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Kohler Magnum M18S Rebuild Advice

Discussion in 'Mechanic and Repair' started by artbuc, Aug 28, 2010.

  1. artbuc

    artbuc LawnSite Member
    Messages: 13

    Just discovered this forum. Have posted on several other forums and received some responses but this forum seems to be loaded with Kohler experts!

    My engine is on a Gravely 18-H garden tractor (basically an Ariens GT 18 with a Gravely paint job). I use it to mow 1.5 acres and blow snow. It is 18 years old with about 12-1400 hours. The hourmeter broke in the first couple years so I am giving my best estimate. Engine starts and runs great. Burns very little oil. Compression is 100 & 105 psi. The only work I have done so far is one new exhaust valve/seat and new voltage rectifier, both a few years ago.

    I wouldn't be thinking about doing anything except crankshaft endplay is excessive at 0.025" compared to the spec of 0.002/0.014". This winter I am planning on tearing her down to install a new thrust washer. I have been advised to replace the governor gear and install new rings. One person suggested a complete overhaul. I will need this tractor for only another 3-5 years.

    I would appreciate any tear down tips and/or advice about what I should do when I get in there. Thanks.
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    These old Magnum engines are far better than any Command, I would go the thrust washer and governor gear and nothing else. This has many more years of homeowner use left in it as is.

    I've got two of these 18's myself, One in my ZTR and one I'm installing in a UTV. The Command 25 I have will continue to sit on the shelf.....
  3. artbuc

    artbuc LawnSite Member
    Messages: 13

    Thanks. It has been a sweet engine. My local expert Kohler technician suggested rings because he said you will always have hi and low spots which won't match up when you reassemble. However, another guy said you can pull the barrels off just enough to disconnect the piston from the rod and leave the piston in the barrel. I may try that.
  4. artbuc

    artbuc LawnSite Member
    Messages: 13

    PS. What causes thrust on the crankshaft? I have an electric clutch on the PTO shaft. When it is not engaged, the clutch brake is pulling the crankshaft towards the engine. When the clutch is engaged, there isn't any thrust on crankshaft, at least not from the clutch. However, a couple years ago I had the electric clutch removed to clean-up the faces. When I reinstalled it, I did not get the plates all the way home tight together and tight against the shoulder on the crankshaft. As a result, when I engaged the clutch it was pulling hard on the crankshaft (towards the engine).

    I don't see how inward thrust from the PTO side would wear the thrust bearing. Is it possible that the endplay is caused by wear between the flywheel sleeve bearing and crankshaft? There isn't any thrust washer/bearing on the flywheel side separating the sleeve bearing from the crankshaft counterweight. It seems like the thrust washer will wear out only when the thrust is coming from the flywheel end, pushing the crankshaft against the thrust washer.

    I hope someone here will explain this to me. Thanks.
  5. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    What's the spec number on this engine and the full tractor model and serial numbers ?
  6. artbuc

    artbuc LawnSite Member
    Messages: 13

    Kohler Spec # 24548, SN 1630306026

    Gravely 18-H , SN 00589431

    The Gravely 18-H does not have a Model number on it but based on Ariens/Gravely Parts radar it is a Gravely Model 931035-000101 which is equivalent to the Ariens Model 931033-004346.

    It has a driveshaft connected to the flywheel shaft which drives the hydro trans.
    Last edited: Aug 28, 2010
  7. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    OK artbuc,

    IMO, Each time you start a engine the starter drive gear pushes it's way into the flywheel with a certain amount of pressure. The crankshaft floats between the steel thrust washer and the brass flywheel end flange bearing, Between starting and the crank floating you will most likely find most of the end play wear on the flange bearing.

    So, What I would suggest is replacement of the flywheel end flange bearing then check/adjust end play with the needed thrust washer to re-gain proper spec.

    As far as leaving the pistons in the barrels, That's no problem at all. That's the only way to get it back together. The pistons have to go in first then the barrels/pistons held in place to install the wrist pins.
  8. artbuc

    artbuc LawnSite Member
    Messages: 13

    Thanks. When you say flywheel end flange bearing, are you talking about the crankshaft sleeve bearings?

    This makes sense because I read that the thrust washer is hardened steel. I don't think it is designed to take the wear.

    In addition to the starter wear you discussed, I am now pretty sure the electric clutch was the major culprit. Now that I know the sleeve bearing has a brass face to take wear, it probably has taken a beating with the electric clutch applying so much force to it.
  9. artbuc

    artbuc LawnSite Member
    Messages: 13

    PS The service manual gives the following specs on the crankshaft sleeve bearing:

    1. max out of round .0005
    2. Max taper .001
    3. Max running clearance (new) .0049
    4. Running clearance max wear limit .0059
    5. New ID (installed) 1.7439.1.7461

    Which of these specs relates to endplay?
  10. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    That's correct,

    None of the above specs pertain to the bearing flange (end play). Reason being, The average person would have to remove the bearing to get a measuring device on the flange which would most likely cause damage to the bearing.

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