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MG TD TF 1500 - Underpowered?

I'm trying to get my 51 TD back on the road. After rebuilding all the brakes (100% rebuild except for master cylinder now I think), I've been gingerly taking it around the block.
Problems: the idle was very low so it would stall. I increased that. It runs ok now but the engine vibrates more than I think it should - but I don't know what is right for this car.
If I start it in neutral it idles fine. But as soon as I engage the clutch, it drops very low and I have to rev it to keep it from stalling. When moving, same problem; once I put in in gear, the revs drop low. Seems like its just very underpowered.
Hoping someone can put their finger on what might be going wrong here...
Too rich? Poor spark? Thoughts? This car hasn't moved for four years.
One thing I noticed and will check closer tomorrow: I think one ignition wire is cracked or not connecting to the spark plug properly, I got a good shock from it when I touched it and it didn't seem to snap onto the spark plug properly.
All help appreciated...
Geoffrey M Baker

Jeff - A couple of things could be causing the problem. First the crank shaft thrust bearing of the center main bearing could be worn, allowing excessive end play for the crank shaft. You can check the amount of end play by using a large screwdriver to force the crankshaft all the way back, set a surface gauge on the end of the flywheel pulley, then levering the pulley forward with the screwdriver and see what the difference is in the two readings (sorry, I don't have that specification at hand, but you should find it in the workshop manual), The other thing that could have a worn out throwout bearing, or the pedal isn't adjusted properly for maximum throw out if you have the old cable clutch, or if the pedal linkage has been changed out for a rod throwout linkage is missing the brake pedal stop bolt. If you have the rod linkage in your car, that means that it has been changed somewhere in the car's lifetime and most likely doesn't have the stop bolt in the pedal box. If you will e-mail me at SUfuelpumps@donobi.net, I will send you an article on how to make and install the stop bolt. Cheers - Dave
David DuBois

Ok - Found what I was looking for - Main Center Bearing Side Thrust .0014 - .0037. Cheers - Dave
David DuBois

Obviously, you would want to check the easy things first,, If one ign. wire is cracked, probably they ALL should be replaced,, this might fix the engine virbation problem,, How are the plugs???
Start the engine, and observe it in COMPLETE darkness,look for spark jumoping between the wires or grounds,, Get the engine running smooth before digging deeper,,

You said >>I'm trying to get my 51 TD back on the road.<<
How long has the car been off the road????

SPW
STEVE WINCZE

How long did you not use the car? The fuel may have gone off in the meantime.

If longer ten 6 months, I'd first ry with fresh fuel.
Willem van der Veer

I agree that the first place to start, on what you have written, is the distributor/spark gap/condenser (rarely) and the leads/plug gap. If that does not remove the problem, then my next port of call would be the carbs. My instinct is that the either the mix is too lean, or that the balance between the carbs is well off.
Ian Bowers

Thanks for the input!
In regards to questions: I've been turning the engine over every week or two for the past four years, but the car has not driven more than six feet back and forth for that period of time.
I think Steve is right; first step is replace the ignition wires, also check distributor. The balance between the carbs is something I need to work on too; I had to strip & rebuild them and haven't balanced them properly yet.
Geoffrey M Baker

Timing could be retarded. That will make it feel very sluggish.
Steve S

Well, one small change made a huge difference. I examined the wire that gave me a shock and sure enough, the copper end was partially exposed from the plug hood; meaning that it almost certainly wasn't getting a spark to that cylinder. As soon as I crimped it a little and put the hood back on and plugged it onto the spark plug, when I started the engine it came on immediately, at a much higher idle, and with hardly any vibration on the engine now. I adjusted the idle down some and its running MUCH better!
Guess what, when you don't have 25 percent of the engine working, it definitely affects performance :)
Anyway, I still need to work on the carbs and tune it; but I'm hopeful the next test drive will be much more successful.
Thanks for the help!
Geoffrey M Baker

80% of fuel and carb problems are electrical. :) Mike
MW Davis

Geoffrey

Dave Braun, one of the folks that posts on this web, has some great tips for setting up and tuning SU carburettors. His web is http://www.dbraun99.com/ May want to take a look at his SU information.
Bruce Cunha

Ok, I've solved the vibration problem, it's running pretty smoothly at a fairly fast idle. I'll be replacing wires and plugs shortly, but for now she's running much better.

However, I still had the "underpowered" issue; when I put it in gear, it feels as if there is no throttle control at all; it drops to a low revolution and then moves slowly forward or back, and no pressing the gas pedal makes any difference in speed.

And that turned out to be very simple and very obvious: the throttle linkage arm. The bar that connects both carbs, which has a pivot bolted to it, had gotten loose enough to turn, so that the throttle linkage was simply trying to push directly up, instead of rotating. The result was that the car had no throttle control at all.

Removing the air filter and manifold, I readjusted the throttle arm so it now revs nicely.

Then I took her out for her first real spin in more than five years... about ten city blocks, top speed just under 40, brakes working perfectly, everything sounding great!

I have a smile from ear to ear right now typing this!

Geoffrey M Baker

Geoffrey

Sometimes the most simple things bring us undone, good news.


G Evans

Geoffrey: I think you discovered something all of us need to consider. These cars, while basic, served their owners pretty well from the get go and many are still alive today doing what they have for 60 years.

In the effort to fix something we often try to improve it but in reality it may just have gotten tweaked or out of kilter a bit. This is especially true when two problems occur at the same time.

Before we doing anything to our cars we should first ask ourselves if it truly is put together and working as it did when it left the factory. Or did somehow something get changed that we just cannot see easily.

A few days ago there was a thread about the top bows not fitting inside the car correctly. We were all dumbfounded and then through luck (or perhaps some significant pondering and research) the owner realized that the hood bow brackets had gotten installed upside down. That was very easy to do and also is hard to spot.

Most fixes seem to be fairly simple in hindsight.
Chris Couper

"Most fixes seem to be fairly simple in hindsight."... a truer word never spoken!
I'm just glad this was an easy, zero-cost fix. What I love about it is that it's just another piece of information added to my knowledge base: now I know more about the car than I did yesterday, and can troubleshoot better.
Sometimes problems are obvious, sometimes they are hidden under other issues (as this was partially masked by ignition wiring issues). And of course, this problem arrived gradually (it revved fine a few days earlier, and then slowly revving seemed weak and then nothing). And like everybody else, I'm actively working on multiple issues (finishing up the brake work, changing polarity on the car) so sometimes it's hard to diagnose it when other things are going on as well.
This weekend, I hope to reach another milestone: instead of having a project in my carport which could limp slowly around, with multiple problems... I have an actual, breathing car. That can (maybe) make it across town.... and someday even further!
Lots to keep doing, but much progress has been made!
Now... to get it legal!
Geoffrey M Baker

This thread was discussed between 07/04/2014 and 18/04/2014

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