Timing Chain Rotation To Hole #3

[Rob1972]

So, bringing my 72 back to life - it was an automatic but I replaced that with the type B 5 speed long ago.  I have a 77 electronic dizzy.

I set out to rotate my cam sprocket, since this is what I saw during my first valve lash adjustment by myself last week.

 

 

I followed Scott Bruning's Z Therapy video from 15 years ago (!) to the letter:

I set to TDC, wedged the chain with a long tip phillips, etc. following the procedures. I removed the sprocket and rotated clockwise to dowel pin hole #2 and could see that the groove hardly moved (in relation to the notch), if at all.  So I rotated to #3 and got the sprocket back on with some tough love.  Now the groove has moved a bit more towards the notch, in fact just touching the right side of the notch.

 

 

I was ready to remove the wedge when I noticed the chain is quite slack on the drivers side.  I think I read that it should be tight. I would say it has no tension on it. The passenger side seems to have some tension, but I can deflect it some (like a fan belt).

 

I think there is almost no chance the wedge moved, especially since I was able to get the sprocket back on the cam.

 

Is it OK to proceed, or should I continue to freak out?

 

Hope you can enlarge those photos.  Thanks.

 

Rob1972

 

 

[Zed Head]

There's always some slack in the chain, but when the engine is running, it's all on the passenger side, taken up by the tensioner.  You just moved the slack to the driver's side when you did your adjustment.  If the sprocket is on, you can remove the wedge and turn the sprocket backward to find out where the notch really ends up.  It's not where it will be when the driver's side is tight.  It's going to be even farther to the left.  Looks like #3 might be too much, to me.  The driver's side of the chain needs to be tight when you look at the notch and groove.

[240260280z]

With the cam on #2 and the chain back on the cam, just torque the cam nut and related (washers eccentric, etc)

then you are safe to pull the screw driver/wedge.

Next rotate the crank around CW twice until you are seeing 0 on the TDC damper mark then look at the marks on the CAM to see cam timing.

[Rob1972]

Thanks Zed Head, I see the physics there. May go back to #2.

So Blue, you think the 2nd hole would be enough too?

[240260280z]

Sorry. If you are on 3 now, stay there and do the full 4 stroke rotation (2 turns at the crank). be sure to stop exactly at the TDC mark on the damper then check the cam mark.

[siteunseen]

I put my brand new (rebuilt) motor on #3.  A mechanic friend said it would give it more bottom end "grunt".  It's runs great with plenty of top end power too.  6,200 RPM redline, saw it 1st through 4th gear Saturday pulling away from a Mustang. 

 

Just saying...

[rossiz]

moving the sprocket advances the cam - it think each cam sprocket number advances it around 4 degrees. this advancement compensates for chain stretch, which would retard the cam.

i don't know where the factory setting (lining up the notches) puts the cam to start with, but in my experience with motorcycle engines, advancing the cam around 5 degrees gives a nice performance boost. 

 

a degree wheel and a dial indicator will tell the story for sure.

[Rob1972]

I wound up at dowel pin #3 and the chain has tension on both sides. Will start it up later today. Expecting a big change - that's about 8 degrees more advanced. 

 

I had trouble 'seeing' the notch and groove from the diagrams before I started this, I hope these pics help others.

 

[Zed Head]

I think I had my befores and afters backward in my other comment.  Looks like you're at after-after now so should accomplish your objective well.