Subject: Re: [Mgs] Timing adjustment on an 18GK engine

From: "PaulHunt73" <[email-masked]>
Date: Sat, 10 Jul 2021 08:48:35 +0100 ntjQwNk67F0ofZnaG4pSXgKCyGFzUOPt0XTd40AyZ05Cr3L6XzrK1KExb6rcpIGbA1vumljFJ2c8BZTirTR1+LcZsowlmJPKnIE=

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If you change to a lower octane then it is more likely to ping/pink, and =
this is more likely to happen in a high compression engine than a low.  =
If you must use that fuel - is it cheaper? - just back the timing off =
until you can't hear pinking at any combination of throttle opening, =
revs and load.

The factory specs on original fuel were conservative to take account of =
engine component tolerances and many engines can run more advance =
without problems and give better acceleration and cruising economy - BT, =
DT back in the day.  Haynes agrees and says to run at full throttle =
between 30 and 50 in top gear and set the timing so that faint pinking =
can just be heard.  For me that's too aggressive, like you I've had =
part-throttle pinking on hills that goes at full throttle, hence my =
modified recommendation.  I also found that the change to unleaded =
increased the tendency to pink, so on this engine that never could run =
more advance than book on leaded has to be slightly retarded from book =
on unleaded.  E5 hasn't made any difference, E10 will be arriving here =
this year but only in the lower of the two octanes usually available, so =
I will continue to use the higher in the roadster, and change to that in =
the 'low compression' V8.=20

PaulH.
  ----- Original Message -----=20

  It appears to run well enough, but I have had a couple of issues come =
up where there was a low-speed but high load situation, like going up a =
short hill with a 15 mph speed limit. I could hear it pinging some.=20
  ...
  I expected the timing to be too far advanced at that RPM, but if =
anything, it was slightly retarded.
  '''

  Does anyone else run 87 in a high compression engine, or have I gone =
off on a fool's errand here?
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<DIV>If you change to a lower octane then it is more likely to =
ping/pink, and=20
this is more likely to happen in a high compression engine than a =
low.&nbsp; If=20
you must use that fuel - is it cheaper? -&nbsp;just back the timing off =
until=20
you can't hear&nbsp;pinking at any combination of throttle opening, revs =
and=20
load.</DIV>
<DIV>&nbsp;</DIV>
<DIV>The factory specs on original fuel were conservative to take =
account of=20
engine component tolerances and many engines can run more advance =
without=20
problems and give better acceleration and cruising economy - BT, DT back =
in the=20
day.&nbsp; Haynes agrees and says to run at full throttle between 30 and =
50 in=20
top gear and set the timing so that faint pinking can just be =
heard.&nbsp; For=20
me that's too aggressive, like you I've had part-throttle pinking on =
hills that=20
goes at full throttle, hence my modified recommendation.&nbsp; I also =
found that=20
the change to unleaded increased the tendency to pink, so on this engine =
that=20
never could run more advance than book on leaded has to be slightly =
retarded=20
from book on unleaded.&nbsp; E5 hasn't made any difference, E10 will be =
arriving=20
here this year but only in the lower of the two octanes usually =
available, so I=20
will continue&nbsp;to use the higher in the roadster, and change to that =
in the=20
'low compression' V8.&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>PaulH.</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 ----- </DIV>
  <DIV><BR></DIV>
  <DIV=20
  style=3D"FONT-FAMILY: arial, helvetica, sans-serif; COLOR: #000000; =
FONT-SIZE: 12pt">
  <DIV><BR data-mce-bogus=3D"1"></DIV>
  <DIV>It appears to run well enough, but I have had a couple of issues =
come up=20
  where there was a low-speed but high load situation, like going up a =
short=20
  hill with a 15 mph speed limit. I could hear it pinging some. <BR=20
  data-mce-bogus=3D"1">...</DIV>
  <DIV>I expected the timing to be too far advanced at that RPM, but if=20
  anything, it was slightly retarded.</DIV>
  <DIV>'''<BR data-mce-bogus=3D"1"></DIV>
  <DIV>Does anyone else run 87 in a high compression engine, or have I =
gone off=20
  on a fool's errand here?</DIV></DIV></BLOCKQUOTE></BODY></HTML>

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From: Robert's New iPad <[email-masked]>
Date: Sat, 10 Jul 2021 07:47:18 -0400

