Seems like an automatic ought to work

Let's say you wanted to build a bike engined toy. More like one of those larger go karts you see around. Exoskeleton, seats, engine and not much more. An aircooled engine for the ultimate in simplicity.

Something you could autocross (not SCCA, but club fun) and also use to do a little lite off roading on your property and maybe trips up to the mailbox.

I'm told that bike transmissions all have a super high first gear which makes it tough to launch (especially repeatedly just puttering around on your property) and I'm also told that mating them to a car manual transmission creates issues due to the heavy weight of the flywheel and clutch assembly.

It seems that motorcycle engines don't like to change directions with the car transmissions on them, it tears up the bottom ends. So to make them work (Miatabusa & Morgan) they use a long, well anchored connecting shaft to divorce the forces from the motorcycle. Not only is this expensive but it also plays havoc with packaging.

So why wouldn't a FWD automatic tranny work? It would give you a 1st gear that would allow you to launch and eliminate all the special adapters to a flywheel and clutch. All you'd have to do is make a well anchored shaft from the torque converter to the engine and I don't believe you'd need any fancy cast adapters to cover all this up.

In the good ol' days transmissions were more or less standalone units with a kick down lever to change shifting characteristics when you floored it. Are any of the little car transmissions still capable of being used that way?

Yaris maybe? Ideally the transmission would be more on the driver's side so that you could put the engine more on the passenger's side, but either side would work really.

Would any particular transmission be better for this than another? I know nothing about automatics. I'm a die hard manual fan, but in this case it seems that if you could make the transmission manually controlled it would work better than a manual without costing you a lot of the fun factor. It might even make you faster on the autocross course since you wouldn't downshift upset the balance of the car entering a corner and you could just concentrate on driving.

Of course this would be a 2 passenger vehicle so you and your buddy could ride together and have fun. It wouldn't be for top time of the day.

I've got a 500cc Yamaha engine that's going to end up on a cart of sorts. I was going to use one of these and just lock the trans in whatever gear seemed to work best.

http://www.hoffcocomet.com/EpiphanyWeb/flexpage.aspx?ID=75

The auto trans idea might just work though. It would give you reverse and might be cheaper too.

That looks like a CVT unit from a 4 wheeler. Will they handle the power of a MC engine? And what happens when you go car fast?

I forgot to mention you also got a reverse. I'm thinking junkyard automatic transmissions would almost be given to me and using a shaft to mate the 2 would make it easier and cheaper than all the other options I've seen on the web.

Hmmm Model 103 says it will handle the HP but it won't engage lower than 2500 rpm? I'm betting a phone call will net a unit that will handle the rpms, speed and power, but as you said - no reverse. Dang it!

I don't see pricing, do you have any?

This will tell you what kind of great forward thinking person I am, I began thinking of a car transmission because I had heard the bike clutches and transmissions didn't last well when you added the weight of a car. That lead to Miatabusa & Morgans and the issues they had with using a car transmission without the special adapter and support. AT NO TIME DID THE FACT THERE WAS NO REVERSE ENTER MY MIND!

Einstein I ain't!

First gear in an automatic is often higher than first in a manual. The more speeds, the better, but also the more expensive and less suitable for a junkyard project like this. I remember my company 99 Neon's 3-speed automatic - guaranteed to ALWAYS be in the wrong gear.

If you use a bike engine (and read the LeGrand project to see how they dealt with oiling issues with their Ninja engine) and chain drive, you can change your final drive by changing the size of the sprockets. You can lower 1st to whatever you want, and then as you scream down the.... not road (because that would be illegal ) it'll sound like an F1 car.

The CVT are tunable using different springs and such. You can set the engage RPM to what ever you want. No reverse kind of sucks though, especially in a off road environment. Prices are kind of steep. I want to say the engine mounted clutch can run in the $300-$500 range. You can get a FWD trans for less. It will also give you axles and a differential as well as uprights, brakes, even the entire suspension if you wanted. Time to do some digging.

As if I didn't have enough projects already.

How do you get rid of the transmission already attached to the motorcycle engine? Or do you have a some kind of V-twin that is seperate? How about getting 2wd, racing style of ATV? They'll have the gearing you're looking for and some of them have reverse. You could probably scavenge a lot of parts from it.

Something like this: into something like this:

RossD wrote: How do you get rid of the transmission already attached to the motorcycle engine? Or do you have a some kind of V-twin that is seperate?

That is what I was wondering... Most motorcycles have the transmission built in with the engine so unless you are going with something like a Harley or Moto Guzzi (I am sure there are some others) you are going to have to deal with the stock bike transmissions. As far as drivetrain ideas look at Formula SAE cars.

Separate tranny and yes it is a big V twin so without a tranny this thing is pretty darn light for the power it puts out.

