first build,bmx chainsaw,chain driven.

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ridingpistonbroke

New Member
Oct 28, 2009
35
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Australia
ok i was reading through this forum yesterday, gaining knowledge
and getting ideas. alot of clever people on here and some wicked
builds. so i thought i would sign up and share my first one.

my next door neighbour bought one of them 80cc conversions and it
goes pretty good so i thought i would make one. i am using a small
(25.4cc) chainsaw i bought new. pulled all the eccess rubbish off
and eventally got it running. had automatic choke and other various
hoses and plumbing for the chain oil thingo and actually woldnt start
out of the box anyway it runs now and ive just got to get a sprocket
on the cultch.

i am copying my neighbours bike with the sproket on the spokes idea.
this wont be for taking off at all really. i will pedal up to speed then
nail the throttle for the most part and i should be off. its not for a
top speed race either and if i hit hills i will pedal.

this is mainly for transport and medium speeds and for me love of tinkering.
heres some pics of what im working with. i need to space my rear sproket
out from the spokes a bit as the chain wold hit the tyre atm.

its very early stages, i need to mount a rack (might cheat and get a s/h one)
a idler arm/ tensioner arm, and organinse the sprokets. notice the sproket is
on the same side as the original chain on the bike? thats the direction of the saw, i will
make it work. havnt seen many like that.

ive got the bug! comments welcome. cheers.


ok looks like theres no pictures. what a shame. dont know
what happened there. this was the intitial post
 
paul

paul

Well-Known Member
Dec 23, 2007
5,547
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Kalamazoo, MI
welcome to the site and sorry about no picture. we have had a terrible problem with spam so the forum is set up that no links can be posted till your third post. glad to have you with us and look forward to hearing more from you
 
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ridingpistonbroke

New Member
Oct 28, 2009
35
0
0
Australia
thanks for the welcome. ile try and get my post count
up so yo can see what im working with. i pulled the front
sprocket off my mountain bike and have that on the rear spokes
about 40t i think.

i can get the sprocket on the rear wheel to run straight but the
sproket still moves up and down a bit at high rpms. does this have
to be spot on? will an idler arm/pulley fix this or will it rattle itself
to pieces?

thanks in advance.

this might be subject for another thread, not sure, let me know
if it is im new here. ta.
 
professor

professor

New Member
Oct 14, 2009
500
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Buffalo ny area
Maybe you didn't know this, but the HT kits ( like your buddy has ) have big time internal gear reduction on the output shaft. You will need a jack shaft deal to slow down the chain before it gets to the rear wheel.
As for the up and down sproket, I would try to eliminate it. Maybe elongate holes and punch closed the other side (or a tab of weld). Leaving it as it is does load the chain more and will likely make some vibration.
I made a jackshaft out of a rear single speed freewheel hub. This way you can coast as soon as you release the throttle. Rather than having to wait for the engine clutch to slow down and disengage.
 
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ridingpistonbroke

New Member
Oct 28, 2009
35
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0
Australia
cheers for the help so far im now thinking about how
im going to get a sproket on the clutch of the motor.
im thinking of just getting a mate to weld on some pipe
around the outside of the clutch with some smaller pipe
and flat steel welded to that for the sproket.

im not even sure if the material of the clutch bell is steel
or can be welded, looks like stainless or something.

try and get these pics going...

the bike-
http://i735.photobucket.com/albums/ww360/the20valveman/DSCF0072.jpg

the donk-


i know i might not have the gear reduction and some problems but
its a first build so im going with what ive got. thanks for the input.
 
a_dam

a_dam

New Member
Feb 21, 2009
351
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Momence, IL
When professor points out the HTs gear reduction, it is because the overall gear ratio is essential for making a small motor power a bike. A clutch can't make up for improper gear ratio.

Lets say, for instance, a HappyTime motor has a built-in gearbox with 4:1 reduction. When the motor is spinning 4000 rpm, the motor sprocket is at 1000 rpm. With a 10-tooth motor sprocket driving a 50-tooth rear wheel sprocket, that's another 5:1 reduction. So the overall reduction will be 20:1 (4 times 5). So the motor at 4000 rpm turns the rear wheel at 200 rpm. With a 26-inch rear wheel, that's about 15 mph @ 4000 rpm. (I'm not going to bother doing metric conversions for you, you sound smart enough for that!)

20:1 is a pretty reasonable reduction. Higher-torque motors can get away with a little less, but a 25cc motor really needs the proper ratio.

