stupid. Any thoughts/pictures you had on the exact details of HOW to make it work better than it did for you would be greatly appreciated. I think you were saying you extended the crankshaft and supported that end with a bearing and then attached the flywheel?

It appears you are saying the flywheel acts like a gyroscope and resists a change in direction putting more strain on the crankshaft that it has been engineered to accept (another reason for a smaller unit).

I was thinking even smaller and simpler than your car. An aircooled engine with no creature comforts like lights really simplifies the build. I was originally going to build it mid engined to shorten the chain, and I might still go that way, but the car tranny &/or snowmobile CVT unit might be simpler (CVT) or solve launch issues (car tranny). Seems it's always a trade off.

Did you say you had cast an adapter? Got a spare one lying around?

The Porsche/Audi/VW transaxle does have the flywheel on the transmission end and not the motor end doesn't it?

BTW the engine was free, or close enough to free not to matter, unless I break it and have to replace it.

Now I'm off to read Jack's Whippet thread.

The New Morgan 3 Wheeler uses a S&S Engine / Miata MX-5 Transmission.

WOW, that's a heck of a shifter relocation device.

Now to find out how many kids I have to hock to buy the adapter parts. I'm betting that IF they will sell them that it will negate the Free aspect of the engine.

Jack, is this anything like you were talking about?

First tidbits.

The S&S might make too much torque for a CVT snowmobile drive. Come to find out I have an ex-Wisconsiner living near me who also has a car & machine shop. He says the Polaris 4 wheelers have just what we need - as long as you get if from a big 4 stroke model.

One big thing he reminded me of, the CVT doesn't have any engine braking which could get hairy on a car.

The Polaris uses a tapered shaft and the S&S doesn't, but that's not the end of the world.

He said we'd want to do just like Jack did & run a supported jack shaft to transition the shafts & keep the engine and CVT from wanting to come together under load. He also said we'd probably want to run a 4.11 rear end and short tires. You don't want to be running 100 mph on the belts.

I know I've seen F500s running 100 mph so I'm sure that's just a limitation to the Polaris set up.

For those of you who have raced F500 how hard was it to compensate for no engine braking? I've driven a snowmobile powered cart and don't remember even noticing there was no engine braking.

I'm going to go look at a new one to see exactly what I'm talking about here and to price new components. How would you find a wrecked one?

I also began looking at small automatic transaxles. It needs to be one that offset the engine towards the passenger side since the output shaft of the engine is on the left or drivers side. THEN I would have to try to find a way to manually control it.

All this and I've been able to get work done too.

MotoGuzzi. .. The stock setup is 2 friction discs with a bolt on cover. Even has a thrust bearing in the rear as I recall.
On a VW trans

On a stock trans (shaft drive, starboard side)

The Motoguzzi looks nice, but this is more or less what I have.

Of course I have the transmission too. It is a separate piece so I can use it or not.

Don't worry about lack of engine-braking with an ex-snowmobile CVT - 'when I was a boy' our Austin Westminster stopped wonderfully for its day (discs on front and big drums in the rear) when the freewheel was on (when the Laycock de Normanville overdrive was engaged.)

Having driven an FSAE car with a slipper clutch, I too don't see the loss of engine braking as necessarily being a problem. That's what the brakes are for. Just don't get back on the throttle too aggressively if you let the revs drop.