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Hi WIlliam,
    There will be as many answers to your questions as there are readers, as=
 there are many variables involved.
    It is my opinion that if the max advance, without vacuum connected, shou=
ld be 32 degrees at 3500+.   That is shared by many.  Another of my opinions=
 is that 10% alcohol makes no difference to the engine=E2=80=99s performance=
.  One can read adverts in British periodicals of the 1950s and 1960s in whi=
ch the brands advertise that they are better because of the alcohol.  =20
    As to the fuel choice, that very much depends on where you are driving (=
hills, dales, flat country) and how you like to drive.  The workshop manual w=
as written years ago, so its timing specs may or may not be valid today.   Fu=
els differ around the country, and certainly are quite different from those i=
n 1974, so you end up selecting one that seems to work OK for you.  It is sa=
id, also, that fuel blends differ regionally in USA.
   One ends up setting the timing to what keeps engine and driver happy. We k=
now that pinging/pinking is hard on the engine. One should avoid that by dow=
n-shifting as needed, checking that the timing is not over-advanced,  or by u=
sing higher-octane fuel. =20
   Mine is 1972 18V, home-market pistons, some cleanup of heads and ports, w=
ith HIF and distributor rebuilt by Advanced Distributors (Jeff Schlemmer).  M=
ax advance, w/o vacuum, is 32 degrees.    I find that alternating tanks of 8=
9 and 91 (sometimes the same pump shows 93) keeps it happy. We have some hil=
ls in CT, so I listen carefully at 2500 rpm.=20
   Over the course of a driving season, perhaps 4000 miles, the annual diffe=
rence in cost of one fuel to another is slight. I try to err on the side of c=
aution.
Bob

> On Jul 9, 2021, at 5:47 PM, [email-masked] wrote:
>=20
> Hello everyone,
>=20
> My car is a 1974 MGB with an 18GK engine and HS4 carbs. The evaporative lo=
ss control and anti-run on controls are connected. The smog pump has been re=
moved and the ports are plugged. The distributor is a Pertronix unit I bough=
t several years ago. It's equipped with vacuum advance, which is working. Th=
e mechanical advance is also freely working. Not too long ago, I read that t=
hese cars, even the high compression ones, should be able to run well on eth=
anol-free 87 octane. This caused no small debate on the local British car gr=
oup on facebook, but the consensus seemed to be that those who used E0 87 we=
re satisfied and didn't have any issues from it. My last fill-up had been et=
hanol-free 93, and I need not tell you that running E0 87 would be far prefe=
rable. It was time for a fill-up, so I filled at at a nearby station that se=
ems to sell decent quality stuff.
>=20
> It appears to run well enough, but I have had a couple of issues come up w=
here there was a low-speed but high load situation, like going up a short hi=
ll with a 15 mph speed limit. I could hear it pinging some. Downshifting wil=
l stop it, but that isn't always practical. So, I decided to check its timin=
g. The Bentley manual and several online sources state that an 18GK is suppo=
sed to have its dynamic timing set to 16deg BTDC at 1500rpm. It's been a few=
 years since I last set the timing, so I disconnected the vacuum advance and=
 plugged the manifold port, and then got the car running smoothly at 1500rpm=
 as indicated by the tach in the dash. It's all I have, so it'll have to do.=

>=20
> I expected the timing to be too far advanced at that RPM, but if anything,=
 it was slightly retarded. If 16deg is between the 20 and the 15, the car wa=
s currently set at around 12deg. I adjusted it to an indicated 16deg, re-che=
cked the idle speed, checked the timing again, was satisfied, tightened the d=
istributor clamp and shut off the engine. I haven't yet test driven it, thou=
gh at idle it sounded smooth at maybe an indicated 800 or 850rpm. For all I k=
now, it'll probably have a little more spring in its step, though it hasn't s=
eemed sluggish lately. I try to drive it at least twice per week, so it's no=
t sitting too often.
>=20
> Does anyone else run 87 in a high compression engine, or have I gone off o=
n a fool's errand here?
>=20
> Thank you,
> -William
>=20
> Donate: http://www.team.net/donate.html
> Suggested annual donation  $12.75
>=20
>=20
> Unsubscribe: http://autox.team.net/mailman/options/mgs/[email-masked]

