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Considering the torquing procedure for the cylinder studs is it possible to retorque them after pulling a cylinder or must they be replaced after a single use?

  • Re: Cylinder studs

    by » 10 months ago


    The procedure is to Torque-to-Spec PLUS another 120° turn.
    That makes this a Torque-to-YIELD Procedure.

    The Stud has been stretched and is now permanently longer than it originally was.
    This is essentially as tight as it is ever going to get without breaking. 
    If you re-do the procedure, Even if you just did it 2 minutes ago you are going to be stretching it even more.
    The stud will be weaker and may fracture once it gets hot and full power is applied.

    Should they be Re-Used?  NO!
    Have they ever been Re-Used?  Sure!
    Have folks gotten away with it?  You Bet!
    Are you feeling lucky today???  Your Call!


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: RotaxOwner Admin

  • Re: Cylinder studs

    by » 10 months ago


    Hi all

     

    The latest version of the 915 heavy manual contains the correct procedure.  This procedure will be added to all the new heavy manuals as they are all updated.  The process is the same as was introduced a few years ago under a Service Instruction but got missed on the last revision of the heavy manual for the 912/914 engines.  If you read the entire process in the heavy manual it is required that if you should remove one head then the other remaining on that side should be loosened and the "pair" from that side tightened together as a set.  While there is no requirement in the manual to replace the studs with this procedure as Bill Hertzel pointed out you may come to a point where the stud elongates enough that it will no longer hold the value.  You will find that the torque peaks below the spec and just keeps pulling.  This is an indication that the stud has failed and must be replaced.  Should you reuse the studs there is that risk or you can just replace them and not worry about it.  For those of you who have overhaul ratings you might remember that you are only allowed a 1% stretch on a stud from new if being reused.  This assumes you know the original lengths and measured it before installing.  if you don't know the best policy is to replace.  

    Cheers

    31081_2_cylinder head assembly torque.jpg (You do not have access to download this file.)

  • Re: Cylinder studs

    by » 10 months ago


    Here is an expanded Information video for Cylinder Head Torque Procedure for the ROTAX 912/914/912iS engines. https://www.rotax-owner.com/en/videos-topmenu/expanded-video-instructions/463-new-torque

     


  • Re: Cylinder studs

    by » 10 months ago


    The video shows a freshly overhauled engine used to demonstrate the procedure.
    However, there is no mention as to whether after loosening the heads the studs Were or Were Not replaced.

    Sam's original question was, " ... is it (Permittable) to retorque them after pulling a cylinder or must they be replaced after a single use?  "

    This still has not been Specifically answered by the Austrian Authorities.

     


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Cylinder studs

    by » 10 months ago


    It states in the Rotax 912 HMM the following: If cylinder stud heads are damaged or if the cylinder baffle clearance is too tight then the cylinder head studs have to be replaced.

    The Cylinder head studs are a 100% replacement part at overhaul.

     

     


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