DeTomaso Mailing List: November 99, Message #320

"Eustaquio, Cal J" wrote:

> Hi All:
> Just wanted to know about some phenomenon that the local engine rebuilder
> informed me about during a phone conversation I had with him yesterday.
>
> During my talk regarding head work on the engine, he told me that installing
> and fitting the head to the engine is not a trivial thing. He told me that
> the rocker arm assembly (using roller rockers) required that during it's up
> and down motion, attention must be payed attention to very carefully,
> otherwise, one can wear down the valve guide very quickly. He said that the
> best way to avoid this would be to be judicious about pushrod selection.
>
> I guess I can see his point. We discussed "side forces" of the piston
> against the cylinder (pretty important when considering stresses to the
> cylinder wall). Pretty much the same phenomeonon is occurring should the
> rocker arm travel be to excessive. Is this correct? Anyone care to comment?
> Thanks. Cal. #2428r.

It's my understanding, this is what the guideplates help prevent.  Well, they
help prevent and sideways motion of the rocker anyway.  With a roller tip, the
valve is allowed to travel in a more linear fashion, as opposed to a stamped
steel rocker which is always "pushing" the valve stem around.  It's this
sideways motion (this is much easier to illustrate in person) that will wear out
valve guides.  Roller rockers (roller tipped rockers anyway) prevent this
sideways force on the valve stem, hence reducing wear.

That's been my education on it anyway.  The thing you must be careful of, is
that the roller tip is rolling in alignement with the valve, if it is not (and
why it wouldn't I have no idea), then it could cause problems.

FWIW,
Asa Jay



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Asa Jay Laughton  Spokane, WA
     1973 Pantera L 5533

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Asa Jay Laughton
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