TR4/4A Why are distributor base plates different, is this a problem?

[TuffTR250]

I've got a TR4 engine in my TR3. I am running a Pertronix in the 25D - 40795 distributor. I am working to build a breaker points based base plate for an emergency replacement if the Pertronix fails while on the road. I got a new base plate from Moss 551-055 and a club member loaned me an original base plate. They are very different from each other. If I use the one from Moss, is that going to be a problem?

In the attached picture, the new Moss p/n 551-055 is on the right and the original is on the left. Notice that the original has a flat spring from the angled piece with the retard spring pin below it. I assume it is a ground. In addition, the original has a long slot on the top with a pin through it. I'm not sure what that pin and slot are for.
Thanks!
p.s I decided to also post this question on BCF
Bob

 

[Madflyer]

I have one in my hand from my TR 6 1973 and it is like the one on the left. Mine is bad and used for show and tell at tec meeting. As I see it they should be like the left only. Not to be to bad about Moss but I would question their part. What is bad or say goes bad is the top slot at the end just before the end it wears and will stick. See what the others say.

 

[TuffTR250]

Madflyer, what is that top slot used for. I looked at my car with the Pertronix but I could not see what the slot does. And does it go bad on the end of the slot that is enlarged or the non-enlarged end? Thanks!

I don't want to remove the Pertronix to take a look and then have to readjust it afterward. And I don't have a spare distributor to look at.
Bob

 

[poolboy]

This is one of mine...the spring is there to stabilize the points plate...the top where you mount the points or Pertronix
When you rotate the top and the pin reaches the enlarged section of the slot, it may get locked in that position. If it locks, there won't be any vacuum advance, just centrifugal.

 

[Madflyer]

As I look at the plate the larger hole end is for assembly of the two plates. full travel does not go that far in normal operation. In Poolboy's pic normal is about where his is sitting. Mine was quit worn and caused a burr that did not let it spring return so mine was stuck in full advanced. The history of my car. I did not look into the Dis when I built the car frame up in 1993 and has many miles. I built this TR 6 as a road car and have been from Canada to the Mexico border and in all the Western States and US Parks, so your plate may be OK. If you have a tuning problem it may need a look and some lube. It is funny that your question as this is my club tec session tomorrow. I have other Dis. so parts were not a problem for me.

Just a word; SOME TIMES GOING FORWARD MEANS GOING A STEP BACK A TIME OR TWO. Just saying

 

[TuffTR250]

Now I see what Moss did. Their two plates are basically not separable. Instead of having that top slot with large rounded hole at the end to allow the two parts to be assembled, and the spring on the other end to hold the two plates firmly together, Moss put a center piece that is more or less "riveted" together with flange on each side of the two plates that still let the two plates turn. Therefore, the slot and spring are not required. The Moss part also does not have the fiber standoffs but is held together with the center "rivet" like mechanism. Looks like it would be important to keep that center piece lubricated from the top between the points. Unless I'm wrong, I think the Moss part will work well. Thanks for the responses that let me understand how the plates work.
Bob

 

[poolboy]

Yes, It will work....the plate in my picture is the only one of 3 that I have that's made like that..the others are basicaly like the Moss, except one has a tall points pivot pin like the early years for 2 piece points and the other has the stubby pivot pin for the 'one piece' points...none of that matters though with a Pertronix Ignitor

 

[Madflyer]

I took my plate for the tec meeting today and found that two members had the same problem and most never looked at theirs or lube the same.
Another day in the LBC's World.