The Drive
I am going to divide this sections into 3 groups. Taking the easiest first. They are as following :
1. Motorbike Engines (Engines with a simple gearbox and clutch)
2. Lawnmower Engines. (Verticle Drive Shafts)
3. General Purpose Engines (Horizontal Drive Shafts)
The Drive is the method involved in getting the power from the power shaft to the wheels. It may be through using chains and sprockets, belts and pulley wheels or even shaft driven. In the case of Lawnmower and General Purpose engines we will have to discuss a method of a clutch and where possible gears.
1. Motor-Bike/Cycle Engines.
This is the easiest way to get your kart moving. It takes little adaption to be able to drive a kart. However some of us are not fortunate enough to have access to a running motor-cycle engine. If you have however then your lucky.
I have also included scooter and moped engines into this section as they have a clutch (though automatic) and a system of gears.
In this page I am just talking about the drive only. Engine mountings etc. are mentioned in the "Advance Kart Plans" section.
Now you have a shaft protruding from your gearbox. What we have to do is make sure we have a small sprocket on this shaft. On Mopeds there will not be a sprocket on this shaft, but a wheel. The ideal sprocket is around 15teeth, for motor-cycle engines which had a rear wheel of 24" (around 600mm). For mopeds this sprocket will have to be around 34 teeth.
( The reason for this is that mopeds have small 12" (300mm) wheels which is approx the same size as Karting wheels requiring only a small reduction needed in gearing. The biggest driver sprocket for motorbikes is 16teeth. The smallest driven sprocket is 34 teeth. This gives us too much down gearing for moped engines. Therefore if we use two driven sprockets we can get a fairly good gear ratio. Sprockets like 34 teeth on the engine and 42 on the rear axle.)
With motorbike engines we will have a small problem. Physics says that the bigger the wheel the faster you go, because the more ground covered in 1 rev. Now because of this the same set-up of sprockets as on a motorbike used on a Kart, we will have a lack in speed, because the wheels are smaller on a Kart. As a result of this we must change the gearing slightly. If we did what was done with mopeds (that is to use two very similar sized sprockets) the gearing would be out the window, you would be doing 50mph in 1st. Therefore what we can do is to have the biggest possible driver sprocket on the Engine (15teeth) and the smallest driven sprocket on the back axle (34teeth) and to see how it runs. We are looking for a ratio of around 1:2. If however you have a sprocket on your engine with 14 teeth, well and good leave it.
Motorbikes -
If your engine has a sprocket - leave it alone.
If your engine has no sprocket, get a sprocket to suit with 15 teeth. Spot weld it. Run the engine. If there are no wobbles weld it proper. When you finish welding pour a bucket of water over the shaft cooling it quick. Otherwise you risk damaging the oil seals.
Mopeds -
Get a sprocket with 34teeth. Go to this link for making a sprocket mounting. And again weld this to the shaft.
Rear Axle Sprockets.
Motorbikes and Mopeds
If you have a sprocket with less than 36 teeth leave it and put it on the rear axle.
If you don't have a sprocket or one bigger than 36 teeth, buy one!. Go to a motorbike dealer and look up his catalogue for odd sprockets. Get one with around 34 teeth. Make sure it fits the chain and width is the same as that of the sprocket on the engine.
Again go to this link for fitting of the rear sprocket on the rear axle.
That should have you sorted out and it is just a matter of getting everything else going- brakes etc.
2. Lawnmower Engines with Vertical Shafts.
This is where the fun begins!.
Now there are a few options you have. You can take the easy option, fast and fairly good, or you can go advanced. It depends on the time you want to put into the kart, Your engineering skills, Speed and acceleration. Don't worry about the mechanics yet.
The options are as follows:
1. Belt and Pulley.
2. Bevel Gears, from a shaft driven motorcycle.
3. Gearbox of a Tractor Lawnmower.
4. Differential of a car!.
Firstly Advantages and Disadvantages.
Belt Drive:
Advs: Simple to set-up. All you will need is two pulleys and a drive belt. Quick solution.
Disadvs: Loss of power through slippage. Heating up. Life of Belt very short.
Bevel Gears:
Advs: Effective. No power loss. Last forever. Low maintenance.
Disadvs: Hard to set-up. Difficult to get right. Time consuming. Can be expensive if second hand parts are not available.
Gearbox:
Advs: Very Effective. Simple. Complete with gears. Low maintenance. Easy to set-up.
Disadvs: Can be far too expensive if no scrap tractor lawnmower available.
Differential!:
Advs: Cheap. Effective. Little power loss. Low maintenance. Relatively available.
Disadvs: Difficult to set-up. Heavy. Awkward.
