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    Sam Carlson
    Tutorial Bot euromobile900's Avatar
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    14 Aug 2010
    Medford, MA
    '90 900 LPT with a flat-nose conversion
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    Rear Main Seal (Flywheel side) Replacement - c900

    Here's a job that you should do as a matter of course when you do your clutch or gearbox (or if you find that oil is being splattered all over the rear of the flywheel and clutch cover). In the past, c900 owners have been afraid of this seal, because it requires a special tool to install. But no longer. Read on!

    Difficulty: 4/5

    Tools Required:
    -Hacksaw or PVC saw
    -drill and bit big enough to make a hole the size of a flywheel bolt
    -Wrench for flywheel bolts

    Parts required:
    -4-inch (3 15/16 OD) plastic pipe end-cap
    -Oil seal

    To use the stock flywheel bolts to press in the seal, you'll need to cut
    the cap down, as pictured here:
    Name:  plastic_rear_seal_driver.jpg
Views: 1985
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    instructions follow:

    --STEP 1-------------------------------------------------------------
    Carefully mark the cap with a line around its entire circumference at
    11/16" from the bottom of the cap*.

    NOTE: You want this line STRAIGHT and PARALLEL to the bottom of the cap.

    --STEP 2-------------------------------------------------------------
    With a saw, cut the cap down to 11/16"**, being careful to cut straight (I
    used a hacksaw, which worked pretty well.) If necessary, use a file
    afterward to get the entire cut parallel to the bottom.

    NOTE: You want the cut surface to be nicely parallel to the cap bottom
    all the way around or else it will not drive the seal in straight.

    --STEP 3-------------------------------------------------------------
    Mark the bottom of the cap with a circle at the same diameter as the
    flywheel bolt circle and drill 3 or 4 holes around the circle at the same
    locations as the bolt holes on the flywheel.

    NOTE: Make the holes' diameter slightly larger than the flywheel bolts to
    account for some lack of precision. (In the pic, you'll notice 7 holes:
    it's not necessary to drill all of these.)

    --STEP 4-------------------------------------------------------------
    Put a bit of Loctite 518 on the outside edge of the new seal to help it go
    in nicely. I'm skeptical that the seal would ever leak between the end
    plate and the seal itself, but if that's somehow possible, the 518 will
    keep the oil on the inside of the motor. Put a bit of moly grease or
    engine rebuild lube on the surface of the seal that rides against the
    flywheel. I have been told by a tech that letting a new seal run dry for a
    bit is not good for it.

    --STEP 5-------------------------------------------------------------
    Carefully place the seal at the end plate, and bolt on the plastic driver.
    Slowly and evenly tighten the bolts in a cross-wise pattern, pushing the seal into the end plate, ensuring that the seal goes in perpendicular to it. When flush, push the seal slightly deeper than the prior seal so that the new seal doesn't ride in exactly the same place as the old one, which may have worn a small groove in the crank.

    *[If you bought a black (ABS) plastic cap, use a silver Sharpie, which is,
    incidentally, really handy for car-related stuff.]

    **[I don't know if you need exactly 11/16" but this is what the one I used
    was cut to; I don't recall how I came to decide on that measurement, but
    it worked.]

    Credit for this tutorial's writing goes to SC member Gorper. SN member Christopher Myles took part in special tool development independently

    0 Not allowed!
    Last edited by euromobile900; 04 December 2010 at 19:21.
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