I blew my cheap ryobi 32cc weed eater engine looking for tips to not repeat?

Discussion in 'Friction Drive' started by Paulypopawheelie, Jul 1, 2013.

  1. Paulypopawheelie

    Paulypopawheelie New Member

    I replaced the main crank case gasket today still no starting - All together i rode about 50 miles.. the piston has some scoring on it and im assuming i may have overheated it warped piston etc?. - the bike i built has no clutch so when i stop the engine stops etc

    Any way any tips for a rookie to not fry the next one from piston damage overheating ?

    Last edited: Jul 2, 2013

  2. 5-7HEAVEN

    5-7HEAVEN Active Member

    Methinks your fuel-to-oil ratio was incorrect.

    Advice is to use the right f/o mix.

    ALSO, engine will last MUCH longer if you fabricate a gravity clutch.

    This is basically a lever allowing the engine and friction roller to lift off the tire when idling the engine.

    That done, your engine should last thousands of miles.
  3. Paulypopawheelie

    Paulypopawheelie New Member

    took apart my motor to fit parts on new one i got for free turns out i striped the shaft / key slot for fly wheel i have new engine with small shaft so im going to have to change the setup i guess with just a smaller bolt any tips on not having the flywheel strip etc i was thinking i might try a large washer on the new set up?

    pics are of old striped and new one
    070213013256.jpg 070213013133.jpg
  4. 5-7HEAVEN

    5-7HEAVEN Active Member

    You might get some results posting on www.motorbicycling.com

    Research the man called deacon

    He's done what you're going thru.
  5. HeadSmess

    HeadSmess Well-Known Member

    where are you driving the roller from?

    or should i say, hows it attached to the shaft?

    looks like its just a bar, drilled, with a nut up the end?

    1, no out rigger bearing. the pressure you apply the the roller bends the shaft, places huge loads on the bearing, and tends to rock flywheel back and forth on shaft til its flogged out then pop.

    remember it will be bending back and forth over 100 times a SECOND!

    2, thrust. when you tighten the roller or nut it forces the flywheel harder onto the shaft. is it tapered or parallel? i think its parallel. theres no face for it to press against unless it has a shoulder, which i cant see... all that stops it is the bearing. designed for radial, not thrust loading. the other bearing inside the engine also experiences a thrust loading. any play, deformation or bending will upset it.

    thats just what i can see? obviously i didna make it!

    but things ive learnt with friction drives is to support the roller on bearings. one on either side of the tyre. then apply the pressure to this frame, not the engine bearings. leave them to support just the crank! attach motor to this frame too, obviously :) self aligning flange/saddle mounting bearings are ideal and easy to use.

    ive only ever bolted a roller directly to the flywheel ONCE. ever since ive always used some sort of flexible coupling between roller and crankshaft. plate with two holes and corresponding pins, etc... commercial options are lovejoy or helical couplings. try fleabay under "cnc coupling" for an idea... ;) or think about the cushdrive in a motorbike rearwheel :)

    when i look at the new engine you have... okay, use a 1 1/2" washer, say. drill two holes on opposite sides, say 1/4". you place this washer on the flywheel, and drill a tiny 1/8 hole real close to the shaft, through washer, and into flywheel. hammer in a lil bit of 1/8 welding rod or something, to "key" the washer. when you place the nut on, either use a washer or dril this pin hole so the nut covers it and holds pin in place.

    thats your "shear" pin. it will break before anything! maybe use two or a thicker rod... no more than 3/16!

    now, you have a drive dog pinned to the flywheel. it will spin with it, and the flywheel nut holds it all on. theres no more load on the assembly than when used as intended ;)

    get your bearings and mount em to a frame so they straddle wheel.