My bike uses a 25cc motor, friction drive with a roller about 1.25 inches. That gives me about exactly the same, 15 mph @ 4000 rpm.

With an 8-tooth on the motor and a 40-tooth on the rear wheel, you will only have 5:1 reduction. It will not pull, the motor will bog, and you will have to constantly ride that little clutch to try to keep the engine from bogging. The clutch will burn up in a mile.

I'm not trying to discourage you from building. That's a fine motor for driving a bike. You seem to have reasonable expectations:

i am copying my neighbours bike with the sproket on the spokes idea.
this wont be for taking off at all really. i will pedal up to speed then
nail the throttle for the most part and i should be off. its not for a
top speed race either and if i hit hills i will pedal.
this is mainly for transport and medium speeds and for me love of tinkering.
Click to expand...
But you can't copy his bike's sprocket sizes if he has an internal gear reduction. Professor suggested a jackshaft. That's common on homemade chain-drive setups.
 
civlized

civlized

New Member
Apr 28, 2009
689
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Alabama
What about using the gear reduction that came with the chain saw. Maybe it could be modified to use with a bike chain instead of a saw blade. My first build was with a weed eater. Trust them about the jackshaft. You need some type of reduction between the motor and the tire if you aren't doing a friction drive.
 
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ridingpistonbroke

New Member
Oct 28, 2009
35
0
0
Australia
ok first off thanks for the help and ideas.
iam slightly discouraged to be honest but you get that
and im sure thats what defines alot of these "projects" into
something i can acutally fill up and got to the shop on.
although i would really, really like a chain drive but my heart
isnt completely set on it.

i have now installed a rack on the rear and it it strong as
an ox. friction drive hey, jackshaft hey , i have little to no
money at the moment and am currently buidling this out of
what i got.

on the friction drive idea (i cant believe im going back on my chain drive)
can the cultch bell be put straight on the tyre? or do i have to fab a spindle?
if i can just get the clutch on the tyre i might go that.
thanks alot again guys.

:-||
 
a_dam

a_dam

New Member
Feb 21, 2009
351
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Momence, IL
It would be nice if you could just run the clutch bell right on the tire. I see three problems with that.

The smooth metal is too slippery. That could be easily solved by gluing on some grit with epoxy.

The bearing probably wasn't made to handle that much sideways load. A bronze bushing would last a little while, anyways. Ball bearings would last a lot longer.

Most important is the diameter of the bell. Roller diameter on a friction drive is just like gear ratio on a chain drive. For your motor, 1.25 inches is about right. (That gives 22mph at 6000 rpm.) If it's much bigger than that, torque will be very poor.

Civilized mentions the gear reduction that came with the saw. Is there one? Does the clutch spin directly off the motor? I'm not familiar with the innards of chain saws.

If that clutch bell is less than 2 inches diameter, I would try it. That motor might have enough torque.
 
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ridingpistonbroke

New Member
Oct 28, 2009
35
0
0
Australia
a-dam said:
It would be nice if you could just run the clutch bell right on the tire. I see three problems with that.

The smooth metal is too slippery. That could be easily solved by gluing on some grit with epoxy.

The bearing probably wasn't made to handle that much sideways load. A bronze bushing would last a little while, anyways. Ball bearings would last a lot longer.

Most important is the diameter of the bell. Roller diameter on a friction drive is just like gear ratio on a chain drive. For your motor, 1.25 inches is about right. (That gives 22mph at 6000 rpm.) If it's much bigger than that, torque will be very poor.

Civilized mentions the gear reduction that came with the saw. Is there one? Does the clutch spin directly off the motor? I'm not familiar with the innards of chain saws.

If that clutch bell is less than 2 inches diameter, I would try it. That motor might have enough torque.
Click to expand...
i think the only way im going to find out is to do it.
the friction drive uncomplicates things to a certain
extent. i was thinking if gluing a band of rubber tread
around the bell? the motor is coming out of its case i think.
for mounting isuues.

spring loaded onto the rear tyre? thats what im thinking.
as i stated and will state again THIS WILL NOT BE FOR
ACCELERATING AT ALL. i will pedal as fast as i can and hit the throttle,
if all goes according to plan i shouldnt have to pedal and it
should hold speed. thats all im expecting out my mini china girl :)
i think thats reasonable. oh and no hills. lol.
 
