Can you still use your shifters?

pprwngs

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#1
Hello all! I'm new to the idea of building a gas bike. I'm looking to set it up on a mountain bike, but I would still like to use it without the motor at times. I'm wanting to keep my 21 speed twist shifters. Can someone point me towards some info on how to achieve this? Build threads are also welcomed.

Thanks!
 


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#2
Yeah you can do this no problem, adding an engine doesn't mess with the bicycle gears.

The only problem is that twist shifters are horrible! You won't have anywhere to put them on your bike. Some people throw away the front shifter and but the rear shifter upside down on the left side of the handlebar. It's much better to change to thumb shifters instead.
 

FurryOnTheInside

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#3
I still use the front and rear gears, allowing me to pedal along with the engine from start-up to very nearly it's top speed, and have a 30T granny ring so that I can get up hills even if the engine breaks down or runs out of fuel.
However the chain and some of the clutch parts will be turning any time the rear wheel is turning because of the fact that the left hand sprocket on the rear wheel is fixed not freewheeling. This isn't too bad, especially if you have a smooth running chain, no tight angle around the tensioner pulley whatsit, and a comparatively small rear sprocket (mine is currently 42T).

Now, personally, since the twist throttle is a bit chunky I decided to put both the shifters on the left hand side. I changed the front shifter to a SRAM one that uses two thumb buttons rather than thumb and forefinger, and I changed the rear shifter to a Shimano compatible gripshift (inverted) so that I can operate both with the same hand. :)

 

crassius

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#5
I like cruisers for comfort, but I replaced bars to get them higher and shorter - used a dogbone for shifter even though I have only shifted gears maybe once in 5 years.

shifter.jpg


on a mntn bike I built, there was room for both used for 21 speed

shifters.jpg
 

KCvale

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#6
I like cruisers for comfort, but I replaced bars to get them higher and shorter - used a dogbone for shifter even though I have only shifted gears maybe once in 5 years.

on a mntn bike I built, there was room for both used for 21 speed

View attachment 81831
Just because there is room for a front derailleur doesn't mean you should install one.
I remove it to free up space and UN-complicate the bars.
Just put the front chain on the sprocket you want.
 

FurryOnTheInside

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#7
Just because there is room for a front derailleur doesn't mean you should install one.
I remove it to free up space and UN-complicate the bars.
Just put the front chain on the sprocket you want.
What happens when you get beyond the speed where you can pedal effectively using that gear? Do you have to pull over, stop, get off the bike and manually move the chain up onto the next gear? Doesn't that make it difficult to get going again?
 

Frankenstein

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#8
What happens when you get beyond the speed where you can pedal effectively using that gear? Do you have to pull over, stop, get off the bike and manually move the chain up onto the next gear? Doesn't that make it difficult to get going again?
Nobody does that, you are one of the few that will care about the front derailleur on this site. Personally I left mine on the smallest cog for max torque for initial starting, the engine handles er'thang else! With a jackshaft you don't even get that option, you don't keep the chainring.
 

FurryOnTheInside

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#9
Nobody does that, you are one of the few that will care about the front derailleur on this site. Personally I left mine on the smallest cog for max torque for initial starting, the engine handles er'thang else! With a jackshaft you don't even get that option, you don't keep the chainring.
Well, you don't; but the OP said he wants to keep the functionality of his mountain bike. He asked for some pointers on how to do this.

I would expect its more trouble to remove the existing front derailleur than it is to just leave the derailleur exactly where it is. A mountain bike needs something there to prevent dropping the chain.
 
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gary55

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#10
The one problem I have found with front derailleurs is it gets in the way of mounting the engine. I'm sure this would vary form frame to frame. Once you jack shaft to a Nuvinci you'll never go back. Seamless shifting at full throttle. Run at a idle smoothly without jerking or dying, This is not a light bike but with a little tug on the bars and gassing it you can pull a respectable wheely. I finally grew a pair and tried it out, and it really puts a smile on your face. Effortless cruising at 35 mph. Worth every penny even though it was a lot of them. Oh and Jake I remember you saying you lost the plastic ring that goes between the grip and the shifter. I wound up making one from the plastic top of a spray paint can. Works perfect.View media item 61261View media item 61260
 

LewieBike

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#11
Rack mounts like the GEBE would allow you to keep both derailleurs and allow you to assist both on dead stop take offs and climbing hills. Not every state allows for multi geared engine drives, In Oregon it's automatically a full motorcycle and needs licensing, an "M" license, and insurance.
 

KCvale

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#12
Not every state allows for multi geared engine drives, In Oregon it's automatically a full motorcycle and needs licensing, an "M" license, and insurance.
Bummer, things are easier here in Arizona, not so much the law, the enforcement of it ;-}
 

LewieBike

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#13
I'm trusting the local enforcement is as consistent as the local Popo have been about our 50 year old Mercedes, which has been stopped nearly every other month this Winter and Spring because it's an old ratty car. It's safe and legal, it's just old looking.

So I expect that any Cruiser bicycle powered by an engine that lets it keep up with traffic will get the same level of scrutiny, my little 30 cc weedie bike already gets a bit of stink eye when I do pass local State and city police, but I haven't been lit up yet.
 
