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Old 08-31-2013, 11:36 PM
e85 e85 is offline
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Default *Budget Build* Big Block, Clutchless, Direct drive Minibike (doodlebug)

I need some quick input on an idea that I had. Im planning to make a direct drive minibike. There are obvious drawbacks to going clutchless such as no idling, cant come to full stop, and a few other things. But I found some pros (please dont suggest a built up 212 or 196 cc engines, I have already done this and am looking am looking to do something different) and with the coupon I have I can get a predator big block for $225 new (346cc)

Some of the pros to doing this would be saving $120 on a 1 inch clutch, I could just use shaft sprockets. And the other main pro would be engine assisted stopping (Engine braking) to help bring the extra weight to a stop. I would upgrade this tires and maybe beef up the frame a bit as well. My question is, are there any foreseeable problems I am over looking like chains snapping or binding under engine braking or anything of the sort? Does anyone else have a suggested speed/gearing ratio they could suggest that would proved adequate yet not overly aggressive engine breaking?

It may seem off the wall but I feel this could potentially be a really cool build. And doing worry about us flipping it too easily. We are all over 6 foot and 230lbs
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Old 08-31-2013, 11:45 PM
philip metzner philip metzner is offline
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If you were racing on a oval track it may be ok, but otherwise I would not build a direct drive bike or kart even if I had to use a belt and idler set up.
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Old 08-31-2013, 11:54 PM
e85 e85 is offline
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Can you elaborate? Besides not coming to a full stop, what could be so bad?
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Old 09-01-2013, 04:40 AM
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fowler fowler is offline
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it would be very hard to start
u would have to lift the back wheel off the ground while u pull the cord
once that wheel touches the ground its all go

and dont forget gearing
if u gear this to get top speed then u are looking at a high idle speed so u cant go slow for narrow parts or rough parts
also u may stall alot trying to get moving

if u gear it to be slow and controlled at idle then top speed its going to suck

ok lets say for arguments sake u have 12 inch tyres with a gar ratio of 4;1
that gives u a top speed of 32
but that means the minimum speed u can do is 14mph
which is bloody quick when u are trying u put your feet down and lift hthe back end up
and with a large engine like then engine brakes works real well when the engine isnt running
so u are heading for a hole or curb
u can try to put your feet down at 14 mph or try to shut the engine off
this will be like hitting a wall
the whole thing will lockup

i dont think u quite realise how annoying not stopping is
i have driven 4x4s with stuck clutches, its not fun and gets dangerous sometimes

have u thought about a belt tensioner clutch?
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Old 09-01-2013, 06:57 AM
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Doc Sprocket Doc Sprocket is offline
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I have to agree with fowler- I don't think the love affair with direct drive will last very long at all. Racing is fun, but it's fairly common to want to start and stop when you're out having fun.

In addition- since you will not have the benefit of a slipping clutch, you will have to gear somewhat lower than you normally would. This will have a detriment on your top speed. Engine braking is a lovely idea too, but you've missed something- you can only go so slowly (decelerating) before the engine begins trying to continue pushing your forward, rather than slow you down.

Now- this is your party and you can do exactly what you want- but IMHO you're better off to pony up the cash for a clutch, or build a belt-tensioner system.
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Old 09-01-2013, 01:31 PM
e85 e85 is offline
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This is why I come to you guys. Ya'll know your stuff! Thanks for the input. I guess a clutch is the route to go. Sometimes I get ideas in my head then I convince myself it will work. lol
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Old 09-01-2013, 03:08 PM
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Ha I think everyone does that

Thinks they have reinvented the wheel
Then u just got to take a step back to see the current wheel works just fine
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