a discussion on Installing new vacuum advance unit

[Member 10617]

This posting picks up on an earlier thread....

I see that Moss is selling new non-generic vacuum advance units.

I am thinking of replacing my old one with a new one, but I don't know the procedure.

Can someone out there give me some directions on how to remove the old unit and install the new unit (or direct me to some posted instructions). It looks straightforward enough, but appearances are always deceptive!

 

[MikeP]

Haven't done a TR distributor but on other Lucas ones all you need to do is unhook it from the inside, a little post on the plate probably with a clip. Then pull it loose while turning the manual adjust knob until the shaft throu it comes out.

 

[Member 10617]

Mike,

Having inspected my vacuum advance from within the distributor, it appears that you are right about changing the one on the TR. There is a sping that hooks to a little post on the plate and that appears to be the only connection.

Moss says that their new vacuum advance units come pre-adjusted, so I assume that I don't have to do much else except fine tune with the micrometer knob.

 

[MGTF1250Dave]

Aloha Ed,

There is a small spring clip that holds the knurled adjusting knob on the vacuum advance unit. Dealing with that and hooking the long spring on to the post on the plate are IMO the hardest part of the job.

Many of us on the forum here have had excellent experience with Advanced Distributors. You may want to consider having him test and rebuild your vacuum advance unit. Here is a link to the website describing the service.

https://www.advanceddistributors.com/services07_2.htm

 

[TR3driver]

There should be a retaining clip on the end of the threaded shaft, that prevents unscrewing the knurled knob all the way. But it may be missing from a previous replacement.

 

[TR3driver]

There is a small spring clip that holds the knurled adjusting knob on the vacuum advance unit.

On re-reading this, I realize that Dave was talking about the same clip I circled above.

But note that there are also a couple of springs that need to be accounted for. The bent flat spring that makes the nut click, is particularly apt to launch itself (and sometimes the nut) if you aren't expecting it.

 

[poolboy]

You can see the little parts here:
https://advanceddistributors.mybisi.com/product/vacuum-advance-hardware-kit

 

[Member 10617]

My adjusting nut just barely "clicks" so I think the flat spring needs to be replaced. There is a retaining clip at the end of the shaft. I'll take care to keep the spring and the nut from "launching" if I remove the old unit. Many thanks for the warning.

As for having my unit rebuilt, I think that it would be easier to go ahead and purchase a new one from Moss. They now make a unit that is specifically for the TR3A and the price has come down from $114 to $89. So a new unit seems to make sense.

I'm still a uncertain as to what further adjustments I would have to make if I install a new advance vacuum unit. Clearly I can mark the distributor and make sure it is rotated to the same spot when I install the new vacuum unit (I have to rotate the distributor to get the old vacuum unit out), but I will have to start from scratch with the adjusting nut on the new unit because I can't mark where the old one was. When I set the timing a couple of weeks ago using a timing light (dynamic method), I didn't have to do anything at all with the adjusting nut because I left it where it was and rotated the distributor. But with a new unit and its new adjusting nut, it seems to me that I will have to reset the timing, either by the dynamic method (advance timing light) or static method (which involves backing off the adjusting nut 4 degrees).

 

[70herald]

When I set the timing a couple of weeks ago using a timing light (dynamic method), I didn't have to do anything at all with the adjusting nut because I left it where it was and rotated the distributor.

The "proper" method of adjusting timing is by using the adjusting nut. The effect is the same, but if you insist on rotating the distributor, it is going to (or already has) wear the body were it is held by the clamp, then the distributor will no longer remain steadily in place... If the distributor was placed in the correct angle, the adjusting nut should provide more than range to set the timing without turning the body.

 

[poolboy]

I'd put the adjustment in the middle of it's range, thenset the timing by rotataing the dizzy and locking it down afterwards.
That way you can fine tune the timing when the mood or conditions change within the limitations of the of the micro adjustments using the wheel

 

[TR3driver]

because I can't mark where the old one was.

I'm puzzled by this, Ed. Perhaps you don't know about the scale on the left, between the vacuum module and the distributor body, that indicates the position of the fine adjustment?

 

[Andrew Mace]

Just so everyone is clear, each mark on the vernier scale of that distributor adjustment equals 4 degrees (advance or retard, depending on which direction you're adjusting). There's provision, therefore, for quite a bit of adjustment without turning the distributor body.

 

[poolboy]

About halfway down this page you'll see the topic entitled "Setting the Rotor Position" which deals with the initial installation of the distributors with the Vacuum Advance. It might be a good idea to do it that way.
https://mgaguru.com/mgtech/books/lts_otcc/Session3_CoilIgnition.pdf

 

[Member 10617]

Randall,

You are right. I wasn't aware of the scale between the vacuum module and the distributor body. I need to take a closer look at all this.

