Distributor repositioning question

[Member 10617]

I thought I was thru bothering you guys with my distributor questions,but one remains.

I had my distributor rebuilt by Jeff. When I received it, he indicated that I would have to change the degrees BTDC from 4 degrees BTDC (as per the manuals) to 12-15 degrees BTDC, he having changed the advance curve.

The problem is that as the distributor is now positioned, the most I can turn it and adjust it is 10 to 11 degrees BTDC. Jeff says it is still about 5 degrees off and says that I can easily reposition the distributor by:

1. remove the distributor
2. remove the cast iron sleeve that adapts it to the engine (usually either 2 bolts or one countersunk screw)
3. pull the gear out, rotate it one tooth in the proper direction, and
4. reinstall.

I know there is a gear moved by the cam into which the bottom of the distributor fits (when the dog is back home in its slot. This is the only "gear" shown in any of the blow-up drawings in the manuals.

Can someone show me the cast iron sleeve and the location of the gear Jeff is talking about?

OTOH. Since I am only 1 degree off of Jeff's lower number, is there any real reason to continue advancing the timing? Performance no doubt is being affected, but in my opinion the car is running extremely well now. My only real concern is that I don't do any damage to the engine by not running the car at the precise recommended degrees BTDC.

AFTERTHOUGHT:After posting this message, I had an idea suggested by something Randall wrote some time ago. One thing I haven't done but could do is to loosen the clamp and, because the holes are not round but oval, try to move the distributor a bit that way. Randall suggested, as I recall, that it is possible to get 10 degrees of change that way.

 

[TR3driver]

The gear Jeff is talking about is the same gear you are thinking of, item 55 below. The "sleeve" (which most of us call "pedestal") is item 59. It is retained by two nuts & lockwashers.

Running the ignition retarded by only 1 degree will certainly not hurt the engine, and likely not affect performance enough to notice. So you can just leave it alone if you want. Personally, I'd want to fix it just so it looks "right", but I am definitely a tinkerer and frequently unable to take my own advice (if it ain't broken, don't fix it).

Assuming your problem is that the advance module is hitting the head, loosening the clamp won't help.

 

[Member 10617]

Once again, many thanks, Randall.

The advance module is close to the head, but not hitting it just yet. There seems to be a little room left, but I cannot turn the distributor any further as it is presently situated. I don't want to force it because, as my Triumph engine designer friend warned, I would "overload it" by over-forcing it.

If I were to pull the gear out and advance it by one one tooth, what is the correct direction: clockwise or counterclockwise?

Also, by changing this configuration, does it have an effect on anything other than the timing? In other words, does it affect anything else in the distributor so that a readjustment is necessary? I assume the is answer is no, but I would like to be certain.

As I said earlier, at 10 or 11 degrees BTDC, the car is running better now than at any time since I acquired it, so I am inclined to leave well enough alone, but I, too, am a tinkerer, and would like to "get it right" if possible. If it were warm here in western Virginia, I'd simply drive the car and igonore all this, but it is very cold here and there sits the car saying "Work on me, work on me."

 

[TR4nut]

Ed-

In my opinion, you want to be a little careful before tinkering.. The part 55 is keyed to the spindle that drives the oil pump. No problem there, but if you move the gear you may not be able to easily get the spindle back into the pump. I believe the way to do it is drive the spindle mostly out of the gear, make sure the spindle is engaging in the pump, then push the gear back into place. It may not be as difficult as I make it out to be, but you do want to make sure the spindle seats back into that pump.

As to direction, I think you may have been moving the distributor clockwise, corrrect? If so, I believe the gear will be moved counter-clockwise, that should bring the advance module away from the head by moving it counter-clockwise as well.

Randy

 

[Member 10617]

Randy,

With my lack of expertise in these matters, my inclination is to leave the distributor alone for now. It is probably simple for most, but I have found that if something can go wrong, it will go wrong. And not being able to get the spindle back into the pump would be a MAJOR problem as the skilled guys are at 40 to 50 miles away from here.

I have nothing to complain about the performance of the car, although Jeff tells me that the performance is significantly decreased if the timing is off by 5 degrees. (In fact, I have the timing at about 11 degrees BTDC, and he recommends 12-15 degrees BTDC.)

