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MG TD TF 1500 - Using an Ajustable Timing Light

I just finished reading DMoore's thread, "Jumping Timing Mark TF 1500," (congratulations on solving your issue) and I have just acquired a new adjustable timing light. Assuming that when my pointer (TD25009, XPAG/TD2/25404)is on the timing notch the engine is at TDC, am I correct that I can dial in 8-10 degrees with the engine at idle and, if the timing is correct, the pointer should appear to be on the TDC notch?

The booklet with the timing light says to "zero" the light and check that the advance at idle is at the manufacturer's spec but my pulley does not have degree marks beside the notch so I'm just guessing at the amount of advance. I'm hoping the adjustable timing light will allow me to make better (more precise?) guesses before I move on to checking the advance at 3K RPM.

Thanks. Jud
J K Chapin

Theoretically, you should be able to adjust the dial on your timing light to the advance you want, then adjust your distributor so the light flashes at TDC (notch on pointer), which would give you the advance as set on your light.

Practically speaking, for whatever reason, an inductive timing light (clamp with magnet surrounding the #1 plug wire) will get some interference such that the timing seems to jump around and it is difficult, if not impossible, to set a specific time.

In that case, the old-fashioned "direct" lights (copper clamp goes on a connector between spark plug and wire) will show a more stable light. That's essentially what the other thread was about.

Unfortunately, you might not be able to find a direct hook up (non-inductive) timing light with an advance setting, so you would be back to using an advance marking on your pulley. If there aren't any marks, then you'll have to add them. You can find dials used for timing cams that will have degree markings or you can even use a protractor.
David Littlefield

That's what I wanted to know. Thanks. I will try it our tomorrow at our Club's tech session and let you know. I'm anticipating jumping but hope I can get close and then maybe fine tune just by touchy-feely. Jud
J K Chapin

Jud, if the magnetic clamp on an inductive timing light is temporarily wrapped with aluminum foil, would that eliminate the interference we are talking about here? As has been noted, the non-inductive lights are almost impossible to find these days. So, a fix of any kind would be very reassuring that we were getting some accurate readings.
Jim Merz

Jim, I'll try it tomorrow and let you know. I hope the AL Foil works. Jud
J K Chapin

For what it is worth the timing marks on the engine and the revs on the TL screen were all over the place when I first used my new adjustable advance timing light (a gift from my son) I was confused as I had never had or used this type of timing light before, I took the fan belt off and everything settled down It must have been picking up the revs from the Generator.


G Mills

I use a metal-bodied Craftsman adjustable timing light. It works perfectly on all my cars. Placement of the pickup clamp may play a part in your interference issue.
Steve Simmons

Good news and bad news: The good news is that my new Innova timing light seems to work great and the flashing is very stable (copper non-resistive wires).

The bad news is my spark plugs. At today's club tech session we tried to check the carb mixture using the ColorTune system (a glass spark plug that you can look through to see the color of the combustion flame). Both my plugs and the ColorTune gizmo indicated that I'm running very rich but no amount of jet adjustment would make it run lean. Resolving that will be another post. The news is that my plugs look just like D Moore's. A 3/4 inch reach in what I'm pretty sure is an older 1/2 inch reach head. There is about 1/4 inch of sooty blackness on the threads just like in the picture that D Moore posted.

The heat in the Club's shop got to me so I didn't check the casting but I'm pretty certain that I recall it being the older head.

Can someone please fill in the following:

Old XPAG Head Casting #: Plug Reach:
New XPAG Head Casting #: Plug Reach:

I'll confirm the had casting and, if necessary get proper plugs and let you know.


J K Chapin

Jud -

My TF-1500 had a 22952 "banana hole" cylinder head on the block when I bought it. It used 1/2" reach spark plugs. I was lucky enough to find an AEF118 TF-1500 head (3/4" reach spark plugs) to replace the 22952 head. I don't know when MG heads first required 3/4" plugs.


Here are head numbers and dates by Paddy Willmer in his "MG T Series in Detail, TA-TF 1935-1955".

LM Cook

would this be the same for those with pertronix?
Keith Yarbrough(TD 1275)


You can check whether it's a 1/2 plug quite easily by bending a piece of wire/paper clip into a small L shape and sticking it in the plug hole. Note where on the wire/clip it catches the inside of the head and measure.


If you're asking whether or not a using an adjustable timing light on a car equipped with the Pertronix unit and not points will possibly result in erratic flashes the answer is yes.
Gene Gillam

Now Gene, your response to Keith is only valid because of the inclusion of the word 'possible'. The basic Pertronix Igniter is nothing but a solid state switch triggered by a magnet. No more apt to cause noise than points. Bud
Bud Krueger


It's not just the points sparking, Bud...there's also a spark jumping from the rotor to the cap and that's more than likely (possibly - grin) the cause of the erratic readings.

Gene Gillam

the reason I ask is because when John Twist is talking about timing on his video but I think he's referring to static timing only
Keith Yarbrough(TD 1275)

But, Gene, that same spark jumps that gap no matter what ignition you're using. Modern ignitions excluded. Bud
Bud Krueger

Lonnie, thanks for the literature. Gene, I can do that and confirm the reach. Jud
J K Chapin


That's why I said the Pertronix would more than likely give erratic readings - it's more the wire being used in the spark plug leads radiating noise than the sparking.

Gene Gillam

Bud and Gene,

Pertronix states that solid core wires should not be used for either the Ignitor I and Ignitor II versions of the Pertronix. When I spoke with them and asked about the use of solid core leads with the Ignitor I, they said that the unit might work with solid core ignition leads but it could lead to failure of the unit over time - some failing quickly - some failing after a longer period of time.

Is it really a good idea to use the solid core leads if Pertronix advises against it?

I have made up a set of wires using the graphite core for my Ignitor I unit - I still have my solid core set as a back up if needed.

Any thoughts?

I'm trying to stay out of this, but it's not easy. I purchased an LU-146 from the late Skip Kelsy in December of 1999 and installed in place of the points. That unit, with the same, solid, ignition wires, was working fine right up until last fall when I decided to do a test of an LU-146LS (Lobe Sensing) unit. The system function of the LS model is quite different from that of the standard Hall-effect Pertronix switching model. The electronics of the LS module are affected by the RFI from the firing of a spark plug. The LS module demands the use of suppressed ignition cables. The been-around-forever RFI is a cause of problems, not an effect of any Pertronix module. Bud
Bud Krueger

This thread was discussed between 17/07/2015 and 20/07/2015

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