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MG TD TF 1500 - Dwell angle and Max advance

Anyone know the dwell angle and max advance at 3000 rpm for a 55 xpeg engine with original point distributor running non ethanol 87 gas. PJ

My dial back timing light is made for negative ground systems and will show dwell but the advance timing feature doesn't work on positive ground systems.
PJ Jennings

PJ, can't you just switch the leads to the battery?

Tim
Timothy Burchfield

If the light is insulated you can just connect the red to ground and black to live terminal of battery I would think.

Dwell for XPEG is 60+-3 deg.

If distributor has been overhauled probably 32BTDC at 3,500RPM I believe.

Paint he timing marks white with a fine brush.

Peter
P G Gilvarry

That's the way I had it hooked up Tim, but connecting the wire to the negative side of the coil to sense the points breaking doesn't work with my light, which tells me the dwell indication on the screen isn't correct either. Since it's very difficult to red timing marks on the TF crank pulley, a dial back light is the best way to go if the car is all together. I don't want to do it, but I just might convert the car to negative ground system and eliminate these PITA problems. PJ
PJ Jennings

Peter, you have a TF and you know without pulling the front off the car, there's no way one can paint timing marks on the crank pulley, it's hard to get a light to show the marks, reason for a dial back light. Dial in the proper advance, run the engine to desired RPMs, put the light on the timing marks, turn the distributor to line up the top dead center marks and the timing is set. The light does the thinking for you, (if it works).
PJ Jennings

Might just be your light. I use a dial-back light and it works on either polarity by simply swapping the leads. It does not have a dwell function however.
Steve Simmons

Thanks guys, I have another idea, these lights are very sensitive, so I'm going to try and clip the dwell wire directly to the distributor connection rather than the coil and see if that works. PJ
PJ Jennings

On my timing light, the directions said for positive ground cars put the black lead on the negative side and put the red lead on a good ground connection on the car. Not easy to get to but I put my ground connection on the ground strap on the bellhousing / bulkhead support.

You can always use a spare battery instead of what is installed on the car.


Frank

TF1414
Frank Cronin

Personally, I hate dial up timing lights, if you had ten of them they would all read different
I don't understand how you are hooking yours up -usually there would be two leads one red for pos. and one black for neg. and a pickup for No1 plug lead--on positive earth cars, if the pickup is the inductive type you need to turn the pickup over and have the arrow pointing towards the dist. instead of the plug
Best way is to measure around the circumferance of your font pulley, get the calculator out, divide by 360, multiply that by 32 if you want 32 and mark the pulley at that distance in front of tdc--dead acurate

Also, really important is to check that although you are setting at 32(for example) at the quoted 3000rpm you have to check that it doesn't advance further with more revs,If for example someone has been fiddling and fitted a heavier spring or lighter weights the max advance mightn't be till somewhere higher like 5000(for example) and if you set it at 3000 ,timing could well go way past that mark when revs are further increased

willy
What wiring connections does your timing light have, connecting to the switching side of the dist. isn't the usual place , it's usually battery power -+ and plug lead
William Revit

If the timing light has a dwell function it would need to connect to the points side of things, I have a Halford unit thst does.

Usually there is an inductive connection that clips onto #1 plug lead, is that missing?

Harbor Freight makes a cheap light with advance, but the knob is tad unreliable.

I am using 10-12deg at idle, the rest is up to the gods that made the springs to control the advance curve.

Currently mine is just where I dropped it in visually after replacing a bad condensor, starts first pull of the started, rattles the gear shifter, may need to knock it back a bit.

Peter
P G Gilvarry

If the timing ligh5 has a dwell function it would need to connect to the points side of things, I have a Halford unit that does.

Usually there is an inductive connection that clips onto #1 plug lead, is that missing?

Harbor Freight makes a cheap light with advance, but the knob is tad unreliable.

I am using 10-12deg at idle, the rest is up to the gods that made the springs to control the advance curve.

Currently mine is just where I dropped it in visually after replacing a bad condensor, starts first pull of the started, rattles the gear shifter, may need to knock it back a bit.

Peter
P G Gilvarry

If the timing ligh5 has a dwell function it would need to connect to the points side of things, I have a Halford unit thst does.

Usually there is an inductive connection that clips onto #1 plug lead, is that missing?

Harbor Freight makes a cheap light with advance, but the knob is tad unreliable.

I am using 10-12deg at idle, the rest is up to the gods that made the springs to control the advance curve.

Currently mine is just where I dropped it in visually after replacing a bad condensor, starts first pull of the started, rattles the gear shifter, may need to knock it back a bit.

Peter
P G Gilvarry

I made spelling corrections, and got 3 posts, Sorry
P G Gilvarry

Setting the points gap using a Dwell meter is far more accurate than using a feeler gauge, however the dwell angle for XPAG engines varies as there are three different distributor cam profiles used.

You need to determine the profile of your dizzy cam (see image attached) and then use the following values.

41-49 degrees - Symmetric cam
45-53 degrees - Asymmetric cam
57-63 degrees - High Lift cam

for feeler gauge adjustment:-

.010-.012" - Symmetric cam
.010-.012" - Asymmetric cam
.014-.016" - High Lift cam

This data was published in The Sacred Octagon in December 1977 by Chip Old (Technical Editor).

Happy Tinkering

Tony



A L SLATTERY

Tony, would certain distributor numbers coincide with which cam they have in them? Would all XPEG distributors have the same cam from the factory? PJ
PJ Jennings

This thread was discussed between 15/09/2019 and 18/09/2019

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