Pocket Bike Engine Project

[lowracer]

Hi,
I've been happy with my (2) 4-stroke MB's, so I decided to turn to the 'Dark Side' & buy a 2-stroke pocketbike engine for my next project.
I've had some 2-stroke machines in the past including a Suzuki RM80, Yamaha RD400 Daytona Special, & a Yamaha QT50 moped (that hit 50mph w/expansion chamber).
I'm going to bolt on the Staton double bearing clutch mount (see pics) that I've got sitting in storage & mount my 1.375" v-belt pulley.
I've already attached a 700c rim hoop to my spoked 700c rear wheel which makes for a 25" pulley. This gets me into the 18:1 ratio for a top end close to 50 mph.
I've already got a small fuel tank & hose in storage from a previous idea that I never implemented.
Now I need to search for an expansion chamber & 2 stroke oil, & I should be good to go.
Here are some pics of the parts & rack construction.
Will post more pics & opinions to this thread as it comes together...
-Lowracer-

 

[lowracer]

Here are some more pics of the rack & bike.
Not sure which expansion chamber to purchase just yet.
Will see how much space I have once the engine arrives & is mounted.
-Lowracer-

 

[cannonball2]

Strangely, I have been considering a similar engine to plug in on my 31cc 4stroke FD. Will be watching your build closely. Feel like I should load my welder in the car, and come over to give you a crash course in welding. You must get tried of drilling holes. On the other hand, I guess you can unbolt it and shuffle it around for the next project, thats a plus. Any way will be watching to see what kinda magical beast you create this time!

 

[lowracer]

Cannonball2,
Welding would be nice, but like you said, changing things around as much as I do, the unbolting makes things easy, like an erector set.
I really am curious more than anything about these 2 stroke engines & the claimed 4 hp is tempting.
I also like the fact that the engine is long & low & lightweight, almost the opposite of my Lifan being short & high & heavy...
It could make its way onto the front of 'The Beast' if it runs out strong & reliable?
-Lowracer-

 

[cannonball2]

Whats the top RPM, I have heard as high as 11K? If that is the case a 1" roller would show nearly 33mph. Wow!

 

[lowracer]

Not sure about the rpm's?
I never trust mfg claims.
If it gets to 10,000 rpm's, I'll be surprised.
Just hoping it has a nice smooth powerband with a kick up top.
If anyone has tried one of these Stage 2, 51cc Pocketbike engines w/upgraded carb, please post some input, or I'll be happy to be the guinea pig.
Thanks
-Lowracer-

 

[cannonball2]

Youre not going to have a lot of belt in that little pulley, may have to baby the take off. Still an 18:1 ratio is gonna be great because it should pull hard, aka fast from the bottom to the top. The high rpms will make for a good top end.

 

[lowracer]

Cannonball2,
I have used the same pulley twice now, on a BMP kit converted to v-belt drive & a homemade front rack mount, both with a EH035 Robin Subaru. Never had any issues with slipping using a cogged v-belt. The notched v-belt wraps around smaller pulleys better than an un-notched belt, & I use a skateboard wheel guide/tensioner system which also helps wrap the belt around the pulley. I'll even bet that the pocketbike engine has less low end torque than the Robin-Subaru, but will sing at higher rpm's?
-Lowracer-

 

[cannonball2]

Yeah, I forgot about you using the idler. Was assuming the relationship for the two pulleys which would make for scant contact in the little pulley. The engine may be weak on the low side, but I bet it has a higher clutch engagement speed and if you were to grab a bunch of throttle initally my gut says it could be a bit of a bear. Ive seen kids squirting the little pocket bikes around and they dont seem to lack power anywhere.

 

[bishop letov]

The two strokes are known for having a higher power band then the fours. Fours are great for the lower end but once you go to the dark side and get use to the two stroke you'll have a blast. A plus too with two strokes and Ive come to understand , and Im sure someone willpoint me if Im wrong into the right direction, but two strokes like to revv where as the fours would rather chug at about 3/4. Used the two and four strokes on my boats and in rc things and the two strokes were always my fav's.

 

[NEAT TIMES]

Low racer
used the stock cag engine on a friction drive with a 1 1/4" driver roller and it seemed fair. camparing to my "up-right common pocket bike 49CC engines"

then installed the cag engine on my rack mount cvt right hand dual free wheel drive. After a day or two the cag engine would not run, no spark. We spun it with electric drill (with plug removed), used coils of a couple other new cags and could not get spark, we tried hard.

I had a new cag with the red anadized head =52cc. You could sure tell the difference in power and sound. The stock cag engine had a plastic gas tank mounted of top of the engine. When we mounted the tank on the top of big bore 52cc, we did not notice the bigger separate cyclinder head touched the plastic gas tank and melted a hole in the tank. We rode the new 52cc around for an hour or so with the cvt tranny and was impressed. Then the tank melted a hole and i seen the gas running on the ground. Put on a new tank raised up but it would not start.

Then i started building my diy scooter guy type shifter build with the hs titan 4 stroke which is awsum. I must have about a dozen of the new cag motors in my china closet!! Lol.

Kinda like the king that had 10 wives, 9 of them had things pretty soft.

Took the bell housing with the little sprocket and dis-assembled it. Took the shaft with the little "tiny 9 tooth" sprocket and screws into the clutch drum to a machinist and had him machine the sprocket and little shaft off level with the out side of the housing where the support cap and bearing bolts on.

