valve adjustments for 50cc and 150cc scooters

Valve adjustment on a 139QMB 50cc 4 stroke scooter motor.

You will need access to the engine bay. For me the easiest way to do this is to remove the seat bucket. But everyone has their own way and there is many different configurations of scooters. What your looking to do first is to have access to the top of the motor. After you get the valve cover removed with 8mm socket or wrench you will need to follow these steps.

Step 1.
Set the engine to Top Dead Center (TDC)

On your flywheel you will see some marks. Make sure the T on the flywheel lines up with the the timing tab.


Also check your camshaft and make sure your timing marks on line up with the top of the head. Make sure that you are setting the engine at TDC on compression stroke. The T that lines up with the timing tab after the intake valve closes.


After that is a simple matter of using a standard feeler gauge and set the valve lash at .004 for both the intake and exhaust valves. How do you do that you ask. Its simple really just take your 9mm wrench and loosen the locking nut on the valve tappet.

Then you loosen the tappet until you can get your feeler gauge between the tappet and the valve stem. You want to tighten the tappet down on the feeler gauge snug but not to tight. You want to be able to pull the feeler gauge out but there should be resistance. Use a pair of needle nose pliers to hold the head of the tappet and tighten down the locking nut. Repeat on the other side and put the valve cover back on.



Once you get the motor back together you want to start it up and listen for excessive tapping from the valves. A tick is ok a loud tap is a problem. If it sounds weird start back at step one and try again.

credit to Enviromoto of scootdawg forums for this guide

gaps are different for the 150cc motor you will need to have the intake set to .004 mm for the intake and .005 mm for the exhaust the procedure for setting the gaps on a 150cc scooter is the same as the 50cc scooter. it just needs different gaps to perform accurately