Subject: Re: [Mgs] MGA crankcase ventilation

From: PaulHunt73 via Mgs <[email-masked]>
Date: Sun, 14 Jul 2019 09:29:11 +0100 RC4YNlEWTq4Jh5d8t5QIKr52VCluNHreptIl0vyAfmyNBf+vFMMzhLF8FBQTqGDqxQCqLKk6jW6gyQ==

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IME you should always hear some hissing when putting compressed air into =
a cylinder, ring sealing isn't perfect.

Removing one plug at a time may show which cylinder or cylinders are at =
fault if the pulsing lessens.

Air pulsing out of the rocker cover definitely indicates a major =
compression leak from somewhere, despite your compression readings. =20

Having said that AFAIK an MGA should also have a 'road draught tube' =
hanging down from the front tappet chest cover, which is another route =
for air to pass in and out of the crankcase.  Perhaps that is blocked.

PaulH.
  ----- Original Message ----- kcase ventilation

  I have an MGA 1600, under 2,000 miles since the engine rebuild. While =
working on an unrelated issue, I discovered that the front air filter =
was thoroughly soaked in oil. The source was the vent hose between the =
air filter and the valve cover. I found significant (to my lack of =
experience with this system!) pulsing air blowing through the hose at =
idle.
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<DIV><FONT size=3D2>IME you should always hear some hissing when putting =

compressed air into a cylinder, ring sealing isn't perfect.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV>
<DIV><FONT size=3D2>Removing one plug at a time may show which cylinder =
or=20
cylinders are at fault if the pulsing lessens.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV></DIV>
<DIV><FONT size=3D2>Air pulsing out of the rocker cover =
definitely&nbsp;indicates=20
a major compression leak from somewhere, despite your compression=20
readings.&nbsp; </FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV>
<DIV><FONT size=3D2>Having said that AFAIK an MGA should also have a =
'road draught=20
tube' hanging down from the front tappet chest cover, which is another =
route for=20
air to pass in and out of the crankcase.&nbsp; Perhaps that is=20
blocked.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>PaulH.</FONT></DIV></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
  <DIV style=3D"FONT: 10pt arial">----- Original Message ----- kcase=20
  ventilation</DIV>
  <DIV><FONT size=3D2></FONT><BR></DIV>
  <DIV dir=3Dltr>I have an MGA 1600, under 2,000 miles since the engine =
rebuild.=20
  While working on an unrelated issue, I discovered that the front air =
filter=20
  was thoroughly soaked in oil. The source was the vent hose between the =
air=20
  filter and the valve cover. I found significant (to my lack of =
experience with=20
  this system!) pulsing air blowing through the hose at=20
idle.</DIV></BLOCKQUOTE></BODY></HTML>

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From: Stan Fickes via Mgs <[email-masked]>
Date: Sun, 14 Jul 2019 15:05:00 -0400

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Thanks, Paul!
I concluded when I cranked the motor with no plugs installed and still felt
the pulsing air that it was not a compression issue. For completeness, I
need to try the same thing with the plugs installed, to see if there is a
difference. I just can't think what else would pump air into the
crankcase/rocker cover! I checked the draught tube this afternoon by
squirting some low-pressure air into the rocker cover tube, and felt a
gentle stream of air out the bottom. I should also check that with the
starter motor turning to see if it's consistent between the two tubes.
Thanks!
Stan

On Sun, Jul 14, 2019 at 4:31 AM PaulHunt73 <[email-masked]>
wrote:

> IME you should always hear some hissing when putting compressed air into a
> cylinder, ring sealing isn't perfect.
>
> Removing one plug at a time may show which cylinder or cylinders are at
> Air pulsing out of the rocker cover definitely indicates a major
> compression leak from somewhere, despite your compression readings.
>
> Having said that AFAIK an MGA should also have a 'road draught tube'
> hanging down from the front tappet chest cover, which is another route for
> air to pass in and out of the crankcase.  Perhaps that is blocked.
>
> PaulH.
>
> I have an MGA 1600, under 2,000 miles since the engine rebuild. While
> working on an unrelated issue, I discovered that the front air filter was
> thoroughly soaked in oil. The source was the vent hose between the air
> filter and the valve cover. I found significant (to my lack of experience
> with this system!) pulsing air blowing through the hose at idle.
>
>

