[pre-xk] Ignition timing, 1950 MkV DHC

The title tells it all, How does one set the ignition timing
on a MkV?
Engine # 1745. I have found a hole in the flywheel housing
top. Is there a TDC marker or some marker somewhere?
this beast is not in the least like my 120.

Roger–
Roger, '54 120 (SE) DHC, BRG, S678300
Tamarac, South Fla., United States
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In reply to a message from Velocette sent Thu 13 Feb 2014:

Ignition timing on the Mark V starts with identifying the
number 1 cylinder as at the rear of the engine.The shop
manual recommends setting the timing on the distributor ‘‘so
that, with the micrometer adjustment in the neutral
position, that is, with the datum line on the zero mark, the
engine just shows a tendency to pink on full throttle under
load at 1,500 to 2,000 r.p.m. in top gear.’’

A timing arrow is stamped on the rim of the flywheel which
lines up with the center of the top dowel on the bell
housing when the number 1 cylinder is at TDC, unless someone
has changed the flywheel position. It is difficult to see
that timing arrow, so taking the spark plug out of the rear
cylinder and using the starting handle to rotate the engine
allows finding TDC. A dash of white paint on the crankshaft
damper at the engine front would be useful when TDC is
known. Make the white line thin enough (say 1/8’’) so a
timing light can look for it. A pointer attached to the
timing chain cover is a good idea and a second white line to
give TDC at the chosen pointer location helps along with a
third white line at 10 degrees BTDC at the pointer. A good
starting point for static ignition is about 5 degrees before
TDC with the distributor micrometer in neutral position. Be
sure to remove the starting handle before starting the
engine with the electric starter.

The DVX H6A distributor has a 0.012’’ breaker gap with
mechanical advance of 13-15 degrees at distributor rpm
1900/2200 (3 1/2, 2 1/2)and max vacuum advance of 11-13
degrees on distributor for the 3 1/2 and 7-9 degrees for the
2 1/2 (which is 22-26 or 14-18 crankshaft degrees of vacuum
advance).–
Roger McWilliams
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Roger has covered it pretty well. The only thing I would add is that yes the
hole in the top of the bell housing is where you can see the TDC timing
arrow. It is shown on Plate E4 in the manual. So it is pretty much like an
XK120 except the hole and arrow are at the top rather than offset to the
left. The distributor is mostly identical, just different advance weights
and driving dog.

In reply to a message from Roger McWilliams sent Thu 13 Feb 2014:

Thank you.

Roger–
Roger, '54 120 (SE) DHC, BRG, S678300
Tamarac, South Fla., United States
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In reply to a message from Velocette sent Fri 14 Feb 2014:

Roger,

I’ve sent you a PM with my solution. I don’t have picture
posting privileges here. You can post the picture if you
want.

Art–
ARTIEFARTY
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In reply to a message from Roger McWilliams sent Thu 13 Feb 2014:

Has anyone tried the Petronix kit in the DVX H6A? I cannot get
it to work. I have the old style side entry cap. Acts advanced
and backfires thru intake.–
CBD
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In reply to a message from DEWITT sent Sat 15 Nov 2014:

There has been some discussion of the Pertronix on the XK
forum, some people having trouble with them. You might check
the XK archives and search Pertronix.
The XK120 distributor is pretty much the same as Mark V
other than the drive end peg and the advance curve.
There have also been reports of defective reproduction rotors.
The side entry cap should not be a problem for this system.
Maybe you have a problem in the advance mechanism.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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In reply to a message from Rob Reilly sent Sat 15 Nov 2014:

Thanks Rob

I have Peteronix in the XK150 and also the SIII E Type with no
issues. That’s why I made the mistake to think it would be easy
for the old car…now I cant even get it to start. I broke the
Jaguar rule - it was working fine and I should not have messed
with it.–
Chuck DeWitt 37 SS100 59 XK150S 73 E-Type 96 XJS
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In reply to a message from DEWITT sent Sat 15 Nov 2014:

Hi Chuck,

I’ve always tried to keep my cars stock, original and
rather just return them to the way they were made. This
also makes servicing them easy as then every thing will
follow the procedures in the factory books, ROM and
owner’s handbook etc.

Sorry I can’t be much of help, I had some ignition
problems myself after the disaster with the camshaft
sprocket bolts had been cut off. The last missing piece
was the brush inside the distributor cap that I probably
had destroyed by mistake (only the spring was left). I did
have anothet side entry cap that I used then, but missed
the fact that the same connector, the one in the middle,
had a blunt end, where as the others have a sharp pointed
end, so I did not have contact to the brush inside the
cap.

When debugging the ignition, which is REALLY simple, I
think measuring the contacts and resistance of wires with
a DVM and you will surely find why it’s not firing.

Is yours still positive ground?

Mine was not, due to a Facet fuel pump, but I replaced it
with the correct SU and reversed polarity back to positive
earth. Just to make things easier and to be able to go by
the factory book.

Now mine fires up every time, but the (new) fuel pump has
become a bit tricky to start, too much just sitting around
and not enough use. I hope to drive 30 miles next Tuesday!

BTW why Petronix on the S3 V12 E-type? I have one with the
original Lucas OPUS mk2 and it is electronic and has no
contact breaker (points) like all V12’s were. Now it is
more complicated than the MKV but still no rocket science.
:slight_smile:

Cheers,

Pekka T. - 647194
Fin.–
The original message included these comments:

I have Peteronix in the XK150 and also the SIII E Type with no
issues. That’s why I made the mistake to think it would be easy
for the old car…now I cant even get it to start. I broke the
Jaguar rule - it was working fine and I should not have messed
with it.
Chuck DeWitt 37 SS100 59 XK150S 73 E-Type 96 XJS


MKV 3.5L DHC, E V12 OTS, XJ6C MOD, XJ8 Executive
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In reply to a message from DEWITT sent Sat 15 Nov 2014:

No Pertronix experience on my part. Assuming car was running well
before installing Pertronix, you may wish to look at spark timing
issues. Are the plug wires associated with the correct cylinders?
As a starting point on that question, does the number 1 cylinder
(rear of engine, use care on this numbering convention) get spark
at 5 degrees static advance before top dead center on the fuel
mixture compression stroke with no centrifugal or vacuum advance?
It is easy to have plug wires wrong or even have spark on exhaust
stroke, maybe the Pertronix is not sending to spark wires as
needed.–
Roger McWilliams
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