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MG TD TF 1500 - Timing Mark & TDC

I removed the #1 plug. With a good flashlight and wearing my glasses I can see the top of the piston.
Using a remote starter solenoid switch,

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I can jog the engine by fractions. On the compression stroke I watched as the piston rose to its highest point. I am assuming that this is TDC. If I jog the engine a fraction the piston starts down. However the groove on the pulley is about 1-1/2" before the indicator on the timing chain housing.

I used this position to set the rotor orientation on the distributor. The car started right away. So far I have been unsuccessful at setting a 30 degree advance at 3,000 RPM.

At 3,000 RPM using a digital timing light if I rotate the distributor (CW) to bring the mark up to the pointer the engine speed decreases to a stall. Shouldn't the RPM's remain at 3,000? The distributor is relatively new and the weights and springs seem to function. Points set at .012" not burnt just a little indication of sparking.

This TDC business and the RPM's dropping have me puzzled.

What say you all?

Mort
Mort TD 1851

Mort -
Been following your adventures.
Since the car is modified with the Judson, you have to be very careful to watch for other changes.

1) Does it have a starter solenoid fitted? Standard would not, but would have a pull cable switch for the starter. If you are using the remote switch to jump the pull cable one, it will have a short life indeed. The remote is rated at 35Amp max, but the starter pulls 100-200A typically.

2) TDC is by definition when the piston is at the top of the compression stroke, a real physical thing, irrespective of any marks. Since the blower installation requires a different crank pulley, I suggest that the mark on the pulley may be wrong. Most engines have the crank keyway in line with the throw for #1, and the mark either straight up or straight down from that. Engines with the fixed timing mark not straight up or down will have the pulley mark moved to match. Since the TD pointer is not straight up but a bit left (after), I think this is the source of your confusion. Is the pulley mark straight up at your observed true TDC?

3) You have to set the 30 degree advance relative to true TDC, not to a wrong mark. So, if I am correct about the mark and real TDC is straight up, your 30 deg setting would be about 1.5" to the right (before) of straight up. If you are using a dial-up timing light, you would dial in 30 and use straight up as a reference point.

4) You can calculate the exact offset from the diameter of the pulley. 30 deg = 1/12 the circumference

5) It is possible that the crank/pulley key has sheared, and the pulley is no longer lined up correctly. This a result of the extra load from the blower and/or a loose crank bolt. This can and eventually will result on disaster, when the pulley comes off. Loose crank pulley bolts will also eventually shear the key for the timing sprocket, and the engine will run progressively worse until it stops. And there will be crankshaft damage. When the key shears and the bolt is loose, the pulley/sprocket hangs up on the ragged edges of the key for a while, but it always fails after more running.

I know you do not want to dismantle the thing, but at the very least check that the center bolt is very tight. If the bolt is found to be loose, I would suggest that you dismantle it and examine everything. If the pulley can be rotated at all respective to the crank with the bolt out, the key has failed.

FRM
FR Millmore

Mort,
Look to see if there is a key for the crank/pulley. You may have to use a mirror or stiff wire to probe to verify it exists or is missing.

Remember, for setting static timing,the sparkoccurs right where the points crack open.
Jim Northrup

Mort,
All above thoughts & cautions need to be addressed. Also, your method of determining true TDC is very prone to error, easily 5 degrees, or more. At TDC the piston will move imperceptibly for a few degrees each side, plus your "jogging" with the starter is hit and miss as to how far it moves & when it stops. I spent many yrs in a motorcycle shop, owner & mechanic, and the only way to be sure of TDC is with a dial indicator, off the top of the piston. That's hard to do in this case, and you may not have the tools.
To make the sight method easier, I'd suggest pulling all the spark plugs to make the engine turn easier, and then it's sometimes possible, if your pulley is keyed, to rotate the engine with a socket wrench on the fixing bolt, or at least in one direction with the crank. I've both in the past on XPAG engines, sometimes it'll even rotate CCW after you've tightened the bolt CW.
good luck,
Al
A W Parker

Thank you all for the good advice.

FRM
"Since the car is modified with the Judson, you have to be very careful to watch for other changes."

My mistake was assuming the groove on the pulley was actually TDC. When the supercharger was installed they replaced the original one groove pulley with a three groove pulley. The notch on that replacement pulley has no bearing to TDC on this engine. I found TDC and painted a new TDC. Now I have a starting point and set the static timing on the dizzy. I didn't have a test light so I set my voltmeter and watched for the points to open when the voltage dropped. The car started up perfectly and runs nice.

Next step is to set the advance to 30 degrees at 3,000 rpm.

Then on to valve adjustment. Then the carb.

Thanks again to all with your wealth of experience and having the ability to talk (type) things out has proved once again invaluable.

Mort

PS. FRM where in PA are you?
Mort TD 1851

Glad you've sorted it out, Mort.
Gene Gillam

does anyone here have an estimate as to how far from TDC you could be using mort's method to find TDC? regards, tom
tom peterson

Tom,
I've been told that the visual is not very exact and that may be the case. With the remote starter switch and a little practice I can jog the engine about one degree at a time.
I borrowed something that looks like a piston stop. Basically a pipe that threads into the spark plug hole with a spring loaded shaft thru it. The end is rounded and made of some soft alloy (maybe brass). As I pulled the engine with a socket on the crank nut I can watch it rise and stop. Several attempts all confirmed my visual method.
I agree that due to the cam geometry I may be off a couple of degrees but I used this as my new TDC and set the distributor at 30 degrees advance at 3,000 rpm. Went for a drive and it sounds and performs great.

Now as soon as I get my hands on a 5/16 Whitworth wrench I will adjust the valves.
Mort
Mort TD 1851

mort, perhaps you are already aware, but if not..using that device if you mark the pulley adjacent to the pointer when the piston contacts the device and then rotate the engine backward until it again contacts the device and mark the pulley at that location ..the distance between those two points is the EXACT TDC.
regards, tom
tom peterson

Tom,
I was aware of that but did not do it. Shame on me. But since the car is running well I will drive more and tinker less. At least till the winter.
Mort
Mort TD 1851

This thread was discussed between 01/09/2011 and 03/09/2011

MG TD TF 1500 index

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