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Thread: Rotax 150 ring replacement

  1. #1
    apriliaforum newb
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    Rotax 150 ring replacement

    Posted a while back about a basket case Scarabeo 150 that I purchase and I am about ready to start fixing. I ordered parts and have the head rebuilt and the broken carb slide replaced and I am about to put the engine back together. However I had one question. This engine had the top ring damaged either by the tech that took it apart or when the broken carb slide got eaten. There is no damage to the piston or cylnder. I have never rebuilt a engine with nickelsil cylnders before and was wondering what the best way to proceed is. Should the cylnder be honed like a cast iron or steel sleeved cylnder or is there a different procedure. Only the top ring was damaged another option would be just to replace the top ring and baby the engine while it wore in without doing anything to the cylnder.

    Unfortunately while I have worked on cars with nickelsil cylnders we don't replace them we put in short blocks so I have no direct experience with this type of repair.

    Thanks for your help. (I also posted on the yahoo scarabeo forum for those of you who like me read both.)

    Tom

  2. #2
    apriliaforum expert
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    this sutterlands blk bike that run out of coolant ??? anyway should make sure the wear ridge isnt or is cut dwn (simple tool) like automotive tool .. Flex hone the bore Lil balls Not the 3 stones type .. Put piston rings staggered and clamp up in a ring compressor with just a wiping of bore w marvel oil slide piston in bore bury it cap the rod tighten er up rings will seat before you get er warmed up good the bore is/ just has a nickel liner or sprayed plasma of nickel in bore for hardness and anti wear ... TomD

  3. #3
    apriliaforum newb
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    No this is not the bike that ran out of coolant. Previous owner was ridding when carb slide broke and piece went through the engine. Bent a valve and lost compression. He took it to a dealer and they took it apart and for some reason would not give him a estimate on what the repair would cost. After a couple months he picked it up and placed a for sale add on Craigs list. Which is where I came in.

    I brought it home and inspected the cylnder and head and found the head had a bent valve and some minor impact damage in the combustion chamber and that the slide in carb was broken. Replaced the bent valve lapped all 4 in and cleaned up the impact damage and was about to reassemble the engine when I noticed the dealership had removed the 2 compression rings. Looked through the box of parts I had been given and found the rings but also found that one of them was broken. So I ordered a set of rings. I now have the rings but have found noting in the manual or in other sources that mentioned if the nickelsil cylnders should be honed. I even looked in the BMW factory repair manuals which deal with nickelsil car engines and they make no mention of honeing cylnders either.

    The bike only has 7100 miles on it and the cylnder has no taper or ridge at all. I would hate to ruin the cylnder by honeing it if its not required. I was worried about possibly wearing through the hardened surface with a hone. And I was wondering if anyone here had ever replace rings on one of these engines and what procedure they used and how it turned out.

  4. #4
    apriliaforum expert
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    he new rings need a good surface to bed into youre not going to remove the nickle just gently scratch it and the rings flyin up n dwn the bore will smooth those scratches out w the ring to bore surfaces which will form a convoluseve seal yeah i cant spell.. lightly hone

  5. #5
    apriliaforum newb
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    Bike is fully back together and seems to be running normally now. So total repairs ended up being as follows.
    Replaced 1 bent intake valve
    Replaced 1 broken carb slide (which caused the whole problem)
    Replaced rings due to damage by tech who dissassembled the engine. (lightly sanded cylinder.)
    Replaced assorted gaskets as required.
    Installed a gasket between head and thermostat flange which was missing and leaking.
    Reassembled the rest of the jigsaw puzzle of basket case pieces.

    Tom

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