Dear all,

We receive 4-stroke Rotax engines coming with *either of the following sizes of cylinder-piston sets.  Either (1) A-type cylinders (red pistons) Or,  (2) B-type cylinders (green pistons). There is delta difference in bore sizes.

During overhaul, if the cylinder-piston sets are fully rejected, can we replace them with either of A or B type? For example, can an A-engine be rebuilt with a mix of A & B-cylinder/ piston set and vice versa?

This situation arises, in particular, when there are shortages in supply of either types of parts. Is it necessary to adhere to the original category of build? If not possible to adhere, does it affect in performance of the overhauled engine, its power etc.?

Thanks for your technical views please.


*Text modified and files attached for clarity



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9347_1_Screenshot 458.png (You do not have access to download this file.)
  • Re: A-Type and B-Type cylinders mix

    by » 10 months ago

    Hi Ray

    Well the simple answer is you can use both A and  B however you need to match the pistons to the cylinder size.  There is a slight difference between the 2.  If you have A cylinders they are very slightly smaller than the B cylinders.  The pistons if you note on the parts manual are also a bit difference to get the correct piston to cylinder wall clearance.  So that said you should not mix the pistons from the smaller group into the larger cylinders and especially never mix the larger piston group to the A cylinders.  In that later case it would perhaps lead to a failure of the piston to wall clearance and might let you down.  

    Use the heavy maintenance manual and go to the forum charts for the pistons and cylinders.  You can find all the tolerance groupings and what is allowable.  It also explains how to measure the piston and the cylinders correctly.  If you are not familiar with that portion look for a accredited iRMT to help you.  As information it is extremely rare to ever have to replace the cylinders as this is a liquid cooled engine and the bores are a special coating that will wear for many thousands of hours in normal use.  Even at overhaul the pistons and cylinders are on condition,, only the rings need replacement at TBO providing all else measures within the limits.  



  • Re: A-Type and B-Type cylinders mix

    by » 10 months ago

    Thank you for your clear explanation on the topic. It matches with our understanding too.

    But just for information, we get engines where cylinders are found badly worn out, leading to replacement of all cylinders.

    Kind regards.


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