My main concern is that I should not damage the engine by running it short of the recommended 12-15 degrees BTDC. I can live with some decrease in performance, but I cannot live with damage to the pistons.

Given all this information, what would you do?

 

[TR3driver]

The spindle is easy. It's just a slip fit in the gear, and frequently will stay behind. If not, just pull it out of the gear and drop it back into place, then turn it (along with the oil pump) about the same amount as you are going to turn the gear. Generally it will then re-engage when you put the gear into place (since the whole assembly turns slightly as the gears engage anyway). But if not, just turn the engine over once (before installing the pedestal), either by hand or with the starter.

Moving the gear by one tooth won't change anything except the timing.

 

[Member 10617]

Thanks, Randall.

I'll have to give this some serious thought. I understand your directions, but never having done this before, it is hard for me to picture all the procedures in my mind.

If it is necessary to perform this operation, I think I'll call on my local mechanic friend and show him all these postings and ask him to decipher them for me. He ran his own foreign car shop here in Lexington for many years, has owned and worked on Triumphs and other British cars, and has been great help to me. But he is retired, and I don't like to ask him for help if I can do it myself. In this case, clearly, I don't think that I can.

I'm still left with the question, however: does it even need to be done, given that I am within 1 degree of the lower range of 12-15 degrees BTDC recommended by Jeff and the car is running very well.

 

[TR4nut]

Ed-

Regarding advance, I think you are fine where you are, 1 degree won't make a difference. It sounds like the distributor has a different total advance than what you started with - others can chime in/correct me, but as far as damage goes it would be the total advance at higher rpms that would be the concern as you could get detonation potentially if advanced too far. So retarding the amount you've done likely puts you in the safe zone. Another check would be if you are getting pinging at higher rpms - if so, it would likely be worth retarding further.

Randy

Edit: Sorry, ignore this rubbish, I've just confused myself - going to more degrees btdc is basically advancing things, not retarding as I stated. Sorry!

 

[Member 10617]

Randy,

After having the distributor rebuilt by Jeff, it came back with his instructions to ignore the standard manual's 4 degrees TDC and set the timing instead at "12-15 degrees BTDC @ idle w/o vacuum." That's what got me started on this thread because I was only able to advance the timing to 10 or 11 degrees BTDC and couldn't rotate the distributor any further.

Using a timing light, the timing mark advances nicely at higher rpms... and the car runs well. So I'm just wondering if I can stick with 10 to 11 degrees BTDC or do I need to reposition the distributor so I can rotate it further. (Sorry to repeat all this, but I just want to make sure I am making myself clear.)

On the highway, at any speed that I drive, and up and down hills, there is no pinging or knocking.

As if to confuse things more, some of my older manuals warn against "over-advancing" rather than "over-retarding."

I might add that I check my spark plugs carefully for signs of trouble. All four are now test-book "normal" with deposits that are light tan. There are no signs of overheating, preignition, or detonation. Reading the spark plugs has always seemed to me like a good way to double check on performance.

 

[Scott_Hower]

Moving the gear by one tooth won't change anything except the timing.

Will it even change the timing? Seems like it will only change the orientation of the dizzy body relative to the block, which will then allow for the desired timing change (advance).

 

[Member 10617]

Now here's another wrinkle on the subject.

I have been reading a Lucas "Tuning the Lucas Distributor" article on advance curve data (dated January 2002). And though it applies in general to distributors with mechanical advance, the degrees of advance at 500 rpms is shown at four degrees BTDC and the degrees of advance at 1000 rpms is ten and a half degrees BTDC.

I have been setting the timing on my car with the idle at about 800 to 900 rpms and was able to achieve ten or ten and a half degrees BTDC.

Does that mean that I'm probably OK with the timing?

 

[CJD]

Ed, the only thing that will happen with a very slightly retarded timing is the engine may run a bit warmer, and you will loose a very slight amount of torque. That's it. It will not damage the engine, so you do not need to worry about hurting anything if you choose to wait.

John.

 

[Darrell_Walker]

Now here's another wrinkle on the subject.

