Another Briggs Build: Help!

twowheeledfox

twowheeledfox

New Member
Picking up a Briggs-style (actually Kawasaki) flathead 4.5hp 160cc motor in a couple days. It fits std. briggs mounts, etc. I have a bunch of bike frames and spare mounting bits and brackets everywhere, but no welder and can only afford limited welding etc. services. Some important questions:

would a mount that clips on to the frame and is made of normal steel be strong enough? My prototype uses two 1/8 thick steel clips that clamp the frame using bolts and have a mounting plate in the middle. It works for larger frames and the gutted briggs I already have seemed to fit okay.

how to make a clutch? I will need to have a disconnect for obvious reasons.

how easy/hard is it to stick a cvt on one of these? how much for a cheap cvt?

dunno if it's chain or belt drive yet, would prefer belt-to-clutch and/or cvt and chain-to-drive-wheel but can compromise.

how to figure out gear ratios? don't want to spend ages building this thing only to realize it has a ridiculously low/high ratio. i am thinking a simple drive system of just motor-clutch-drive wheel.

and just to throw something out there: those cheap little LED flashlights make excellent headlights. rode on my (push)bike at night with two of them mounted motorcycle-style on the bars and was almost brighter than the cars that passed me.

thanks.
 
as for ratio's here's how i do it first the tire size for example 26" and a 3600rpm motor with a desired top speed of 35 (it should do that easily)
-find tire circumference in feet 26/12=2.6' diameter, now 2.6*3.14(pie)=8.164' is the circumference
-now take 5280 (ft in a mile)/8.164=646 rpm at the wheel to do 60mph but we want 35
-we want 35 and our answer is for 60 so 35/60=58.3%, 35 is 58.3% of 60mph
-now take 646rpm we firgured out before and multipy by 58.3%, 646*.583=376wheel rpm to do 35mph
-now it's easy take 3600(engine rpm)/376(desired wheel rpm)=9.57 overall ratio
 
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^I was thinking about that... prefer a manual clutch, but if it's expensive or a real PITA to make I'll get a centrifugal one... does ebay sell them? Heard they were popular in the karting world.
 
twowheeledfox said:
^I was thinking about that... prefer a manual clutch, but if it's expensive or a real PITA to make I'll get a centrifugal one... does ebay sell them? Heard they were popular in the karting world.
Click to expand...

AFAIK they can be purchased at any place that sells karts or kart parts. maybe northern tool or whatnot. id say ebay has them too. heck ebay has pretty much everythign. also check one of our many sponsors on the sidebars. perhaps one of them has them as wella:-||
 
Thanks for the advice everyone- how would I get better valve springs? maybe the kart places sell them?

I already have some spare mini-airfilters and steel tubing lying around, freeflow should be easy.

Question about riding with a cent. clutch: when slowing down, do you just drop the throttle and then put on the brakes? From what I learned, the cent. clutch only engages at a certain rpm (like 1500) so when below that engagement rpm it acts like a disengaged manual clutch.
 
You have it right about the cent. clutch. As for the valve springs you'll need to look at sites that specialize in B&S engines performance upgrades. I don't have a link for that.
 
look at my west coast chopper build in this DIY forum. Try everything you can but you need a very low gear ratio. I ran a centrifugal clutch 12 teeth to a sprocket bolted to the hub of the rear wheel it was like 84 teeth and it wouldn't pull me at all hardly. I think i am going to use a 20 bicycle wheel welded to the other rear bicycle wheel and belt drive it.
 
Your big issue will be the size of the engine. Do you need to be able to pedal? If so, how do you fit the engine?
A china kit would be a whole lot easier but your idea would probably be more reliable.
I put a HF79 in my bike and I thought it was a large engine to fit into the frame (the width is the biggie), I stretched the frame 3" and put the engine forward and up.
 
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