[Supras] cam journal caps

[Hacker J]

While everyone is free to what they want, I also resized my cam caps two years ago during a major
rebuild.  It is relatively easy, and gets rid of a lot of top end clatter.  I mostly DD this car
to work, so any reliability issues would have surfaced after two years.

If you think about it, the intake lash clearance is 8 mils.  If you have 6 mils of bearing slop,
how can you possibly expect the lash numbers to be stable.

Jon
90T


--- supras-request at supras.com wrote:


> 
> 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
> 



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