RE: engine roll- or dowel pins

[Hirsch <Catenary@domain.elided>]

Bob McKeown wrote:
> In my humble opinion, the roll pins don't help at all.
> The notion of O-rings "collapsing" makes no sense to me,
> since the oil pressure inside the O-ring is much greater
> than the (possible) water pressure outside (and there can
> only be water pressure present around the O-ring if the
> head gasket fails).

Within the last few years, I've removed 3 4-cylinder heads
from cars not fitted with roll pins, and at least some of the
O-rings in each engine were heart-shaped. That is, part of the
circumference of the O-ring was bent down towards the center
of the ring. I won't try to explain the physical forces that
cause this phenomenen, but the O-rings do collapse and roll
pins prevent it. With heart-shaped O-ring the oil can seep
around the O-ring and get under the head gasket and ruin
the gasket to block seal.

Perhaps modern square-cut Viton O-rings are better able to
withstand the applied forces and don't need extra support,
but as I understand it, it is standard practice is to install
roll pins and seems good insurance against gasket failure.

> Remember, too, that the oil flow through these passages is
> very small.

I realize oil flow is restricted by using roll pins. This is
one advantage of using the small rings instead.

Regards,

Rich Hirsch

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