Pocket Bike Engine Project

[lowracer]

gera229,
There are different belt sizes (ex. A, B, 3L 4L) & each can ride differently inside the same pulley.
Doing gear calculations using math is great, but it is often wrong due to small variances such as this.
Gotta do a rollout test on any finished project to see how many revolutions the crank is spinning in relation to one complete revolution of the driven wheel.
That is your drive ratio...
-Lowracer-

 

[5-7HEAVEN]

I can't go wrong because I got it for free.
What's a tapered crank nose?

A crankshaft nose(shaft) is where the clutch bolts onto. Some are tapered at this end;some are not. The clutch hole must be tapered to fit onto a tapered crank snout. The shafts that are not tapered accepts clutches with center holes which are not tapered.

It seems that the clutch in your picture is not tapered. If your engine's crank nose is not tapered, the clutch will slip right on.

If not.....

 

[lowracer]

Here is a link to a pic of the Stage 2 crankshaft from an advertisement by the same seller. Looks tapered to me?
Stage 2 Big Bore 44mm Upgrade Kit - Big Motor Sport
-Lowracer-

 

[lowracer]

I did a little experiment today to see what would happen if I replaced the short piece of flex-pipe that connects the engine to the expansion chamber with a piece of curved handlebar I salvaged from a beach cruiser bar. The flex pipe has a 1" inside diameter & the handlebar closer to 3/4". The difference was noticeable & not in a good way. The flex pipe allows the engine to build more power at higher rpm's probably due to less restriction & better sonic wave movement from the expansion chamber back to the cylinder. I quickly switched back to the flex pipe & will leave it like that unless I can find a nice piece of curved tubing with a 1" inside diameter.
-Lowracer-

 

[NEAT TIMES]

lowracer
Thats a nice kit, have several of the stock motors new and used and some incomplete engines. Could build more nice engines with the kits. Dont see any crankshaft seals, should install new ones I suppose. Have read that the reed valves create more crankcase pressure. Would definately also install head studs.

Your thread has brought new life into the cag motors. Have a diy plan with a friction drive type housing with the 1.5" pulley under the channel where the friction roller usually is located. Would use the the bell housing that comes with the motors, have the clutch drum threaded to 3/8" ns thread, install the 1/2" id bearing and use a 5" long 1/2 shoulder bolt for the drive shaft.

Will edit in a pic of that diy system I built for my first mab, a friction drive. Would need the motor on the other side for belt or chain drive

Ron

 

[gera229]

Hey should I build my own engine mount? Where can I get one for cheap? By the way as far as sprockets goes do you know anyone that actually mounted the pocket bike sprockets (Because that one fits the chain)? By the way you can answer this question in the new thread I began for my own build.

Neat Times as far as studs goes, high grade head bolts hold up perfectly based on lowracer's words.
http://motorbicycling.com/f4/my-first-motorbike-project-33877.html

 

[lowracer]

Neat Times,
Here is a thread I started awhile back with a similar setup to what you are planning.
http://motorbicycling.com/f42/bmp-friction-drive-kit-converted-v-24697.html
-Lowracer-

 

[gera229]

Something came to mind.
If these Stage 2 motors are more powerful than the China Girl 66cc motors then how come a china girl will pull a 36T rear sprocket and these motors won't?

 

[lowracer]

China girl engines have an internal gear reduction transmission & pocketbike engines do not...

 

[NEAT TIMES]

Lowracer

Checked out your other thread. A very neat set up. Am supposing you went to your present set-up as it is more cost effective.

Like you, was trying to keep the build cost low. The sheet metal shop cut and bent me 3 motor channels for $36., from the scrap bin. Now we use the flat smooth scraps, not the skid proof alum. The harder sheets of alum drill so smooth with the hole saws, but can`t be bent. Drilled about a 3.5" hole for the whole bell housing to slide in the channel. Never liked the el cheapo aluminum 1/4 x 3/4" engine spacers and the motor is near 1" closer.

Did you have any problems with the fd housing build? Do you feel like I do that studs are better/stronger if needed?

You have me thinking about the cags and belt drive, been thinking about the rim to rim thing with other motors for a couple yrs. My first mab had a BS direct drive to a whizzer sheave 61 years ago, lots of fun at 11 yrs old, before girls got more important.

Edited in a couple pics.

