Distributor Advance

[Galwaylotus]

I'm installing electronic ignition and have pulled my 23D4A 40953 distributor apart to clean and check it. I was skeptical about the mechanical advance working. There was a bit of sticking in the mechanical advance, I think but that's all been sorted after cleaning and lubrication. Before I reinstall it, I wonder how critical the advance profile is. The primary spring is under tension at zero advance which is probably ok but the slack in the secondary spring seems significant. It looks like it wouldn't start contributing until perhaps 9? or more and with a total mechanical advance of 12? that seems very late. I'm not prepared to spend on a programmable "black box" system like Stealth or Aldon Amethyst just now and there doesn't seem to be anyone in my area who has a distributor machine and springs to check out my current setup. Am I risking much by trying it as I have it now or must I bite the bullet and either send the unit away or . . .? Anyone have any advice? Thanks, folks.

[RogerFrench]

Why not fit it and see? Drive gently at first in case you have too much advance and pinking. If it doesn't work, then fix it.

[peterako]

Ditto to what Roger says.

At worst it may advance too quickly, but only to the 12 degrees total dizzy advance.

That's what my worn 23D did. I had full advance 'too low' down in the rev range but it was 'fine'.

I do have a Black Box in now, but 'too low' full advance is NOT what forced me to change dizzy.

My 23D is very worn so there's a lot of scatter.....

Peter

[AHM]

There is supposed to be slack in the secondary spring. Otherwise it wouldn't be secondary and the advance curve would be a straight line.

Se the curves in Wilkins book.

[Galwaylotus]

Yes. I'm well aware of that. It's the amount of slack that seems to be bringing in the secondary at over 9? advance instead of lower in the range as per the spec!

[AHM]

What you describe sounds just like the spec to me!

The curve has lots of advance up to 2000 rpm 28 deg then from there to 36 deg at 6500rpm
that would be a difference of 8deg on the crank which equates to 4deg on the secondary spring in the distributor and you have 'measured' 3deg by "looking" at the distributor.

Doesn't sound too far wrong - certainly not "very late"

do you have the right spec.
see Miles Wilkins book P168 & 169

[Galwaylotus]

I took the unit apart again this morning and with careful measurements I now know that the primary advance is from 0-9.55? leaving the secondary from 9.55? to 12? at the distributor. The specification for the 40953 in both the Lotus factory manual and in Miles Wilkins book shows the secondary coming in at 8? advance. I think I can get access to a distributor testing machine early to mid-next week in the local tech institute. If they have the machine and springs I can set it up properly there. I also found the distance between spring posts slightly different and the heavy spring is on the closer set so by swapping the springs I'll reduce the difference between my current setup and the correct spec. I'm going out now to get a proper spring hook as prying them off with a small screwdriver is getting annoying!

[dpo#4]

2 ways to find out for sure. First is a distributor tester that spins your unit to various revs and displays timing for each lobe/cylinder. Clean, sexy & rare.The more usual way is on the engine, starting out at as low an idle speed as possible, and reading off the timing at intervals of, say, 250 rpm. Pencil, graph paper, safety glasses, & adjustable timing light (or non -adjustable light + extra painted timing marks on the pulley). Make that a face shield if doing the upper rev range: a bit of v-belt gave me a welt once & it could have been an eye or torn lip. The observed curve is the product of all sorts of backlash, thrust on accel/decel from the helical gear, chain slack, wear at weight pivots & cam slots, bent shafts, fatigued springs, shaft bushing wear...with resonances superimposed. On the engine is really the best way, since it's what you'll actually get. If the mark is dancing, there's wear and it's no longer an advance curve, it's a band. - Ray
Galwaylotus, I read your above entry just as I was posting. Good luck with the tester, they're fun to use!

[AHM]

I now know that the primary advance is from 0-9.55?

So bend the spring ends until the primary advance is from 0-8.00? Job done!
Tools needed = Pliers
Time taken 5 minutes.

This isn't an exact science.

As Roger says fit it and see how it goes.

[Galwaylotus]

Update.
I took the distributor apart again to ensure I had the optimum setup for the springs I have. When I was taking off the secondary spring it decided to take a tour of my "garage"! I thought I'd have to tear the place apart and the proverbial needle in a haystack came to mind. After looking and looking I finally found it perched on a box of ceramic tiles! What luck!!
Next job was to find the optimum distance between spring posts. As I couldn't get my caliper into to gap between post and body I set the distributor up in a tin can to hold a steady position and my camera on a tripod focussing on top of one of the posts. By taking shots with the advance shaft in two orientations 180? apart and looking at each set of posts I could, by enlarging the shots on screen and measuring with a transparent scale ("ruler"), get the relative distances between pairs and between the two orientations. Actual distances don't matter, only relative ones.
I then reassembled the unit and connected the secondary spring to the posts with the greatest gap.
Next week Wednesday I have access to a distributor machine and I'll see just what I have. I'm hoping I won't have to change springs again!

[Johnfm]

The black box is about ?99 and took me 30 minutes to install.

I will find out next week (when my webers are back together) how well/not well it performs.

Seems that having control of advance via a laptop is a decent way of tuning the timing on these cars.

[Galwaylotus]

John, where did you see one for ?99? The ones I've seen are about twice that price!
I agree that it would be great to have the option to tailor the advance curve. Of course programming by laptop presents a problem as I use a desktop and don't have access to a laptop. The distaff side of the house uses iPads.

[Johnfm]

I think it is ?99 just for the black box.

I bought the electronic ignition and black box together for ?130ish and used my existing 23D.

Lack of laptop is a hassle. I have 4 macs in the house. Luckily I had an old windows desktop machine in the loft which manages to run the software.

[billwill]

I'm surprised it only took you 30 mins if you also did the "take distributor out, remove springs & wire weights up with binding wire" bit?

[AHM]

And the phone insurance company and explain bit!