Poolboy,

That sounds like a good approach to me. Using the scale that Randall has mentioned, I should have no trouble putting the adjustment in the middle of its range.

70herald,

I have set the timing only once since I acqired the car in October 2009, so the distributor hasn't been rotate much "on my watch." And when I did rotate it, the movement was probably about 1/2 inch. So I don't think I've worn the body much... but I will pay attention to what you have said and take care. Once I have the timing set, and the adjusting nut is in the middle of its range, I believe that all future adjustments will be done with the adjusting nut and not by turning the distributor.

Many thanks to you all.

Sorry I didn't get back to you sooner, but it was a beautiful day today in the Valley of Virginia so I took the opportunity to drive up the valley (north) to some of the battlefields where Generals Hunter and Sheridan fought with Confederate Rangers in 1864.

 

[glemon]

I understand your question is how to keep the timing the same when you switch out the advance units? I guess I would try to get it as close as possible to what it was on the old unit, but there is really no way to be sure unless you re-check re-set the timing for the car. If you have not done this there are a wide variety of instructions on how to in the manuals and on the web.

As others have said good idea to start with the vernier adjustment in the middle of the scale.

You can wear out the distributor body by turning it on the clamp, but most of those problems would be caused by either tightening down too much to secure (clamp digs into the aluminum) or not loosening enough when you adjust it (once again digging into the aluminum).

 

[TR3driver]

Just so everyone is clear, each mark on the vernier scale of that distributor adjustment equals 4 degrees (advance or retard, depending on which direction you're adjusting). There's provision, therefore, for quite a bit of adjustment without turning the distributor body.

Also for clarity, I don't think it is safe to assume that a 60+ year old advance unit has exactly the same length of spring as a new one. Duplicating the marks should be good enough to start the engine, but you could easily wind up 10 degrees different than where you started, just from the variation in vacuum units. Even my collection of originals has some variation from unit to unit.

Probably also a good idea to disassemble, clean and lightly lubricate the points plate where it turns/rubs against the base plate. If it were stuck, that would explain why turning the knob didn't do anything.

 

[Member 10617]

Someone else worked on this for me, and he said the knob didn't do anything. That is: when he turned the knob, the timing as shown by the timing light didn't change. Perhaps the change was too minute to be easily observable. At any rate, he then turned the body of the distributor slightly and got the timing by the timing light "correct."

As for a scale, there is no scale on the side of my advance vacuum unit. I think it is located on the shaft that goes through the unit that holds the vacuum unit in place(as shown on page 21 of the Lucas Technical Service Manual, Section 3, coil/ignition). But none of the hash marks are showing on mine, which I take to mean that the unit is screwed to the end of the scale (where it was when the distributor was rotated for setting the timing.

As the car is running extremely well at this moment, I think I'll leave well-enough alone for the present. At some later date, when I check and reset the timing, I will begin by setting the vacuum unit to the middle of its scale before setting the timing (probably with a timing light). I'll also probably take the opportunity to replace the 50+ old vacuum unit with a new one from Moss (new spring, etc.).

In the meanwhile, as spring has finally arrived here in the Valley of Virginia and in the Blue Ridge Mountains, it's time to hit the road....

 

[poolboy]

Yeah that's a good idea, because if you keep asking questions we'll keep you busy under the bonnet or on the computer instead of out in the fresh air and sunshine.
On the other hand if something actually does break, this is a good place to get various ideas or theories as to the possible causes. Then once you do finally uncover the culprit, we can suggest several different ways to fix it.

Are you getting my point here ?

 

[Member 10617]

poolboy,

For me it's hard to imagine confronting the occasional problems without this Forum to lean on. It has been a real support! I have many more questions, but I don't want to wear out my welcome.

By the way... I discovered today that the real culprit behind the dieseling in my car was the timing. I had the timing set too close to TDC and not close enough to the recommended BTDC position. It's amazing how readjusting the timing instantly fixed the dieseling.

Heading off to a car show with a friend tomorrow in his Amilcar... and to the Blue Ridge Parkway on Sunday with two friends and their TR4 and TR6.

 

[poolboy]

Ask away. Obviously <span style="font-weight: bold"> <span style="font-style: italic">we </span> </span> have nothing better to do and have you greatly outnumbered, so don't think you'll wear <span style="font-weight: bold"> <span style="font-style: italic">us </span> </span> out.