Ok, when I was first researching how to do valve adjustments, I thought that adjustable cam gears would have to be put back to 0,0 before doing the adjustments are made. I did a search back then and everybody said this wasn't necessary. I let it go for a while but today, I wanted to get an explanation. So I did a search and I found posts that say that you do need to zero out the cam gears. What's the real deal??

From my limited knowledge, the valves must be in the closed position for the particular cylinder that you are working with and this of course happens at TDC. Now, if you introduce cam advance/retard at TDC, isn't it possible that the cam lobes are still keeping the valves open?

 

maybe its because the 2 or 3 degrees of cam adjustment is so slight. remember that the cam and crank dont rotate at the same speeds. for every 180 degrees the crank rotates, the cams only rotate 90 (IIRC).


Modified by RTW DC2R at 5:31 PM 1/20/2006

 

The cam gears adjust the cam only a few degrees which isn't enough to get the cam off of its "low-spot" when you're measuring.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tommymoose &raquo;</TD></TR><TR><TD CLASS="quote">The cam gears adjust the cam only a few degrees which isn't enough to get the cam off of its "low-spot" when you're measuring.</TD></TR></TABLE>

You sure about that?

 

Unless you have cam gears adjusted something like +/- 15 degrees then yes, I'll agree with him on this.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Pondus &raquo;</TD></TR><TR><TD CLASS="quote">Unless you have cam gears adjusted something like +/- 15 degrees then yes, I'll agree with him on this.</TD></TR></TABLE>



It shouldn't be too difficult to determine if you're on the base circle with the sprockets still adjusted, and if you aren't, setting them back to zero for the adjustment is a simple matter.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Padawan &raquo;</TD></TR><TR><TD CLASS="quote">

It shouldn't be too difficult to determine if you're on the base circle with the sprockets still adjusted, and if you aren't, setting them back to zero for the adjustment is a simple matter. </TD></TR></TABLE>

Please school me on the meaning of base circle.

 

Basically, the smallest/lowest area of the cam lobe, where no pressure is being applied to the valve.

 

Imagine a camshaft without any cam lobes. It would just be a dowel rod. That's the base circle.

 

.....what Ben said.

I always do valve lash at tdc and wherever my cam gear settings were tuned for (I don't go back to zero).