Can I use an old lawnmower engine?

A pic of the engine might get some more responses, and the bike as well!!

Saca's bike in the background has a 3 1/2 hp brigs. He built it up from scratch. It weighs a ton compared to mine, but runs good.

If the motor is horizontal shaft then yes you can but if its vertical like most lawn mowers it won't be worth it unless it is 2 stroke. If its 4 stroke you would have to make a friction drive on one side of the tire, and the side wall of a bike tire isn't gonna hold up to it. If its 2 stroke you can just flip it on its side and turn the carburetor around to work side ways.

Yes- it would have to horizontal shaft
You'd probably want to use a centrifical clutch- and there are a number of issues with chain sizes and gearing-
You'd probably have to have wide cranks or mount the motor high enough to clear the cranks- some people use shorter cranks I think
I had a Briggs and Stratton on a Rupp mini back in the '60's- it was dependable but not all that fast, and with the small wheels

Here are some 4 stroke motors at Harbor Freight
http://www.harborfreight.com/engine...////Gas+Engines&RequestData=CA_CategoryExpand

If you want a 4 stroke motor, I think I'd go with a kit myself

O.P. is in the U.K. and I doubt that he has a Harbor Freight nearby or access to a Briggs and Stratton.

The engine that you link to states the engine produces 1.1 hp. This isn't going to be enough to power to take off from a standing stop or go up any hills, unless you weighed about 90 lbs. You would have to pedal to help the engine along. Another issue would be finding a clutch to fit that engine or how to make it into a friction drive, not knowing what the engine shaft looks like.

What type and size of engine depends upon how you want to mount it, your weight, 2 stroke or 4 stroke and what is your purpose - do you want the engine for pedal assist or do you want the engine to fully power the motorized bike. Many people have built friction kits with 4 stroke 35cc Honda and Robin engines. However, these engines are more powerful due to their modern designs.

You can convert a vertical engine to run horizontal. You can also use them as friction drive, but these are bigger engines than the one you referenced.

Here's a YouTube link how to convert a vertical to horizontal and a MySpace page of a forum member who converted a vertical engine to friction drive. i don't know if the information will help in your engine selection:
http://www.youtube.com/watch?v=0Mba3BS1oRM
http://www.youtube.com/watch?v=mFnZkldAwy8

http://www.myspace.com/retiredtinkerer/photos

Good Luck,

Chris
AKA: BigBlue

andrewjb 101,
Welcome to the forum. Check with your licensing people but you are going to find that the bike won't be legal. Thank the Euro people for that. I believe you are only allowed electric bikes and not more than 250w and if you don't pedal with the bike when the motor is on it won't work.

Look up page 16 in the Board Tracker section here on the forum. Towards the bottom you will see the thread, "Villiers 98cc BTR is finished" by Harry76. He built a super nice board track bike with a Villiers 98cc mk1 lawn mower motor.

Also my mate Silverbear is building a bike powered by the same engine. He will be back at it this summer to finish it up.

Steve.

Wouldn't it be a lot easier to just buy a china girl motor?

I've heard that a portion of downtown London is a 'zero emission zone'.........China Girls are certainly far from 'zero emission'. Sounds like electric would be your best bet.

Then again, I may just be talk'n outa my arse......