The Pocket Bike Engine and Your Opinion...

[conradcliff]

Ok, so I've been posting bits and pieces of questions and info about these 47cc pocket bike engines all over the place and I thought I would wrap it all up into one dedicated thread.

Just as a precursor, and although I appreciate the concern, I've pretty much got the mounting and gearing all figured out. I plan on rack mounting the engine and running it to a jackshaft just like the SBP kit and then to a freewheel crank just like the SBP kit and then back to my hub gears just like the SBP kit.
What I'm hoping we can do with this thread is lay down some solid experiences with these pocket bike motors and determine what kind of reliability one can expect from them.

Some of the advantages to these engines is that they are cheap, have incredible parts availability, can be upgraded like crazy and they look cool to boot.
Some disadvantages, well, I don't really know. That's what I'm trying to figure out. I pretty sure this engine in particular does not have a cast iron sleeve like the GXH50 (which is my other option) so it probably wouldn't last quite as long, but I wouldn't be surprised if you could find an upgraded cylinder with a sleeve considering how many parts are available for these things.

In summary, what do you think? Have you owned one either on a pocket bike, a motorized bike or anything else for that matter? What can you say about the characteristics of these engines, are they powerful, are they reliable or are they just plain finicky pieces of junk?

It's waiting on your opinion that keeps me up at night, so please drop a line if you've got some time..hey that was almost a rhyme!

Thanks for any help, you guys are great!

 

[Technocyclist]

Yup, I also have been thinking about it. There are lots of pocket bike engines out there. They're smaller but more powerful, 7 to 8 HP for a 48cc that can reach insane RPM's. There are 2 major concerns actually which I am still figuring out. 1) Engine mounts and design. 2) The RPM has to be reduced substantially to have workable torque. I'm also thinking of using a jackshaft and freewheel cranks like the SBP.

I think these pocket bike engines are more practical than the chengines. I just don't understand why nobody has marketed a universal engine mounts and jackshafts for these babies. It would cost a lot more to modify the chengines to match the power of these babies, than to design or manufacture engine mounts and jackshafts for the pocket bike engines.

I have already contacted a pocket bike engine seller, and he's actually willing to provide the engine mounts with extra cost ofcourse. I'm still saving $$ for this.

 

[conradcliff]

Thanks for the reply. Great to hear someone else is thinking about using one of these! We need to swap thoughts on design ideas.
From what I've seen the bottoms of these engine look like they would mount up pretty easily to a flat plate..all that would need be done is drill some holes in the appropriate places and mount the plate to the bike.
I'm almost sure at this point that this is the way I'm going to go unless someone pipes in with some seriously negative info on these motors.

Thanks again for the reply!

 

[MyPC8MyBrain]

I've been pondering those as well for the reasons stated. I would be more interested in frame mounting, but understand that these motors are longer than the HT motors. Maybe they would settle nicely into a stretch cruiser frame. That's the angle I'm looking at.

The availability of parts and upgrades is what has perked my interest. If I'm building them to sell, I want bolt on parts. Having to make parts from scratch or customize to fit sucks.

 

[ebmvegan]

Although I do understand the want of more horsepower, I am concerend that the motors will be mounted on to a vehicle that was designed to be man powered. Imagine the wear and tear on your bike. It's scary enough going down the street at 35mph on a HT motor mounted bike. Imagine when you are going 45mph on something that was really meant to sustain no more than 25mph. You got to also consider that most center fram mounted motorized bikes are powered by using a sprocket that is mounted directly to your spokes. Good luck but please be safe.

 

[Technocyclist]

The four stroke engine mount is the easiest way that I can think of to mount these babies. I know these engines are a bit wide same as the 4 stroke. Nothing like a wide crank can easily solve. Or since these engines are smaller, I think it can be easily mounted a little higher than the cranks, or use shorter cranks. I am a little bit concerned on the amount of torque that can be harvested from these engines, that the freewheel crank might not be able to handle. I do plan to use a more heavy duty one-way bearing cranks, but have to find a machine shop that can do this.

For safety, I think either a steel, Cromoly, or titanium frame should only be used for this. I hope I can find a very good frame for this or find someone who can customize frames. Disc brakes are a must.

 

[hiker472]

Uhh.....excuse my ingnorance, but what is a "jackshaft?"

I checked out that site and like the price on it and I think this is a great idea.

 

[Technocyclist]

Uhh.....excuse my ingnorance, but what is a "jackshaft?"

I checked out that site and like the price on it and I think this is a great idea.

see pics for reference on jackshaft... It is a great idea. However, it would require you to have a 125mm or longer bottom brackets, or else you won't be able to get the correct chain alignment.

 

[Scotty]

I ran this engine on one of my prototypes, they are more powerful than the 49 china as they have full bearing construction and run reed valving. I ran a jackshaft and managed 50 mph top speeds. This requires disk brakes and a strong frame. I found out the hard way that a bike frame is not up to the stress of this kind of speed.

