1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Crankshaft Oil Seal Friction

Discussion in '2-Stroke Machines' started by Robin172, Mar 5, 2023.

  1. Robin172

    Robin172 Well-Known Member

    It's been a long time since I built a two stroke and at present I'm putting together a 250cc single engine and I can't remember how easily the crankshaft should rotate after putting the cases together with the oil seals in place.

    I have a Ducati single engine that the crank will always rotate to it's natural position if located away from it and just let go. Should a two stroke engine do the same, bearing in mind the drag/friction from the crank seals?

    The engine I have have isn't doing this and does feel a little tight.
  2. 90kacoupe

    90kacoupe Novice seeking Help

    You will feel the oil seals but it shouldn't be tight. Is it a vertically or horizontally split case? It can be a very common to disturb the crank truing when installing a crank in vertically split cases.
  3. Robin172

    Robin172 Well-Known Member

    Vertically split. I'm going to measure everything again to make sure I haven't over shimmed it causing it to bind up. Failing that I have thought that it might have gone out of true, I did have to tap the main bearings onto the crankshaft and also tap the crank into one half of the cases. I rebuilt this engine multiple times years ago and never had this problem before.
  4. fastfreddie

    fastfreddie Midnight Oil Garage

    Doesn't matter if your tapping caused seals to bind (doubt it), you've ruined any "true" you may have dialed in on the crankshaft. It's gonna run like shit and quite possibly grenade.
    Start over. Press the bearings and case halves onto the newly dialed-in and properly supported* crankshaft.
    I can only assume these are new seals but, if not, wtf?

  5. backho

    backho Well-Known Member

    I always test fit assembled parts without the seals in place. Easier to feel binding, end play, etc.

Share This Page