Chain saw motor
- Thread starter seabee
- Start date
maniac57
Old, Fat, and still faster than you
I had a husky 50cc mounted in radio controlled boat a few years ago and it was an awesome little motor! Excellent quality and big power! Highly recommended! Good luck with the build!
JMO, a 3.5hp engine has the power to climb tall hills and fly on flat ground.
Ya just have to find the most effective way to harness its power. I would choose a frame that has a 7-8 speed cassette. There are no kits to install chainsaw/weedwhacker engines onto bikes. That's where your skills come into play. A friction drive with no clutch is your basic install. Add a gravity clutch and your engine becomes VERY versatile. Or add pulleys or a centrifugal clutch, two jackshafts and a shift kit with proper gearing.
THENNN, your bike should climb steep hills and fly on flat ground!
There is someone on this forum who is installing a chainsaw engine on his bike. When you find his thread, you will gain knowledge from what he's doing.
Last edited:
cannonball2
Well-Known Member
Would make a heck of an FD. As I remember the no load speeds are well over 12K. If it makes 10K with a 1.75 roller(reasonable size for the HP, mabe even a 2") Speeds would be 52 and 60mph respectively. WOW! even if it only makes 9+K its still a heck of a ride.
The reasons that most builders lean towards friction drive is because of
1. lack of an effective centrifugal clutch, and
2. difficulty in attaining the correct gear ratio via sprockets or pulleys.
If your clutch can survive and transfer effectively, your problems are half over.
Chainsaw engines do not have built-in gear-reduction. They also do not have the generic 76mm clutch w/4-hole mounting bellhousing. If they did, all of your driveline issues would be solved. Since you cannot easily bolt on a gear-reducing transmission, a series of jackshafts and sprockets have to be used to create effective gearing. A single jackshaft won't work, because your custom-made driven sprocket would have around 200 teeth!
Do you know at what rpm your engine produces its optimum horsepower and torque? That'd be a great rpm range to shoot for?
How fast do you plan to go?
1. lack of an effective centrifugal clutch, and
2. difficulty in attaining the correct gear ratio via sprockets or pulleys.
If your clutch can survive and transfer effectively, your problems are half over.
Chainsaw engines do not have built-in gear-reduction. They also do not have the generic 76mm clutch w/4-hole mounting bellhousing. If they did, all of your driveline issues would be solved. Since you cannot easily bolt on a gear-reducing transmission, a series of jackshafts and sprockets have to be used to create effective gearing. A single jackshaft won't work, because your custom-made driven sprocket would have around 200 teeth!
Do you know at what rpm your engine produces its optimum horsepower and torque? That'd be a great rpm range to shoot for?
How fast do you plan to go?
I don,t know what R P M the motor spins at i,ll have to go to the chain saw forum for any info on it.
I did not figure on doing any more than 25-30 mph ,i can where the clutch
would not handle the load.
As far as the friction drive goes,would the cent. clutch houseing drive the rear wheel?
Thanks!
I did not figure on doing any more than 25-30 mph ,i can where the clutch
would not handle the load.
As far as the friction drive goes,would the cent. clutch houseing drive the rear wheel?
Thanks!
I might be wrong, but I don't believe the small clutch will allow the bike to pull away from a stop. HOWEVER, the OEM clutch might survive if you just use it to idle while standing still. If the motor is only used after the bike is up to speed, I believe the OEM clutch would work. It might take a lot of discipline not to use the clutch. If that's not possible, then a gravity clutch and friction drive would definitely work.
A 1.125" friction roller or smaller would keep limit the bike to 25-30mph. It would also allow more torque @ low speeds.
Last edited:
Good idea to start the learning curve w/friction drive. I started with friction, then single chain drive, now shift kit w/8 gears. It's a natural progression.
When you do fab your friction drive, don't forget to create the gravity clutch. Basically, your engine is mounted on a platform that hinges/pivots from the front or center. Springs or bungee cords or lever action pushes the friction roller onto the tire. Another lever within the rider's reach activates the back lever, which raises or lowers the engine's friction roller away from or onto the tire's tread.
This mechanism, is called a gravity clutch. Without it, your engine will die at every stop. If your route includes heavy city traffic, you will not be able to use the engine in stop-and-go traffic. You COULD try to incorporate the OEM clutch along with the gravity clutch. However, if this clutch burns out, then you'll have to remove the mechanism from your design, then re-engineer the friction spindle to run without it.
Maybe it'd be best simply to run without the OEM clutch, and design your gravity clutch. Here's a nice version of a gravity clutch:
http://motorbicycling.com/f36/another-friction-drive-last-one-i-31318.html
Good luck.
Last edited:
NormO
New Member
Hi all
Sorry i missed this one. FD would be the way to go if you don't know much about chain drive. It's just my opinion that in-frame chain drive is so much more fun. It's also so much more hassle though figuring out gear ratios. But if you had in frame, weather wouldn't bother the drive as much. Wet weather tends to make the FD slip more. Many people seem to think the clutches are weak on chainsaws. I don't agree. They are very tough units. but they are made to slip very easily, For a good reason though. Years of using chainsaws has taught me this. A little prep work and they can stand a whole lot of abuse. Anyway i've already started another saw build. This time i'm using a Jonsered CS2152 Turbo. The auto chain oiler has stopped functioning so i thought it would be perfect for a bicycle.
Sorry i missed this one. FD would be the way to go if you don't know much about chain drive. It's just my opinion that in-frame chain drive is so much more fun. It's also so much more hassle though figuring out gear ratios. But if you had in frame, weather wouldn't bother the drive as much. Wet weather tends to make the FD slip more. Many people seem to think the clutches are weak on chainsaws. I don't agree. They are very tough units. but they are made to slip very easily, For a good reason though. Years of using chainsaws has taught me this. A little prep work and they can stand a whole lot of abuse. Anyway i've already started another saw build. This time i'm using a Jonsered CS2152 Turbo. The auto chain oiler has stopped functioning so i thought it would be perfect for a bicycle.