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<p>Probably due to aeration (foaming) of the oil due to cavitation.
When I was bringing my BJ8 home from my dad's after after
installing a rebuilt engine, I cracked the pan on the concrete lip
of his shop (but didn't realize I was leaking). As I drove home,
I saw the pressure at speed drop from 55psi to about 35psi and
thought: "Hmmmm ... that's odd." Stopped on the driveway for just
a couple minutes while I opened the garage door and when I pulled
the car into the garage there was a small puddle on the driveway
(mystery solved). Welded the pan and added a couple quarts and
drove it a couple hundred miles--at normal pressure--before
replacing the pan.</p>
<p>The oil pressure gauge indicates both long-term trends (e.g.
bearing wear) and short-term (oil loss). If you had an oil
temperature gauge you'd see the temp go up if you're losing oil,
as the oil becomes less viscous.<br>
</p>
<br>
<div class="moz-cite-prefix">On 10/30/2018 4:24 PM, Michael MacLean
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:446433529.477837.1540941878400@mail.yahoo.com">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<div style="color:#000; background-color:#fff; font-family:times
new roman, new york, times, serif;font-size:16px">
<div id="yui_3_16_0_ym19_1_1540941154761_17385" dir="ltr"><span
id="yui_3_16_0_ym19_1_1540941154761_17384">Well then please
explain to me how a Bugeye I owned in 1971 would drop from
60 PSI at speed to 40 PSI over a period of time. When I
checked the oil it was a quart low. Adding a quart, the "at
speed" pressure returned to 60 PSI. I mean it was great to
have a low oil indicator like that, but I never understood
how it worked.<br>
</span></div>
<div dir="ltr"><span id="yui_3_16_0_ym19_1_1540941154761_17384">Mike
MacLean</span></div>
<div class="qtdSeparateBR"><br>
<br>
</div>
<div class="yahoo_quoted" style="display: block;">
<div style="font-family: times new roman, new york, times,
serif; font-size: 16px;">
<div style="font-family: HelveticaNeue, Helvetica Neue,
Helvetica, Arial, Lucida Grande, sans-serif; font-size:
16px;">
<div dir="ltr"><font size="2" face="Arial"> On Tuesday,
October 30, 2018 2:22 PM, Michael Salter
<a class="moz-txt-link-rfc2396E" href="mailto:michael.salter@gmail.com"><michael.salter@gmail.com></a> wrote:<br>
</font></div>
<br>
<br>
<div class="y_msg_container">
<div id="yiv4771867940">
<div>
<div dir="ltr">
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">Yes, absolutely
true Bob. <br clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">Decreasing oil
pressure can certainly be an indicator of
increasing clearances.</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;"><br clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">M<br clear="none">
</div>
</div>
<br clear="none">
<div class="yiv4771867940yqt5563999807"
id="yiv4771867940yqt15117">
<div class="yiv4771867940gmail_quote">
<div dir="ltr">On Tue, Oct 30, 2018 at 12:22 PM
Bob Spidell <<a rel="nofollow" shape="rect"
ymailto="mailto:bspidell@comcast.net"
target="_blank"
href="mailto:bspidell@comcast.net"
moz-do-not-send="true">bspidell@comcast.net</a>>
wrote:<br clear="none">
</div>
<blockquote class="yiv4771867940gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex;">
<div>
<div>re: "... delivery pressure itself is
not that important and is really just an
indicator that oil is being delivered to
the bearings ..."</div>
<div>Pressure is useful as a trend
indicator.<br clear="none">
</div>
<br clear="none">
<div
class="yiv4771867940m_4764773932981263630moz-cite-prefix">On
10/30/2018 8:54 AM, Michael Salter wrote:<br
clear="none">
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">I have a
book "Repco Engine Service Manual"
produced by Repco of Repco-Brabham
fame that I use as my bible for engine
building. <br clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">On the
subject of oil pressure it states that
delivery pressure itself is not that
important and is really just an
indicator that oil is being delivered
to the bearings. <br clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">Of much
greater importance is "thin film
pressure" which is generated by the
engine forces on a bearing which can
be as high as 8000 p.s.i. at high RPM
and is determined by the oil type and
temperature, and the engine design.</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">Based
upon this I believe that concentrating
on having good oil pressure at idle is
wasted effort. What is important is
that the engine has some pressure at
idle but good pressure in the normal
operating range. <br clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">A pump
which puts out a huge volume uses
excessive horsepower and can result in
accelerated wear of the pump drive.</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;"><br
clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;">M<br
clear="none">
</div>
<div class="yiv4771867940gmail_default"
style="font-family:comic sans ms,
sans-serif;font-size:small;"><br
clear="none">
</div>
</div>
<br clear="none">
<div class="yiv4771867940gmail_quote">
<div dir="ltr">On Tue, Oct 30, 2018 at
11:30 AM Bob Spidell <<a
rel="nofollow" shape="rect"
ymailto="mailto:bspidell@comcast.net"
target="_blank"
href="mailto:bspidell@comcast.net"
moz-do-not-send="true">bspidell@comcast.net</a>>
wrote:<br clear="none">
</div>
<blockquote
class="yiv4771867940gmail_quote"
style="margin:0 0 0
.8ex;border-left:1px #ccc
solid;padding-left:1ex;">
<div>
<div>I'll offer what I know/have
heard*. I have the 'high
capacity' type in my BJ8, which is
what the DWR techs/sales people
recommended for a road car. Older
6-cyl cars had a rotor type pump.
