Would you like to help a bunch of teenagers go fast?

[Nathan113]

Good evening,
My name is Nathan. I live in South Dakota and I often attend my boy scouts class. We were given the assignment of building something, anything. We all agreed on building a go kart or a motor bike. We chose the bike, naturally. Tomorrow afternoon we are going to be trying to put some of the stuff together, but no one really knows anything, besides myself. We have a 6.75 HP motor and an old bike frame. We can get parts easily, but we don't know what to get. The motor spins at the bottom, like any other lawn mower. Our goal is to transfer the power to the chain so that it can power the bike. I've spent a huge amount of time of thinking how to do this. That, for now, is our main issue.
Other issues include: brakes, some sort of clutch/accelerator, and mounting the engine. For all these, we have a clue on how to handle it, but we want to know the best way possible to achieve this. We are meeting tomorrow, so a speedy reply would be greatly appreciated. Thank you.

 

[nightcruiser]

Seems like you might have a hard time transferring the power from the bottom shaft over the right angle to drive a sprocket.
If your not set on that motor you might be better off looking for a motor that has a side shaft drive, much easier to translate to drive a bike tire. I was looking at my old Toro S-200 snowblower the other day and noted how the small 2-stroke motor is about the right size and has a side shaft that should be easily adaptable to a drive sprocket. So a small two stroke snow blower motor would be something I would look at... that is if you dont want to build something from a kit like is available from the sponsors here....

 

[silverbear]

First off that is too big a motor for a first build in my opinion. Second, it is a wrong configuration unless you are a mechanical wizard. I'd suggest as a first build a 2 stroke kit. You will all learn a lot and some will go on to bigger and better things. Keep it simple and be successful.
SB

 

[thegnu]

First off that is too big a motor for a first build in my opinion. Second, it is a wrong configuration unless you are a mechanical wizard. I'd suggest as a first build a 2 stroke kit. You will all learn a lot and some will go on to bigger and better things. Keep it simple and be successful.
SB

YES that motor is too big an too many mechanical issues will follow with it , secondly I should hope your goal is not just to go fast .

 

[Al.Fisherman]

First off that is too big a motor for a first build in my opinion. Second, it is a wrong configuration unless you are a mechanical wizard. I'd suggest as a first build a 2 stroke kit. You will all learn a lot and some will go on to bigger and better things. Keep it simple and be successful.
SB

YES that motor is too big an too many mechanical issues will follow with it , secondly I should hope your goal is not just to go fast .

Thinking the same thing.... By the way....Welcome

 

[2door]

Welcome to the forum. I hope the advice given so far will steer you away from your original concept. If this in fact is a "class project" you'll want success. The mechanics involved with mounting an engine that size and transferring the power to the rear wheel will require a lot of design and fabrication skills. I concur that a simple 2 or 4 stroke kit will be a far better choice for you and your classmates.

As for "going fast", it is and will always be a bicycle. You have to keep in mind that what you're building will have bicycle wheels, brakes and bearings. 25 to 35mph is reasonable, especially for a first build. Reaching higher might be more than your skills and the bike is safely capable of of delivering. Keep it simple and keep it safe.
Tom

 

[Nathan113]

The motor we have wasn't really a choice. It was free and easy to get. We only have about $50. We have all the tools we'd need, i.e. Welder, ratchets, sheer force, etc. We're not really just trying to go fast, it was just a title. We wanted to make something motorized. We have no set time limit on it, but I'm the smartest there and most skilled, and with some general "know how" I think I can manage it.
The only problem is everyone is DEAD SET on using what I have, so I'm just gonna have to manage. Later tonight, I'm gonna convince them to let me take it home and work on it here. So I know its gonna take a while, I'm willing to do whatever it takes to get it running. If there is nothing you can do to assist me, I understand. Thank you for your time.

 

[Nathan113]

Also, I would like to learn alot and try new things, but for now we have to use what we've got for this project.

 

[nightcruiser]

The motor we have wasn't really a choice. It was free and easy to get. We only have about $50. We have all the tools we'd need, i.e. Welder, ratchets, sheer force, etc. We're not really just trying to go fast, it was just a title. We wanted to make something motorized. We have no set time limit on it, but I'm the smartest there and most skilled, and with some general "know how" I think I can manage it.
The only problem is everyone is DEAD SET on using what I have, so I'm just gonna have to manage. Later tonight, I'm gonna convince them to let me take it home and work on it here. So I know its gonna take a while, I'm willing to do whatever it takes to get it running. If there is nothing you can do to assist me, I understand. Thank you for your time.

