Top End Rebuild Question

Discussion in '2-Stroke Engines' started by PeterG, Jul 18, 2016.

  1. PeterG

    PeterG New Member

    Wanted to do a complete top end rebuild because I think my compression is starting to come down. Canadian supplier is out of stock on the complete kit (cylinder, piston, etc). Is it worth it to just put a new piston and rings in it?

  2. crassius

    crassius Well-Known Member

    a lot of work just to find piston & cylinder that fits with all the diff types out there now

    if you used a compression gauge when it ran well, and it reads lower now, a top end *may* help

    a muffler will clog over time too

    I've always considered these motors as disposable, such that it is often cheaper & easier to replace them rather than rebuild them. Other folks enjoy rebuilding as a hobby.
  3. jaguar

    jaguar Well-Known Member

    probably a head gasket leak
  4. PeterG

    PeterG New Member

    Thanks for the responses. No specific problem. Just want to freshen it up.

    Question is:. Is it beneficial to put a new piston and rings in a used cylinder?

    I'm assuming the piston and rings will wear before the cylinder walls.
    Last edited: Jul 18, 2016
  5. jaguar

    jaguar Well-Known Member

    it depends if the cylinders chrome plating has flaked off or not.
    if still in place then it don't need to be replaced
  6. Steve Best

    Steve Best Well-Known Member

    Jag has the right answer. Only 10 minutes to pull the head and have a look at it. I'd suggest YES, replace the piston and ring.
    Crassius is right about the muffler too, especially if you are using conventional mineral 2 stroke oil.
    I had great luck with the Canadian supplier's $19.99 chrome muffler. Quiet and good revs and power.

  7. PeterG

    PeterG New Member

    Yep, cylinder looks fine. Already had a look. Muffler's fine too. Again, not trying to troubleshoot anything here; just want to keep it fresh. Seat of the pants (on the bump start) feels like compression might be down a shade. Was wondering if new piston and rings without a new cylinder was beneficial (sounds like a "yes"). Engine didn't get an ideal break-in (see my thread "chronic four-strokeing").
  8. Frankfort MB's

    Frankfort MB's Well-Known Member

    What's your idea of an ideal break in? I don't see anything about breaking it in on your thread
  9. PeterG

    PeterG New Member

    Ideal for me would be moderate load and running freely through the rev range; roll-on / roll-off the throttle; don't lug it but don't rev the crap out of it either. Decent load on the engine to bed the rings; don't pussy-foot around. Frequent stops during the first day or so to let things cool down. But everybody has their own break-in technique. I couldn't follow mine because it ran like crap.
  10. butre

    butre Well-Known Member

    my break in technique is to let the motor warm up and find the tallest and steepest hill in town and go wfo up the thing. works every time
    Frankfort MB's likes this.
  11. jaguar

    jaguar Well-Known Member

    high stress/load for short bursts is the best way to get the rings to seat good.
    also use regular mineral oil at 20:1. synthetic oil protects the rings too much at break-in.
  12. Diamond Back

    Diamond Back Active Member

    Steve, I have been looking for a good short (stubby) silencer to go on the end of a 2004 RM85 expansion pipe,,cheap in price too,,, also ight try to make a dual setup,,, I heard you mention nice chrome silencer $19.99 .. can you help me out with a picture and sme contact ordering info,,, or if at worst I send you the money..

    Does any one know where to get low priced stubby silencers,,, I would like to have a cool exhaust system, something different that turns heads and sounds and performs good,,,

    this is an exhaust i modified slightly to go on my buddys 33cc 2-stroke scooter,,, it sounds nice (zippy) and game him a few mph and tad bit of rev power.. I could modify this to fit easy,, WHAT YOU ALL THINK,,????? gold.jpg