PK Rebuild After Top End Failure

Discussion in 'Performance Mods' started by 210061741, May 19, 2010.

Tags: Add Tags
  1. 210061741

    210061741 Guest

    Iv'e been rebuilding a PK-80 that someone sent me.
    It was siezed up and wouldn't turn over.

    Here's what i found.

    A large amount of metal dust behind the clutch and around the countershaft bearing housing.

    Take a look.

    Initially you would expect that the bearing spun in the housing.
    In fact it didn't.

    All that metal was from the clutch cover.

    The 3 guide pins on the clutch assembly and the star nut were wearing through the clutch cover.

    I have noticide this on a few of the PK engines.

    After further dissassembly of the engine i could easily determine the real cause of the failure.

    The wristpin needle bearing was severly damaged.
    Several needles were broken to pcs.

    You can see the needle fragments and severe damage to the wristpin as well.
    Deep gouges around the pin where it broke in half.

    After the needle bearing failed it caused extreme loads on the wristpin and got very hot.

    The wristpin was snapped into 2 pcs after the bosses inside the piston fragmented due to the extreme heat.

    You can see the fragments from the piston and it is also cracked on both sides from the skirt to the piston dome.

    You can see the top of the boss is gone.

    The good thing here is this is all easy to fix.

    I have a new piston, Wristpin, And Needle Bearing for this engine.
    I will be replacing all the gaskets and seals and also have a set of the Quality 6202 mainbearings. The engine Cases and Crank are in good shape as well as the rest of the engine. The cylinder has 1 minor scratch in it and is still usable.

    However i will be replacing the cylinder with a ported cylinder.
    I cut the transfer tunnels much larger to help with flow and produce higher power.

    The exhaust port it cut a bit larger and the intake is substancially dropped.

    This engine will soon be going back to it's owner who will be using it with a shift kit and a nexus hub.

    Cant wait to see what he gets out of it.


  2. GearNut

    GearNut Active Member

    That all is right on par with the common failures I have learned of with most any HT engine.
    These things would last sooo much longer if there were initially made with good quality bearings.
    I have 2 engines, one used, one brand new, that I plan on cleaning up the ports on before I run them.
    Can you or would you sell the quality bearings you use to the common tinkerer so we can upgrade these engines before they fail like that?
  3. 210061741

    210061741 Guest

    Yup there all commonly available.

    I get them from erie Bearing.

    For the bearings in the case...


    F.A.G. 6202.2RSR.C3.J22R Pull the bearing seal on one side for the mainbearings.
    The bearing should be open sided inside the crankcase to get oil.

    F.A.G. 6202.2RSR.C3.J22R
    Leave both sides sealed.

    And for the wristpin bearing
    INA Needle roller and cage assemblies K10X14X13-TV

    It's pretty common too and cost $5.00. Rated to 29000 rpm

    Erie Bearings has them or can get them.

    The 6202 bearings are $10.00 ea.

    You cant change the crankshaft big end easily.
    It's an odd size
  4. 210061741

    210061741 Guest

  5. give me vtec

    give me vtec Active Member

    you're the man rich.

    You are pioneering work that people will reference for years. I think this thread should be made into a rebuild sticky others can use in the future.
  6. GearNut

    GearNut Active Member

    Thank you VERY much, rich!
    This is definitely an upgrade that everyone should do if they can.
  7. 210061741

    210061741 Guest

    I have never run an engine out of the box.
    I take them all apart.

    But yup...Them are good bearings.

    I run my little engine to death and haven't had a critical failure yet.

    The good thing about putting a sealed bearing on the crankshaft is it keep the spring on the crankcase seals from getting into the bearing.

    I have experienced that 1 time.
    Destroyed the bearing cage real quick.
  8. Fabian

    Fabian Well-Known Member

    Hi Rich,

    It's refreshing to see that you've taken good quality, high resolution and in-focus photos.

    Nothing is more frustrating than lousy, out of focus photos in this day and age of digital automatic, point and shoot cameras.
    It's just not possible to get a bad photo these days with digital cameras, but some people manage to do the impossible.

    Regards Fabian
  9. Fabian

    Fabian Well-Known Member

    What you can do with the conneting rod big end bearing is to modify the connecting rod by reaming it out to 22mm and driving a high carbon sleeve back in the hole and machining the I.D back to 20mm.

    You can then use a high specification caged needle roller bearing of the size: K16 x 20 x10, instead of the standard K16 x 21 x10


    You can just use a new style crowded roller bearing replacement crankshaft which solves all the previous big end bearing problems.

    I've written about my surprisingly simple solution to prevent big end connecting rod failures (the only thing that has ever failed) in all my 5 engines, by a simply jetting the carburettor correctly and using 98 octane fuel and 20:1 fuel/oil ratio.

    Last edited: May 20, 2010
  10. 210061741

    210061741 Guest

    Yes you are correct about the bearing Fabian.
    But that is beyond the means of the average tinkerer.

    If i was going to rebuild the bearing i would use the full complement of rollers. "Cageless"

    But it seems that buying a cheap Moped Crank Solves them issues.
    Plut then you have something that is properly balanced up to 12000 rpm reliably.

