Hello, I own a 2005 400ex. I decided to do a valve adjustment since I was hearing a slight tapping noise at idle. I did everything by the book except on one exhaust valve I had some trouble getting the feeler guage in it. I really had to back it out, like 2 full turns. I was able to get the guage in but not as far as the others. I adjusted it accordingly. .10mm on intake and .12mm on exhaust. It has a louder tap now. I did make sure cylinder was lined up with the t in the window as well. This is my first ever attempt and any help would be appreciated. Still not sure why I had troubles with the one valve.

 

It isn't just the T mark you have to line up, it is the T mark on the right stroke. From the amount you adjusted it, I recon you did it on the exhaust stroke instead of compression. Do it again, making sure it is the first time the T mark shows after the inlet valve has closed. If you did adjust it on the right stroke, that much adjustment indicates the valve seat must have come loose.

 

How can you check if your on the right stroke.

 

Make "sure it is the first time the T mark shows after the inlet valve has closed."

Alternative method, plug out, finger on plug hole, feel compression trying to blow your finger off as piston rises on compression stroke, either look through plug hole to see piston getting to top, or watch for T mark as piston nears top. On the exhaust stroke which you don't use for timing, the exhaust valve will be partly open, and no pressure on the plug hole.