Then he drilled and tapped the shaft 5/16' nf thread. Used a 1" long allen head set screw and attached a golden eagle 25 tooth cog for the cogged belt. Now that looks nice in one of my parts drawers!

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

 

[lowracer]

neat times,
Thanks for the input.
I may need to find one of those fuel tanks you mentioned that bolts right onto the cag engine.
Where did you find that item?
-Lowracer-

 

[NEAT TIMES]

lowracer

Most of the 49cc cag motor`s come without gas tank. That engine did have a gas tank. It was a couple years ago. I pulled a inner thigh muscle and can`t go out to shop for a couple days. I need to find a good repair method for the white plastic looking tanks.

Will post some of the pics I took a couple days ago. Was sorta waiting for approval for posting pic`s on your thread. The pic`s are explained in my previous post.

Will try to get tank info to you later. I have never even checked to see if any of my
49cc cag engines have reed valves! I do have hopes of mounting my cags.

Ron____________________________________!

____________

 

[NEAT TIMES]

Also;

I had the dime size sprocket that use`s #25 chain cut off the clutch drum shaft. Then bored and 5/16" nf thread`s tapped into clutch shaft. Then the 1 inch dia belt cog can be attached, and use other tooth count cogs.

My plan is also to use a longer allen set screw, have end machined to fit into the 1/4" id bearing in the support cap/


The clutch shaft could be bored and threaded @ 3/8" with no proplem, maybe even 7/16" with a stable outer support bearing. The shaft is 5/8" with a short shoulder so it will clamp main sealed bearing against clutch drum. We left just enough shoulder so cog clears housing. Thin shaft spacer`s can be purchased.

If the whizzer type wheel sheave is used, my thinking is to secure a 3/8" wide v belt in the 1/2" channel to provide grip for a cogged belt, don`t forget a moderate spring tension = tensioner.

Or if bicycle rim is modified for a wheel sheave, secure a length flat belt in the channel.

All of this effort is to save a buck of course and narrow engine width.


Ron

 

[lowracer]

Ok,
I finally got the engine mounted up & hooked up a temporary exhaust & temporary gas tank. Went to my local No-Ethanol gas station & picked up some Premium along with a quart of 2-Cycle oil. Mixed it at 30:1 for break-in (not that I do too much break in) & took it for its maiden voyage.
First impressions:
1) Loud
2) Fast
3) Lightweight
I was instantly impressed with the power to weight ratio of this engine. I believe I can hit the same speeds I did with the 2.5hp Lifan with alot less weight. I like the fact that off-the-line its not too torquey (which could damage fragile bicycle wheels) & it screams at higher rpm. I do plan on purchasing an expansion chamber pipe in the near future & I have a better fuel tank on its way from Thats Dax. Lets hope the reliability of this 2 stroke is as good as my Robin Subaru & Lifan 2.5...Here are some pics.
Cheers,
-Lowracer-

 

[NEAT TIMES]

Lowracer

Looking good. Does the engine need much help getting going?? The more help it needs starting out, the less it will rev when cruising.

Have been wondering if the flywheel fan blowing on just one side of the cylinder is problematic. When using one of mine again, plan on making a full shroud with a couple soda cans or something. just a thought. Almost thinking a lack of fan would be better than cooling one side, but am not sure.

Been thinking of trying a wide rim fastened to rear wheel rim for tire clearance. the belt should track to the left to align with engine cog/pulley.

You no doubt have a lot of guy`s thinking about simular builds. Thanks for sharing.

Ron

 

[lowracer]

Ron,
At the gearing I got, the bike needs no pedalling help from a stand still (but I often pedal a bit to assist the clutch) and should hit around 50 mph. I took it easy yeasterday since the engine is brand new & just started for the 1st time & needs a little break-in before going WOT in a full aero tuck. It felt like I was in the mid 40's sitting up with more throttle to go. My engine pulley is 1.4" & wheel pulley is 22.25" and with tire the wheel is 25". Assuming 10,000 rpm = 46.8 mph. I've heard these Stage 2 pocket bike engines are good for close to 11,500 rpm's but we will soon find out.
I am not too worried about the cooling. The engine sits out in front of me in the unblocked airstream (front wheel drive). Hopefully it is reliable. It did start on the 2nd pull everytime so far...I just need to work on the noise since this little engine sounds alot like my old loved & long gone 1980 Suzuki RM80 dirtbike. Will advise on my dual muffler project going on today to silence the beast.
-Lowracer-

 

[cannonball2]

Hey Lowracer, how is it on vibes?

 

[rustycase]

Wow!

50mph is FAST !

(I'd be trying to slow it down some, and improve my start-off a bit in the meantime!)

Good luck with that!
rc

 

[lowracer]

Cannonball2,
Vibes are not too bad even at the high revs. I do use foam grips that also helps the hands. So far I'm very impressed with this little engine. it starts on the 1st pull eveytime now.
Rustycase,
It pulls good right off the line (better than my Subaru Robin EH035) & pulls real hard once the revs start to build up. Once I get the expansion chamber, I'm sure it will have an even more impressive top end & I'm already impressed without the pipe.
50 mph on this DH MTB feels fine (not scary like on my other 2 hardtail MTB's), in fact it feels more like a small motorcycle than a bicycle probably due to the heavy duty frameset, wheels & long travel suspension.
-Lowracer-