Catastrophic aluminum bushing faliure.

Discussion in 'General Questions' started by Gear_Head_717, Aug 31, 2014.

  1. Gear_Head_717

    Gear_Head_717 New Member

    It happened, today was the day...... Catastrophic engine failure. For the sake of others I was testing the aluminum upper connecting rod bushing sold from juice motor parts. The bushing wore away from the connecting rod friction. With all the play in the piston a small piece of the piston snapped off. It was the remaining material from skirt cut on the intake side. Along with that the opposite side retaining clip snapped. The bottom clip also snapped into 3 or 4 pieces (some are still in the crank). Amazingly only the transfer port skirts were damaged on the cylinder. And the steel piston pin is undamaged. Piston and rings are done however. SO could I open the transfers and still use the same jug? I have inspected thoroughly. I also wanted to know if the con rod is still usable? With my caliper the ID measured and avg. of 14 mm. on the upper connection. I'm glad I killed the engine when I did because it could have been much worse. Best place to buy new parts???? besides JNM, CMB's, arrow, jake, or ebay.
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  2. HeadSmess

    HeadSmess Well-Known Member

    aluminium bushing? thats a bad idea! get the piston and bearing with the correct diameter... bushes will always fail unless pressed/heat shrunk in and glued... thats a sales gimmick, if i ever saw one! get the correct pin and bearing... thats not "friction" failure, thats "incorrect application, badly designed, lets sell parts" failure. the conrod will be fine, as long as it hasnt gone oval or anything. stock standard needle bearing just slides right in, no need to use bushes or brass bearings or anything. remember that piston accelerates and decelerates a few hundred times a SECOND! any extra parts are just begging to break and wreak havoc...

    scores only at the lower side of worries :) just rub back any burrs, and try getting it re-honed for new rings. its ABOVE the ports that matters.

    who told you to make the piston cut SQUARE? (dont worry, i have a vague idea who... you seriously clicked on that signature link? :jester:)

    best shape is round, reduces noise on induction, and reduces fatigue failure... taking that much off, that you have...better just to continue all the way round to the existing cutaways, that lil dangly bit was bound to let go! and unless you were running reeds... you took way too much off :( only has to match the top of the intake port at TDC, DEFINITELY NO WIDER THAN THE PORT, and even thats bordering on too much cut... still need to retain some blowdown time, skirt strength, AND prevent too much reversion at low speed. (piston ported)

    looks like you got all the bits out, so bottom end should be ok still... should be...

    remember to face the tag on the end of the clip with piston travel, else they buzz up and down and break off.

    reminds me vaguely of using a brass bearing in a motorbike once... set the reamer wrong, over did it...and not just the piston copped it, but the end of the rod was smashed up into lil pieces...never found the wrist pin at all :) no fault of the bushing, just operator error :) rings were fine but!
  3. Fabian

    Fabian Well-Known Member

    :iagree: When i reat that line i said to myself "WTF" - aluminium bushing, you must be pulling our collective legs.

    Why would a person install an aluminium bushing when you can install a needle roller bearing.
  4. Fabian

    Fabian Well-Known Member


    If using a standard exhaust system, i have found no appreciable performance improvement when modifying a standard piston.
  5. butre

    butre Well-Known Member

    juice moto parts is selling them as an experimental item. in conjunction with a titanium wrist pin it's apparently a 10 gram weight reduction, and with some lightening holes in the piston it's worth roughly 15% top end mass reduction. It would probably be really great for the guys who are doing one race and rebuilding the engine but I don't think it's too good an idea in a normal engine.

    I imagine the typical hardened steel wrist pins would wear the bushing out too quickly, and a softer wrist pin would improve the life of the bushing. not to mention that the thing probably wasn't press fit in
  6. Fabian

    Fabian Well-Known Member

    I would say that a catastrophic bushing failure and subsequent piston disintegration probably shaves more than 15% off the weight of the top end mass.

    It appears to be a very useful modification for reducing top end reciprocating weight if engine reliability is not a primary concern.
  7. butre

    butre Well-Known Member

    I think reliability would have to be no better than quaternary concern for me to use one of these things
  8. HeadSmess

    HeadSmess Well-Known Member mean someone is selling that bush as the LITTLE END BEARING?

    i thought maybe it was because the piston has, say, 12mm pin and for some strange reason its been bushed to take a smaller pin as the bearing is 10mm ID, but that...that just makes me reel in disbelief!

    back to my first impressions! WTF?

    balance is of no concern in my opinion, and ive never found any reason to start worrying about it yet. maybe its my bike. maybe its my determination to use nothing but the 48cc. maybe its just me! but i dont seem to get these "terrible vibrations" everyone complains about. hands used to go numb riding my roadbike around, in just a few minutes... but these things? i can ride all day :) bare hands, hard as *^%& grips that come supplied with the kits, etc etc etc...

    maybe it is me, because half my job involves standing on a jackhammer? and ill tell you exactly which ones send your hands numb!
  9. HeadSmess

    HeadSmess Well-Known Member

    :iagree:...that ones a cracker :jester:

    shame half that removed weight invariably ends up in the bottom end :rofl:
  10. butre

    butre Well-Known Member

    my buddy's harley shakes worse than my 66cc. I think a lot of people just have sensitive bottoms or something
  11. Fabian

    Fabian Well-Known Member


    My chainsaws "all" vibrate more than the 66cc engine. After 4 hours on the chainsaws, my hands go tingly numb, but i can ride all day on my bike and they never experience that sensation.

    That said, reducing the normal operating rev range of the 66cc engine greatly reduces vibration to where it is not even a concern. You just need to boost torque output to compensate for lost power and then to change the bicycle/jackshaft gearing to give similar road speed as to what you had before.