Calling All Pros-For Build

[BikeMan]

Hi All,
I have been dreaming of putting a motorized bike together(with help,me know not much) and did find what I want.I have no idea if this will work and need advice,suggestions etc. on it.The bike below is a Yuba Mundo cargo bike.It's very heavy duty with heavy duty wheel spokes.I asked on a couple of mini bike websites about this but no one knows for sure if my idea will work.Ok,I would like to put a 3.5-6.5 hp Tec,B&S or Honda/Clone engine clear to the rear of the bike.I would have a platform made off the back end.(would have to figure out what is the best vertical placement)Then I would run the chain to a 60 or 72 tooth mini bike sprocket.(to bikes rear wheel)My main question to others was,can you run an engine to the rear of a sprocket? You know just the opposite of a motorized bike or mini bike where the engine in forward of the sprocket.I want to run the engine this way to keep it out of the way of the cargo platforms.This is the only way I know how to do it.Is this doable? If so what would be if any,problems,challenges I would face? I havn't got this bike now but will IF this would work.I would need to have someone make up a 9 hole sprocket too.I sure hope you pros here have good news.Please though,give it to me honestly.Thanks so much...

 

[Porkchop]

I know, you asked for the pros, which I am not, but I don't see that engine location would be an issue. It will be the rear wheel that will propel your bike. Think about this, cars come in different configurations. Front engine, mid engine and rear engine, with rear wheel drive, and they all go. I've never seen or heard of those bikes. Looks nice ! Good luck !

 

[BikeMan]

I know, you asked for the pros, which I am not, but I don't see that engine location would be an issue. It will be the rear wheel that will propel your bike. Think about this, cars come in different configurations. Front engine, mid engine and rear engine, with rear wheel drive, and they all go. I've never seen or heard of those bikes. Looks nice ! Good luck !

Thanks Porkchop,yea I was picturing the chain running opposite of the usual standard way.It seems like the forces change from pulling to pushing.I even envisioned the chain trying to bunch up if I ran it the opposite way.And then since I have never seen an engine ran to the rear of the sprocket I thought maybe there must be a reason such as it can't work.Hopefully I will get enough input here to come to a census.

 

[SimpleSimon]

Chain won't push anything. What such a placement will do is take the tensioned side of the chain (normally the top run) and reverse it to the bottom run, with the untensioned return side being uppermost. Not itself a problem - virtually all chain driven conveyors work that way - you do need to be careful about chain clearances and getting a return chain guide which will hold mild tension on the return side.

Other than that, the biggest issue is going to be CoG - that much weight back that far will result in a strong tendency for the tail to wag the dog, so to speak.

 

[graucho]

IMO. Personal taste only. leave the bike alone. Pusher trailer.

 

[loquin]

You know, with a Honda gsx50 & staton's gearbox, you could have the engine just aft of the seat, have the gearbox mounted vertically, then drop down to a short jackshaft mounted between the pedels and the rear hub.

Have your pedels spin a freewheel on the jackshaft, have the MOTOR spin a freewheel on the jackshaft, and have a solid sprocket & chain drive the rear hub...

 

[BikeMan]

Chain won't push anything. What such a placement will do is take the tensioned side of the chain (normally the top run) and reverse it to the bottom run, with the untensioned return side being uppermost. Not itself a problem - virtually all chain driven conveyors work that way - you do need to be careful about chain clearances and getting a return chain guide which will hold mild tension on the return side.

Other than that, the biggest issue is going to be CoG - that much weight back that far will result in a strong tendency for the tail to wag the dog, so to speak.

Thanks SS,

If I understand your last sentence correctly your talking about the rear end swaying back and forth? If so I'm hoping since this bike is made for heavy weight on the back end I'll be ok there.If this means anything,the bike is rated at 160lbs for overhang pass the platforms.Whats your opinion on chain size and clearance? I was thinking of a # 35 mini bike chain.

 

[Porkchop]

Something I just thought about, if the motor is mounted behind the rear wheel, it might have a tendency to pull the wheel towards the back of the bike. You would probably need to do something about making sure you have a darn good strong connection between the wheel and the frame. Are you familiar with motorcycles ? They have adjustments that pull back and helps hold the rear wheels in place to keep the power from the chain/belt from pulling the wheel forward. This helps keep the chain drive/belt drive from coming loose.
I like the bike you posted. I'm going to search around on them. I just might be intersed in one for myself ! That bike and frame looks like it has a lot of possibilities, potential and options for a motor kit !
Thanks !

 

[Happy Valley]

Short answer is yes, of course it's doable. The devil will be in the details though.

Time well spent would be searching the archives here for 4 stroke in-frame installs such for Titan, EZM, etc, to gather ideas. There are others as well where details can be gleaned. Mounting, gearing and particularly freewheel aspects will vary on a case by case basis to suit the particular needs. Point is, there won't be a cookie cutter plan out there, you'll have to design and fabricate as needed.

A leg up would be to look at this thread by nwguy:
http://www.motoredbikes.com/showthread.php?t=14200

Also, a another member here Mabman has a number of posts you could search on a longtail bike he is developing with innovative details and perhaps he'll chime in if he sees this as he's very knowledgeable in these concepts.

I've ridden the Mundo and they are sturdy bikes and I appreciate their World Bike campaign though for about the same price I like the Kona Ute better for frame geometry, handling and components. The Ute has a disc in front which is a good feature for a cargo bike. I also like the Madsen cargo bike because the smaller 20" wheel in the rear offers good load stability with a lower center of gravity.

On engine choice, not sure where you live and what the moped laws are but it's something I'd consider for it's certain the 3.5-6,5hp range engines are going to put you well outside just about any state regs I know of.

For myself, I choose to stick with the 35cc to 49cc class engines, mostly 4 stroke Robin or Honda though Mitsubishi makes some appropriate 2 stroke engines as well. These fit the moped guidelines in almost every state and have the, to me anyway, huge advantage of being EPA and CARBII certified as well.

Initially I liked the look and idea of the rear cargo platform bikes and I'm sure they'll do fine. After trying some Dutch cargo bikes and then a Bilenky front platform bike:
http://www.bilenky.com/Step_thru_Cargo.html
at a show I attended my thinking has swung a bit toward that design.

Recently I've been in contact with an excellent frame builder near me who makes among various designs, a front platform cargo bike:
http://antbikemike.files.wordpress.com/2008/10/bikes-080.jpg
I'm liking this direction because of the ease, simplicity and cleanness of adapting power assist, it leaves open some options to get power to the rear wheel.

BTW, for fun check the blog in my sig for some musings on this.

 

[mabman]

As mentioned putting a heavy cast iron block motor as you describe off the end of the bike beyond the rear axle would compromise the handling too much. You would also need a gear reduction box that would reverse the clockwise rotation of the motor. The motors mentioned are all above the cc and hp classification for motorized bikes also.

Although Cargo bikes offer the most amount of space to mount an engine between the seat tube and the rear axle the stock ones like the Mundo and the Kona Ute with the lat tube back there eat up that space and make it unusable. A solution could be found with a GEBE type setup mounting the engine high and tight to the saddle however and that would make the motor more accessable for starting. A frame designed to fit the motor in the center space has been prototyped and will at some point be manufactured, we are busy working on the single frame model currently however.

BTW we use standard bicycle chain for the motor drive side and it works very well. We have made an adapter that mounts a standard 130bcd chainring to a ISO 6 bolt disc mount on the hub.