    I know you have some pics of what you did with the bearings.
    Can you post them for us.

    Options are allways good.
  11. Fabian

    Fabian Well-Known Member

    The pics i have are of the damaged bearings.

    Initially, i bought a few caged needle roller bearings and pulled the rollers out with the intention of setting up the crank to run a crowded roller arrangement.

    Never got around to doing it though, as the shop where i bought my engine from, gave a very good deal on replacement engines, as i was providing them with valuable info and hi-resolution photos of where engine damage was occuring.
    This info was personally delivered to the Nantong Jali factory in Japan, and they decided to go the route of using a crowded needle roller bearing, as it was the cheapest and most effective solution.
    Having said that, the factory was already in the process of converting to the crowded roller bearing setup, as it was the only thing left for them to change, as they had significant numbers failing in their prime export market - America.
    The photos, just confirmed that they were going in the right direction.

  12. 210061741

    210061741 Guest

    Ok that's cool.

    Ya i like the crowded / Full complement bearing.
    Stays alot tighter and i never had 1 fail yet.

    But there are lots of options. I was incorrect about my earlier statement.

    I measured up several rods and bearings and here's what i found.


    bearing = K16X22X12 and are available.*K16X22X12;aI-KogwPZIu5?clrsb=1 K16x22x12 $8.00
    INA are considered 1 of the best.


    bearing = K16X22X12 and are available.*K16X22X12;aI-KogwPZIu5?clrsb=1 K16x22x12 $8.00
    INA are considered 1 of the best.

    PK Cranks vary.

    bearing = K16X22X12 and are available.*K16X22X12;aI-KogwPZIu5?clrsb=1 K16x22x12 $8.00
    INA are considered 1 of the best.


    bearing = K16X20X10 and are available.*K16X20X10;a5b0myRjccb8?clrsb=1 k16X20X10 $3.81
    INA are considered 1 of the best.


    bearing = CROWDED 2.5MM x 10MM NEEDLE ROLLERS.

    OR*K16X20X10;a5b0myRjccb8?clrsb=1 k16X20X10 $3.81


    And last but not least the pics of everything.

    I called erie bearings and the INA Bearings are available.
  13. 210061741

    210061741 Guest

    Posted by Fabian and fits good here. Good data all in 1 place. Yessssaaaaa !!!

  14. 210061741

    210061741 Guest

    One other note about the connecting rods.

    The center to center distance is different between them.

    The GT-5 AF has a longer rod but a shorter stroke than the PK-80.

    The PK80-J rod is about the same length as a GT-2B 50cc engine.

    I'll post the exact lengths and respective strokes later.
  15. 210061741

    210061741 Guest

    Now a couple of other things to consider here.

    The center to center length of the connecting rods changes the Con rod to Stroke Ratio.

    That affecte the port timing of the engine and the angle of the con rod.
    Less con rod angle = more efficcent

    The Pistin Pin offset compensates for the difference in lengths.

    So remember the pistons are different.
  16. Fabian

    Fabian Well-Known Member

    I certainly like the look of the Puch Roller Crank Rod

    Rich, where abouts are you up to with production of reed valve intake cylinders for the 69cc engines (47mm bore size).

  17. 210061741

    210061741 Guest


    I am Unemployed and since i got screwed by Pirate Cycles i'm not doing any production.

    I was the brain and he was the money.

    So you see i don't have the money.

    I have offered to build you the engine if you sent the parts i needed to do it.
    I have offered to give you a parts list and instructions to do it yourself.
    You pay for it and i'll build it.
    Heck i won't even charge you labor just because i'll have so much fun building it.

    And i mean that.

    If you look at the logistics of the situation heres the deal.
    I have been running the reed valve modifyed cylinder..and it is awesome.
    Between the portwork involved and the welding of the block to the cylinder it is very time consuming. And the crappy thing is your still left with a cheaply plated cylinder that won't last.

    So if you want it buy the Puch Top End Kit. $120.00
    I have 1 and it is really nice quality.
    Has a 3 transfer port and a nikisil lined bore.

    Definatly worth the effort.

    + you get a new much better piston.

    If you want an engine get me the parts and i'll build it.
    I won't charge you any labor and i'll post details the whole way.

    For now thats the best i can offer you.

    In a couple of mothns when i get a big settlement and have the cash i may start my own thing.
  18. Skyliner70cc

    Skyliner70cc Active Member

    Based on pirate's latest change to their performance engine website (no porting, no reed valve intakes, etc..), I'm thinking you were the brains behind the operation. I wish you luck and hope you are succcessful in producing a high pwoer HT engine.
  19. Fabian

    Fabian Well-Known Member

    Hi Rich,

    So whats the go here.

    After you get your divorce settlement, will you be adapting Puch top end parts to fit on the Happy Time style bottom end?


    Will it be a Puch top end on a completely redesigned bottom end?

    How will it work engine installation work with those who already have a SickBikeParts shift kit, or will you be designing your own custom shift kit to fit your specific engine combination?

  20. Joeeastman

    Joeeastman New Member

    Hey, do any of you guys know exactly what motor used the crank with the ZAF60 con rod and where I could get a replacement? I need one badly! Thanks