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Message started by Digger on 07/09/09 at 20:38:45

Title: Top Dead Center - Removing the Mystery
Post by Digger on 07/09/09 at 20:38:45

Everything in this procedure references my bike (see signature).

The engine is supposed to be rotated to Top Dead Center (TDC) on the compression stroke to perform numerous procedures, including, but not limited to, setting the valve clearance, removing the head cover, and adjusting the free play in the automatic de-compression cable.

The problem is that there are two different TDC's on a four stroke engine. One occurs on the compression stroke and one occurs on the exhaust stroke.

To find the one you want (the one on the compression stroke), remove the valve timing inspection plug. I use this tool to remove this plug, the middle sized bit works great:

Motion Pro Timing Plug Tool (http://www.motionpro.com/motorcycle/partno/08-0087/)

Now you've exposed the flanged nut on the port side of the crankshaft. On my bike, this nut takes a 17mm socket. Rotate this nut counter-clockwise (trust me, not Clymer) until the index marks on the nut lines up with the index mark (notch) in the valve timing inspection hole:

http://i235.photobucket.com/albums/ee201/Digger109/TDC-IndexMarksE.jpg

Now, you've got to determine if you are at TDC on the compression stroke (YAY!) or if you are at TDC on the exhaust stroke (BOO, HISS!).

If you've got at least one of the valve inspection caps off, just try to jiggle the rocker arms with your fingers. If there is some play present, you are on the compression stroke, where you want to be. If they are all tight, with no play, you are on the exhaust stroke. In this case, you will need to rotate the crankshaft nut counter-clockwise through another full rotation and line the index marks up again. Then, you should be on the compression stroke, but perform the above check just to be sure.

NOTE: The possibility exists that the valve lash is set too tight and you will not be able to detect any rocker arm movement, regardless of the position of the crankshaft. This is but one reason I prefer the following method when finding TDC of the compression stroke.

If you don't have at least one of the valve inspection caps off, you will need to make note of the position of the decompression valve lever when you rotate it counter-clockwise against the stop. You will be able to rotate if farther at TDC on the exhaust stroke than you can when at TDC on the compression stroke. You may need to rotate the crankshaft a few times to get a feel for this.

Here are some pics illustrating what I am talking about:

Here is how far I could rotate the decompression valve lever counter-clockwise when I was at TDC on the compression stroke:

http://i235.photobucket.com/albums/ee201/Digger109/TDC-CompE.jpg

And, here is how far I could rotate the decompression valve lever counter-clockwise when I was at TDC on the exhaust stroke:

http://i235.photobucket.com/albums/ee201/Digger109/TDC-ExE.jpg

When I am finally where I want to be (i.e. TDC on the compression stroke, I just put some clear tape over the valve timing inspection hole to keep dirt out. That way, I can look every now and again and reassure myself that I'm still at TDC:

http://i235.photobucket.com/albums/ee201/Digger109/TapeonTimingHoleE.jpg

IHTH someone!

Title: Re: Top Dead Center - Removing the Mystery
Post by Yonuh Adisi on 07/10/09 at 06:02:25

Or you can do it this way.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1223943569