2 stroke with bad compression

Discussion in 'Mechanic and Repair' started by themow, Jun 4, 2008.

  1. themow

    themow LawnSite Member
    Posts: 41

    I recently acquired a 2 stroke trimmer that wasnt running. First thing i did was empty the tank and find that the previous owner ran it on straight gas. Its got 50psi of compression. It turns over freely. Should the piston and ring be replaced? I was thinking about just the ring. Could the bearings be shot on the crank as well? Should I not even bother?
     
  2. B&A lawn care

    B&A lawn care LawnSite Member
    Posts: 70

    In most cases you will find the piston to be trash also, remove the muffler and look into the port for scoring. Bearings and seals are likely to be OK. The cylinder bore will be covered with aluminum from the piston and it needs to be removed. The chainsaw guys remove the piston particals from the bore with an acid solution, muratic I think. Bottom line is if it's a high quality unit of recent vintage you should be able to find parts and its probably worth some time and effort, if not find a dumpster.
     
  3. themow

    themow LawnSite Member
    Posts: 41

    I pulled the cylinder off. The piston is trash. It clearly needs to be replaced. The cylinder has gouges in it. Not very deep, but they do catch my finger nail. I could probably hone them out but, im concerned i may have to take too much material off.
     
  4. Ridin' Around

    Ridin' Around LawnSite Senior Member
    Posts: 266

    What kind of trimmer are we dealing with here. Is it cost effective for you to throw parts at this thing?
     
  5. jkason

    jkason LawnSite Senior Member
    Posts: 548

    You will need to replace the piston, ring(s), AND the cylinder. (plus the intake, exhaust and cylinder gaskets.)

    For anything that retails for less than $299.00, it really just isn't worth it.
     
  6. themow

    themow LawnSite Member
    Posts: 41

    No ots a junk homelite trimmer, but i could use another one at this time. They are selling a new piston and ring for $7 from homelites website. I was thinking i may be able to get away with just a hone on the cylinder. the gouges in the cylinder are deep enough to grab my nail i dont know
     
  7. S DIAMOND

    S DIAMOND LawnSite Member
    from South
    Posts: 108

    Most 2-cycle manufactures use either a chemical impregnation, or chrome plating for the cylinder bore. They do not spec for oversizing (especially the lower cost units) Once the surface of the cylinder is damaged (gouged), it's over. The cylinder will heat up, become "ply-able" (where damaged) and fail again. replacing with a new piston and ring kit without the jug will not solve the problem. Honing will not help.:(
     
  8. Ridin' Around

    Ridin' Around LawnSite Senior Member
    Posts: 266

    I say for a 7 dollar piston, I say go for it. If you have the free time, it's a good learning experience and the thing may give you a couple of good weed whackins before it lets go again. If you're willing to take the risk and deal with possible disappointment what have you got to loose? Besides what else are you going to do until the water goes down! Until they make lawn mowers that float, nobody around here can get anything done!
     
  9. jkason

    jkason LawnSite Senior Member
    Posts: 548

    It's Junk.
    If you put the new piston & ring in WITHOUT changing the cylinder, the ring is going to eithger catch in the groove and break, or it won't develop enough compression.

    Either way, a waste of time and money.

    Brands to NEVER rebuild (not worth it) - Ryobi/Ryan/IDC, MacCulloch, Homelite.
     
  10. themow

    themow LawnSite Member
    Posts: 41

    owell i ordered it...........i will post pics of the rebuild and let everyone know how i make out
     

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