Question about 2011 kawasaki KLX 250

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Motorcycle is losing compression and noisy

Recently some 500 miles ago i replaced the cylinder but after riding some miles Piston skirt touched the cylinder from both side. crosshatch isn't visible in skirt area of cylinder only.Pistons rings haven't seated yet. how can it be possible while all manufacturers give proper clearances between Piston and cylinder. i never overheated or abused this motorcycle. in this case what should i do ?? ride the bike till rings seating, is there any scope for rings seating after this incident or open the cylinder and hone it with oversize rings ??

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  • kawasaki Master
  • 53,757 Answers

If it is a water cooled engine the ring gap at the bottom of the cylinder should be around .010"
rings have to be installed the correct way up or the compression doesn't help push the rings against the cylinder walls for effective seal
piston skirts will touch the cylinder walls as the pressure pushes the piston to one side as it pushes the piston back down the cylinder
I have to ask did you put an old piston back in the new cylinder
was the new cylinder standard size or over size
what was the ring gap before you fitted them to the piston
did you use new rings or the old ones --maximum rin gap is .025"
rings don't wear in , just wear out
why did you replace the cylinder in the first place
was it because of low compression or taper wear
as silly as all this seams it is all very relevant to your question

Posted on Mar 11, 2016

  • Anonymous
    Anonymous Mar 11, 2016

    No i installed new standard size piston and rings with new cylinder, my motorcycle was burning oil.

  • Bill Boyd Mar 11, 2016

    I think you have to go back to basics and that means pulling it down again and start from scratch
    you could give the bore a light hone but you will be doing a lot of honing to get it big enough for the next size rings so that will be out of the equation
    The purpose of honing is two fold
    one thing is to give the bore surface something to hold the oil and lubricate the piston and rings and the second is to create a turning action so that the rings rotate in the ring grooves ---honing angles of the hatch section are set for best actions
    remove the rings from the piston and measure the ring gap at the bottom of the bore
    use the piston up side down to get the ring square in the bore
    measure the gap using a combination of feeler gauges
    as I said for water cooled engines that gap should be no smaller than .010" and no bigger than .025"
    the closer to .010" the better as that lets the least amount of compression past the piston
    Now if the gap exceeds say .015" then you could fit .010" oversized bore rings and use a fine mill file to get the gap back to .010" rings ( the oversize rings will not fit in the bore to start with so you have to be careful in the filing to get the ring in and then file to the correct gap
    remember that you are filing a circumference so a small amount equals a big gap
    check the crown of the piston (top) as many have an arrow to indicate that the piston has to be fitted with that arrow facing the front of the engine ( stator end )
    next rings are marked with a top sign etched in them and that means that the ring has to be fitted with that top facing to the top of the piston
    lastly when installing the piston and ring assembly use liberal amounts of engine oil and ensure that the ring gaps are equally spaced around the piston (120 degrees between each gap)
    with the gaps right, hone good, piston in right there is no reason that the job will be successful
    NOTE -- if the engine is air cooled then the ring gap is a lot more for minimum than the .010" but everything else is the same ( check the new gap with a bike rebuild shop)
    Some times the quality of oil used has to be as specified as a multigrade oil will quickly glaze the bore and allow it to burn oil as the rings do not get a chance to seal on the hone marks
    Above all a good workshop manual will be of enormous help in the assembly procedures



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