Valve check/leaking air sound

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I've got the valve cover off and I'm turning the motor by hand -- there's a sound of escaping air coming from somewhere in the valvage area as the engine makes a rotation. Can't tell exactly from where.

Is this most likely a leaking valve? Could I be hearing something like the oil pump? I'm sure checking the compression would answer the question but I don't have a gague yet (it's otw).

 

I am not sure about the 650 but my 1100 does have an oil tube that attaches to the back of the head and shoots oil on to the valve chain you maybe hearing that when you turn it over. It does not oil the chain when I turn the motor over by hand.

 

If you're rotating the Engine by hand, ... WITH the Spark Plugs still in it ... you will hear (and feel) the changes in compression as the Valves open and close.

You should have the Plugs OUT while measuring Valve Clearances.
Especially if using the Yamaha Shim Tool.

Having the Crank move against Cylinder Pressure could be costly with the Cam Lobe moving in the Tool.

 

Thanks Rick, shoulda thought of that. Once I swap some shims and get the clearances in check, I'll do a compression test and go from there.

 

Just checked my clearances yesterday and noticed the same sound. I figured it was air pressure building up and being released when I open a valve. Good to know that I should remove the spark plugs when changing the shims. THanks RickCoMatic!

 

I just loosen them to relieve compression rather than remove them completely and have them suck in debris. Or you can loosely wad a shop towel and push the "ball" into the spark plug cavity. (Recommended for compression test.)

 

As long as I dont have to pull the head and replace some valves!

 

You don't have any that are bone-zero tight do you? As long as that's not the case, you should be fine.

You will need to re-vacuum sync the carbs after the valve adjustment though.

Back to your original question: Even with the plugs out, you'll likely hear all sorts of interesting gurglings and "air moving" sounds when you turn the motor over with the valve cover off. These motors have a number of jets and nozzles in them that spray oil on various components, and when turned over slowly they tend to gurgle and spit. It's normal.

 

Whew, I was getting a little nervous! There are just a few valves that need the next shim up or down.

And I've put down a Benjamin for a Morgan Carbtune. I've heard way too many good things about them to not have one in my garage!