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MG TD TF 1500 - Irregular Spark
|I'm working on getting my father-in-law's MG TD on the road after a very long 20 year slumber and have run into a slight snag. I have spent all winter nipping away at various things getting it ready for a spring start-up. Well, a few weeks ago I fired her up and I was amazed at how nice everything ran. I had it static timed at 10BTDC. Carbs tweeked for an initial set-up after rebuild. New spark plug wires. Old cap and rotor and condenser with new points nicely gapped. Like I said it ran nicely. Yesterday I start it up to sync the carbs and give 'em a nice tweeking and it runs terribly. I get out my timing light and the light is flashing like mad and then not at all then like mad again. Spark problem right? I get out my inline spark tester and it too is flashing weakly with no discernible pattern. I suspect the condenser. It is old and generally crappy looking. The cap and rotor look good although the rotor seems to fit loosly. When I grab the rotor and give it a little twist it seems to have a few degrees of slop in there. Is that normal? Could that be my problem? As I am new to MGs everyday brings something new to learn. I've been lurking here and looking at archives for answers to stuff. If anyone is interested, I have been blogging about my experience here http://mgtdrevival.blogspot.com/|
|KG Kevin Gallagher|
|A commom problem is "shorting" on the tach drive...make sure that isn't happening. |
Mixed feelings on here about it ...but I love my pertronix ignition. (I still carry a set of points as a spare but have only used it for somebody else in the last 10 years.
Another thing you might want to check is your plug/coil wires. If you purchased one of the "kits" from Tiwian...IMHO: They are absolute crap! Pitch them to the trash and buy some Lucas Bumble-Bee wires.
Get your wires right first ...then you can determine if new coil/condenser is needed. Or just go with the Pertronix and their flame thrower coil and "forgetaboutit". Make sure you order the correct one if you decide to go that route...they make them for pos & neg ground cars!
Let us know how it goes.
|Copper stranded wires rarely fail. Unless you are running a radio stay away from the carbon/silicone filiment wires.|
Play in the distributor shaft can radically affect timing, as can slop in the advance mechanism, missing weights, missing or stretched springs.
It sounds to me that you have wobble in your shaft.
Before I had my distributor rebuilt, I could only time it at TDC (statically) any more advance and it wouldn't run. After distributor rebuild, I can run it at 11 to 14 degrees BTDC statically, or with the way my car is set up, at any idle below 700 degrees I can time it dynamically. My points work great and I can adjust them on the side of the road if needed. At the time my distributor was rebuilt, my 57 year old condensor was found to be marginal. My rotor also had wobble, it HAS to be a tight fit.
Jeff Schlemmer is the guru on this. He also has new really great rotors available. find him at http://www.advanceddistributors.com/ no financial interest etc.
Dave B is right on about all the potential issues with an older distributor. I just received my distributor back from Jeff Schlemmer and put it back in the car yesterday. Before I sent it out to Jeff, you could see the cap wobbling and I also had a loose Lucas rotor. Check for the short as Dave S. describes and then check wobble and make sure you have a tight fitting rotor.
|Thanks guys. I'm going to see what a new condenser does for me but it looks like a rebuild of the distributor is in order. The price from Advanced is quite reasonable. My distributor has slop in the shaft AND at the rotor. A bad combination for sure. I haven't taken the distributor out, is there only one way for it to go back in or can I inadvertently get it 180 out?|
By the way, this is a great board. Everyone is helpful and polite unlike some boards I've been on. It must be a MG thing.
|KG Kevin Gallagher|
Agree with you on the board.
There is no key for the distributor. You put it in with the engine at TDC with the compression on Number One and align the rotor at the location on the cap where you want the Number One plug wire at.
Actually, it's kind of fun.
Incidently, placing a rubber washer in the tach reducer to generator connection will prevent the tach reducer from rotating.
David didn't actually say it but yes, you can put it in 180 degrees out of whack (as well as a number of other degrees as well as long as the gear on the distributor meshes with the gear on the cam). Follow his instructions though and you'll be golden.
|Got it. Thanks.|
|KG Kevin Gallagher|
What is the easiest way to determine that #1 is at TDC.
|Jim, the easiest way is to take the spark plug out and rotate the engine until the timing mark is close to lined up with the notch in the pulley. As the piston comes up, it should push on your thumb (you may need a helper for this) if it doesn't push on your thumb, it is in the exhaust portion of the stroke, not the comrpession.|
Remember, The four cycles in two revolutions are: Intake (intake valve open) Compression (both valves closed) TDC, Power (both valves closed) Exhaust (exhaust valve open) TDC, but not on the power stroke!
An alternative way is to take off your valve cover, when both rockers for number one cylinder are able to wiggle with the pully coming up on the timing marks, your valves are closed and you are at TDC. If the exhaust (the one closest to the front) can't wiggle but the inlet (the next one from the front) can, you are on the exhaust stroke.
|Thank you Dave.|
Here's an update. I received a new condenser and got it installed. The bad condenser was my main problem. I had my timing off by a few degrees so I set it dynamically with my timing light to 5BTDC. There is still the slop in the rotor that I will need to address later but as of right now she's purring like she hasn't done in 20 years. I must say that I have never gotten more satisfaction out of working on a car than I have this TD. It's like I have some karma-type connection with this little car. Sorry for the hippie philosophy, it's my nature.
|KG Kevin Gallagher|
|I'm not convinced you necessarily have wear in your distributor shaft; when you say the rotor wobbles, do you mean you can move if frontwards and backwards? If so, that is the advance mechanism at work, and is not a problem. If you can hold the rotor in one position and wiggle the shaft (not turn it) left or right, then you have wear. After lubricating the distributor get a timing light on it, and see if the strobe is flashing regularly, or jumping all around. IF you need repair, Jeff is the best!|
|In addition to Tom's excellent comments, there are a lot of poorly fitting rotors out there. Advanced Distributors are excellent. He has some specially made up.|
Do have a look under the points plate also.
One of my springs was broke and other was rusted.
Replacing those and proper lube made a big differance at higher RPM's!
Glad to hear she's up and purring ...don't you just love the sound of these little 4 bangers!
|Guys, What I do know is that the "slop" is rotational and not side to side. And there is also "slop" at the rotor as it fits quite loosely. Perhaps a new rotor is in order. I must confess that the intimidation factor is high for me when it comes to getting into the guts of the distributor. That being said, I will likely not dig in under the points plate. If anyone has a pic showing a exploded view of the distributor I may give it a shot but none of my books appear to have that detail.|
|KG Kevin Gallagher|
|Kevin, Remove the rotor. There is always a tiny bit of back and forth rotation/slack in the shaft. Grab the shaft firmly, and it should twist several degrees in one direction, and the force required increases as it turns. This verifies that the advance mechanism is working. There should be no slack or slop between the rotor and the metal shaft. To remove the points plate, just remove the two screws that hold the 'ears' of the plate to the body, then lift it out. You will see a simple mechanism- two weights, two springs, and two brass "toggles". Pretty simple to understand when you eyeball it. George|
This thread was discussed between 14/03/2010 and 18/03/2010
MG TD TF 1500 index
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