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Distributor repositioning question

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Darrell and Randall,

Just to put this one to bed, then, when I use the timing light to measure initial advance, or when I use it to set initial advance, it is giviing me CRANKSHAFT DEGREES. And when I move the vernier knob, I am advancing in DISTRIBUTOR DEGREES. Thus, 2 degrees on the vernier scale is 4 degrees on the crankshaft.

If I am right about this, then I think my problem has been solved (not mechanically but mathematically)!
 
LexTR3 said:
But now I have another mystery: how many degrees are in a click of the vernier knob. Sounds simple, but I have read the following:
[...]
2. 1 click equals 1 degree (talking about Spitfire).
Click to expand...
The rest of this has been answered, but I thought I'd clarify this one statement for anyone following the thread or finding it in the future. For whatever it's worth, pretty much any Spitfire with a vernier knob is a Delco distributor, not a Lucas, so comparison is irrelevant. (To my knowledge, the only Lucas distributors on Spitfires were the later electronic ones on 1500 models.)
 
LexTR3 said:
And when I move the vernier knob, I am advancing in DISTRIBUTOR DEGREES. Thus, 2 degrees on the vernier scale is 4 degrees on the crankshaft.
Click to expand...

Well, at least one manual I have for my TR4A says the divisions are 4 degrees, but in the context there, I believe they are in crank degrees (as it is talking about setting the timing to TDC, then using the knob to dial in 4 degrees of advance).

But ultimately you should set what works best for you. The fuel we run today has different characteristics than what was available in the 50s and 60s, and why Jeff advocates more advance at idle than the manual does. Even the manual for my 4A has the final setting be to advance until you hear pinging under load, and backing off a bit.

BTW, the whole reason for this is that you want peak pressure in the cylinder where it will translate to the most torque, which I've heard is 15 degree after TDC. But it takes time between the spark and when that peak pressure is generated, some of that is accounted for with the static timing, but the time is fairly constant, so it also needs to vary with the engine speed. The vacuum advance is a further optimization for light load situations.
 
Hi, Darrell,

As I understand it, the change in the advance curve is, indeed, to deal with modern fuels, which are not formulated as fuels were in the 1950s. Not only do they no longer contain lead, but they have been changed to reduce emissions from the fuel. The fuels also have density differences which means that they burn at a different rate during combustion. Modern fuels, I read, even flow differently thought the jets of the carburetor.

I'm pleased that Jeff changed the advance curve when he worked on my distributor, and the only problem I have had with it is that I wasn't able to reach the 12-15 degrees BTDC at idle. But if a division of the vernier scale in fact represents 4 degrees of (crankshaft) advance (and not 2 degrees of crankshaft advance), then I should be able to come close. I was figuring only 2 degrees of advance, but that, apparently, represented only distributor degrees.

As you say.... ultimately I should set it what works best for me. Perhaps I have done this by accident because I kept working on the timing until I got was I believe is optimum performance. But now I will go back, set the initial timing again with the static procedure, use the vernier to advance not four (crankshaft) degrees but 12 to 15 (crankshaft) degrees, and then double check it with my advance timing light and take it for a road test --- once we recover from temperatures of 15-20 degrees now gripping us.

If you see anything questionable about this plan, please let me know. I'm learning, but slowly...


BTW: If all this is correct, how do we explain Macy's Garage instruction for setting timing: "There is a reference line through the middle of the thumbscrew, and one complete turn is equal to 8 degrees of adjustment. Therefore... turn the screw 1/2 turn in the A direction to set your ignition timing at the factory recommended 4 degrees BTDC."?
 
LexTR3 said:
BTW: If all this is correct, how do we explain Macy's Garage instruction for setting timing: "There is a reference line through the middle of the thumbscrew, and one complete turn is equal to 8 degrees of adjustment. Therefore... turn the screw 1/2 turn in the A direction to set your ignition timing at the factory recommended 4 degrees BTDC."?
Click to expand...

How do the hash marks change with a half-turn of the thumbscrew? It could be resulting in the same movement.
 
A half turn of the thumbscrew doesn't move the scale a full division, which would be 2 distributor degrees or 4 crankshaft degrees by my calculation. It seems to me that a half turn of the thumbscrew would be more like 1 distributor degree or 2 crankshaft degrees.

I could be more accurate if I only knew what one click of the vernier thumbscrew represents. As I wrote earlier, some say that 1 click equals 1 degree, if this is correct, or if this is in distributor degrees, or if this is in crankshaft degrees, it not said. Knowing what one click represents is the key... and I hope someone out there has the answer.
 
This is from an electronic copy of the TR3A manual that I have.

-Darrell
 

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Yep, I have the same page in front of me. So if a full turn of the thumbscrew happens to move one division, or 2 degrees on the distributor and 4 degrees on the crankshaft, then a half turn should only move it 1 degree on the distributor and 2 degrees on the crankshaft.

But I think it takes two turns to cover one division.

This is what puzzles me about the Macy's Garage instructions.
 
I don't know where they got that. Everything I've seen talks about using the vernier scale, and has been consistent on what it means.
 