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<div dir=3D"ltr">Thanks, Paul!<div>I concluded when I cranked the motor wit=
h no plugs installed and still felt the pulsing air that it was not a compr=
ession issue. For completeness, I need to try the same thing with the plugs=
 installed, to see if there is a difference. I just can&#39;t think what el=
se would pump air into the crankcase/rocker cover! I checked the draught tu=
be this afternoon by squirting some low-pressure air into the rocker cover =
tube, and felt a gentle stream of air out the bottom. I should also check t=
hat with the starter motor turning to see if it&#39;s consistent between th=
e two tubes.</div><div>Thanks!</div><div>Stan</div></div><br><div class=3D"=
gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Sun, Jul 14, 2019 at =
4:31 AM PaulHunt73 &lt;<a href=3D"mailto:[email-masked]" target=
=3D"_blank">[email-masked]</a>&gt; wrote:<br></div><blockquote =
class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px sol=
id rgb(204,204,204);padding-left:1ex"><u></u>

<div bgcolor=3D"#ffffff">
<div><font size=3D"2">IME you should always hear some hissing when putting=
=20
compressed air into a cylinder, ring sealing isn&#39;t perfect.</font></div=
<div><font size=3D"2"></font>=C2=A0</div>
<div>
<div><font size=3D"2">Removing one plug at a time may show which cylinder o=
r=20
cylinders are at fault if the pulsing lessens.</font></div>
<div><font size=3D"2"></font>=C2=A0</div></div>
<div><font size=3D"2">Air pulsing out of the rocker cover definitely=C2=A0i=
ndicates=20
a major compression leak from somewhere, despite your compression=20
readings.=C2=A0 </font></div>
<div><font size=3D"2"></font>=C2=A0</div>
<div>
<div><font size=3D"2">Having said that AFAIK an MGA should also have a &#39=
;road draught=20
tube&#39; hanging down from the front tappet chest cover, which is another =
route for=20
air to pass in and out of the crankcase.=C2=A0 Perhaps that is=20
blocked.</font></div>
<div><font size=3D"2"></font>=C2=A0</div>
<div><font size=3D"2">PaulH.</font></div></div>
<blockquote style=3D"border-left:2px solid rgb(0,0,0);padding-left:5px;padd=
ing-right:0px;margin-left:5px;margin-right:0px">
  <div style=3D"font:10pt arial">----- Original Message ----- kcase=20
  ventilation</div>
  <div><font size=3D"2"></font><br></div>
  <div dir=3D"ltr">I have an MGA 1600, under 2,000 miles since the engine r=
ebuild.=20
  While working on an unrelated issue, I discovered that the front air filt=
er=20
  was thoroughly soaked in oil. The source was the vent hose between the ai=
r=20
  filter and the valve cover. I found significant (to my lack of experience=
 with=20
  this system!) pulsing air blowing through the hose at=20
idle.</div></blockquote></div>
</blockquote></div>

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[email-masked]

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From: PaulHunt73 via Mgs <[email-masked]>
Date: Mon, 15 Jul 2019 11:41:59 +0100 JXJDqttdoE0R9duzNDBqF+lQ3mG8XwbI8/mHDlVzqGqCWNLOjKRNuX7f+wPaEkowKc6ch++f7EQhTw==

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If it's not compression leaking then I can't think what would cause =
excessive pulsing out of the breathers.  Except ...

Although two pistons are going down while the other two are going up, =
the movement is not symmetrical.  Don't ask me to explain the physical =
logic behind it, but when the crank has turned 90 degrees from TDC the =
piston has moved more than halfway down the stroke, and from that =
position to BDC the piston moves less than half the stroke.  So for that =
90 degrees of crank movement the undersides of the pistons coming down =
the first 'half' of the stroke are displacing more air than the ones =
going up can 'absorb' so you get a positive pressure, but for the second =
half of the strokes the situation is reversed to give a slight negative =
pressure.  But on my MGB - different crankcase ventilation system but =
still two routes in and out of the crankcase - I can seal off one and I =
get no more than a slight fluttering in the other.

Maybe the problem is not so much excessive pulsing, with you expecting =
there to be no movement in the breather at all, but excessive oil in the =
rocker cover around the vent.  The road-draught system is pretty hit and =
miss as to which way air will flow through the crankcase, and I wouldn't =
have though that suck unfiltered air in from the road-draught tube was a =
Good Thing, but if the intake can suck air through the rocker cover tube =
at any time, then it will draw oil along with it.  The question is why =
there should be enough negative pressure on that tube to do it.  I don't =
know about the MGA but on the MGB that tube is on the 'dirty' side of =
the filter, which in theory shouldn't be under significant negative =
pressure, unlike the 'clean' side of the filter at wide throttle =
openings.  Unless the intake to the can is restricted somehow.  But if =
the tube is connected to the clean side of the filter then the intake =
system will be continually sucking air through the tube, and any oil =
droplets that are in the vicinity.

PaulH.

