Air pressure after killing engine - weird!

[Adamastor]

Hi!
Today I noticed a very strange thing: I arrived home, killed the engine, turned the petcock off and got the bike on the stand.
I was going to close the garage when I listen to what seems to be an air pressure sound...
I thought: "Oh boy, I have a flat tire!"

I got near the engine and the noise came from the right cylinder...  :-?
It continued for about 3/4 minutes and gradually diminished till gone. What could justify this noise?
There is no pressure on the cylinder when engine is off, right?
 Can anyone tell me what caused this noise?

Thanks in advance!

Sergio

[Crossrodes]

There can be pressure in the engine if the piston was on the compression stroke.  So the question is, if that is what happened, why was the air leaking....my first guess would be a loose spark plug.  Another possibility is a loose head or shot head gasket.

My first action would be to try to localize where the noise is coming from.  If you can't tell whether it is coming from the plug or around the head gasket...check the torque on the plug first; if that doesn't appear to be the problem check the torque on the head bolts (when the engine is cold).  The last option would be to replace the head gasket.

If you have to re-torque the head you will have to redo the clearances on the valves.

Others may want to chime in here.

[montmil]

Check sparkle plug for snug. Next...

Prepare a squirt bottle of soapy water. The next time you pull in to park and the engine is hissing at you, squirt the solution around the head gasket joint and watch for bubbles.

Monte

[Adamastor]

Good ideas... I will check sparkplug first and go on if that doesn't solve it
You guys rock!  8-)

[Bob_Roller]

Check sparkle plug for snug. Next...

Prepare a squirt bottle of soapy water. The next time you pull in to park and the engine is hissing at you, squirt the solution around the head gasket joint and watch for bubbles.

Monte

I think if you squirted water on a hot engine, it would just boil away .

You may want to try it on a cold engine, remove the spark plug leads from the plugs, ground them out, then rotate the engine with the starter, check the head/cylinder joint with soapy water .

Then try it on the spark plug itself .

If I'm not mistaken, you had the heads off recently .

Did you ever recheck the cylinder hold down nuts after that .

A new head gasket will probably compress a bit in a few hundred miles or so after installation .  

[Rob Valdez 79 R65]

A leak-down tester might be the tool for this job?

[Adamastor]

Sorry guys, it was a much simpler thing after all... I had been cleaning the R65 the day before, and the noise was not air pressure, but boiling water on a small hole on top of the cylinder, between the cylinder head and the top cover.
I went for a ride today after checking sparkplugs were snug and after I stopped the noise was there and on both sides now, and I could easily see (yesterday it was already nigh) the water bubbling over those tiny holes. After a 30km ride (and today is quite hot) the noise and water were gone...

All is well when it ends well, but thanks for the fast replies and ideas... sometimes I feel just like a noob

Regards,

Sergio

[montmil]

Yep. That little watering hole catches quite a few peeps. Glad it was nothing.

Monte