Darrell,

I, too, am puzzled by it. There is a two-part article on Triumph Ignition Timing by Macy's Garage on the Internet ( https://www.macysgarage.com/myweb6/ign-timing.htm ) that is very good, but it ends up with those instructions to turn the vernier knob 1/2 turn to achieve 4 degrees "to set your ignition timing at the factory recommended 4 degrees BTDC."

I hope someone can tell us what one click of the vernier know represents in distributor and crankshaft degrees.
 
LexTR3 said:
Darrell and Randall,

Just to put this one to bed, then, when I use the timing light to measure initial advance, or when I use it to set initial advance, it is giviing me CRANKSHAFT DEGREES. And when I move the vernier knob, I am advancing in DISTRIBUTOR DEGREES.
Click to expand...
That's right; but I find it simpler to just think of the vernier as being 4 degrees per division.
 
startech47,

I did loosen the bolt on the clamp plate to set initial timing (using the test light method) and in an attempt to advance the timing further, but the distributor hit some sort of obstacle that has kept it from moving further.

Randall, You are right. From now on I'll ignore "distributor degrees" and think only in terms of "crankshaft degrees."

I am going to start from scratch today. I'll use the static method to set initial timing by (a) getting to TDC on the timing marks, (b) setting the vernier at its half way point, (c) loosen the clamp, (d) use the test light while rotating the distributor until the light just goes on and out, (e) and then advance the vernier. But here is the rub: the vernier will have only 2 divisions available to me if it starts from half way on the scale, or 8 degrees, and that is not enough to meet Jeff's recommended 12-15 degrees BTDC. Can I start the vernier from one division back (towards retard) after reaching TDC so I can get 3 divisions or 12 degrees?
 
LexTR3 said:
But here is the rub: the vernier will have only 2 divisions available to me if it starts from half way on the scale, or 8 degrees, and that is not enough to meet Jeff's recommended 12-15 degrees BTDC. Can I start the vernier from one division back (towards retard) after reaching TDC so I can get 3 divisions or 12 degrees?
Click to expand...

Yes, that it fine. Starting from center is just to ensure that you have some adjustment left in both directions, but since you are going to dial in much more advance, it makes sense to start with the scale more on the retarded side. In fact, I might dial it all the way to the retard side, you will be advancing it 12-15 degrees, which will give you more than enough adjustment to retard it if needed for some reason.
 
LexTR3 said:
I also found in doing all this that the points gap was incorrect. Perhaps it had slowly closed for some reason.
Click to expand...

The usual cause for that (beyond some slight initial bedding-in) is that the point cam is not lubricated. It needs to have a light smear of oil or grease applied at every tune-up (or yearly IMO, if you drive less than 5000/year). There are several more lubrication points inside the distributor cap, check your Practical Hints for details.

Personally, I hate taking my car to a "professional" as they screw something up almost every time. Last year, a local repair shop forgot to tighten the lug nuts on my "LBC support vehicle", with the result that I nearly lost a wheel on the freeway. And they are a well-respected shop, in business for over 50 years at the same location. You've got the timing nearly right, you said yourself the engine runs fine, and we've all told you that having the spark slightly retarded won't damage the engine in any way. Seems to me that you should also "know when to hold em".
 
Just a joke...!?!




Really....



Aaaawww. Now I feel bad that I killed this thread with my bad joke!!!
 
Well... after this long and "dizzying" thread, I want to thank everyone most warmly for all the good advice and guidance you have given me.

I think I finally have things well in hand.

By wrestling the thumbscrew to the end of the Advance range, I was finally able to get the engine to 12 degrees BTDC at idle. It's still not at 15, as Jeff recommends, but it is in the range he gave me of 12 to 15 degrees BTDC at idle. Good enough for government work, as they say!

I rechecked everything yesterday before going on a long test drive. While doing so, I found that the points on the rebuilt distributor were misaligned (one face was noticeably higher than the other face). I don't know if this made much of a difference in performance, but I installed a new Lucas points set with the faces perfectly aligned. Somehow, also, the points gap was too large, so I corrected that.

To make a too long story short, the car performed extremely well.

You guys have a great deal of patience, and that is what makes the forum the best on one the net.

Again.... many warm thanks.
 
sounds like you got it worked out, Jeff rebuilt my distributor and took the vacuum advance off because I run DCOE webers, he replaced it with the thumb screw advance thing and Its nice, how ever I found that if you dont center the thumb screw first and then set your initial timing by moving the dist and tweeking with the thumb screw, what happens is you have moved your advance plate all the way with the thumb screw and when the mechanical advance trys to kick in your plate cannot move so you never get the total advance like 35 degrees total( just picked a number) to check it hook up your timing light, make a mark on the damper in the area you think total advance would be rev the engine and see if your mark comes up to the pointer

Hondo
 
I didn't think the mechanical (centrifugal ) advance weights moved the points plate at all, Hondo.
Seems to me the weights rotate the distributors point cam.
Messing around with the thumb wheel adjustment in combination with the position of the distributor housing/points plate can affect the
"phasing" of the distributor whereby the rotor becomes misaligned with the contacts in the distributor cap as the centrifugal advance increases necessitating a large energy robbing arc across the gap.
However, the thumb wheel can be used to advantage to correct an out of phase rotor.
Using the thumb wheel for the coarse adjustment is not a good idea. It's design is for fine tuning adjustments.
 
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