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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charset=3D=
utf-8"></head><body dir=3D"auto"><div dir=3D"ltr"></div><div dir=3D"ltr">Hi W=
Illiam,</div><div dir=3D"ltr">&nbsp; &nbsp; There will be as many answers to=
 your questions as there are readers, as there are many variables involved.<=
/div><div dir=3D"ltr">&nbsp; &nbsp; It is my opinion that if the max advance=
, without vacuum connected, should be 32 degrees at 3500+. &nbsp; That is sh=
ared by many. &nbsp;Another of my opinions is that 10% alcohol makes no diff=
erence to the engine=E2=80=99s performance. &nbsp;One can read adverts in Br=
itish periodicals of the 1950s and 1960s in which the brands advertise that t=
hey are better because of the alcohol. &nbsp;&nbsp;</div><div dir=3D"ltr">&n=
bsp; &nbsp; As to the fuel choice, that very much depends on where you are d=
riving (hills, dales, flat country) and how you like to drive. &nbsp;The wor=
kshop manual was written years ago, so its timing specs may or may not be va=
lid today. &nbsp; Fuels differ around the country, and certainly are quite d=
ifferent from those in 1974, so you end up selecting one that seems to work O=
K for you. &nbsp;It is said, also, that fuel blends differ regionally in USA=
.</div><div dir=3D"ltr">&nbsp; &nbsp;One ends up setting the timing to what k=
eeps engine and driver happy. <span style=3D"background-color: rgba(255, 255=
, 255, 0);">We know that pinging/pinking is hard on the engine. One should a=
void that by down-shifting as needed, checking that the timing is not over-a=
dvanced, &nbsp;or by using higher-octane fuel. &nbsp;</span></div><div>&nbsp=
; &nbsp;Mine is 1972 18V, home-market pistons, some cleanup of heads and por=
ts, with HIF and distributor rebuilt by Advanced Distributors (Jeff Schlemme=
r). &nbsp;Max advance, w/o vacuum, is 32 degrees. &nbsp; &nbsp;I find that a=
lternating tanks of 89 and 91 (sometimes the same pump shows 93) keeps it ha=
ppy. We have some hills in CT, so I listen carefully at 2500 rpm.&nbsp;</div=
><div dir=3D"ltr">&nbsp; &nbsp;Over the course of a driving season, perhaps 4=
000 miles, the annual difference in cost of one fuel to another is slight. I=
 try to err on the side of caution.</div><div dir=3D"ltr">Bob</div><div dir=3D=
"ltr"><br></div><div dir=3D"ltr"><br></div><div dir=3D"ltr"><br></div><div d=
ir=3D"ltr">On Jul 9, 2021, at 5:47 PM, <a href=3D"mailto:[email-masked]=
m">[email-masked]</a> wrote:<br><br></div><blockquote type=3D"cite"><d=
iv dir=3D"ltr"><div style=3D"font-family: arial, helvetica, sans-serif; font=
-size: 12pt; color: #000000"><div>Hello everyone,</div><div><br data-mce-bog=
us=3D"1"></div><div>My car is a 1974 MGB with an 18GK engine and HS4 carbs. T=
he evaporative loss control and anti-run on controls are connected. The smog=
 pump has been removed and the ports are plugged. The distributor is a Pertr=
onix unit I bought several years ago. It's equipped with vacuum advance, whi=
ch is working. The mechanical advance is also freely working. Not too long a=
go, I read that these cars, even the high compression ones, should be able t=
o run well on ethanol-free 87 octane. This caused no small debate on the loc=
al British car group on facebook, but the consensus seemed to be that those w=
ho used E0 87 were satisfied and didn't have any issues from it. My last fil=
l-up had been ethanol-free 93, and I need not tell you that running E0 87 wo=
uld be far preferable. It was time for a fill-up, so I filled at at a nearby=
 station that seems to sell decent quality stuff.</div><div><br data-mce-bog=
us=3D"1"></div><div>It appears to run well enough, but I have had a couple o=
f issues come up where there was a low-speed but high load situation, like g=
oing up a short hill with a 15 mph speed limit. I could hear it pinging some=
. Downshifting will stop it, but that isn't always practical. So, I decided t=
o check its timing. The Bentley manual and several online sources state that=
 an 18GK is supposed to have its dynamic timing set to 16deg BTDC at 1500rpm=
. It's been a few years since I last set the timing, so I disconnected the v=
acuum advance and plugged the manifold port, and then got the car running sm=
oothly at 1500rpm as indicated by the tach in the dash. It's all I have, so i=
t'll have to do.</div><div><br data-mce-bogus=3D"1"></div><div>I expected th=
e timing to be too far advanced at that RPM, but if anything, it was slightl=
y retarded. If 16deg is between the 20 and the 15, the car was currently set=
 at around 12deg. I adjusted it to an indicated 16deg, re-checked the idle s=
peed, checked the timing again, was satisfied, tightened the distributor cla=
mp and shut off the engine. I haven't yet test driven it, though at idle it s=
ounded smooth at maybe an indicated 800 or 850rpm. For all I know, it'll pro=
bably have a little more spring in its step, though it hasn't seemed sluggis=
h lately. I try to drive it at least twice per week, so it's not sitting too=
 often.</div><div><br data-mce-bogus=3D"1"></div><div>Does anyone else run 8=
7 in a high compression engine, or have I gone off on a fool's errand here?<=
/div><div><br data-mce-bogus=3D"1"></div><div>Thank you,</div><div>-William<=
/div></div></div></blockquote><blockquote type=3D"cite"><div dir=3D"ltr"><sp=
an>_______________________________________________</span><br><span></span><b=
r><span><a href=3D"mailto:[email-masked]">[email-masked]</a></span><=
br><span>Donate: <a href=3D"http://www.team.net/donate.html">http://www.team=
.net/donate.html</a></span><br><span>Suggested annual donation &nbsp;$12.75<=
/span><br><span></span><br><span>Archive: <a href=3D"http://www.team.net/pip=
ermail/mgs">http://www.team.net/pipermail/mgs</a> <a href=3D"http://autox.te=
am.net/archive">http://autox.team.net/archive</a></span><br><span></span><br=
><span>Unsubscribe: <a href=3D"http://autox.team.net/mailman/options/mgs/mgb=
[email-masked]">http://autox.team.net/mailman/options/mgs/[email-masked]</a=
></span><br></div></blockquote></body></html>=

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