[Supras] valve shim rotation mystery

[berniek at technicaldevelop.com]

Last night I wrote about the lack of rotation of some buckets and shims when running-in the exhaust cam side of the head with a drill.  

If anyone has experience with this, I would really appreciate some insight.  The problem is:  I do not see how the shims and buckets are supposed to rotate.  The shims are flat.  There is absolutely no taper in the cam lobes, even on the base circle, which does not wear.  Moreover, the lobes ride directly in the center of the shims (in some engines the lobe center is offset to make the lifter rotate).  So how in heck are the shims and buckets supposed to rotate?

I resorted to manually lapping the lobes and flanks, offset, with a diamond paste charged flat copper lap to get about .001" to .003" of lobe and flank taper, taking about 15 minutes per lobe (less in total than a toolpost grinder follower setup would have required).  But for some reason the 7M engine was designed to not require that.  The frustrating thing is:  I don't understand why.

One other thought occured:  Maybe there is a slight included angle between bucket bores, but measurements do not confirm this.  It is possible that all bucket bores are inclined longitudinally by a fraction of a degree, but checking for that will not be easy.

Again, any advise or insight would be appreciated.

Thanks.

        BernieK