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Yes, flat tappet lifters are off center so that they will rotate.

"...With “flat tappet” pushrod engines, the bottoms of the lifters appear to be flat. But actually on most applications the bottoms of the lifters are slightly convex. The center is about .001 to .002˝ higher than the edge. Also, the lobes on flat tappet cams are not perfectly flat but have a slight taper (.0007 to .002˝) to one side. In addition, the centerline of the lifters are offset slightly with respect to the cam lobes. This makes the lifters rotate as the cam turns, which helps to reduce friction and wear...."

"...While operating, any flat tappet is allowed to rotate in the bore as it moves up and down. To get there, the cam lobe is tapered slightly. Ditto with the camshaft contact face of the lifter (it’s slightly crowned and not exactly “flat”). The rotation of the tappet within the bore evens out the wear of the lifter (particularly at the edge where it comes in contact with the camshaft lobe)..."

http://www.sweethaven02.com/Automotive01/fig0349.gif

Roller lifters roll centered on the cam lobes. They do not rotate.
 

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Yes, flat tappets are not supposed to be centered so that they'll rotate - as BigD said. If you have the engine out of the car, one thing to check is the fit on the front of the cam drive gear, behind the fuel pump eccentric. The cam is supposed to 'stick out' a little past the face of the cam gear in order to center the outer ring for the fuel pump eccentric.

Bear
 
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