I have just modified the motor for ethanol/castor mix (as I can get pure ethanol from work), I raised the compression, hotter plug, drilled the jet out to 1mm and i'm trying to adjust the timing now. I would like to fit it to the next build, a bmx framed cruiser.

 

[Technocyclist]

I ran this engine on one of my prototypes, they are more powerful than the 49 china as they have full bearing construction and run reed valving. I ran a jackshaft and managed 50 mph top speeds. This requires disk brakes and a strong frame. I found out the hard way that a bike frame is not up to the stress of this kind of speed.

I have just modified the motor for ethanol/castor mix (as I can get pure ethanol from work), I raised the compression, hotter plug, drilled the jet out to 1mm and i'm trying to adjust the timing now. I would like to fit it to the next build, a bmx framed cruiser.

Got any pictures you would'nt mind to share the design of your engine mounts and jackshaft...

Did you use 25H chain or just BMX chain or 415 chain?

 

[Scotty]

Check out "scotty's bikes" thread in pictures section. The Yellow bike is a dual suspension GT LTS MB which ran this motor, I used bmx chain for crank, gocart chain for motor and 9spd chain to the cassette.

You can get a cheap 3to1 reduction box with this motor which helps keep the motor central and revs down.

 

[hiker472]

What if a guy were to buy one of these pocket bikes......say on Ebay, and strip it, and put everything on a bike? Would it be cheaper this way, than to get these parts seperately?

BTW, thanks for enlightening me on what a jackshaft is

 

[Technocyclist]

If you did buy a pocketbike, I guess the only parts you won't be using are the wheels. You can sell the parts that you don't need. You would need to cut out the engine mounts to put it in your bicycle frame.

I guess if you do remove the fork and shorten the swing arms of the pocketbike, it can actually fit a bicycle frame. And use the swing arms to attach the jackshaft. hmmmm... not a bad idea...

 

[hiker472]

I may just get one and do that. I see them on Ebay new with free shipping for $225-$260 and up. Since I installed my first engine kit and dressed up the bike with all the other things you can put on them, I bet I already have close to $250 into it.

Don't get me wrong, I love the bike and want another one, but to build a stronger, faster MB with a better return on performance......well, I believe this thread has made a spark into what I'll get my fingers in next

 

[UncleKudzu]

this is an interesting thread. i'll venture my two cents and say that part of the popularity of HTs is 1) the look - they look like a tiny motorcycle engine and not like re-purposed lawn equipment (like pull-starts, cooling shrouds and such), and 2) the lesser width compared to some of the other options. sounds like the pocketbike engines might be a bit wide for pedaling (as i found my Morini engine to be).

OTOH, the PB engines sound like thy're decently priced and possibly of a better quality/sophistication than the HTs. i look forward to hearing more about this option.

 

[conradcliff]

Wow! Lot's of replies on this thread of mine..thanks for all the interest guys! I'm going to be getting my bike tomorrow and then the fun begins. I'll be making a detailed thread concerning my build and I'll link to it in all of my current threads including this one.

 

[Technocyclist]

If this really works out, then the moderators might come out a new section specific for bicycles with pocket bike engines...hmmm...I wonder...

Anyways, we really need a very durable and sturdy frame for this... How about a cromoly BMX 26" frame? but where to get one?

 

[superhawk]

I've been playing around with pocket bike motor powered bicycle for a little while, check your local Craigslist for great bargains on broken pocket bikes, anywhere from free to $75.
I got 2 free ones, one with good motor, one with scored cylinder but complete.I also got a water cooled one with a bad crank(cost me $50 for a new crank) for work done on a second water cooled one. So there are lots out there to be had.
Also there's lots of speed equipment for these motors, some are Chinese clone of ADA and are very reasonable(MINI MOTO ADA TOP BIG BORE 4 PORT CYLINDER CIRCLE CRANK - eBay (item 230253318206 end time Dec-12-08 11:37:17 PST))
. These motors are actually 40cc(40mm x32mm) with big bore kit u get 48cc(44 x 32mm). I 'm running the 40cc one at the moment, it has lots of power ,I have one at 48cc with a ADA clone kit that has full circle crank 2 extra boost ports and claimed 14 :1 compression that I will try later on.These motor are nicknamed "Cag" motors.

 

[Technocyclist]

Hi Superhawk,

How do you mount these babies? Did you use a jack shaft to reduce the RPM? Would you mind sharing some pictures? Thanks...

 

[superhawk]

Hi Technocyclist, here are some pics. of a pocket bike motor, this one has the "big bore kit", there are mounting holes on the bottom. There are some pocket bike transmissions available, the one pictured has the clutch bell and 3.25:1 ratio so u would have to go 6:1 on the final drive to get a 20:1 total.(probably hard to find a small enough drive sprocket. Besides the one pictured is a oddball 8mm sprocket.
Like u suggested a jackshaft would probably work better , there are also a CVT (continuously variable transmission)transmission available.
I used a one off rear wheel from a Honda moped with a build in 12:1 gear reduction with a neutral lever.(http://motorbicycling.com/f36/work-progress-3733.html) I used a Stanton clutch on my build.
Rack mounted would work best as this motor combo is quite wide.