Re: Tapping

["Brant M. Miller" <brant@xxxxxxxxxxxxxx>]

Brian -

I was hoping for other responses on this, but since there are none to dat=
e:

I agree with your analysis, but I believe there are actually two separate=

problems.  First, loss of oil pressure in sweeping, high-g turns - which
can be hard on bearings, etc.  Second, lifter tapping - which may be
contributed to by oil pump air pickup due to suction pipe unporting, but =
is
also a consequence of foaming.  I have no personal experience with the
first problem, although the existance of baffled pans suggests to me that=

just adding a quart of oil is either not a cure-all or that it has side
effects.   My personal experience with foaming came at a Skip Barber car
control clinic.  The graduation exercise was an autocross.  After a few
laps around the circuit, with no sweeping, high-g turns, the 325i sounded=

like it was about to self-destruct.  Very noisey lifters.  It took severa=
l
minutes for the tapping to stop.  Foaming was blamed for the problem.

Brant
Message text written by INTERNET:bmw@domain.elided
>Date: Sun, 15 Nov 1998 19:05:24 -0600
From: Brian M Kennedy <kennedy@domain.elided>
Subject: Re: Tapping

> > Okay, we all know the M3 (and a few other Bimmers) have this problem
> > of oil starvation in high-g turns that cause the valves to start
tapping. =

> > What I don't understand is why they keep tapping for many minutes aft=
er
> > the car has stopped high-g cornering.

Brant M. Miller wrote:

> One source of continuing tapping is foamed oil.  The foaming is caused =
by
> the same performance driving that can unport the oil pump pickup.  Oil
> manufacturers include anit-foaming agent in the oils (a surfactant, I
> believe, that assists air bubble breakage), but it does not completely
> prevent the problem.  The air component of the foam is compressable and=

> does so in the lifters, with tapping the result.

Interesting.  But I thought adding an extra quart to reduce the tapping
would actually increase foaming (since the oil level gets high enough
that it gets churned a bit).  Is that not so?  Or are there some addition=
al
dynamics at work?

Thanks for the info,

Brian<

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