Engine Trouble connecting rod to crank locked up. need some info

Discussion in '2-Stroke Engines' started by tigatron, Jun 17, 2014.

  1. tigatron

    tigatron Member

    So while riding home from work last night my motor died.
    Got it ripped as far apart as I can for now and found that the reason it died is that the connecting rod to crank is locked up.

    I know there is a clutch removal tool (my kit didn't have one) does this tool remove the small gear next to the clutch too and the left side drive gear? If not what will I need?
    Do I need and a special tool to remove the mag setup from the left side?
    Does the crank come apart where I could replace the connecting rod to crank bearing or would I be better off just ordering a new crank / rod when I order gaskets.

    Trying to weigh fixing this motor vs. A new motor.

  2. crassius

    crassius Well-Known Member

    you need that tool for the small bezel gear

    rotor comes off OK, but sometimes the key inside hangs up a bit

    unless you're good with engines, I'd recommend getting a new one & using old one for parts
  3. tigatron

    tigatron Member

    Thanks. So I can get the rest out of the way to crack this thing open with just that "clutch tool" then?

    I've dabbled a bit with 2-strokes but mostly work on car engines (including full rebuilds) so I'm thinking I should be able to fix this once I can get the crank case apart.
  4. crassius

    crassius Well-Known Member

    getting the crank trued up (and keeping it true while pressing cases back together) takes a bit of skill that is different from that which is needed for cranks you may be used to
  5. tigatron

    tigatron Member

    I could see it being "fun" but i had to open the case in my old moped to inspect everything (sat 5+ years before I got it) and managed to get it back together and used it for years (now somebody else is using it)

    I'm thinking I'll see about locating a puller tool and crack it open ang from there worst case I spend $5-10 on the tool and decide not to fix the motor.
  6. butre

    butre Well-Known Member

    I say just pull the piston off and smack the connecting rod with a mallet until it frees up. It won't be pretty but it'll keep it running long enough for you to get a replacement in. just lubricate the **** out of it, run like 15:1 in the mean time.
  7. tigatron

    tigatron Member

    Might give it a try lol can't make things much worse.
    I was looking at a bunch of sights for parts and am seeing different connecting rods for 49 & 66 cc (assuming piston pin size is different); what's got me tho is every place that offers a crank with rod already installed doesn't list if its a 49 or 66 cc rod.

    Not sure where to order from yet either. Figuring while its apart I'll need new gaskets, better bearings (where should I get these and what ones)
  8. Fabian

    Fabian Well-Known Member

    :iagree: and it's a +1 for me.

    I couldn't have given better advise myself
  9. Fabian

    Fabian Well-Known Member

    Last edited: Jun 18, 2014
  10. tigatron

    tigatron Member

    Thanks for the link.
    Probably going to be thevend of the month before I can see about working on this too much but trying to gather info and find where is best to get parts from.
  11. Fabian

    Fabian Well-Known Member

    Commonly, 2-stroke replacement crankshafts come with the connecting rod preinstalled, because the crankshaft is a 5 piece item; requiring an accurate press fit of the pin into the left hand side and right hand side of the crankshaft halves.

    A crankshaft should cost around $30, though there are some sites where you can buy the individual crankshaft parts and assemble the crankshaft yourself.
    My recomendation is not to waste your time. Simply purchase a replacement crankshaft (for your engine capacity 48 or 66cc) with the crowded needle roller bearing design.
  12. tigatron

    tigatron Member

    That was what I was planning.
    Could you point me to a crank with the crowded needle roller bearing design for a 66cc motor?
  13. Fabian

    Fabian Well-Known Member

    I would think that most of the manufacturers have converted their cranks to the crowded needle roller design.


    this is the difference between the traditional design (as seen in just about every Japanese and European 2-stroke engine) and the crowded needle roller design, which distributes load over a greater number of needle rollers:

    Crowded Needle Roller Design


    Caged Needle Roller Design

    Last edited: Jun 18, 2014
  14. tigatron

    tigatron Member

    Seems I'm just having trouble finding a place with 66 crank assembly
    Last edited: Jun 18, 2014
  15. Fabian

    Fabian Well-Known Member

    You should have no problems, because it's a commonly available spare parts item.
  16. tigatron

    tigatron Member

    Where should I check? So far all I'm finding is sites that don't specify and ones for 48cc; found 1 listing (pistion bike) 66cc but is out of stock and doesn't list if its crowded or cage bearing
    Last edited: Jun 19, 2014
  17. HeadSmess

    HeadSmess Well-Known Member

    get a new engine, plain and simple. by the time you stuff around doing anything anyone here has told you to do, you could have bought two...

    reading the post just above this boxy thing im typing in...youve already found theres a plethora of confusion on what parts fit what.

    i wont even read this thread because ill be smacking my head really hard :)

    if anyone suggested getting the crank pressed apart, and replacing with crowded needles, just remember that crowded needles dont like high speeds AT ALL. when they rub on a cage, thats stationary. bad enough. when they rub against each other? one side goes up. one side goes down. the speed at the contact point between two rollers is DOUBLED. also, if they skew in the race...crunch.

    i assure you, the person that recommends crowded rollers runs his engine far too slowly, and blames all subsequent failures on china technology and its inadequacies.

    for maximum LOAD bearing capabilities...do what the harley draggers do...throw away the needles and use bronze bushes. needles suffer this problem called BRINELLING. maybe i have too many engineering books that always say the same things? of course, thats being silly, as it involves splitting and repressing a crank, when the cheapest easiest option is a new crank or engine...

    just my ha-penny ;)
    Last edited: Jun 28, 2014
  18. Fabian

    Fabian Well-Known Member

    With respect to a newbie i completely agree with your advise.

