Mr. Wizard type question -------

Discussion in 'General Questions' started by Marhsall, Jul 16, 2016.

  1. Marhsall

    Marhsall New Member

    Ok so was experience what I interpreted as a lot of compression loss at valve cover. Bike ran like sh*t. couldn't climb small hill, no power, and seemed to get hot fast. Can't even ride a block on it. Tore engine all the way down. 49cc 4 stroke. Now the small hole That all that pressure that kept beat with engine rev, Is actually a tubed chamber that goes down to the crank case. Now in my mind as the piston goes up and down that is going to create a suction as the piston goes up and a outward pressure as the piston goes down. Same as it would on the top of the piston. Wouldn't that positive-negetive pressure need somewhere to vent? Wouldn't this be then be normal? Valves look good, very, very slightest wiggle on exhaust valve. piston looked good. Broke rings as I took them off as mine as well replace them while engine is apart. The only thing that was at all noticeable other then a little carbon build up on piston and exhaust valve. Was the exhaust valve more lubricated then the intake valve. I am also assuming the valve guides on these can't be replaced, but it is extremely slight wiggle. So that's my Mr. Wizard question. Wouldn't crank case need to vent through that chamber?

  2. jaguar

    jaguar Well-Known Member

    having that tube connect the crankcase to the head cover means there is more air to compress and so the max psi is slight and nothing to worry about.
    If you vented it then it draws dust and water into the crankcase.
  3. crassius

    crassius Well-Known Member

    I don't work much on 4-strokes these days, but crank venting is always done somewhere on a motor (EPA moves type of venting from time to time). I'd be looking for a timing problem with both power loss & heat buildup (probably too advanced).

    Though clogged muffler could do that too.
  4. jaguar

    jaguar Well-Known Member

    If it was designed without one then I'd just leave it that way.
  5. Marhsall

    Marhsall New Member

    I just put the valves and springs back on, put water in the cylinder. Valves are good. I know I don't know how to tell if it's a compression stroke or not for adjusting the valves, Seems it really wouldn't matter as long as springs are all the way up. Funny I just started to think about that muffler, I'm starting to wonder if a baffle didn't break. Arg!!! I would hate to tear this thing down for nothing. Maybe I'll shave the head while it's apart. LOL. :)