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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: mgs@autox.team.net=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. Except =
...</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Although two pistons are going down while the =
other two=20
are going up, the movement is not symmetrical. Don't ask me to =
explain the=20
physical logic behind it, but when the crank has turned 90=20
degrees </FONT><FONT size=3D2>from TDC the piston has moved more =
than halfway=20
down the stroke, and from that position to BDC the =
piston moves less=20
than half the stroke. So for that 90 degrees of crank movement the =
undersides of the pistons coming down the first 'half' of the=20
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=20
the situation is reversed to give a slight negative pressure. 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> </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. The road-draught system is=20
pretty 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. The =
question is why=20
there should be enough negative pressure on that tube to do it. I =
don't=20
know about the MGA but on the MGB 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. Unless =
the=20
intake to the can is restricted somehow. 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> </DIV>
<DIV><FONT size=3D2>PaulH.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2></FONT> </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=3Dspridget@gmail.com href=3D"mailto:spridget@gmail.com";>Stan =
Fickes</A>=20
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dpaulhunt73@virginmedia.com=20
href=3D"mailto:paulhunt73@virginmedia.com";>PaulHunt73</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Cc:</B> <A =
title=3Dmgs@autox.team.net=20
href=3D"mailto:mgs@autox.team.net";>mgs@autox.team.net</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>
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class=3Dgmail_quote>
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dir=3Dltr> </DIV></BLOCKQUOTE></DIV></BLOCKQUOTE></DIV></BLOCKQUOTE>=
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