ETZ 251 Engine Oil Leak

Forums Technical Two Stroke: Help needed ETZ 251 Engine Oil Leak

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    • #14738
      ‘AAA Dummy

      My ETZ 251 has a persistent transmission oil leak, coming from a cast-in recess on the drive side of the engine, in a raised boss that it shares with the tapped hole that houses the neutral switch that’s right next to it. It’s heavy enough to leave a small puddle, if the bike is left parked for a few weeks.

      There appears to be the end of an internal engine shaft visible inside this recess, which is pretty illogical!

      It’s been leaking from here since I bought the bike 3 years ago, though with little use, I’ve so far just put up with it.

      Looking at parts and workshop manuals, there doesn’t appear to be anything missing that might seal this hole and there are no threads or circlip grooves to retain any such plug.

      I’m not inclined to split the motor to investigate, without first finding out a bit more about this, so do any of you good folk know why there is oil emerging from this part of the motor, and if so what might be done to stop it?

      I have a photo, but can’t seem to work out how to paste it into this topic. I anyone has any thoughts on the leak I’ll happily mail it out to you.



    • #14751
      Matthew Nichols


      What goes here is a 10mm core (or welch) plug. I have replaced a few on my bikes. The available plugs are a bit tall so time with the file was needed. Some RTV paste (sometimes) helps, but only the smallest amount!

      One of my bikes despite changing this plug still leaks, because some previous owner mashed up the internal wall of the recess trying to put it in backwards! This oil leak also annoys me!

      But yes- 10mm core plug should suite you right (i’m guessing it’s missing?), but also make sure not to punch it in too far as it will touch and interfere with the shaft inside (for gear change mechanism)- because, at least for a little while, the gear change might be a bit stiff if you go too far! 🙂


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