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MG TD TF 1500 - Question about strong and weak distributor springs

From my reading I understand that the distributor should have a different spring connected to each weight. When RPMs are such that the weak spring is extended and the strong spring not, there will be an unbalanced load on the distributor shaft. Is this sufficiently transient as to not overly wear the bushings in the distributor?

Right now I have two springs of the same strength and am debating whether to install one strong and one weak spring instead. I believe the spring I should substitute is slightly longer and is certainly stronger than the identical pair in place today. What difference in performance might I expect if I install this spring?

Thanks.

Larry
Larry Shoer

These springs control the advance curve of the mechanical advance portion of the distributor. It sound like it is wrong now, so you should expect some improvement. How stock is the rest of the engine?
David Lieb
David Lieb

1952 MG TD
1250 cc engine
The engine is very close to stock.

Larry
Larry Shoer

Keeping the shaft lubricated will make more of a difference to bushing wear than the springs will.

Since your engine is effectively stock, you should probably be looking for stock springs for it. What the difference in the length and strength of the springs does for you is to create the bend in the mechanical advance curve. If you look at the advance curve, the steeper bit at the lower rpms shows the effect of the shorter spring, the "kink" is where the longer spring hits the post and adds its strength to the equation.
David Lieb
David Lieb

David,

Thanks for your comments. I expect the stock spring would make an improvement, I was just curious what that might be. Perhaps the advance curve my engine is presently operating with is like that of the YA (because it doesn't have a "kink," as shown in the Distributor Advance Curves at http://www.ttalk.info/Tech/Advance_curves.html), compared to what it should be, as shown in the TD curve at this same link. Anybody want to hazard a guess as to what that might be?

Larry
Larry Shoer

Larry What you need to do is find somebody that has a distributor test machine and have the curve run. Then change the spring and run a new curve.

Remember that the curves you find published were made using the pump petrol of the early 1950's in the UK. Not at all like the stuff we get today. I had hoped that someone on this BBS had a curve made on a dyno with modern fuel. So far no luck.
Cheers,
Bob
R. K. (Bob) Jeffers

Larry,
I would highly recomend talking to Jeff at Advanced distributors. http://www.advanceddistributors.com/ He is the ultimate GURU on all kinds of dizzy's. He did quite a nice job rebuilding mine after the Cape May GOF. Good workmanship, quick turnaround, and great price. Send him an email,,,,

SPW
Steve Wincze

Thanks for all the input. In some ways I feel that "If it ain't broken, don't fix it." The TD runs well, so.....

I will send Jeff an e-mail to see what he says. I don't know if he can comment specifically about the TD, but I'll report back what I hear.

Larry
Larry Shoer

As suggested by Steve, I contacted Jeff Schlemmer at
Advanced Distributors, LLC. His response is below. I have also attached a picture of two springs. I have several springs that appear identical to the small (weak?) spring and one that is a slightly larger (strong?) spring. I'm going to leave well enough alone at the present time and continue to run with two smaller springs.

------------------------

From Jeff Schlemmer:

Its common to see too much emphasis is placed on what the springs should look like versus how they perform. I have yet to rebuild a T series distributor that didn't need both springs repaired or replaced, regardless. The springs changed virtually every year of production, so there's no blanket statement as to what was original for all TDs. Personally, I change the springs on every application to a set that's matched in strength - both springs are identical IF AND ONLY IF I can do it and get the desired results. Just swapping springs without knowing how they perform is like just turning the distributor to set the timing without verifying the setting with a timing light. Its a recipe for disaster. How would you know how your advance mechanism performs? It may not offer any advance until 4000 rpms, or it could dump all the advance in by 1500 rpms. Your advance needs to be precisely metered, allowing advance at a slow, steady, prescribed rate. Its also critical to check the amount of advance in your distributor. Most TDs came with 15 degrees at the distributor - 30 at the crank, but the hammering effect of the weights on the timing plate can easily stretch that to 17-19 degrees. Personally, I've found that the cars run better with 12-13 degrees of advance.

Now on the topic of buying springs, its likely that if you just buy a pair of springs from Abingdon Spares, Moss, or whoever, that the pair you get isn't going to be correct. I can vouch for that, typically trying 3 sets of springs on every distributor I rebuild to get the right set. Sometimes I hit it on the first try, but that's luck. Sometimes it can take 10 tries to find the correct spring combination to achieve the desired results. Chances are good that out of the 4 springs you have, you may not have the right combination. That's why I offer a recurve service starting at $30 + shipping. Getting ANY play out of the advance and shaft assemblies is just as critical as getting the spring combination correct too. You have to look at your distributor more as a clock or watch than a just an assembly of parts. Its a precision assembly - ALL clearances and spring strengths are critical in order to work precisely in conjunction with one another as prescribed.

Jeff Schlemmer
Advanced Distributors, LLC
612-804-5543
jschlemmer1@comcast.net




Larry Shoer

Larry,

Thanks for posting Jeff's email. I also have been thinking, "If it ain't broken, don't fix it." When I restored my TD, I rebushed the distributor but used the weights and springs that were in the tired old unit. Maybe I should pull the dizzy and send it to Jeff this winter.

Does he need the complete unit? (cap, rotor, etc?) I have a pertronix installed, should I put the points in to use his service?

Let us know if you send yours...

Thanks!
Evan
Evan Ford - TD 27621

I guess I don't keep up on this forum very well anymore! I don't need the cap, rotor, or wires to test a distributor - just the distributor itself and the triggering mechanism - be it points or Pertronix, or whatever. Bushings are about half the battle, so if yours are worn, it means the dwell is going to bounce all over the place. Good points are equally important, but there aren't too many options, so we make due!

