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1995 KTM 300 2stroke top end rebuild

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by cyrax, Mar 25, 2006.

  1. Hi, I know this forum is mainly for road bikes, but i'm hoping you'll forgive me if i ask a question about the cylinder of my ktm300 that i bought back in december.

    The head gasket is a silicone o-ring type, and a few months back it tore in one place.. don't know how it happened, but the engine got very hot, and i had to have the cylinder replated because of chipping around the top (coolant went inside the cylinder). After taking the head off, i noticed a couple of the bolt threads had been stripped before and re-threaded (on the cylinder), one was sticking up a bit, and was pinching the o-ring by narrowing the groove a little (not sure if this caused the problem in the first place), which the shop told me they would fix up with a new helicoil threading.

    They put in a new threading but the groove where the o-ring sits is still a little narrow.

    Here is a pic:


    So i took it back and they shaved it down and put another helicoil in so that it looks like this:


    Now they've told me it should be fine like that, just to put some sealant between the bolt threading and the o-ring... That to me sounds pretty risky considering how much i've already spent trying to get this thing going again, around $1000 including piston kit, replating, tools etc. The bike cost $3000.

    Do you think sealant will do the job? What other options are there?
  2. Sorry to dissappoint but that groove will not seal an O ring. About the only thing I can suggest is aproduct called Devcon. It is an industrial strength liquid metal. Fill around the area & a decent fitter should be able to file it back into shape.
    The problem is not the water but the combustion pressure causing the o ring to fail. Had you noticed this before the re-plating, then a decent Tig welder would be able to re-weld & get the groove re-machined. Bit risky now -more than likely damage the plating & disort the bore.
    The devcon should do the job.
  3. 2

    Hiya Cyrax.Sorry to bring bad news, but your barrel has never seen a 'shave in its last 2 photos' all that has happened is someone has made the o-ring situation worse than it was before.
    A barrel that has seen any machining work from a milling machine looks like piece of kit from a factory race bike! The top of yours looks exactly the same as the first photo except its its had a 'brillo'pad rubbed over it. You Have before & after photos .Go back an show them the difference,kick up a stink!!
    They couldn't denie they've made the barrell worse than before~!!!
  4. So it really is that bad? I wasn't sure because after I got it back off them the second time, they didn't say anything, I had to ask them "are you sure that's gonna seal ok?" and they said just to put some sealant on there between the bolt thread and o-ring and make sure i got the torque settings right... from everything i've heard from people, it doesn't sound too promising.

    The place i went to is BTX motorcycles in Ferntree Gully, the guys there seem ok, but i can't be sure, i did tell them at the start that i'd never done a top end job before, and was new to this kind of stuff, maybe they took advantage?
  5. Hi cyrax sorry but the only way to repair it is remove the recoil thread and have it Aluminium welded then remachined and retap with a new oring it has to be a vition oring its high pressure high temp
  6. Yep, that's quite bad. Look at it from the O-ring's point of view. When the plug fires, the combustion pushes the O-ring outward, and the groove holds it in place. Where that helicoil has been put in, there is now nothing to support the back of the O-ring.

    If the shop give you hassle, try the MTA or similar industry body, or consumer affairs dept in your state- don't be loud or abusive, be smart and calm. Put things in writing... try to deal with the manager and possibly get an opinion from KTM's Australian distributor on the issue, so you have some authoritative backup in any argument.

    Good luck.