Have you even begun to conceptualize how you are going to transfer that motors power from a horizontal rotation to vertical? I think everyone is trying to tell you that is more than you bargained for, if you know it yet or not.
Do yourself a favor, find about $75 more dollars and buy a kit, or find a dead 2-stroke snow blower that has a motor with the shaft coming out the SIDE instead of the bottom. Good luck whatever you decide to do....

 

[Nathan113]

Yes. We have been thinking about it. I have a lot. Its not about taking the "Easy way out" but to have the experience. If we wanted to do it the easy way, I wouldn't have joined the forum in the first place. I would have just dropped 300 to get a old snow blower, bike, and welded it myself.

 

[streetpirate]

look into what is required to mount the engine horizontally, its more than you think. I think you will have a hard time doing the right angle thing especially with your budget. I'm new as well, and have a 6.75 mower engine and have already looked at it. id say sell your motor, but a minibike motor off craigslist that already has the clutch and is horizontal and go from there.

 

[Al.Fisherman]

I have extensive mechanical skills, worked on 2 cycle, small 4 cycle, large gas burners and diesel engines. What you are thinking about doing will cost you much more then what is worth. Good luck, because you're going to need it. But that's me.....

 

[Easy Rider]

I thought if he changes the twist of the intake manifold it would run as long as the float bowl is level? Or you could change your carb to a Walbro pumper carb. I don't know a lot about 4 strokes.
I have to agree with most of the guys on the forum that speed shouldn't be your goal with your first build let alone a DIY bike,
Good luck, have fun and check all your bolts after every ride.

 

[5-7HEAVEN]

Yes. We have been thinking about it. I have a lot. Its not about taking the "Easy way out" but to have the experience. If we wanted to do it the easy way, I wouldn't have joined the forum in the first place. I would have just dropped 300 to get a old snow blower, bike, and welded it myself.

Here's my suggestion:

Sell your engine for whatever you can get.

Scrounge around for a weedwhacker/trimmer/chainsaw motor. In the dead of winter, you should be able to find one for free or cheap.

One of your friends must have a spare BMX foot peg. That'll be your friction roller. Remove all unecessary shrouds, clutch and attachments. Mount/bolt/weld foot peg to engine shaft.

Fabricate an engine mount with hinged connection. Trial-fit first, engine onto mount, mount onto bike. Line everything up, weld into place so that bike peg can push .75" into the rear tire. Make a scissors-type rear mounting strut that will allow the front part of the mount to pivot up and down. Install bungee cords or springs so that the peg digs deep into the tire. Now use a bike brake lever and cable to activate the scissors struts. This is called a gravity clutch. You activate it when the bike is at a stop. The springs apply downward pressure of the peg into the tire tread. The lever raises the peg off the tire and allow the engine to spin while off the tire. Without the gravity clutch, the engine will die at every stop, and that's less fun.

Good luck. Figure out the rest. You'll be able to complete this bike with $50.

 

[Mike B]

Make a rack for the back and put the motor right on top.

Put a some friction material on the shaft (at least 3" dia.) and drive the side of the tire.

You will go real fast and wear out tires quick.

Probabley hurt yourself real bad.

I wouldn't do it if I was you.

 

[Easy Rider]

Make a rack for the back and put the motor right on top.

Put a some friction material on the shaft (at least 3" dia.) and drive the side of the tire.

You will go real fast and wear out tires quick.

Probabley hurt yourself real bad.

I wouldn't do it if I was you.

and don't forget get A LOT of flat tires. Friction drives are a waste also if it rains or play in the dirt, it's going to slip like crazy.

 

[Dirt Road Cowboy]

The main problem is going to be the oiling system. I believe you'll need to rebuild the engine and get a connecting rod that will sling the oil up, rather than sideways.

Go to Youtube and search for videos on converting a Briggs vertical to horizontal.

That will give you a starting point.

