Pocket Bike Engine Project

[lowracer]

Hi,
I have 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-

 

[cpuaid]

i want to do a similar build and will be anxiously waiting on how this project progresses. keep up the good work and best wishes.

 

[atomichurley]

looks like a nice build coming along there, keep up the good work i'm looking forward to see the finish product

 

[lowracer]

Worked on the rack some more today & took a few more pics of the rack & the pulley clutch drive system. Fortunately the pocketbike engine will bolt to the rack using its bottom mounting holes.
Still waiting for the eBay engine to arrive before I can finish the engine mounting metal rack pieces.
Also I got a few different expanion chamber exhaust pipes I'm considering. There are a few pics of those too.
Gotta see how much room I have before I buy one...
-lowracer-

 

[schulze 123]

Hi Lowracer,
Another good expansion chamber to look at would be a Jet Pro Rhino as they are quite a compact design and suited to engines of 46 - 50cc.

Cheers BJ

 

[HeadSmess]

pipe 3 and 4.

1 is just a joke. bling for lil kiddy quads for people that dont know better.

no 4 appears(could just be the pic) a REVERSE taper from the port to the diffuser cone... starts wide and seems to get narrower thats a great way to lose power, sure... also meant for a HT.

problem is fitting those straight pipes neatly to a rear engine configuration

 

[lowracer]

Headsmess,
Thanks for pointing that out.
The engine should arrive today per UPS tracking.
I have been looking at motocross dirtbike expansion chambers & havent figured out what I'm going to get just yet. Gotta do some mock ups & measuring. I may try to put the engine in-frame into my other MB (has a bit more room in there). I also glued & bolted up another front wheel w/rim pulley incase I go front drive again.
Also thinking about modifying something like an 80cc pipe for the RM/KX/CR/YZ's.
-Lowracer-

 

[HeadSmess]

youll find the volume of an 80 pipe is much to big for a 50, especially a high power pipe like a cr80's...

the pipe diameter is governed by the engines port area. too big and they just wont work (as well as they could...theyll still work) plus a bit of maths governed by the intended rpm of operation, exhaust gas temps, and most importantly PORT TIMING.

youll find a narrower pipe also gives a wider less peaky powerband.

no idea what the timing is on a pocket engine, and theyre hard to measure without that crucial tool i dont have yet... the problem with unified head/cylinder designs. the measurements are only really critical if you plan on making your own pipes... funny! i designed a pipe for a HT to "tune" at 10 rpm... it would only be about 480 metres long dont think i can manage making that one for some reason...

unfortunately that engine isnt really good for a pedally, youll find more info looking on a minibike forum... regards port timing etc.

i quite like this one but its only really for a 30... http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=270775048051

 

[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) & its 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-

 

[lowracer]

I added another smaller sausage muffler to quiet down this little monster & it definitely has helped although it looks weird. I will probably do something similar once I get the expansion chamber pipe I'll be ordering this week. (see pic)
-Lowracer-