    HINT. use (order lots of, so easy to replace:D) 5/8 ID star washers for the roller! and order 5/8 ID bearings! then a simple 5/8 bolt long enough to go through the lot! if its high tensile it might be ground and really accurate with a nice fine pitch thread with a nylok nut ;) also, ensure the shank of the bolt is long enough to ride on both bearings! eiether space bearings to suit or use washers under end nut, but do not run the threads on the bearing race itself!

    then you have to make another "dog" from another 1 1/2" washer, weld bits of bar into the 1/4 holes for teeth so they engage with washer on flywheel. place washer behind bolt head, assemble bolt, star washers and bearings, tighten, then weld washer to bolt head. you may need a spacer or two between washer and bearing to clear things. grind back bolt head for min clearance and shortest "dog teeth" as possible.

    use the thickest, widest washers you can find that are a good fit on the shaft!
    alternatively, use flat plate and drill all the holes, etc... whatever works.

    flexible coupling finito and never experience flywheel failures again :) then you just gotta mount motor to bearing frame in line :)

    and you should be able to do it all at home with basic stuff :)

    the star washers? they have way more grip than a plain shaft, they can be flipped and reversed on the shaft when worn, they high tensile so dont wear much at all, and the OD is around 13/16 which is the PERFECT roller diameter on a 2stroke :) also very cheap :)
    Last edited: Jul 4, 2013
  6. Paulypopawheelie

    Paulypopawheelie New Member

    thanx for all the info! i just put together everythng and took it for a ride and its rolling i just connected the drive aka bike peg to the shaft bolt - im trying to make this motor last - im a novice to all this i got a little lost on all the specs is there any pics to reference? thanx P DSC05284.jpg
  7. HeadSmess

    HeadSmess Well-Known Member

    this is gunna be the best you get. 5 mins of quick drawing and no more!

    friction drive.jpg

    (rear view)
    drive dog washer. one has two holes, and mounts to flywheel. one has two holes with 1/4" bar welded in for teeth. weld that one to end of 5/8 bolt and grind back til near flat.

    push bolt through bearing, through starwashers, through end bearing, tighten 5/8 nut, locking starwashers to shaft. easy to service when required. bolt bearings via saddle brackets/flanges to mounting frame.

    work out how to attach motor to mounting frame via lugs etc so its in line with shaft.

    mount frame to pushy.


    if it doesnt make any sense after reading twice and having a vague diagram... you want full cad drafting? pay me 140 an hour :)

    dont ask cus i aint repeating anything? except "bolting pegs to shafts with no outrigger bearing spells short life" remember that at 6000rpm any bending happens 100 times a second. it adds up real quick :)
    Last edited: Jul 11, 2013
  8. keatonx

    keatonx Member

    The fd weedeater bike my friend and I made had the same problem with the flywheel- make sure that the nut holding the peg on stays tight!!!!! The peg will start to rock back and forth and let the flywheel rattle around and eventually shear the key, if it's loose.

    When we first made it we were both worried about the crank bearings wearing or the crank snapping, but we haven't had a problem yet and it has hundreds of kms on it. Alot of people
    Think that half-cranks have just 1 bearing and by side loading the shaft you are twisting
    It. But actually there's 2 bearings, they're just on the same side of the crank. 1 right under the flywheel, 1 right at the crank. They are 1 1/2" apart at least, up I 2". So side loading isn't twisting them; 1 bearing is
    Pushed directly up and the other is pushed down.
    But if our worried a out it bending, deflate the tire after riding, and inflate it the next time you go out on it. You can also keep the tire running as far down on the peg (the engine side) as possible, to minimize leverage.
  9. HeadSmess

    HeadSmess Well-Known Member

    ill agree with all this. there are two bearings. or one big long plain bush on old girls :)

    but if the crank itself is flexing...it is only 10mm or 12mm in diameter... and if theres any side load on the flywheel that it just wasnt designed to take...ie, an extended shaft with side load...somethings gotta give. usually the flywheel because its only soft aluminium riding on hard steel

    tightening nuts works to a degree but never eliminates the problem... pumping up tyres for every ride is a hassle.

    problem. flywheel gets side loading and chews out because theres a lot of leverage rocking it back and forth a few hundred times a second.

    cure. take load off flywheel, use it to drive only, just as intended. not as a structural support.

    i havent done a friction drive in years... the itch is hitting me.
  10. 5-7HEAVEN

    5-7HEAVEN Active Member

    Pauly, how about this?

    Weld or bolt an angle bracket from the housing to the other end of the peg.

    Use the bracket to support that end.

    Good luck.