 

[porch lizard]

Nathan113... I have often wondered how to use the common lawn mower engine for something like you are trying to do. One thing that I thought of is how Honda has a shaft drive on some of their motorcycles. I come from a farming background and there are alot of farm machinery parts that use gears to transfer power 90 degrees from one shaft to the next. Combines and planters both have them also balers, etc. They use beveled gears usually to do this, and have some pretty good bearings that they mount them with. I'll think about this some more and post again if i can come up with more. I admire your determination. Keep thinking outside the box.

 

[porch lizard]

After a quick search, I found out that Dynamic Bicycles still sells chainless bicycles, there used to be the Hill Climber bike with driveshaft, and the inventor W. Stillman Jr. patented the bike driveshaft in 1891.

 

[MEASURE TWICE]

I can say I would like to see it done as with the motor you have just to see if it would work, but I do have to agree it is more than I think you would want.

By the way when I am done with a motor bike project I am looking to use an engine like the one you mention to do a hovercraft. With ducting one engine can work the thing. But it is a little better with one Vertical shaft engine for the lift and a separate horizontal shaft for the propulsion. I dreamed of it long ago and am going to see with time given to do it also.

Discarding that anyway, about do the easier way, I have seen the same 6 to 7.5 hp called vertical shaft engines used to make not just a lawn mower blade spin, but on an axis 90 degrees opposed spin the front wheels of the mower itself. The self propelled mower. How it is done is quite simple. Just having two pulleys and then put a half twist in the belt to accommodate the axis change. A belt is not like a chain so it can do this without a lot of additional wear. It has to have enough length so it does not rub at a cross.

The other place I saw this done was on a replication as best I can tell of a Radio Flyer Wagon with the half twist belt. It went not fast at all because it was at the Burning Man Event (too many people to have fast vehicles moving) and the rules are 5mph and under.

The wagon did not have any other than the usual steering and so it would be very dangerous if not numb skull stupid to try to configure it to go fast. Not to say a motor bike should be this slow, but 20 mph is quite alright I’ve found and for off highway vehicle woods areas, hill climbing is nice to be able to do! With this wagon I saw I'm sure there also was gearing down with some method I did not see, but it had to be some. Even though the tires are like 1/3 to 1/4 th the diameter of the motor bike tires gearing down was still necessary to be able to go slow enough.

For a motor bike with the engine you have being vertical shaft engine mounted, I still would like it where where it would be in the most balanced position on the frame inside the 3 bars that make a triangle. Maybe it would fit, but most likely it would involve modifying by cutting and adding and re-welding back tubes and having a platform for the engine. Adjustment for when the belt stretches built in also very important and I would have to engine able to slide forward and aft.

I’m finishing a motor bike like I made before long ago, but it just is a bit more refined with what I have done. There is a short chain to a jack shaft that allows further gearing down as well as allowing the engine to be centered by weight on the frame and the shaft sticks out a bit to the left. Then on a pulley on the same live jack shaft axle the smallest pulley I could use to go to a larger pulley attached to the spokes on the rear wheel with a v-belt (gearing down). Also note I'm using a Link Belt. It allows for lengthening and shortening the belt. This is something that never existed as far as I know back in the 70’s.

The half twist on other than what I have mentioned and seen works would be what you might devise to do.

I have in my mind what it could look like, but quite a number of jack shafts and pulleys with one of the sets of pulleys having a belt off to the side of the frame parallel to the bike with a half twist. Then it runs a jack shaft as I have mentioned above. To get to a position where a pulley could turn and have enough length for a half twist (as too short a length cannot work) an extremely short belt would go sideways and connect to a small jack shaft right from the engine. There could be a centrifugal belt clutch mounted right on the engine shaft too, so you could idle and not move and you would not have to shut off the engine and restart it again when moving.

Yes Rube Goldberg would probably approve and Milton Bradley might come looking as Mouse Trap is probably at least fifty years old now and maybe time to do another Rube Goldberg project. I mean at least I found that Shlitz Beer has arrived at BevMo and touts a Classic 60’s Formula made by a small brewery under license. I just love it when on 70’s show Red Foreman grabs a can of beer that was from an ice bucket that Michael had shook every can in it before unknowingly Red Foreman takes a can to open. Sprays all foam from the can then and he shouts Shlitz. Why mess with a good thing except that it can work for a sitcom! Maybe Michael did a good thing not even knowing it….. the writers anyway for the 70’s show

Measure Twice