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#14
What happens when you get beyond the speed where you can pedal effectively using that gear? Do you have to pull over, stop, get off the bike and manually move the chain up onto the next gear? Doesn't that make it difficult to get going again?
One of these 66cc engines, completely standard, with no modifications not even port matching, makes two kilowatts on the Dyno. Given that this is ten to twenty times the output of a comfortable human being, asking "what do you do when you can't pedal fast enough to keep up" sounds incredibly daft.

You might as well ask how you row a cruise ship or a speedboat. The answer is you just don't because its totally redundant.

And nah a bike doesn't need anything there to stop it from dropping a chain. There's millions of bikes out there with 1x drivetrains, that was the cheapest and most common derailleur setup for probably 30 years continuously and none of them had any kind of chainguide. Guards, yes, but that was only about not getting your trouser leg chewed up. Real cotter pin days.
 

FurryOnTheInside

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#15
One of these 66cc engines, completely standard, with no modifications not even port matching, makes two kilowatts on the Dyno. Given that this is ten to twenty times the output of a comfortable human being, asking "what do you do when you can't pedal fast enough to keep up" sounds incredibly daft.

You might as well ask how you row a cruise ship or a speedboat. The answer is you just don't because its totally redundant.

And nah a bike doesn't need anything there to stop it from dropping a chain. There's millions of bikes out there with 1x drivetrains, that was the cheapest and most common derailleur setup for probably 30 years continuously and none of them had any kind of chainguide. Guards, yes, but that was only about not getting your trouser leg chewed up. Real cotter pin days.
An extra 10% power will make a difference to your speed, that's why we do things like port work and tuned pipes.

1x drivetrains do drop chains. This lead to the invention of the chain devices like Dr Crud, Blackspire, MRP which some still use, although now we have the clutched derailleur and the narrow wide chain ring so dropped chains on 1x are now less of a problem..
And we do still have the dual chain devices for the lower part of the chain on dual chainring mountain bikes.

The OP stated very clearly that he wants to still be able to use his mountain bike with full functionality under pedal power just like a normal mountain bike.
"I'm looking to set it up on a mountain bike, but I would still like to use it without the motor at times. I'm wanting to keep my 21 speed twist shifters. Can someone point me towards some info on how to achieve this?"
 
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Frankenstein

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#17
From an outside perspective this thread looks like it needs some life support, everyone seems to sound a little insane.

ctrl+alt+delete...

The op needs to just get a large enough frame that can handle the motor and the pedals and gearing clears the engine. Beyond that the shifters can stay but you will likely need longer bars to handle the extra clutter. I'd switch to a thumb shifter, when I used a derailleur with a jackshaft I did that since it was way smaller and even then I had to extend my bars 3 inches on each side, which is fine because wider bars are more comfortable for me anyway..
 

FurryOnTheInside

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#19
From an outside perspective this thread looks like it needs some life support, everyone seems to sound a little insane.

ctrl+alt+delete...

The op needs to just get a large enough frame that can handle the motor and the pedals and gearing clears the engine. Beyond that the shifters can stay but you will likely need longer bars to handle the extra clutter. I'd switch to a thumb shifter, when I used a derailleur with a jackshaft I did that since it was way smaller and even then I had to extend my bars 3 inches on each side, which is fine because wider bars are more comfortable for me anyway..
Now that's more like it. Yes it can be done by anyone who can build ordinary mountain bikes. :)
You're right to point out that the frame needs to be big enough.. We might find out that the OP's frame won't even have room for the engine, after all this! :confused:

If the downtube on the frame is oversized then it'll need a "custom" front mount and that will raise the engine an inch or so. Mountain bikes generally have a largest chainring of only 44T so the FD should be quite low down, compared to my 52T anyway.
I had so much room I had to fill it up with the rear fender mount and the velcro strap that holds the frame bag under my engine. So I'm sure there's plenty of room for both the engine and FD on the seat tube. :)

I had so much room left on my handlebar I ended up filling it with tach and cycle computer so it didn't look empty ;) but I have decided to move them elsewhere and try a narrower bar.
I had a 720mm bar, now going to try a 610mm. I actually thought I'd like the extra width for control, and it is nice under power, but I keep wanting to move my hands in when I'm pedalling unassisted for up to a mile, using the gears lol.
I'm sure all the controls can fit on a handlebar even narrower than 600mm if need be. :)
 
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LewieBike

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#20
I see a lot of support for a shifter kit but if the bike had 21 speeds with a triple front chainring, no I don't see how a HT engine could be used with a shifter kit and the all the gears the bike had originally.

GEBE 'rack mount' engine kits look more and more like the viable alternative. The China Girl engine and shifter kit add how much extra weight, in addition to the steel shelled peanut tank?

It's rapidly gaining weight and pedaling ergonomics are going away. Let's also remember that with the shifter kit comes the fact that you have to disengage the clutch when you pedal while the engine is shut off, there is considerable drag in this. I'll wager it's close to the drag of my DIY friction drive engaged to the tire with the engine off.
 

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