    I also agree with this logic because even from my vendor, i have found that just 6 months can give variation in the pressed width of a replacement crankshaft as well as the internal width of the crankcase.
    When i have bought spare cranks, i have done so using crankshafts from the "SAME" shipment that the engines were delivered from China. This ensures that replacement crankshafts fit the internal width of the engine case.

    I also completely agree with this statement, but from my experience the crowded needle roller design can safely rev to 4,800 rpm and will handle short bursts to 5,200 rpm, but is far happier with a max rev limit of 4,500 rpm to give long term engine reliability.
    4,500 rpm is enough rpm to give a reasonable balance between longevity and power.

    If you call my self imposed absolute maximum rev limit of 4,800 rpm slow, then we have different definitions of the term "slow rpm".

    This is a completely unnecessary modification; yielding no real world benefits when it comes to the superiority of the crowded needle roller big end connecting rod bearing system, with respect to the Chinese 2-stroke motorized bicycle engine, when fitted with the Jaguar CDI system.

    This is pertinent advise for a newbie, especially if they have no mechanical aptitude or no mechanical experience with 2-stroke engines or their design and/or operating theory.
    It's not a difficult process to install a replacement crankshaft (once the engine is sitting on the workbench) taking me about two hours to split the cases; extract the damaged crankshaft, install a new crankshaft and reassemble the engine.

    That said, i have seen someone who claimed to have good mechanical knowledge (mentioning that he worked on his 2-stroke dirt bike engine) make a monumental f$#kup of the engine disassembly and rebuild process; having me standing back scratching my head, saying to myself "it's just not possible that one person (working on their own) can so completely f$#k it up; presenting a level of mechanical butchery that had to be seen to be believed.
  19. HeadSmess

    HeadSmess Well-Known Member

    yep. slow vs slow.

    i call a diesel running at 4800 FAST. i call a car at 5200 near its redline usually.

    i call a small 2 stroke at 4800 as barely breaking idle.

    coming from a background of chainsaws running at 11000 rpm, and small nitro engines up at the 28000 rpm range.

    not having a tacho, but having perfect pitch, i still reckon im doing around 7000 rpm... maths backs me up. 26" wheels, 36T rear, 60km/h...

    and with no mods, thats as fast as a HT seems to go, because it makes no difference down a hill if i pull the clutch in or not! ie, unloaded, they still dont rev out :) maybe 8000 max, unloaded, stock.

    the occasional one does, but they usually have "clean" ports... but, take the chain and clutch off a chainsaw, put it in a heavy steel box and give it WOT... theyll get to around 15000 when things start breaking. even when the con rod is simply a stamped piece of alloy. listen to even a cheapo ryobi brushcutter rev out compared to a HT...

    im not saying a HT is anywhere near capable of doing that! i wouldnt ever aim for more than 9G.

    i did say a bronze bush is silly :) but for maximum load bearing, bushes still reign supreme!

    the argument i raise. any ball only has point contact. any roller only has line contact. a very thin, narrow line.

    all engineering texts mention that only ONE roller EVER takes the full load. except in the case of taper roller bearings that are preloaded.

    some scans...(not sure if i can get the resolution up...soz) since 1953, nothing has changed in regards to bearings, exception being, possibly, ceramic bearings. also mentions "in the early days, all bearings were of the "full type", still used for SLOW speed, HEAVILY LOADED areas..."

    bearing load diagram-1.jpg
    bearing load diagram-2.jpg

    now, a bush...well, a bush when it fails, doesnt fill the case up with shards of hardened steel. the arc of contact is almost half of the shaft diameter. sure, the friction is higher at high speeds, but the load rating is much higher.

    but, i still think its silly :)

    stick with the cage bearings. they were developed for a reason.

    oh! last thought! if you want to go with the press crank and replace rod and bearings alone....you will ALSO require a new CRANK PIN, as if its seized up, that will be damaged. badly.
  20. Fabian

    Fabian Well-Known Member

    That might be fine in theory, but in practice i have never had a crowded needle roller assembly prematurely fail, yet every caged needle bearing assembly has failed in a surprisingly short time.

    The crowded needle roller crankshaft is a superior design when it comes to the Chinese 2-stroke motorized bicycle engine.
    Don't leave home without it!