I have been reading a Lucas "Tuning the Lucas Distributor" article on advance curve data (dated January 2002). And though it applies in general to distributors with mechanical advance, the degrees of advance at 500 rpms is shown at four degrees BTDC and the degrees of advance at 1000 rpms is ten and a half degrees BTDC.

I have been setting the timing on my car with the idle at about 800 to 900 rpms and was able to achieve ten or ten and a half degrees BTDC.

Does that mean that I'm probably OK with the timing?

Without knowing how Jeff recurved it, it is hard to say. It might not be advancing at all at your idle speed.

BTW, have you used the thumbwheel to try to get more advance, or is it fully advanced already?

 

[Member 10617]

Good point, Darrell.

I started the thumbwheel at the middle of its range and advanced it one line or notch. It still has a little way to go, and that might, indeed, give me the extra four or five degrees of advance that I need. I thought that I could achieve the proper advance by rotating the distributor, reserving the thumbwheel for "fine tuning."

As for advancing at idle speed, I have an advance timing light that I set at ten degrees and then turned the distributor so that the mark on the pully appeared directly under the fixed indicator when the strobe flashed. Again using the advance timing light dial, I then set it at 12 degrees and tried to get the same result, but couldn't rotate the distributor sufficiently.

Many thanks.

 

[TR3driver]

Will it even change the timing? Seems like it will only change the orientation of the dizzy body relative to the block, which will then allow for the desired timing change (advance).

Moving the gear CCW by one tooth without changing the position of the distributor body will advance the timing, by too much in this case. Ed can then move the dizzy body CCW to bring the timing back to the desired value.

But I'm a bit puzzled by the comment that the vacuum module is not hitting the head. What is keeping the body from turning farther CW?

 

[Member 10617]

Randall,

I am puzzled also. It just binds and won't go any farther. I've looked carefully and perhaps it is the steel vacuum tube that is stopping the rotation. It is mighty rigid, whereas a copper tube would be more pliable.

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:

1. One half turn equals 4 degrees (talking about Triumph).
2. 1 click equals 1 degree (talking about Spitfire).
3. 11 clicks equal 1 degree (talking about MGs).
4. Each division of the scale is equal to 2 degrees
on the distributor (Practical Hints)


I can't believe there is so much variation in the information. Either someone is wrong, or each is talking about a different vernier knob.

If #4 is right, then there is no way to reach 12-15 degrees advanced from the middle of the scale, if one were trying to achieve it that way.

 

[Darrell_Walker]

As for advancing at idle speed, I have an advance timing light that I set at ten degrees and then turned the distributor so that the mark on the pully appeared directly under the fixed indicator when the strobe flashed. Again using the advance timing light dial, I then set it at 12 degrees and tried to get the same result, but couldn't rotate the distributor sufficiently.

Do you know what your static (no mechanical advance) is? What I was trying to say, is that if Jeff changed the curve, it could have any amount (from zero up) of mechanical advance at idle. The stats you were quoting were for the factory advance curve.

 

[TR3driver]

#4 is correct. But don't forget that the distributor turns at half the speed of the crankshaft, so 2 degrees at the distributor is 4 degrees at the crankshaft. The timing figures from Jeff are in crankshaft degrees.

 

[Member 10617]

Randall,

I think you have solved it. I knew that the distributor is half the speed of the crankshaft, but I didn't know that the figures from Jeff are in crankshaft degrees. As he and I have spoken only of the distributor, I assumed he was talking about distributor degrees.

I will set the initial timing using the static method. No problem. But when I check things with the advance timing light, will it be measuring crankshaft degrees or distributor degrees? The information on the advance timing light makes no distinction.

Thanks for setting me straight. I think the answer and solution are finally in sight, and I hope others will benefit from this long thread.

 

[Darrell_Walker]

I will set the initial timing using the static method. No problem. But when I check things with the advance timing light, will it be measuring crankshaft degrees or distributor degrees? The information on the advance timing light makes no distinction.

I believe that is in crank degrees. I used to always worry about crank vs. distributor degrees, but I've found everything is almost always in crank degrees, and always crank degrees when something is done on the engine. It seems to only be standalone specs for the distributor that might list distributor degrees.