Camshaft position when adjusting valves on a scooter

Adjusting valves is a simple thing to do if you know what you’re doing. You should always adjust the valves when the piston is at the end of the compression cycle at TDC. In this position:

  • the valves are closed
  • cam lobes are pointing downwards

The later is valid for scooters with single overhead camshaft as shown in the photo below. Where the valve rockers, seat on top of the cam.

How can you make sure the piston is at the compression cycle and not exhaust?

  • BOTH intake and exhaust valves are closed
  • another way, although less suggested, is to block the plug hole with your finger and turn the engine manually forward by turning the variator or the magneto (always in a direction of the front wheel). The moment you feel compression, continue turning carefully until camshaft line is parallel to the head, just like in the picture.
In most scooters, there's a LINE carved on the outer side of the camshaft (see the two smaller holes). This line should be parallel to the head surface, just like in this example. Click picture to enlarge.

If you want to do it by the book, you can. However you will have to open the cap on the ignition cover. Turn the engine forward slowly until you see a “T” mark on the flywheel appear. Align it to the mark on the case (usually a groove)  and make sure the bigger circle on the timing chain sprocket, is visible (see photo, and circle above the two smaller ones).


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