Cam regrinds feasible? (roller regrind)

[goflo at pacbell.net]

Not real familiar with Subaru grinds, but involute ramps are
common in some designs - Chrysler went through many permutations
of such on 2.2/2.5 motors, for instance. Regrinding such profiles
with conventional regrinding equipment is possible, but a poor
job will result in an engine which runs poorly, for no obvious
reason... 

Regards, Jack

Howard Wilkinson wrote:
> 
> Jack:
>     I have long suspected that many cams have considerable error in
> the alignment of lobe centers.
>     I once was asked to change out the third Subaru (EA 81) engine for
> a fellow who had installed 2 rebuilt engines only to have to return
> them to the rebuilder due to rattling.  This was a major Seattle area
> rebuilder.  When I looked at the engine pior to removal to determine
> exactly what was happening, I discovered that it was valve noise, but
> that it couldn't be adjusted out of it.  This seemed odd to me, so I
> took measurements with feeler guages while turning the engine over a
> little at a time, an discovered a low spot right at the base of the
> ramp which when proper adjustment was made opposite the lobe yielded a
> measurement of about .025.
>     Human error seem to be inescapable.  Unfortunately with camshafts
> it is very difficult to verify that they are what they are supposed to
> be.     H.W.
> 
> -----Original Message-----
> From: goflo at pacbell.net <goflo at pacbell.net>
> To: diy_efi at efi332.eng.ohio-state.edu
> <diy_efi at efi332.eng.ohio-state.edu>
> Date: Sunday, May 02, 1999 2:39 AM
> Subject: Re: Cam regrinds feasible? (roller regrind)
> 
> >An additional consideration with re-grinding cams is the
> >torsional relaxation caused by removing significant amounts
> >of metal. This changes the phase relationships between lobes.
> >I have in my possession a performance regrind TR6 cam which
> >has a 14 degree phase error between front and rear lobe pair
> >centers. The grind was done by a national rep grinder (and
> >purportedly checked with their cam doctor).
> >
> >This is probably a worst-case deal, as this cam is long and
> >slender, and has ~.125" additional lift ground-in, but much
> >smaller phase errors screw things up noticeably.
> >This too can be avoided by proper regrinding techniques, but
> >once again, by the time you do it right, you coulda bought a
> >new one...
> >
> >I check new ones too :)