I thought about the transmission off an ATV but didn't think they could handle the power or the speed. Also aren't most of them 2 cycle engines with a totally different powerband than a big 4 cycle MC engine? Wouldn't the torques kill it?

If I read it right, the Torqconvertor said they didn't engage till 2500 which would be too high. It made sense that there were adjustments available but I don't know to what level. I'll be calling them later today.

Even if an auto has a higher numerical first gear than a manual transmission it would still be a lot lower than the gearing of the motorcycle AND there's a torque convertor that gives you a lower ratio than the numbers would suggest. In any case

What worries me the most about an auto is how do you control the shifting characteristics? I've read that most automatics are controlled by a computer. I could add a TPS to the pedal to keep the transmission from always being in the "I'm floored and going to shift as hard as I can mode" but what else would I need?

Has anyone transplanted an automatic before? Am I over thinking this?

I'm also going to check LKQ to see what it would cost to get a Yaris front clip minus the engine. I don't know that the Yaris is a good choice I just know it's small and the engine in it is only slightly less powerful than the MC engine and it probably has a narrower track than most. But it's newer and I would guess is more likely to need a computer to control it.

carguy123 wrote: What worries me the most about an auto is how do you control the shifting characteristics? I've read that most automatics are controlled by a computer. I could add a TPS to the pedal to keep the transmission from always being in the "I'm floored and going to shift as hard as I can mode" but what else would I need?

Manual valve body? Essentially, an automatic that would ONLY shift when you tell it to. The drag race guys have been doing it for a loooong time.

I would think a good cheap option would be the A-413 out of a Mopar L-body...there's a lot of information out there about them, drag race guys have been messing with them for a long time, narrow track, and they're pretty tough for a FWD automatic. On the downside, only three speeds (if you were going to want overdrive).

Also, MOST ATV's nowadays are 4-stroke...and I think pretty much ALL of the utility ATV's (which are the big-displacement ones that have a reverse gear) are going to be 4-stroke. These are generally large engines tuned for low-range torque...which means the gearing characteristics are probably pretty close to what you're looking for. As for making the trans mate up to the engine, you're on your own.

What you need is the engine from something like this, 4 cyl 4cycle+ cvt +reverse= WIN!

I used manual valve bodies on the old Mopar 727 but that didn't work well on the street. Every shift felt like a full throttle shift and was very harsh.

I've not been into the ATV scene other than a couple of small ones and hadn't realized most were 4 cycle, but they still don't attain anywhere near the speeds I'd be able to reach even on the autocross course so will they handle 80+ mph?

Mating it up to each other will be a snap compared to figuring out which one to use in the first place and how to control it. I'm thinking to separate them slightly and use a short shaft to connect them. One end of the shaft would have the means to attach to the engine and the other have whatever it takes to mate to the transmission. Then all I need is a simple dust shield to keep the dirt out of the parts. That would also make it easy for me to mount a different engine or transmission if need be.

Does anyone know for sure about the computer controlled aspect of automatic transmissions nowadays?

BTW: most MCs and ATVs engines & gearboxes are unit construction. Engine and gearbox share the cases and often the same oil. Separating the engine from the gears would be challenging to say the least.

See my other post, a snowmobile drivetrain is what you want.

White_and_Nerdy wrote: If you use a bike engine (and read the LeGrand project to see how they dealt with oiling issues with their Ninja engine) and chain drive, you can change your final drive by changing the size of the sprockets. You can lower 1st to whatever you want

This. You'll top out at 100, but who cares?

I've got all the bits to do that, but clutch, transmission life and 1st gear ratio bothers me.

carguy123 wrote: I've got all the bits to do that, but clutch, transmission life and 1st gear ratio bothers me.

Is this an offroad toy? I think you could gear it down far enough with sprockets that the first gear ratio wouldn't be an issue....what are you wanting for top speed? Personal experience is that 60 mph on anything other than flat, open ground offroad is generally enough, and most modern sportbikes are geared to run 150+ from the factory (admittedly, with a 12,000 rpm redline).

It's not just an offroad toy. I'd like to be able to drive it offroad as well. I'd drive it in the pasture and around the neighborhood between autocrosses.

60 mph won't cut it.

Gearing down still doesn't do anything, or much, for clutch longevity or bike transmission strength.

WEEEELLLL, it seems the Hoffco/Comet manufacturer of those Torq A Verters went out of business suddenly in 2009.

I've been looking for an alternative and might have found a company that is manufacturing part of the Comet line, but I still haven't been able to reach him. So this might not really be a viable alternative and that makes the automatic look even more attractive.

I'm still set up to spend some quality time with a large Polaris this weekend to see how their system works and check out the reverse on it.

The reverse that I've used on a snowmobile actually ran the engine in reverse. At least that's what the owner said, and he's usually pretty knowledgeable/does his homework.