79cc Preddy with true direct drive?

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Mr.B.

Mr.B.

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Oct 21, 2008
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Has any one built a 79cc Preddy with true direct drive (as in a idler pulley that allows the belt to slip for a clutch)?

I know there’s a couple good available options often discussed here for clutch/transmissions, but I’m curious if these engines are torquey enough to work well just straight up and direct...

I intend to use a 24” bicycle rim attached to a 26” rear wheel for the final pulley

Thanks,

-Kirk
 
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racie35

racie35

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Nov 17, 2012
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You'll need a 2" pulley or smaller at the front and . I think Ive seen 1.6 or 1.7" ax pulleys.......get too small and it'll slip there......I think that'll move okay ..not positive, but you can slip it if you do as you say.
 
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Mr.B.

Mr.B.

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Oct 21, 2008
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Thanks,

With direct I know I’ll have to pick a ratio that works well from 0 to top speed.

But I’m not building a racer so I’d be plenty happy just being able to max out at 25 mph.

-Kirk
 
Dan

Dan

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May 25, 2008
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Would look really cool, too. Kinda old world motorized bicycle.

As Racie suggested, using a 2" up front and then a 24" on the rear (@ 5K RPM) would max at around 30 MPH and give you a ratio of 12:1

Thinking a 24 rim could be ninja'ed to work?

Dunno but sounds like a cool project, Mr. B.
 
racie35

racie35

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Early simplex servi cycle's were direct drive..no clutch etc.....they hopped on and pushed em...off they went.
 
Mr.B.

Mr.B.

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Oct 21, 2008
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Piece of cake!

Same system I’ve used before with a beefier engine.

And that’s my concern about HF79cc, if it has enough guts to work. 200lbs of rider and perhaps another 100 for the bike...

BTW: A 24” rim is actually closer to 19.75 where the belt would ride”

Pics when I get to it, but I still have some exterior house stuff to finish before winter. :- (

Thanks,

-Kirk
 
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racie35

racie35

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you could get a simplex sheave which is close to the size of a 26" rim...bolts on way out there!....then you'll need BX belts as opposed to ax though....little thicker
 
Mr.B.

Mr.B.

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Oct 21, 2008
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Finally got a chance to do a little work this project...

I had already started a earlier thread about it in the BTR & Vintage section- http://motorbicycling.com/showthread.php?t=49939

But I was having 2nd thoughts about using the HF79cc and that’s why I started this thread.

I am now committed to this little engine and will probably just refer to the “1903 Harley” thread for future updates on this project from here on.

Thanks again everyone!

And here’s a pic of the proposed rim wheel pulley...

The straps are made from some old gate hinges, I liked the little scalloped ends.

This is just a start- The final width to be determined, filling the spoke holes, sandblasting, and painting are yet to be done.

-Kirk
 

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