Using 35cc chainsaw engine for bike?

[thgrahamjr]

My son has a chopper bicycle that I would like to mod with a chainsaw engine, I want to put this:

On this:

What do you all think?

 

[bigfootrules31]

looks easy peasy, just the clutch might give you a bit of trouble

 

[Kaptain Krunch]

you will need a few jackshafts, or some huge sprockets, im doing something similar except i have a 50cc saw, and a mountain bike. Chainsaws run anywhere from 6000-12000 rpms easily so you will need a gear ratio of about 20:1 if your planning on going up even the slightest hills. you will also need to be able to weld a bike sprocket to your chainsaw clutch, and it must be perfectly centered. And dont think a direct drive from saw to back sprocket is going to work unless your rear sprocket is the size of the tire.

 

[thgrahamjr]

What I was planning on doing was going with a 12T on engine to a 24T on jackshaft with 12T clutch on other end of jackshaft to 60T on rear wheel. That is if the engine runs at 8000 RPMs Do you think that will work?

 

[Kaptain Krunch]

so if your going to be using 2 clutches? that could mess you up, the second clutch wouldnt need much weaker springs since the jackshaft will be spinning at 4000 RPMs. Also with that reduction your top speed is calculated at 48mph(that is if the back tire is 20 inch), and with the clutch on that chainsaw you will just end up slipping alot and burning out the clutch. for your project i would aim for a top speed of 20-30mph since your using small engine and on a bike thats pretty fast.

I ran into the same problem, and i ended up deciding on 2 jackshafts and i calculated mine to a top speed of 35mph, since i have an old beastly chainsaw that has a very good clutch on it (better than the comet clutch on my gokart).

 

[thgrahamjr]

Well only the jackshaft would have the clutch, I would just have a 12T sprocket mounted to the engine and maybe a 54T sprocket on jackshaft then the 12T clutch and 60T sprocket on wheel?

 

[Kaptain Krunch]

Well that would give you a good gear ratio (about 22:1) but you have to be careful with the clutch on the jackshaft instead of the engine, you will have to get a clutch that is fully engaged by 1,700 rpms which would be the top rpm of the jackshaft when your saw is topped out at 8000 RPMs (if thats what it tops out at). So if my math is correct you need a clutch with very weak springs, since the average go kart clutch doesnt engage till 2200 rpms and your chainsaw clutch probably doesnt engage until over 5000 RPMs. so if i were you i would try attaching the clutch directly to your crankshaft.

 

[thgrahamjr]

What if I just used the chainsaw clutch? Would that be an option?

 

[thgrahamjr]

How do I find out how many RPM's my engine turns?

 

[ed1380]

most chainsaws do about 12k rpm

 

[2or3wheels]

well it can also depend on the carb pirpe and size of the bar. Bigger bar the better the engine will be. just aim for about 25 MPH at 8000 rpm and you will be in the right ball park gearing wise.

 

[Kaptain Krunch]

You can use the clutch from your chainsaw, however the newer ones dont have a lot of grabbing power, if i were you i'd look for a late 70s saw, there cheap or free at places like craigslist and have a lot more balls than the new saws.

This is a newer clutch from a craftsman - http://img98.imageshack.us/img98/1917/staplelr9.jpg

This is a clutch from an early 70's Mcculloch 10-10-http://i17.ebayimg.com/04/i/001/24/35/7ef9_1.JPG

Mcculloch and craftsmen are in the same range of quality, and as you can see the one thats nearly 40 years old is of much higher quality and construction. Although you cant see the clutch bell, the older one is about twice as thick and has its own roller bearing.

 

[thgrahamjr]

Well I have just come across a 49cc mini pocket bike engine that I think will be much more suited for what I want to do. Actually it is the whole bike that I bought 2 years ago for my son that I just got back from his mothers house so I should have must of the parts needed for this build. HOPEFULLY

 

[Kaptain Krunch]

well that solves your problem, sounds like its gonna be good.

 

[thgrahamjr]

I will post up-dates and pics on the build process.

 

[rgvkid]

Don't waste your time with that chainsaw. The shaft is a weird reverse thread. Look in the motorbicycling.com forum for some info on friction drive setup and the poulan 33saw. That motor will over heat after about 10-15min. of riding and seize until you let it cool down again. I used a poulan on my MB and i put alot of work into it just to realize it was too small of an engine. Try a better chainsaw or at least a 45cc Poulan. Good luck

 

[Kaptain Krunch]

Don't waste your time with that chainsaw. The shaft is a weird reverse thread. Look in the motorbicycling.com forum for some info on friction drive setup and the poulan 33saw. That motor will over heat after about 10-15min. of riding and seize until you let it cool down again. I used a poulan on my MB and i put alot of work into it just to realize it was too small of an engine. Try a better chainsaw or at least a 45cc Poulan. Good luck

I know you already said you were using a pocket bike engine, but if for some reason you go back to the chainsaw, dont use a friction drive, it wears the hell out of your tires and will slip on hills more than a clutch would. It may be the easy way out, but as most of you mechanics out there know, the easy way is almost never the best.