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ridingpistonbroke

New Member
Oct 28, 2009
35
0
0
Australia
ok so i had a bit of a look at the size of the clutch bell
and a rubber "band" i guess for around it. i have some
remote control car wheel liners which are 1.9 inch and
stretched fit beautifully. on second thoughts the case will
stay, i need the pull start.

well with the rack that i got and the plastic case the motor
is in, i can hopefully make some brackets and get a mate to
weld it up. i will need a smoother rear tyre like a freestyle one,
and find a h/d spring.

this will take a while but it should be interesting. im going friction drive.
im also going to have to change the thread title? anyway i should be able
to line up the drive wheel pretty straight with the rear wheel as in the 2nd pic.
the clutch wheel is 55mm without the band, and is like 63 with it on. so
2.5inches it will be. im gonna do it. im tired and rambling, heres the pics-



cheers.
 
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a_dam

a_dam

New Member
Feb 21, 2009
351
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Momence, IL
I think it will work.
I like the idea of putting rubber on the bell. I make my friction drive wheels from hockey pucks. The rubber is a little harder than the tire, but grips great (when dry), and really wears out the tire less than a grit wheel. How are you going to secure the rubber on the bell?

Is that motor rotation going the right way? Mine is opposite.


Proper spring tension is a trial & error process. At first, my build didn't have enough. It was hard to tell that the roller was slipping, but tire wear was extreme. Got the tension right (about 15 lbs. + motor weight) and the tire wear is not bad at all.
 
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ridingpistonbroke

New Member
Oct 28, 2009
35
0
0
Australia
a-dam said:
I think it will work.
I like the idea of putting rubber on the bell. I make my friction drive wheels from hockey pucks. The rubber is a little harder than the tire, but grips great (when dry), and really wears out the tire less than a grit wheel. How are you going to secure the rubber on the bell?

Is that motor rotation going the right way? Mine is opposite.


Proper spring tension is a trial & error process. At first, my build didn't have enough. It was hard to tell that the roller was slipping, but tire wear was extreme. Got the tension right (about 15 lbs. + motor weight) and the tire wear is not bad at all.
Click to expand...
the rubber is held onto the bell with this special glue
for r/c tyres. should be ok. spring tension is going to
trial and error like you said,and as i dont want to wear
the clutch bearing prematurely.

on the direction a pic i thought was easier, (please excuse the bad drawing)

cheers.
 
Elmo

Elmo

New Member
Sep 3, 2009
748
4
0
Mississippi
a-dam said:
I think it will work.
I like the idea of putting rubber on the bell. I make my friction drive wheels from hockey pucks. The rubber is a little harder than the tire, but grips great (when dry), and really wears out the tire less than a grit wheel. How are you going to secure the rubber on the bell?

Is that motor rotation going the right way? Mine is opposite.


Proper spring tension is a trial & error process. At first, my build didn't have enough. It was hard to tell that the roller was slipping, but tire wear was extreme. Got the tension right (about 15 lbs. + motor weight) and the tire wear is not bad at all.
Click to expand...
use a turnbuckle with the spring to fine tune the tension. You need 1/8 to 1/4 inch deflection of the tire and use at least 45 psi in the tire.
 

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ridingpistonbroke

New Member
Oct 28, 2009
35
0
0
Australia
thanks for the idea elmo ;)
i was bored so i fitted the motor with
what i had lying around. i used a shimano
tension thingo off the front sprocket of a mountain bike
for a mount, and a sliding type bolt mount thing, so i can adjust
it a bit.

sorry for the poor language, school is something i didnt excel
in. i need a new tyre and maybe another mount spot but it feels
rather strong and sturdy. got the motor fired up and it spins the wheel,
but she threw off my rubber band, too much load for glue i think.
(someone mentioned that)

anyway on the minimalism, that is the key to my build. KISS- keep it simple
stupid. get chainsaw, put on bike, go vroom. that is my build plan lol.
just need a new tyre and work out somethings when i get the cash.
cant wait to ride it. i need to hook up the throttle and an air cleaner too.

cheers guys. heres some pics.
slide bolt thingo (back mount)-


front mount (shimano tension thing modified)-




 
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Elmo

Elmo

New Member
Sep 3, 2009
748
4
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Mississippi
If you have a dremel tool with a cutoff wheel you can cut grooves across the clutch bell and get good traction. My steel friction roller was knurled and it slipped pretty good. I took my dremel and the large cutoff wheel (the fiber reinforced one) and cut grooves across the part that contacted the wheel and no more problems. I made the grooves aboyt 3/16 inch apart. 1/8 inch would work. Hope this helps.
Elmo
 
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