New guy with a few questions - Chainsaw Engine + Bike = Great Success

Hello everyone; I have looked over this site a bit and it seems to be a great resource for us newbies

As the thread title states, I have a chainsaw engine that is just dying to be put on my old BMX bike. (Not my picture but it's the same model bike)

Ideally, I hope to have the engine drive the wheel by chain and still keep the bike pedal-able, but I'm undecided on the placement of the engine. In addition, I don't really know how the engine would engage with the wheel if the pedals are still attached via chain to it. I've seen other builds that feature a custom-made platform over the rear wheel, would this be a solution for me?

If I am able to go with chain-driven, what will I have to do with the clutch drum for the chainsaw? Obviously, in its current condition it cannot engage with chain.

Are there custom-made ones with teeth for chain, or would I just weld a sprocket to the face of it? Or am I just crazy? You decide.

Thanks for reading all this, and I hope some can provide insight to my build. Oh, and feel completely free to suggest alternate methods of powering the bike, but I would like to keep it chain driven if possible.

I have seen one where the clutch drum was used to run directly on the rear tire- super simple to set up.
Some have welded a sprocket to the drum, or maybe you could just replace the clutch with one with a regular sprocket?

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If it ain't broke, and you mess with it long enough, it will be.

Thanks for replying! I have looked for a while for a clutch with a regular sprocket, but I have yet to find one. Do you (or does anyone else) know where I could buy one from? If not, then I could weld a sprocket to the drum or just use the drum directly.

Have you measured the shaft? There are a lot of clutches available on ebay and at your local Tractor Supply Co. with a "standard" sprocket.

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If it ain't broke, and you mess with it long enough, it will be.

The shaft's measurement is 5/16. I have found many sprocket clutches on the web thanks to your advice and some research, but 5/16 ones are nowhere to be seen. The closest shaft measurement for sale that I've seen is 3/4. I'll keep looking for a 5/16 one, but if I can't find one could I purchase the 3/4 and adapt it to the chainsaw?

Thanks again,
PD

I had some spare time today and headed down to Tractor Supply. Unfortunately, all of the clutches there were too big. I've found one or two that would fit on the internet, but they appear to be custom made and cost over 100 dollars, so that's not really an option for me. I'm still keeping an eye out for some on the net, but I'm leaning towards welding a sprocket on the stock clutch right now.
PD

Hello again - It's been a month or two but I've decided to give this one more shot =). I have come into possession of a 19-tooth sprocket that fits perfectly around the chainsaw clutch if welded and a 38-tooth sprocket that I plan to have drive the rear wheel. Is the 2:1 ratio a good option for me?

You are going to need more like an 80 tooth rear sprocket.

A happy time has a four to one reduction in the engine. and then another four to one reduction , at the chain.
A ten tooth chain driving a 44 tooth rear sprocket.
See Deacons posts.
A friction drive is easier.

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Motorized bicyclist

I have just successfully fitted a chainsaw to a bike using the original sprocket and an adapted sprocket welded to it. Took about 4 hours to design the thing but - easy!!

I think most people with chainsaw engines go the friction drive route, but if you're dead set on chain drive, you could get a machinist to find some way of reducing the clutch you have to 5/16" bore. I just don't think this bore is available off the shelf anywhere. 1/2" bore is the smallest I've ever seen. Or yes, you could weld a sprocket onto the clutch as long as you kept it perfectly centered. Who did you find sources that would make a custom clutch for $100? It would actually be nothing for them to make the bore 5/16" instead of their standard sizes, but that's not the way it works. Or any of them could easily sell you a clutch that was NOT bored and you could have it bored and keyed at a machine shop.