Pocket Bike Engine Project

Discussion in '2-Stroke Engines' started by lowracer, Jul 2, 2011.

  1. lowracer

    lowracer Member

    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-
     

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    Last edited: Jul 2, 2011

  2. cpuaid

    cpuaid Member

    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.
     
  3. atomichurley

    atomichurley Member

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

    lowracer Member

    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-
     

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    Last edited: Jul 3, 2011
  5. schulze 123

    schulze 123 Member

    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
     
  6. HeadSmess

    HeadSmess Well-Known Member

    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 :thinking: 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 :)
     
  7. lowracer

    lowracer Member

    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-
     
  8. HeadSmess

    HeadSmess Well-Known Member

    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
     
  9. lowracer

    lowracer Member

    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-
     

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    Last edited: Jul 15, 2011
  10. lowracer

    lowracer Member

    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-
     

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  11. lowracer

    lowracer Member

    I received my Dax fuel tank today, installed it, filled it, went for a ride & took some pics. Its larger than the temporary tank I started with (which is a good thing), but I noticed that the fuel cap spits fuel thru the breather hole & needs a better fuel cap to prevent this. Anybody got any good ideas? My other engines all have different fuel cap thread patterns from eachother, but they dont leak.
    -Lowracer-
     

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  12. lowracer

    lowracer Member

    I had to fix my new Dax 'fuel tank cap spitting problems' & came up with an easy & effective solution.
    I have another smaller fuel tank that also has a crummy fuel cap that allows fuel to spit out at high revs or over bumpy terrain, but also allows the engine to bog & konk out by not allowing the fuel tank to breathe. I remember as a kid riding dirtbikes with fuel caps vented by a long length of tubing to keep fuel from escaping & allowing the tank to breathe.
    I pulled the plastic insert out of each cap with a needle nose plier & drilled a small hole thru the top of the cap just a bit smaller than the fuel hose I planned on running thru the hole. I cut each end into a diagonal angle like this pic '/' making it easier to feed thru the tight hole. Then I grab the end with a needle nose plier & pull it thru a few inches. They work real well & now I can fill the tank close to the top & not have to worry about wearing fuel that spits out of the tank & onto me (front wheel drive) or konk outs. Here are 2 pics of both tanks.
    -Lowracer-
     

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  13. lowracer

    lowracer Member

    Ok,
    I dont think the Red Loctite is holding up too well. I noticed that sound again...You know, that sound of compression coming out of the engine. Very glad I have this engine mounted in front of me to See & Hear all of its little Sights & Sounds.
    I removed the suspect loose headbolt & inspected the threads. Threads looked good. I took it to the local Lowes hardware store to measure & its an M6 X 1.0 X 80mm cap bolt. Lowes doesnt carry long bolts, but McMaster Carr does & I ordered 10 @ 90mm's. I also ordered a bag of stainless steel split lock washers. I'm hoping that the extra bolt length finds threads inside the engine case, along with more Red Loctite, & the split lock washers will keep these bolts from vibrating loose. This engine is such an exciting screaming package that I have become quite fond of it & will order another if I can get a handle on the 'Mystery of the Loosening Headbolts'. At 'Ludicrous Speed' (Spaceball's) turning 10,000+ rpm's, something is gonna vibrate itself loose.
    Will post my findings once all new items are installed.
    -Lowracer-
     
  14. lowracer

    lowracer Member

    Ok,
    I received my new headbolts today & ran down to the hardware store on 'Wimpy' (EH035 powered rear friction drive bike) to pick up some lock washers. I have a bunch of lock washers on order that haven't arrived yet but for 17 cents for 8 of them, I would splurge to get this project rideable today.
    I posted a pic of the stock M6 x 1.0 x 80mm bolt (black one) & the new M6 x 1.0 x 90mm bolt (blue one). With 2 lock washers on each bolt, & Red loctite on all the threads, I am hoping that it stays tight. The longer bolts definitely grab more threads in the engine case & hopefully the lock washers help prevent vibration loosening. I took it out for a few test runs & so far so good. It sounds like it is all nice & tight even at ludicrous revs. Time will tell...
    If it holds up, I may have cured the woes that many people have using these Cag type engines (especially the higher compression head kit hop-up versions).
    I really want to finish up another bike project that is ready for the engine to go on it, I just need to order up another engine & will get another of these once convinced the head bolts stay tight.
    -Lowracer-
     

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  15. lowracer

    lowracer Member

    Oops,
    I did a gearing experiment yesterday by changing my engine pulley from a 1.5" to a 1.75" in an attempt to lower my engine rpm's at higher speeds. It totally changed the way the bike felt (too tall). It made it tough for the engine to get 'on the pipe' & hurt performance all around. I'm thinking the clutch would have worn out if I kept it set up this way. I quickly switched back to the 1.5" pulley & called it a good $4.00 experiment.
    -Lowracer-
     
  16. lowracer

    lowracer Member

    I pulled the trigger today on another engine, pipe, & expansion chamber purchase today for yet another MB project.
    Here are a few pics of whats on order & will get a few more items to complete the job.
    This will be the 2nd of the same engine (really love this motor).
    I'll be swapping head bolts as soon as UPS delivers the engine.
    The 90mm bolts with lockwashers & red loctite seem to do the trick.
    -Lowracer-
     

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    Last edited: Aug 5, 2011
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