new plans for 80cc bmx with shifter

TorqinDirty

TorqinDirty

New Member
hey guys, while camping in donnybrook for a few nights with freinds, i was able to ride a few quad bikes and 2 wheelers. anyway i came home and went for a ride on my 31cc ryobi bike and i was hating it, i guess when i was riding them 400cc quads around something must have triggered in me and now im addicted to power. well my new project is going to go like this:

80cc chinese kit used on 20 inch bmx with the kit sprocket going to the left side of the pedal shaft and on the right side of the pedal shaft going to a 15 tooth bike sprocket then to the back hub with a derailleur setup from a mountain bike, 1st gear i want to be supper low so i can start riding on a hill and the 5th gear i want to be overdrive so when im upe in exmouth i can fang along the ocean roads to get to the beach.

now your asking why a bmx? well i think its worth the trouble because i want something sporty, that i can do tricks and stuff like that, basically i want to make a equivalent of a bmx motorbike. .shft.

this is were im going to mount the engine but with front tube supporting tubes, this is not my bike
 

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you could try looking into BMX cruisers. if you could find a 24 incher that the motor would fit into, you can get all kinds of good parts for it, it'd be a little bigger, and you wouldn't have to chop it all up to make it work.
 
bairdco said:
you could try looking into BMX cruisers. if you could find a 24 incher that the motor would fit into, you can get all kinds of good parts for it, it'd be a little bigger, and you wouldn't have to chop it all up to make it work.
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good idea . Torqin, if you want to go this route ... I have an early 80's Murray X24 frame and fork that I would sell ya for relatively cheap . I may even be able to dig up a set of 24 wheels . I'm on old school BMX nut too :P
 
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treyverb said:
good idea . Torqin, if you want to go this route ... I have an early 80's Murray X24 frame and fork that I would sell ya for relatively cheap . I may even be able to dig up a set of 24 wheels . I'm on old school BMX nut too :P
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its okay, i live in australia anyway, thanks for the offer. hardwaste pickup is on now so i will look for a bike there
 
My criteria for my ongoing build is very similar, it needs to be tough enough and small enough to be able to hoon around. So like the other guys have suggested to you, I have gone with a 24" dirt jump bike build, the frame is a saracen amplitude 1, the engine that is going in is a Cag (pocket bike motor). the cranks I am using are BMX 3 piece cranks (gusset pigmeys) and the Forks i plan on using are a long travel 150mm single crown (manitou stance blunts). It is to be a single speed, geared similar to a BMX as the engine will never have the torque my legs do but the engine itself should propel the bike to 35-38mph with the gearing i have worked out.

With a few alterations in spec I think this would be the kind of build your looking for?
 

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pedro5189 said:
My criteria for my ongoing build is very similar, it needs to be tough enough and small enough to be able to hoon around. So like the other guys have suggested to you, I have gone with a 24" dirt jump bike build, the frame is a saracen amplitude 1, the engine that is going in is a Cag (pocket bike motor). the cranks I am using are BMX 3 piece cranks (gusset pigmeys) and the Forks i plan on using are a long travel 150mm single crown (manitou stance blunts). It is to be a single speed, geared similar to a BMX as the engine will never have the torque my legs do but the engine itself should propel the bike to 35-38mph with the gearing i have worked out.

With a few alterations in spec I think this would be the kind of build your looking for?
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great, this is a very sturdy plan you have set out for yourself, i recommend using an 80 cc bike motor instead of a pocket bike motor, you will need to have about a 23 or 25 to one gear ratio for any chances of it working but a 80cc bike motor already has a 4 to one ratio in the engine itself oh and not to mention a clutch, that could come handy in hooning, pocket bike motors are fun but they lack reliability, there built to ride only tiny amounts and are built like crap so i would recommend a 80cc engine with a few mods like rubber engine mounts, chain guides and a tuned exhaust in the end its all up to how you want your bike to turn out
 
