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Yamaha 90hp four stroke timing belt

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  • Yamaha 90hp four stroke timing belt

    Does anyone know the socket size on the flywheel nut on a 2004 90 hp four stroke Yamaha. And the bolt sizes on the flywheel to use a puller. I have to change my timing belt and the boat is 100 miles away from me. I want to be sure to have the right tools with me. Thanks for all the great post. Rick

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    Re: Yamaha 90hp four stroke timing belt

    Rick, I have a 2006 four stroke which may or may not have the same flywheel. (Probably, but I can't say for sure.) I measured the flywheel nut at 35.8mm, so that looks like a 36mm nut. The three puller bolt holes appear to be 8mm-1.25mm (8mm being the major OD and 1.25mm being the thread pitch distance.) Here are the instructions out of the factory service manual.

    Do not turn the drive sproket counter-clockwise, otherwise the valve sysem might be damaged

    Do not remove the ignition timing pointer

    Do not turn the drive sprocket or the driven sprockets when the timing belt is not installed. Otherwise the piston and valves will interfere with each other and be damaged.


    1-3. Remove the flywheel.

    4. Remove the woodruff key and stator assembly. Do not loosen the pulser coil screw.

    5. Turn the drive sprocket (i.e., crankshaft) clockwise and align the hole on the retaining plate with the projection on the cylinder block. Note that the projection on the cylinder block is aft of the crankshaft on the top of the engine Therefore, the hole on the retainer plate will be pointing aft (in the direction of the spark plugs). ALSO - each driven sprocket has an indicator arrow on it. The arrows on the two sprockets should be directly facing each other (and therefore close together).

    6. Disconnect cooling water hose (?) and remove the bracket.

    7. Remove the spring, timing belt tensioner. Remove belt from the driven sprockets and the from the drive sprocket.

    8 -9. Before starting the reinstall, make sure all of the aforementioned timing marks are still lined up.

    10. Install a new timing belt on the drive sprocket with the part number on the belt in the upright position, then install the belt onto the driven sprockets

    Do not twist, turn inside out or bend the timing belt beyond a 1" bend radius or it will be damaged. Do not get oil or grease on the timing belt.

    The lower edge of the timing belt should be 2 mm from the bottom of the driven sockets.

    11. Install the timing belt tensioner and finger tighten the bolt until the bolt seat contacts the timing belt tensioner.

    12. Loosen the timing belt tensioner bolt 90 degrees.

    13. Install the spring

    14. Take up the timing belt slack by turning the drive sprocket (crankshaft) clockwise at least two full turns

    15. Tighten the timing belt tensioner bolt to 39 Nm (3.9 kgf-m or 28.8 ft-lb)

    16. Turn the drive sprocket two full turns and ensure that the aforementioned timing marks will all line up again correctly

    17. Install bracket and cooling water hose.

    18. Install stator assembly and Woodruff key

    19 Install flywheel. Tighten nut to 215 nm (21.5 kgf-m or 158.6 ft-lb)

    Again, these are the instructions out of a 2006 F90 Yamaha service manual. You can buy a service manual for your particular engine on-line at the Yamaha web site. Also, there are some great techs on this forum that can probably improve the above instructions with some sage advice. Enjoy working on your boat.
    Construction Photos At:
    https://forums.iboats.com/showthread.php?t=306152

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