----- Original Message -----=20
  From: Stan Fickes=20
  To: PaulHunt73=20
  Cc: [email-masked]=20
  Sent: Sunday, July 14, 2019 8:05 PM
  Subject: Re: [Mgs] MGA crankcase ventilation

  Thanks, Paul!
  I concluded when I cranked the motor with no plugs installed and still =
felt the pulsing air that it was not a compression issue. For =
completeness, I need to try the same thing with the plugs installed, to =
see if there is a difference. I just can't think what else would pump =
air into the crankcase/rocker cover! I checked the draught tube this =
afternoon by squirting some low-pressure air into the rocker cover tube, =
and felt a gentle stream of air out the bottom. I should also check that =
with the starter motor turning to see if it's consistent between the two =
tubes.
  Thanks!
  Stan

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<DIV><FONT size=3D2>If it's not compression leaking then I can't think =
what would=20
cause excessive pulsing out of the breathers.&nbsp; Except =
...</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>Although&nbsp;two pistons are going down while the =
other two=20
are going up, the movement is not symmetrical.&nbsp; Don't ask me to =
explain the=20
physical logic behind it, but when the crank&nbsp;has turned&nbsp;90=20
degrees&nbsp;</FONT><FONT size=3D2>from TDC the piston has moved more =
than halfway=20
down the stroke, and from that position to BDC&nbsp;the =
piston&nbsp;moves less=20
than half the stroke.&nbsp; So for that 90 degrees of crank movement the =

undersides of the pistons coming down&nbsp;the first 'half' of the=20
stroke&nbsp;are displacing more air than the ones&nbsp;going up&nbsp;can =

'absorb' so you get a positive pressure, but for the second half of the =
strokes=20
the situation is reversed to give a slight negative pressure.&nbsp; But =
on my=20
MGB - different crankcase ventilation system but still two routes in and =
out of=20
the crankcase - I can seal off one and I get no more than a slight =
fluttering in=20
the other.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>Maybe the problem is not so much excessive pulsing, =
with you=20
expecting there to be no movement in the breather at all, but excessive =
oil in=20
the rocker cover around the vent.&nbsp; The road-draught system is=20
pretty&nbsp;hit and miss as to which way air will flow through the =
crankcase,=20
and I wouldn't have though that suck unfiltered air in from the =
road-draught=20
tube was a Good Thing, but if the intake can suck air through the rocker =
cover=20
tube at any time, then it will draw oil along with it.&nbsp; The =
question is why=20
there should be enough negative pressure on that tube to do it.&nbsp; I =
don't=20
know about the MGA but on the MGB&nbsp;that tube is on the 'dirty' side =
of the=20
filter, which in theory shouldn't be under significant negative =
pressure, unlike=20
the 'clean' side of the filter at wide throttle openings.&nbsp; Unless =
the=20
intake to the can is restricted somehow.&nbsp; But if the tube is =
connected to=20
the clean side of the filter then the intake system will be continually =
sucking=20
air through the tube, and any oil droplets that are in the=20
vicinity.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>PaulH.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV>----- Original Message ----- </DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"=20
dir=3Dltr>
  <DIV=20
  style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: =
black"><B>From:</B>=20
  <A title=[email-masked] href=3D"mailto:[email-masked]">Stan =
Fickes</A>=20
  </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=[email-masked]=20
  href=3D"mailto:[email-masked]">PaulHunt73</A> </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Cc:</B> <A =
title=[email-masked]=20
  href=3D"mailto:[email-masked]">[email-masked]</A> </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Sunday, July 14, 2019 =
8:05 PM</DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [Mgs] MGA =
crankcase=20
  ventilation</DIV>
  <DIV><BR></DIV>
  <DIV dir=3Dltr>Thanks, Paul!
  <DIV>I concluded when I cranked the motor with no plugs installed and =
still=20
  felt the pulsing air that it was not a compression issue. For =
completeness, I=20
  need to try the same thing with the plugs installed, to see if there =
is a=20
  difference. I just can't think what else would pump air into the=20
  crankcase/rocker cover! I checked the draught tube this afternoon by =
squirting=20
  some low-pressure air into the rocker cover tube, and felt a gentle =
stream of=20
  air out the bottom. I should also check that with the starter motor =
turning to=20
  see if it's consistent between the two tubes.</DIV>
  <DIV>Thanks!</DIV>
  <DIV>Stan</DIV></DIV>
  <DIV class=3Dgmail_quote>
  <BLOCKQUOTE=20
  style=3D"BORDER-LEFT: rgb(204,204,204) 1px solid; MARGIN: 0px 0px 0px =
0.8ex; PADDING-LEFT: 1ex"=20
  class=3Dgmail_quote>
    <DIV bgcolor=3D"#ffffff">
    <BLOCKQUOTE=20
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PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px">
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dir=3Dltr>&nbsp;</DIV></BLOCKQUOTE></DIV></BLOCKQUOTE></DIV></BLOCKQUOTE>=
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