What's with my timing chain?
 

I finished my cam timing, valve adjustment, and is buttoning everything back up. This is a stock 3.6 rebuild using existing p&c and no machining work done. Now when I go to sping the crank pulley, I am seeing the timing chain really stretched on one side of the cam sprocket and at the same time with lots of slack at the other side of the sprocket. See the pics.

This is how things look normal.

http://forums.pelicanparts.com/uploa...1115794352.jpg

When the crank at 60, 300, and 540 degrees, the chain on upper side of the sprocket is really tensed and compressing the tensioner all the way up. At the bottom of the sprocket, there is enough slack to put a pen cap in there. See pic.

http://forums.pelicanparts.com/uploa...1115794517.jpg

It's repeatable at those angles. The same thing is happenning on the right side except the angles are 60 degrees out of phase /w the left side.

There is no hangup in the chain. What is going on here???

Did I mess up on the install, cam timing, or something? Is the chain stretched? This is a top end rebuild. I did not split the case.

Please help.

thanks,
anthony
92 C2 under surgery

With the chain off, does the cam turn semi-smoothly?

-Wayne

Wayne,

When I iinstalled the cam housing, I checked by turning the cam. It turned VERY smoothly per your book. Of course without the rockers or anything installed.

---anthony

It looks to me like you are turning the crank backwards. I wouldn't be suprised to see this if there is no oil pressure on the tensioner and the crank is turned backwards. No harm should be done as long as you haven't jammed any valves into pistons. Assuming you haven't hit a stoppage with the crankshaft then you haven't hit valve to piston. Don't turn the crank backwards without keeping tension on the chains (easiest to just not turn crank backwards at all).

-Andy

How would I go about fixing this?

BTW, I only turned the crank backward only when I was timing the cam /w #1 and #1 intake rockers installed. From there on....everything is only turned clockwise.

I don't think there is anything to fix. The cams should turn by the pulling of the chain on the side that is supposed to be tight. The cam will sometimes move forward when the spring from a valve pushes it forward on one of the cam lobes bit this should only be if the tensioner isn't pushing on the chain. If the cam "jumps" ahead then maybe the tensioners aren't pushing down on the chain hard enough. Is there something that prevents the tensioners from pushing hard onto the chains? (I haven't worked on a 3.6).

-Andy

Hmmm...how would I go about testing this besides looking at the cam & rockers which I don't think would tell me that they are putting pressures which is causing the tension/slack.

I also hope that I don't have to pull the rockers.

The pressure from your rcokers will sometimes rotate the cam "ahead" of the crank when there is no tension. It would result in slack on the chain on the side of the chain sprocket that is being pulled by the crank...