Tired springs in a TD or TF can mean your timing is off by as much as 20 degrees at 1500 -2500 rpms. It can also drop the amount of total advance you get by 20 degrees, depending on how you set your timing - statically or dynamically. If there's much of a difference between the two, your springs are fatigued!!!
Jeff Schlemmer

I had Jeff do my dizzy, and it came back like new. Excellent service and fast turn around!

Cheers

Larry
Larry Karpman

Sounds like a good winter fix. Keep Jeff busy.
BEC Cunha

Larry, That is a very good picture of springs. Don't know how you get up that close to take pictures.

Those springs look like those in my dist. My curve is what is published for a TD. Notice that the heavy spring has a longer loop at the right hand end. That fits loosely at rest then as the weights move out it comes tight and adds it's tension to that of the weaker spring giving a break or bend to the curve.

With two of the weaker springs you would get too much advance at lower RPM's.

Now let me also say that I bought new springs from both of our usual suppliers and they were so heavy that I did not get any advance at all. I wound up scrounging springs from old dist.

Good Luck,
Bob
R. K. (Bob) Jeffers

Bob,
You've got your logic a bit backward. The light spring is the one that applies tension at low rpms, so two light springs will provide slightly more tension (and resistance to fatigue) than one light spring. The heavy spring is just dead weight until you reach the point in advance where it has tension, and from that point on, you're lucky to get two more degrees of advance. Its acts more as a stop than a spring since they are SO stiff. By doubling up two appropriate lighter springs, you have more control to cater the curve to your needs. Personally, I just received a PERFECT batch of light springs that I've been designing for many months. I'll be applying the first set into a TD distributor today to verify they work as well as I hoped. They're very similar to the original MGA advance springs. Quite a contrast to the factory springs!
Jeff Schlemmer

Bob, my old Canon G1 digial camera has a number of manual settings that can be selected. For pictures like this I set the camera to macro, spot focus, and back the flash down one or two f stops.

Jeff, thanks for joining this discussion. I'm intrigued by the fact that you have a batch of consistent springs of the proper strength. With these as a starting point, shouldn't it be possible to install such springs in a distributor in the field and obtain at least close to the desired advance curve (assuming the bushings are good and there are no other problems with the distributor)? Unless the weights vary from distributor to distributor, I would think this is an option. Maybe I'm being too thrifty at this point but, like Evan, I have a distributor that was rebushed only a few hundred miles ago and a TD that runs strong. I'd gladly swap out the springs for a known good pair, but am not inclined to pull the distributor for more extensive work at this time.

Thanks.

Larry
Larry Shoer

Jeff Your right, two light springs will lower the rise of the curve at lower RPM's. Don't know where my mind was!!

I hope your new batch of springs work out. Because what has been available was not good!!

Do you know of anyone who has had a dyno curve run on a XPAG engine? I am sure that the published curves no longer apply with the fuel available now. And the E-15 fuel just makes it worse. There has got to be three or four ponys lurking in there somewhere that a proper curve will put to work.

Congrats on all the nice things that have been said about your work.
Sincerely,
Bob
R. K. (Bob) Jeffers

Larry, I still struggle with the TD distributors in general because they go from lead to aluminum weights, and I see people mixing and matching parts over the years that just don't work well togther. In fact, sometimes they neither work, fit, or function at all. One I did recently had CW rotaion weights in a CCW distributor. That locked it up tight. Another had aluminum weights in a lead weight distributor (the one on my bench right now) which pushes the rotor into the cap. Sometimes they're just so worn out that the weights drag on the advance plate, or the holes in the plate that allow the correct advance are hammered out and elongated. All of these issues compromise the igniton curve, so I never sell springs outright. That's why I offer a distributor recurve for $30. The truth is, although I offer it, I never get in a distributor that ONLY needs a recurve unless its new though. In the end, fixing ALL the problems is necessary to get it to work right, even if it looks good to the average mechanic!
Jeff Schlemmer

Jeff,

Thanks. This discussion has provided a real education.

Larry
Larry Shoer

Hi Jeff,
You talk a lot of sense about the T series distributors which I have read with much interest, and you say that you rarely get a distributor that only need calibrating.

You mention worn parts and I would like to know how you deal with a worn shaft, as inserting new bushes in the body will not help should the shaft be worn.

You cannot grind down the shaft to suit smaller bore bushes as the drive gear would not fit, or do you have a supply of new shafts?

Regards,

David Tinker. Wales UK

David Tinker

David, I have a fair supply of good used parts on hand. The shafts very rarely wear, unless they were run with no oil for extended periods. The bushing material is MUCH softer than the shaft. You CAN install a full length bushing if there is minor (spotty) wear on the shaft as well - to make up for lost surface area. Typically its not even an issue though.
Jeff Schlemmer

Jeff,

Can you tell me where one can get the new or new old stock singular long bush for the TF 40367 Distributor bodies ? The slightly earlier Distributor,40368 also had this bush.

Cheers for now.
Rob.Grantham
TF3719("Aramis"),TF("Athos").
Rob.Grantham

>I just received a PERFECT batch of light springs that I've been designing for many months.

Does this mean I need to return my distributor for an upgrade? ;-)

Cheers!
Rob
Rob Edwards

Rob G, I think I have one still new in the box - they're pretty hard to come by. Normally you'd have to have them custom made.

Rob Edwards, I managed to find a set that I think you'll be quite happy with! :-)
Jeff Schlemmer

I correct all that, including varying quality of fuel, thanks to a spark advance control I have on the dashboard. It is not difficult to build and if someone sends me e-mail I am willing to send a description. It's fun to fumble with that control since you have nothing else to worry about when driving a T-Type!

Denis
1950 TD
Denis L Baggi

This thread was discussed between 02/11/2007 and 07/12/2007

MG TD TF 1500 index

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