Thread on thread...

[Carney]

Okay, so I'm fairly new to all these mini bike/go kart/etc... so please bare with me.

Yesterday i went out and got myself a used Briggs & Stratton 3.5 HP engine but it had a gear reduction unit on it.

(This one->http://www.google.ca/imgres?imgurl=http://www.newhavenpower.com/Briggs3.5hpside.jpg&imgrefurl=http://www.newhavenpower.com/Briggs_3.5hpside.html&h=363&w=350&sz=32&tbnid=DiI0-vCWT2KELM:&tbnh=121&tbnw=117&prev=/images%3Fq%3DBriggs%2B%2526%2BStratton%2B3.5%2BHP&hl=en&usg=__mYE5-KGLAEN3A07vDTdpIKOmF4g=&ei=6TSxS77RHIGdlgeTkciRAQ&sa=X&oi=image_result&resnum=8&ct=image&ved=0CBsQ9QEwBw

I had plans on using this motor on a minibike by adding a centrifugal clutch . However when I started to take the gear reduction unit off I realized that the crankshaft wasn't what i was looking for.. Instead, it had like a spline shaft end (1" wide teeth around the entire shaft). Usually the crankshaft would be smooth with a key or keyway. So my question is, what should i do in order to fit a centrifugal clutch onto my motor? I am available to welding etc... but no machining nor money for another engine. I'm really worried that it will be impossible to attach a clutch. I don't want to realize i just wasted a fair amount of money getting this motor . Any help would be much apprenticed.

(I forgot to mention, at the end of the crankshaft it has a internal thread)

 

[Kaptain Krunch]

You can just use a belt tensioner clutch, like a lawnmower.

 

[Russ2251]

Yup, I had the same problem with an Ebay purchase. I was fortunate to find a good used crankshaft to replace the splined shaft.

Can you reassemble and return it?

 

[Carney]

Thank you for the responses, i apprentice it. Ill look into the belt tensioner clutch since i have no idea what it is.

I'm afraid it can't, got it off a kijiji guy and i highly doubt he would want his engine back.

 

[motor_head]

You can just use a belt tensioner clutch, like a lawnmower.

just use the reduction box and put a pulley on it's shaft and on the axle use a loose belt and an idler pulley that can be tightened or loosened with a pedal

 

[Carney]

just use the reduction box and put a pulley on it's shaft and on the axle use a loose belt and an idler pulley that can be tightened or loosened with a pedal

But wouldn't that reduce the speed still if Im using the reduction box??

 

[solomon]

then change the gear ratio with the pullies

 

[Carney]

So basically, i put on a 3/4" sheave onto my splined shaft. Put a bigger sheave onto the wheel axle. Add a loose v-belt. Make a pulley system that can be tightened or loosened with a pedal (just like Motor_head said). Add throttle, couple of those expanding spring thingys (forgot the name) and voolla! Thanks guys for the idea. I have hope now. . ill try and get photos and keep updated.

 

[Carney]

then change the gear ratio with the pullies

Like a big sheave for the axle, and another big sheave for the tension pulley? I just want to be able to use as much power as possible.

 

[anderkart]

I was wondering how much further out the pto ends up with Briggs gear reduction units compared to standard pto engines?

To line up with his minibikes rear wheel pulley, his engine would need to be mounted offset to the right to compensate for this. Either that or mount the engine normally and leave the pto hanging way out the left side, and then install a jack shaft to line up with the rear wheel pulley. (or maybe center the whole engine assembly plus use a jackshaft)

But... If he's going to use a jackshaft anyway, maybe he could just get a drive gear to fit his reduction box pto and then simply mount a clutch on the jackshaft instead of using the belt tensioner system.

 

[Carney]

Uhhhhhh. I can't just add a belt onto the existing crankshaft or it would probably slip off (Im guessing). I'm afraid if i use the reduction unit with pulleys gear ratio etc... i won't be able to unleash all the power the little 3.5hp motor can give out.
I think the most realistic approach would be welding a sprocket to the crankshaft. Then a jackshaft with clutch however it would probably cost more then the motor (i think)...

 

[Kaptain Krunch]

Welding to the crank is the worst possible idea. You will melt your oil seal, and never be able to change sprockets, and you wont be able to take the side cover off.

you wont lose any power using the belt tensioner idea. What is the ratio in the thing? if its like 6:1 or so you can just run it belt tensioned 1:1 to the back tire.

 

[r_chez_08]

Have you got any pics of the crankshaft?

 

[Carney]

Have you got any pics of the crankshaft?

Not at the moment, its in the shop at my highschool

 

[Carney]

Welding to the crank is the worst possible idea. You will melt your oil seal, and never be able to change sprockets, and you wont be able to take the side cover off.

you wont lose any power using the belt tensioner idea. What is the ratio in the thing? if its like 6:1 or so you can just run it belt tensioned 1:1 to the back tire.

Right now the gear reduction has a sheave on it's crank (don't know the size). So, if i go out & get the same size and put it onto the back tire. I won't lose any power?

If the sheave on the reduction crank is large. Wouldn't i need a smaller sheave for the axle? So it would reverse the effect caused my the reduction.

Has anybody even done the belt tensioner idea? Wouldn't the belt cause a lot of friction and essentially break?

 

[Carney]

How would i make a toggled belt tensioner?

 

[solomon]

Why dont you just buy a crank for that motor? If a 5hp crank will fit (IDK IF IT WILL) i do have one. Putting a good crank in it will fix all of your issues

 

[Carney]

Why dont you just buy a crank for that motor? If a 5hp crank will fit (IDK IF IT WILL) i do have one. Putting a good crank in it will fix all of your issues

I havn't had much luck trying to find a crank.

 

[solomon]

If anyone knows if a 5hp crank fits, i have 1. Can you take pics of the Shaft on that thing? i want to see it bad haha.

 

[Carney]

If anyone knows if a 5hp crank fits, i have 1. Can you take pics of the Shaft on that thing? i want to see it bad haha.

ll definatly get some asap. I just keep forgetting to get pictures when i'm in the shop, i get carried away working on my bike frame.