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  1. #1
    Buck3yeRideR's Avatar
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    School me on Top End Rebuilds & Reeds

    I'm looking for some info on these 2 subjects. I have to replace 1 pistons/cylinders each one two different 1995 sl 650's. One starved from oil with compression at 100psi, and the other just keeps stalling with compression at 10psi, but not a meltdown.

    PISTON/CYLINDER

    What is Honing? Does this require an oversized piston, or oversized rings? Or does it just lightly remove any imperfections allowing the use of stock pistons and rings? What is an average price to have this done per cylinder and what types of places do this?

    If the cylinders are bad enough to get them bored out. Do you have to buy bore specific pistons or can you just buy oversized rings? prices?

    When does it become necessary to sleeve a piston? prices?

    With my 10psi comression check how do i determine what the cause is since the piston has not melted down?


    REEEDS
    I understand reeds but am not totally sure what the symptoms can be of bad reeds. Would these effect a compression check? Do these need replaced regularly, b/c mine are probably original. It just seems like i have replaced all maintenance items and am wondering if reeds are one of them?


  2. #2
    johnsonmtz's Avatar
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    Quote Originally Posted by Buck3yeRideR View Post
    I'm looking for some info on these 2 subjects. I have to replace 1 pistons/cylinders each one two different 1995 sl 650's. One starved from oil with compression at 100psi, and the other just keeps stalling with compression at 10psi, but not a meltdown.
    Take a close look at the bottom end before buying a bunch of parts. Oil starvation can cause big problems with bearings. You need to at minimum check side and send play of the rods to make sure the crank turns smoothly before you start doing cylinder work.

    Quote Originally Posted by Buck3yeRideR View Post

    PISTON/CYLINDER

    What is Honing? Does this require an oversized piston, or oversized rings? Or does it just lightly remove any imperfections allowing the use of stock pistons and rings? What is an average price to have this done per cylinder and what types of places do this?
    Any machine shop should be able to hone the cylinders. A light hone removes cylinder glazing and recreates a crosshatch pattern. New rings should be the only necessity if the piston is okay. The new rings and crosshatch will wear together and give you a well sealed cylinder. A ball hone should be used and not a stone hone. I think the shop at my local Carquest charged me $10/cylinder.

    Quote Originally Posted by Buck3yeRideR View Post
    If the cylinders are bad enough to get them bored out. Do you have to buy bore specific pistons or can you just buy oversized rings? prices?
    The best thing is to measure the cylinder diameter, determine the amount of oversize necessary, buy the pistons, then take the cylinders and new pistons to the machine shop. Have them bore and hone the cylinder to match the piston specifications.

    Quote Originally Posted by Buck3yeRideR View Post
    When does it become necessary to sleeve a piston? prices?
    I believe most piston manufacturers make a maximum 1mm oversize piston, but I believe SBT offers up to 1.25mm. They all increase in 0.25mm increments. If the cylinder needs more than 1.25mm larger diameter than OEM you'll to have it resleeved or use a cylinder exchange service.

    Quote Originally Posted by Buck3yeRideR View Post
    With my 10psi comression check how do i determine what the cause is since the piston has not melted down?
    With the piston at bottom dead center, can you see any scoring on the walls? Most likely you'll need to pull the cylinder to really have a good look.

    Quote Originally Posted by Buck3yeRideR View Post
    REEEDS
    I understand reeds but am not totally sure what the symptoms can be of bad reeds. Would these effect a compression check? Do these need replaced regularly, b/c mine are probably original. It just seems like i have replaced all maintenance items and am wondering if reeds are one of them?
    Bad reeds will allow air/fuel charge to spit back up through the carbs.

    The 650/750 engines are notorious for chipped or broken reeds. The cages set very close to the crank and the forces of turbulent air can cause damage. The 780 motors were less prone to this because the 3/8" spacers between the reed cage and engine case moved them away. Removing and inspecting the reeds is probably a good idea.

    KJ

  3. #3
    Buck3yeRideR's Avatar
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    Quote Originally Posted by johnsonmtz View Post
    Take a close look at the bottom end before buying a bunch of parts. Oil starvation can cause big problems with bearings. You need to at minimum check side and send play of the rods to make sure the crank turns smoothly before you start doing cylinder work.
    Once i got oil back in the engine, i drove it for around 3 hours with no problems other than it sometimes being very difficult to start. If that says something for the crank turning smoothly. So your advice is to remove all cylinders and check the rod bearings? Should i also remove the driveshaft/stator to check for play and smoothness?


    Quote Originally Posted by johnsonmtz View Post
    Any machine shop should be able to hone the cylinders. A light hone removes cylinder glazing and recreates a crosshatch pattern. New rings should be the only necessity if the piston is okay. The new rings and crosshatch will wear together and give you a well sealed cylinder. A ball hone should be used and not a stone hone. I think the shop at my local Carquest charged me $10/cylinder.

    Quote Originally Posted by johnsonmtz View Post
    With the piston at bottom dead center, can you see any scoring on the walls? Most likely you'll need to pull the cylinder to really have a good look.
    Yes i can, and i can feel slightly more scoring on 2 sides of the chamber. If scorings that bad can it deem a cylinder not usable?

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