Engine Woes - Less than 300 Miles (smaal end bushing)

Discussion in '2-Stroke Engines' started by Kielohawk, Jun 6, 2007.

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  1. Kielohawk

    Kielohawk Guest

    Ok guys, under 300 Miles on my bike. My upper arm bushing fragged out. Any advise? Can you buy bushings for the arm?


  2. Guest

    Guest Guest

    Have you contacted your seller?

    How did it happen?
  3. Kielohawk

    Kielohawk Guest

    I was cruising along and the engine started getting a tad bit louder (like an exhaust leak or weird vibration. Then it started losing power and eventually died. I peddled home, found the spark plug contacts pushed up making contact with each other. I took the engine top off and found some minor damage to upper piston edges. I took the top half off and found the piston had a lot of play. I looked under the piston and saw that the bushing was practically gone. It had broken apart and just the part inside the actual arm was still there. I punched that part out but can't find anything around the house to make another. Is it brass or copper? It looks kinda like brass.
    I purchased the engine on EBay from a seller named Powerkingshop. I emailed them to see if they offered replacement or exchange. It is a Power King 80CC.

  4. OldPete

    OldPete Guest

    The wrist pin bushing is brass and the fit to the wrist pin has a clearence of about .0005" to .00075". Yep! It's that close.
    The big end of the connecting rod is probably one piece. In other words, there are no rod bolts on the big end. This means it is a pressed-up crank with roller bearings in the big end or crankpin as some call it. If this is the case, the case must be split, the crankshaft removed, pressed apart, the connecting rod repaired or replaced, then the whole plot cleaned 'n reassembled.
    When I worked on my Mercury outboards in the early '60s, they had bushed small ends on the rods, we ran 28~32 to 1 oil 'n gas. They smoked!

    Some of these Chinese engines have roller small ends, it might be cheaper just to buy one of those. I have no idea what brand or type they are. Someone here is sure to know.
    If you were running cheap oil, mixing it lean or ran with a fresh air leak into the crankcase for a time or ran over heated for long periods ( like long full throttle runs on 100+F days, any of those could have helped kill the small end. Could have been a defect. The seller might have felt it going bad and sold it before it went catastrophic. Who knows? Only you and the seller.

    Good luck.
  5. Kielohawk

    Kielohawk Guest

    Thanks. I am running synthethic. 36:1 ratio. When I first took the piston off the arm, it looked like the bushing that goes through the hole at the end of the upper arm was in the hole unevenly. The hollow steel pin that goes through the piston, then through the bushing and the upper arm is good to go. I hope to hear something from the seller tomorrow or maybe something from Dax about parts. Daxs is supposed to ship my 36T sprocket this Friday too.

  6. Kielohawk

    Kielohawk Guest

  7. OldPete

    OldPete Guest

    Post parts pics if you can or pics from the catalog. If you wish to kick this around.

    I used to think synthetic was where it was at. Read the link in my post. If you have questions...ask them. I may not know but someone might.

    This guys info is dated, just like these Chinese engines. Current state of the art strokers can run 50 to 1 with ease but not these crude, inexpensive power-plants. Sure wish I had one to blue-print for review.

    Mark this site's home page and read his two stroke info. Good stuff from this old nut case. No less than 32 to 1 if I had one of these guys.
  8. Guest

    Guest Guest

    Here you go.....[​IMG]
  9. Kielohawk

    Kielohawk Guest

    I have that diagram on the back of my book that came with the engine. THe numbers aren't so clear. It's number 29 that went bad. I am gonna give Dax a call here in a few minutes.

  10. OldPete

    OldPete Guest

    Thank you for the pic.
    Just about all strokers and most of the old 4 stroke m/c engines had cranks like that, those are called built-up or pressed-up cranks. The rod big end has no rod cap or the bolts used to remove/install a rod cap. This is lighter, permits a smaller crankcase for compression on the down stroke and maintaining tolerance during manufacture is easy compared to a plain beaing crank/rods. The roller 'n ball bearing bottom ends are also tolerant of more dirt/grit or misalignment, than plain bearing cranks.

    The wrist pin or small end is a bushing and that IS the weakest link in this motor. The better way to install a new piston would be to lube the bore areas where the pin rides, chill the pin in the freezer, warm the piston 'n rod small end with a hair dryer on high, then slide the pin home with the piston facing the right way and one circlip inplace to stop the pin from going too far. Open portion of the circlip always faces down.

    Ya know OP,
    If the small rod end and pin were properly hardened a caged roller bearing might fit. Please do a good follow up in this thread.
  11. Kielohawk

    Kielohawk Guest

    I snapped some pics of the damage from running the engine with a bad upper arm bushing.