They (the rotor type) are supposed
to be more efficient--i.e. they
pump more oil--at lower RPMs. At
some point it was discovered,
probably from service bay repairs,
that this type of pump put an
excessive shear load on the bevel
gears on the cam that drive the
pump, causing them to wear out.
Later cars started getting the
gear type pump, which is less
efficient at lower RPMs but puts
less of a load on the cam, and is
probably less expensive to
manufacture as well (esp. if the
gears are the sintered iron
variety). I think the bevel gears
on the cams were re-engineered,
IIRC they got an additional tooth
to spread the load.<br
clear="none">
</div>
<div>The Welch HC pump is the rotor
type. I did a full engine rebuild
and installed the DWR HC pump; I
didn't notice any pressure change
worth mentioning--I 'gained' 15
PSI at idle when I had my gauge
overhauled--but the 'high
capacity' I believe refers to
volume rather than pressure
(which, of course, is mostly
dictated by engine speed). The
'standard type' pump is a gear
type, hence it's more appropriate
for high-RPM race engines as pump
flow is proportional to RPM, and
at 6K RPM or more you'll get
plenty of oil with less load from
the gear type.</div>
<div>I'm not positive, but if you
look at the photos closely, you
can see the 'gallery plug' on the
top of the case. I suppose it
allows inspection of the innards
of the pump without having to
break the case. I believe it's
threaded so not likely to pop
out. If you're getting a new pump
you'll likely need a new drive
shaft and, surprisingly, DWR sells
it cheaper than our (US) vendors
sell it at (I think they might
import the DWR shaft).<br
clear="none">
</div>
* apply appropriate grains of salt<br
clear="none">
<br clear="none">
Bob<br clear="none">
<br clear="none">
<div
class="yiv4771867940m_4764773932981263630m_-555035641554905656moz-cite-prefix">On
10/30/2018 5:12 AM, <a
rel="nofollow" shape="rect"
class="yiv4771867940m_4764773932981263630m_-555035641554905656moz-txt-link-abbreviated"
ymailto="mailto:simon.lachlan@alexarevel.plus.com" target="_blank"
href="mailto:simon.lachlan@alexarevel.plus.com"
moz-do-not-send="true">simon.lachlan@alexarevel.plus.com</a>
wrote:<br clear="none">
</div>
<blockquote type="cite">
<div
class="yiv4771867940m_4764773932981263630m_-555035641554905656WordSection1">
<div
class="yiv4771867940MsoNormal">Hi,</div>
<div
class="yiv4771867940MsoNormal">Has
anyone got the Denis Welch oil
pump ENG672M? See:-</div>
<div
class="yiv4771867940MsoNormal"><a
rel="nofollow" shape="rect"
target="_blank"
href="https://www.bighealey.co.uk/performance-parts/austin-healey/engines/3000-bottom-end?page=3"
moz-do-not-send="true">https://www.bighealey.co.uk/performance-parts/austin-healey/engines/3000-bottom-end?page=3</a></div>
<h2
style="margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm;line-height:20.25pt;">Their
text:- “<span
style="font-size:9.0pt;">Heat
treated castings for longer
life and removable gallery
plugs to be sure it is clean
are advantages of both types
of oil pumps we offer. We
recommend the high capacity
for all road engines using a
standard type crank up to
6000 rpm and the standard
pump for race engines, steel
cranks or anything over 6000
rpm. Both are precision
machined and assembled
in-house to control the
highest quality.<br
clear="none">
</span><span
style="font-size:10.0pt;">-
ENG672 is the standard type.</span><span
style="font-size:9.0pt;"><br
clear="none">
- ENG672M is the high
capacity pump.”</span></h2>
<div
class="yiv4771867940MsoNormal"
style="margin-bottom:12.75pt;line-height:14.4pt;"><span
style="font-size:9.0pt;">What
are “removable gallery
plugs”?</span></div>
<div
class="yiv4771867940MsoNormal"
style="margin-bottom:12.75pt;line-height:14.4pt;"><span
style="font-size:9.0pt;">Is
it just me or is the above a
bit counter-intuitive? “High
capacity” for road cars and
“standard” for race engines?
Surely the highest capacity
is needed where the engine
is working hardest ie
racing? </span></div>
<div
class="yiv4771867940MsoNormal"
style="margin-bottom:12.75pt;line-height:14.4pt;"><span
style="font-size:9.0pt;">And
don’t I remember that, with
the standard BMC pumps, the
older type is reckoned to be
better than the newer type?
Is this something similar to
Denis Welch’s two pumps?</span></div>
<div
class="yiv4771867940MsoNormal"
style="margin-bottom:12.75pt;line-height:14.4pt;"><span
style="font-size:9.0pt;">Anyhow,
if anyone’s got one…..what’s
it like? Did the oil
pressure improve at all?</span></div>
<div
class="yiv4771867940MsoNormal"
style="margin-bottom:12.75pt;line-height:14.4pt;"><span
style="font-size:9.0pt;">I’m
guessing that most people
will have fitted one as part
of a big rebuild thus they
won’t have straightforward
“before and after”
comparisons. I’m thinking of
fitting mine to my engine as
part of a small winter
project and hope I can
squeeze a few more psi into
the system. </span></div>
<div
class="yiv4771867940MsoNormal">Thanks,</div>
<div
class="yiv4771867940MsoNormal">Simon</div>
</div>
<br clear="none">
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class="yiv4771867940m_4764773932981263630m_-555035641554905656mimeAttachmentHeader"></fieldset>
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