Again it depends on the materials you have or can get easily. If you can get a tractor lawnmower gearbox, then your sorted!.
The problem with lawnmower engines is that they have a vertical drive shaft, usually coming out from underneath the engine itself.
With the belt an pulley system, it's a case of mounting a small pulley wheel on the end of this vertically drive shaft, and another on the back axle (or any horizontal shaft). What happens the belt is that it actually is turned through 90 degrees, what you are hoping that the sides of the V pulley and the tension on the belt will keep the belt on!. As a result of the belt rubbing off the side of the pulley wheels, heat is produced, and as result slippage occurs. Another factor is that belt ware is a matter of hours of operation.
However specialised round pulley wheels are available that take a round belt and are used for such simpler application of changing the motion of drive by 90 degrees.
With Bevel Gears from a shaft driven motorcycle one can "Bodge" (make out of scrap) together a drive system. I made the whole thing myself. I wouldn't be too enthusiastic about the idea, but it works. I found it hard to connect up the engine shaft to the pinion shaft of the bevel gears. However if you can couple them up correctly, then your problem is solved. It's just a case of mounting a sprocket on the other bevel gear which is now horizontal with respect to the engine shaft. The only thing is, coming across this mechanism, of a friend or going out to a motorcycle scrap yard/ breaker to get it. Don't choose this method if you want a quick fix.
Gearbox of a Tractor Lawnmower. The marvellous thing about these, is that their driven shaft (input power shaft to the gearbox) is actually a vertical shaft. It's just a case of linking up a chain or a belt in a straight line linking the vertical shaft of the engine to the vertical shaft of the gearbox. And the great thing is that the drive shaft from the gearbox (output shaft) is horizontally driven. From this shaft, sprockets and a chain can be used to give power and torque.
A Differential of a Car can be easily adapted to turn the vertical rotation of the engine into horizontal rotation of the rear axle. If you are thinking of making a real off-road vehicle, then this could be the solution for you!. It is a case of implementing the differential/ entire back axle of a small car into the back axle of your kart. Turn up the differential so that the input shaft is pointing up in the air, and in line with the engine shaft.
Well these are all I have come across. If you have any more, please tell me, I'd love to experiment around with other ideas.
Go to these respective links for detailed info and pictures:
<Note these links will not work until this page is completed first!>
3. General Purpose Engines
In this section we will be talking about how to use an ordinary horizontal shaft to drive the rear axle via gears and a clutch. Now this can either be the horizontal shaft from the engine or a shaft from a secondary shaft from a vertical shaft engine.
Choices have to be made. Depending on the use of your kart, off-road, racing, general purpose, you will have to make a decision here on the number of gears you will need, if any at all!.
Options:
One single gear direct chain drive. (not ready yet)This is where you have a direct connection from the engine to the rear axle. No clutch, no gears. All you need is a small sprocket on the engine and a large sprocket on the rear axle. You will have to push the kart in order to start it.
One single gear belt and clutch drive. (not ready yet) This is where, instead of using a chain, you can use a drive belt and drive pulleys. However you can have a crude clutch, in which when the kart is stationary, the drive belt is loose, when you want to move the kart, you simply apply tension to the drive belt with a third pulley to take up the slack and provide drive.
One single gear, using a centrifial clutch, and chain drive. Very easy to set-up. The easiest method of driving a kart. These clutches are mounted on your engine shaft, they have a small sprocket on them that will drive a corresponding sprocket on the rear axle via a suitable chain. Just step on the accelerator (gas) and off you go. This is sufficient for most small engines with a top speed of around 40mph.
Four gears and a manual clutch.(not ready yet) This is one of the complicated methods of connecting up a lawnmower engine etc. to drive a kart. This is tricky to set-up. It involves connecting your engine to a broken motorcycle engine or a gearbox of a motorcycle via chain and sprockets and from the gearbox output shaft to the rear axle via more sprockets and a chain. You will be able to see the pictures of this set-up. Disadvantage is weight and noise of two chains.
Two or Three gears and a Belt Clutch. (not ready yet) This isn't too bad of an idea for getting your kart to go a bit faster. It involves the set-up as with the "one single gear and clutch drive", only in this case there are two/ three pulleys on the engine and three on your rear axle, and having three belts. It's a case of tensioning one set of pulleys and belt for first gear and then to release the tension on this set and tensioning another set of pulleys and belt with a lower gear ratio, and the same for the third set of pulleys. Again you will see the set-up in this section.
That's most of the ways covered. There are a few more, but they aren't too practical to use. Of course if you know of any other ideas/ ways then I'd be happy to hear them.