`cam timing confusion with degree wheel

[randy 77zt]

putting my turbo motor back together after i cracked a piston ring land.cam is the isky 290/280 duration 490/480 lift turbo cam.intake valve is suposed to open at 26btdc and close at 74 after bottem dead center.exhaust is suposed to open at 74 before bottem dead center and close at 26 after tdc.these specs are at .050 lift.problem is if i set the cam up for the intake valve to close at the spec on the cam card the intake valve opens at 32 after tdc.the exhaust valve will close at spec but opens at 10 before bottem dead center.to get the cam to these specs i had to retard the cam gear 2 teeth from the normal line up the links/dots settings.cam was not checked before removal-i dont know what the cam timing was set at.i have been playing with this thing for hours-i am just happy its not in the car.somehow i dont agree with the cam card on the exhaust opening -74 before bottem dead center-seems like the piston is still in the middle of the power/combustion stroke.any body had this problem?

Edited October 1, 2010 by randy 77zt

[Tony D]

Check out the comments on the cam thread sticky. Are you talking cam or crank degrees for the differential?

Valve lash of 0.001" can affect your opening and closing events radically like 5+ degrees, and 'how' you determine TDC for the pointer is another matter---some people will run the dial indicator on the top of the piston and when the crank stops providing upward movement call it TDC.

Others will use a stop and go forward and back and average the center.

 

The difference can be radically different because of the swing of the big end of the rod, the longer the rod (or shorter) can impact the difference dramatically in terms of degrees.

 

It sounds like you might have a cam that had an oops on the lobe separation. I'd call Ron with the build spec and talk with him about it. He can set you straight, listening to him for a while on the subject should set you straight, or at least figure out what 'YOUR' cam is doing. (Then again is it really your cam if his name is actually on it? )