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Thread: RD250LC Project

  1. #121
    A348W's Avatar
    A348W is offline Only 37 known common faults - The Ferrari 355 Club Member
    Join Date
    Oct 2013
    North Wiltshire


    Quote Originally Posted by Modificato View Post

    ....knowing a bit about two stroke engines that looks almost 100% manufacturing defect to me

    failure in that plane is normally only down to two things - Gudgeon pin to tight / small end heating problem or manufacturing defect / materials issue

    It looks like the latter to me because the former would show signs of excess heat build uo around the gudgeon pin area of the piston
    I was going to say manufacture defect but didnít know about the gudgeon pin causing that type of failure; interesting thank you.

    Suspect if you pull that apart there will be a nice little inclusion lurking.

    Bit to luck finding that when you did; bits of piston floating around in the crank never makes for a good day!!!

  2. #122
    sssdu01 is offline No I'm Spartacus Committee Member
    Join Date
    Dec 2012
    Gloucestershire UK
    Simon Dutton


    I would say thats a crack caused by something "exploding" the small end hole in the piston. I think I see a retaining clip in the picture which suggest the gudgeon pin is a floating fit with a needle bearing small end ? If it is a floating fit the small end movement will be in the small end the rod bearing so you wont get overheating witness marks visible on the piston. (But clean up the small end needle bearing and inspect for overheating damage, as whilst you wouldnt re use the bearing it might give some clues what has gone wrong ??)

    Aluminium expands more than steel so I wouldnt expect the pin to burst the piston with normal running. I would check the diameter of the gudgeon pin to compare against standard spec. I think the more likely culprit is a duff piston, either crap alloy or just a badly made copy.

    EGR valve cleaner, or alloy wheel cleaner(with acid in it) and a scotchbright pad can help to get all the carbon off and help you find makers marks or part numbers.

    You are very lucky to have found it as it wouldnt be long before it disintegrated and grenade'd the engine

  3. #123
    Join Date
    Nov 2005


    Cracks like this is usually down to either a coolant leak OR water in the fuel.

    Manufacturing faults that cause cracks like that are quite rare and usually show themselves up very early on in use.

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