    Here is the engine after I punched out the bad bushing (what was left of it) This shows the upper (wrist?) arm where the bushing gets pressed into...
    Here is what's left of the bushing that I punched out. Lots of metal missing[​IMG]
    Here is the Piston. Lots of damage on upper part, the rings have some scoring also.
    And the upper engine.. Not too damaged.
    The wrist pin and clips are Ok
    Thatsdax is supposed to be adding some bushings to his site so we can buy them. Looks like I will be purchasing a new piston, rings, and bushing at least. Do you guys think I should replace the cylinder?

  12. Kielohawk

    Kielohawk Guest

    Oh yeah, does anyone know if the Dax 70/80 parts will work inside the Power King 80 engine?
  13. OldPete

    OldPete Guest

    Fact: The bike should have been pushed or pedaled home as soon as this noise/vibration started. I post that for others as well as the OP.

    Piston pin to bushing fit must be very close as I noted above. Nothing over .001" will really do. If pin fit is .003", the repair will do for selling to a non-friend. :evil:

    The bushing must be pressed into the rod and not all rods will have the same press fit, that will alter the bushings inside diameter, then the bushing must be precision reamed for fit. With the rod off the crank the bushing would be reamed close to fit, then finished with a Sunnon honing machine. I have done this work, allbeit 40 years ago.

    Two things about the cylinder bore will be considered.
    Are the scratches deep enough to catch a finger nail? If yes, it will need a proper honing. Are there aluminum deposits on the cylinder wall? If yes, these MUST be removed by honing or the piston will start to seize after a few hours of operation at best.

    Like it of not, the con-rod just might have bent from this internal activity. If it is bent too much the piston will drag, over heat and seize. If it is bent just a tad, the motor will work but in a labored state. Power output will take a real hit.

    Like it or not, there will be debris in the crankcase that MUST be removed, otherwise it will find a home on the cylinder wall. True, some will be blown out but the gamble to my work would force me to split the case and clean it out properly.
    The real debis of this failure are hidden behind the flywheels of the crankshaft around or in the crank's ball main bearings.

    My intent is to be honest not mean. Take it for what its worth. :cool:
  14. Guest

    Guest Guest

    Put some butter on it, 'cause that jug is toast!

    Nikasil lined cylinders with that much (or virtually any) damage are goners.
  15. OldPete

    OldPete Guest

    Opps! Thought it was a cast iron bore.
  16. Egor

    Egor Guest

    Sorry to say that I think you will have to put most of those parts in the dust bin. I have put a Kings top end on a Dax engine, I had to drill out the 6mm head bolts to 8mm. I am not sure about the Gudgeon pin bush. On a Hodaka one of the only motorcycle engines I can think of that came with a bushing, we had to ream it out after install, but it was not made to use as made. The bushing for the china engine is a large thick bushing it might make the press fit, anyone know? I have taken these cranks apart, but you need a special tool, if you like I will make a drawing of one, it is not hard to make. I have never found a proper place to get the small parts for these engines, I need the big end rollers and cage, with a new rod. A few outfits have the complete crank but I have never used a new crank unless I had to, just me. Some of these engines seem to go forever and others last a few days, I will not say who failed, but everyone is good about the replacements as a general rule. I rode a Whizzer as a kid and never got over it, I would have one now if not for the cost. Have fun, Dave
  17. Kielohawk

    Kielohawk Guest

    Thanks man. I have been talking to Thatsdax (Duane) a lot in emails. I had ordered a cylinder, piston, rings, and new upper wrist bushing (bearing) to fix my PK80 engine. I asked him if the dax engine parts were interchangeable with the PK80. He told me that his engine came with 8mm engine studs instead of 6mm and that his parts might not work on the PK80 engines especially the cylinder. So we cancelled the cylinder, and he is sending me a grab bag used engine that a customer had sent back for some minor issue. I am going to tear the upper half down on his Dax 70, upgrade the piston and rings, check the upper bearing for wear (replace if needed) and now I will be a user with a Dax70 instead of the PK80. I should have just ordered a Dax first.
    My fault as a rider was not knowing what particular vibration and noise came from the engine when the upper bearing goes out. While it was happening, I thought it sounded like the muffler baffle rattling inside the muffler body. I know now. And knowing is half the battle!! G.I. JOE!!!
  18. Egor

    Egor Guest

    My every day rider is a Dax engine. A friend of mine was the original owner, and Duane replaced the first engine, I like there engine, it has a built up crank shaft. It uses hidden balance holes as not to increase the volume of the crankcase, that is important in a 2 stroke. It is smother running also. Have fun, Dave
  19. locoWelder

    locoWelder Guest

    I agree, unless you can have it rebored, time to get a new one.....now handa70 hop up rings and pistons will work but they take alot of work to piston and jug to get them to match
  20. Kielohawk

    Kielohawk Guest

    FYI everyone. I ordered this kit from EBAY. Its a Power King 80 from seller POWERKINGSHOP. I got an email from them after I told them what happened and if they could do anything about it. They pretty much told me, Sorry bout your luck. Sold brand new as is. I paid $188 usd total.
    Oh they do cover "dead on arrival" from shipment or manufacturing damage or defects up to 7 Days from receipt of item.