[Supras] cam journal caps

[berniek at technicaldevelop.com]

Dear Jeff:

You are a well respected member of the list with quite of bit of racing
experience and resourcefulness about brake parts, and probably much else. 
You have apparently learned by doing, a perfectly viable way of gaining
education and knowledge.


That does not work to the exclusion of viability of findings of others. 
For years I had a startup knock in my essentially stock '90 which I knew
came from the top end, yet it made no sense.

Only when I tore down the head from the relatively low mileage JDM did I
find that the last exhaust cam journal had a diametral clearance of .006",
rather large for a journal that is only about 1.3" in diameter and turns
relatively slowly.  Others were worn as well.  Would you leave it in that
condition?

I would not.  The reason for cam journal scoring emanates from lack of
boundary lubrication, let alone hydodynamic wedge formation.  I mentioned
that very subject as covered in Shigley, a noted mechanical engineering
text, and will not go into the details again here.  If you reduce the
clearance (fortunately easy to do), the problem disappears.  Once the wear
starts again, it should be attended to because the wear is regenerative,
expecially for the last exhaust journals.  That is one reason the MKIV
feeds the center journal, not the front journal with oil supply.  All of
the journals are cross drilled, so little oil gets to the last one in the
III once the cap wear progresses.

In the final analysis, we need to maintain mutual respect.  You were
correct about some of my street shenanigans and I accepted your words in
that regard.  By the same token, accept what others are correct about as
well.  Others have followed the procedure I layed out and have been
satisfied with the results.

Bernie