TorqinDirty said:
great, this is a very sturdy plan you have set out for yourself, i recommend using an 80 cc bike motor instead of a pocket bike motor, you will need to have about a 23 or 25 to one gear ratio for any chances of it working but a 80cc bike motor already has a 4 to one ratio in the engine itself oh and not to mention a clutch, that could come handy in hooning, pocket bike motors are fun but they lack reliability, there built to ride only tiny amounts and are built like crap so i would recommend a 80cc engine with a few mods like rubber engine mounts, chain guides and a tuned exhaust in the end its all up to how you want your bike to turn out
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That would be ideal but to get the 80cc engines over here is not cheap, particularly recently with how bad the pound is against the dollar. My perfect engine would have been a morini but they are far to expensive for my budget. I also was given a pocketbike motor for free, and with the addition of a 3.25:1 reduction gearbox that cost me all of £13 (around $18 i think) delivered it has made it a very viable powerplant for me. As with the clutch I always wanted a centrifugal (I only want brake levers on the handlebars) which this has so that has also been ideal. I would say (having almost no experiance of either) that because of there origins are going to be similarly unreliable but with the saved money from getting a free engine I am planning on rebuilding the engine from scratch with the 52cc bore and stroked crank. On top of that i will port match it and replace all the chinese bearings with there swedish counterparts.
 
pedro5189 said:
That would be ideal but to get the 80cc engines over here is not cheap, particularly recently with how bad the pound is against the dollar. My perfect engine would have been a morini but they are far to expensive for my budget. I also was given a pocketbike motor for free, and with the addition of a 3.25:1 reduction gearbox that cost me all of £13 (around $18 i think) delivered it has made it a very viable powerplant for me. As with the clutch I always wanted a centrifugal (I only want brake levers on the handlebars) which this has so that has also been ideal. I would say (having almost no experiance of either) that because of there origins are going to be similarly unreliable but with the saved money from getting a free engine I am planning on rebuilding the engine from scratch with the 52cc bore and stroked crank. On top of that i will port match it and replace all the chinese bearings with there swedish counterparts.
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alright, sweet plan what your doing with your motor is exactly what im doing with my 80cc

porting, polish, replacing all screws with high tensile stainless steel alan key bolts, new ngk spark plugs, expansion chamber, all new bearings, new air filter. so you can tell im going to have some fun with this engine.

with your bike have the biggest sprocket you can find on the back wheel so you will have a nice ratio,


YOURS: .wee. MINE: dnut


in the end its about having fun.... and showing off lol
 
TorqinDirty said:
with your bike have the biggest sprocket you can find on the back wheel so you will have a nice ratio
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Yep i'm running an 9 tooth on the front and a 68 on the rear should be good for around 38mph, might have to experiment though.

Are you planning on taking the bike offroad?
 
i wouldn't go with stainless bolts. stainless vs. aluminum is a bad combination. the threads of the bolts like to seize, and destroy both surfaces. i've dealt with this a lot. sometimes, you'll be threading a bolt in nice and easy, and it just stops. you try to back it out, and it seizes. it's like the thing was welded in there.

the black, grade 8 allen, cap socket heads are the way to go. they sit flush, they're black, and they'll out last your motor.

also, in my opinion, which i value highly, is use anti-seize compound on everything, NOT loctite. i've NEVER had a bolt loosen up, and they come out when i need them to.

there's been hundreds of threads about loctite, as it's just a great controversy starter.
 
I concurr, the only bolts i would use locktite on are the ones holding your discs of your disc brake systems on. Other than that copperslip them all but be careful as it is carcinogenic, if your posh get a PTFE based grease.
 
you can get a cheap anti-sieze, it's uh... Bostick.

the stupidest thing about the whole Loctite argument, to me, is, everything i've ever used it on came right off anyway. i've never had a bolt stuck that i had to use heat to release, never had a bolt that was actually "locked" in the threads, and never stripped any threads because of it. i personally think it's completely useless.
 
alright that was the sortoff bolt i was talking about but im not going to use stainless anymore i have seen them black bolts used quite alot so thanks for the help
 
yeah im planning to take it offroad and maybe jumps, im going to have rubber engine mounts to help with vibrations and hard landings
 
TorqinDirty said:
yeah im planning to take it offroad and maybe jumps, im going to have rubber engine mounts to help with vibrations and hard landings
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I wouldn't recommend rubber mounting the engine, it isn't a comfort cruizer. I would just put up with the vibrations and ride it. You never see motocross engines rubber mounted. Even on on less offroad biased machines like KTM LC4s they don't rubber mount the engine and they are one of the vibeyest engines around. Even ducati road bikes with all there vibes don't rubber mount there engines. rubber will just allow the motor to flex around maybe changing chain tensions etc...
 
Actually it tends to cause engine mount fasteners to sheer and can lead to fuel foaming problems (you mighta reduced the frame vibration you feel - but ya increased the engine's lol) , as well as the engine tends to cut down/through the rubber after a while - letting the engine twist like you just mentioned ;)

Yeah - rubber mounts are terrible lol, seems like such a good idea...
 
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