 

[lowracer]

Neat Times,
You channel looks great!
I still have the BMP kit but its on the back of a bike I am running friction drive with a Robin Subaru engine. I rarely ride that one (its setup for riding 2UP w/2 seats). I think studs would be great but only if the case was machined to take 8mm studs. I havent had any more loose bolts since I went w/longer bolts & loctite. Maybe since its broken-in now things are staying tight?
Funny you mentioned the 11 yr old build...I too had a motorized bike as a kid & it was a rim to rim build very similar to what I got now....We stick with what works!
I really like the Vbelt pulley drive system & although there are certain design limitations to my method of drivetrain (cant run a wide tire), it works well & is simple.
I thought of mounting a Cag using its bottom holes onto the top of a channel & having the 1/2" shaft stick out both sides, engine power to the left & geared to run down to a 5 or 7 speed thread-on cassette.
Also run the crankarms flipped around & pedal drive the left side with a lefty freewheel on a dual threaded fix/free hub.
-Lowracer-

 

[NEAT TIMES]

lowracer

Don`t know if you are aware or not, built a rig for threading left hand threads on the left side of most common wheels. Had the die made in N Y near 2 years go.

The die looks like a big thread chaser nut style, but it is a thread cutter. Have an hours work of tapping threads in the wheel jig and it is good to go. The wheel , tire and all attachs to the jig and you turn the wheel by grabbing the tire and turning it to cut the threads. A car valve spring pulls the hub into the die untill good threads are started straight, then the split collar is released to finish. Have a nice colored sketch of it that has been posted. Went with my right hand side dual free wheel set up and did not finish it yet. The Schwinn oc chopper hubs are also the correct size for threading.

My friend Crazy Horse paid a machine shop $300. to thread 2 hubs and he had to unlace the rims. He is near N Y and has not answered my email since the storm and all the flooding.

Yes, think your set up is as trouble free as it can get. "Parts left out never break"! Would post a pic of the jig here or email you one if you like. It would be very hard to find a lathe that can swing a complete 26" piece.

Ron

 

[lowracer]

Neat Times,
Wow, I didnt realize it was something that needed a custom fab.
I know there were some BMX bike hubs that have just the left threading for opposite side crank chainrings to run on the left but wouldn't also have the right side threads.
Nothing seems to ever be easy building these MB's...lol
I think I'll stick with my single ratio setup for now...maybe just add a friction drive 2nd Pocketbike stage 2 engine over the rear wheel w/roller on a one-way bearing & have something similar to 5-7 Heaven. I'd probably have to rename 'The Beast' into 'The 2-Headed Beast'...lol
-Lowracer-

 

[gera229]

Will it work to use a 14T front and 40T rear sprocket using a 7:1 reduction gearbox?

What size are the wheels on your bike?

 

[lowracer]

Sounds like that ratio would work to approx 43 mph @ 11K rpm.
My wheels are normal MTB sizing aka 26" (559).

 

[gera229]

I really wonder how you did the calculations to calculate speed. Please show me your work if you really did do any calculations.

 

[lowracer]

I use a gear ratio calculator found on this website (or the other one).Its pretty darn accurate, but i still do rollout tests & the rpm meter

 

[happycheapskate]

What is the "bell housing "?

You can upload photos for free at
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(shortened message)
After several months thinking about how to use the bell housing it came to me laying bet one morning, so simple and cheap. Paid him a 12 pk of mountain dew.

Have posted the pics before, cant repost them. Can resize or retake easy if anyone wants to see them. Have a kawasacki 49cc polished alum engine with the double bearings like you have from staton. Which cost near a hundred with sh. Many of the cag engines come with the little bell housing, it will be a couple inch`s narrower which may help.

Ron

 

[5-7HEAVEN]

What is the "bell housing "?

You can upload photos for free at
SadPanda.us - A hassle-free image upload host (no account)
or get a free account at Multiply, Facebook, etc and host photos long term. (photobucket and flickr seem to re-assign their link numbers, then you get stupid pictures. )

A bellhousing is that rear area of the engine which encloses the clutch. It might be part of the engine block, or a bolt-on component.

 

[lowracer]

I bought the housing from Staton for $70. Its a nice cnc machined black double bearing 1/2" shaft pulley driver & includes the bell housing.
I got two of them & they work real well.
-Lowracer-