A reviev of Wrist Pin Bearings

Discussion in 'Performance Mods' started by 210061741, Mar 2, 2010.

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  1. 210061741

    210061741 Guest

  2. professor

    professor Active Member

    Very good Rich!
  3. 210061741

    210061741 Guest

    Thank you.
    Im trying to help everybody !!!!
  4. Fabian

    Fabian Well-Known Member

    My Happy Time style 80cc engine uses a wrist pin bearing that's 14mm wide.

    So far, i've never had a wrist pin bearing fail (which really surprises me) and all the bearing failures i've experienced have been the caged needle roller bearing on the connecting rod big end, BUT i've worked out the reason for these failures and the solution to the problem has turned out to be non mechanical in nature and very simple to fix.

  5. Dilly Bar Rob

    Dilly Bar Rob Member

    Awesome! Nothing like direct comparison! Looks like you have a bunch more to "compare" on that table :)

    All my motors so far have been PK 80's... looks like all my future ones will be too.

    Fabian: what was the reason, and what was the fix? More oil or simply just don't over rev?
  6. Fabian

    Fabian Well-Known Member

    The first engine destroyed the big end connecting rod bearing at 700 kilometers (450 miles)

    The second and third engines did the same thing at almost exactly the same distance.

    The fourth engine did the same thing at 800 kilometers (500 miles).

    I rebuilt the fourth engine with a replacement crankshaft and after 350 kilometers it started to show early signs of destroying the big end connecting rod bearing.

    After some research, i found that the Chinese have copied a carburettor that originally used a No 82 Dellorto main jet.
    I experimented with a No 82, No 83, No 84, No 86 and No 90 main jet, together with the same 98 octane fuel and 20:1 oil ratio i've always used.

    The change was just unbelievable when going to the No 82 but it was still detonating slightly.
    The No 83 was better but i wanted an insurance margin and ended up using a No 84 (slightly rich at 3000 rpm).
    The No 86 was too rich at 3000 rpm at wide open throttle.
    The No 90 had the engine drowning in fuel.

    The engine ran noticeably smoother with the No 84 main jet and with far less vibration.

    I've spent an extensive amount of time documenting and photographing problems with these engines and all information has been sent back to the Nantong Jiali factory in China.
    As it turns out the factory knew about these problems because so many of the engines were failing in the American market - they had to do something about it.
    The factory solution was to convert the big end connecting rod bearing from a caged needle roller to a crowded needle roller bearing setup, yet i believe for the most part the main reason for such rapid bearing failures is incorrect jetting.

    What seems to be happening with the shipments arriving in Australia, is that the carburettor used on the 48cc engine and the 66cc engine both have the the same main jet - a case of the factory using a "one carburettor fits all" policy.
    As a result the 66cc engine runs lean and detonates itself to pieces, hammering out the big end connecting rod bearing.

    I've now passed the 1200 kilometer (745 mile) mark and the engine is still running on a partially damaged bearing, rattling away the same as it did at 350 kilometers, which confirms my idea that severe detonation with the standard main jet was killing all previous engines.

    Cheers Fabian
    Last edited: Mar 4, 2010
  7. Pablo

    Pablo Motored Bikes Sponsor

    ThanksRich for the vid, too bad the camera doesn't have a close focus. Couldn't see the rollers at all.

    A few comments. So Grubee uses a smaller bearing. Interesting. Canadian guy called me yesterday about his exploded Grubee.

    Fabian - interesting, but the stock 0.70mm jet is too rich in many engines, so how does that figure? I've been running a 0.66mm for 2 years of hard running, time trials, STEEP hill climbs on my test pig 67cc mountain bike. (constantly smoking and adjusting the clutch to get a HARD bite). Whenever I pop my head or plug - the fuel evidence is on the rich side. Never blown an engine up. Am I just lucky?
  8. Fabian

    Fabian Well-Known Member

    In relation to all four, or technically 5 engines that i've had, they all sounded a bit rattly, but i just thought they were poorly machined and assembled so accepted these rattles as normal.

    I didn't realise that the engines were severely detonating and that's with 98 octane fuel!
    The only modification i've made are that of grinding out the aluminium intake tube for a smoother turn radius at the elbow.
    I'm sure the larger D-sized hole adds a bit more flow to the system, but i can't see it allowing such an increase in air flow that a massive increase in fuel flow would be required.
    I know some may suggest the intake tube to cylinder or intake tube to carburettor might have air leaks for it to be requiring a No 84 main jet, but this is not the case as i've sprayed mineral turps all over the carburettor and intake tube when the engine is idling and the rpms do not change at all.
    This suggests absence of air leaks.

    I've read many times, how people have found their engines to run optimally on a No 72 or No 70 main jet - compared to my engines, i don't know how this is possible.
    When i ordered my Dellorto SHA clone carburettor from Rock Solid Engines, it came with the standard No 76 main jet and a Rock Solid Engines "preferred" No 72 main jet.
    For the life of me, i couldn't get the carburettor to run correctly - the engine ran poorly with the No 76 and even worse with the No 72 main jet.
    In the end after about 2 days of frustration, i gave up on the Dellorto clone and went back to the standard NT carburettor which ran a lot better.
    In hindsight, i should have tried experimenting with larger jet sizes.
    Who knows, with a No 82 or 83 or 84 main jet, the Dellorto clone might have worked very well.
    Having said that, the NT carburettor works perfectly with the No 84 main jet and the circlip installed on the highest setting (the needle sitting in the lowest possible position in relation to the needle barrel and the carburettor slide).
    I have no reason to change carburettors as the NT works perfectly well with a No 84 main jet, not to mention a noticeably cooler cylinder head at cruise, providing a smoother and more powerful engine.

    The fact that i've traveled 1200 kilometers (745 miles) on a partially damaged big end connecting rod bearing which is 400 - 500 kilometers (248 - 300 miles) longer than all 4 previous engines suggests that the No 84 main jet is playing a significant if not a complete part in the longevity of the engine.

    I can't say if others have just been lucky or if there are manufacturing differences between Australian and American shipments of these engines.
    People will just have to try it for themselves.

    My suggestion, based on my own experiences - order three jet sizes (No 82, No 83, No 84) and experiment.
    There are only two outcomes - either it will be operation success or operation failure, but if it's operation success, it will be the cheapest power up option you can get; not to mention a smoother, cooler running engine that has greater longevity.

    Last edited: Mar 4, 2010