unidentified electronic ignition needs different rotor arm

[GrahamFountain]

While I was looking for a spare set of points I found this distributor with an electronic ignition unit fitted. I have no recollection of where I came by it, could have been in a box of bits. So I thought, having time, I'd see if it works.

Problem is that the sender unit fouls the standard rotor arm, so the cap won't fit.

Now I seem to remember something about alternative rotor arms from the days when the standard ones were hard to find, but I can't find aught. I looked at the 45d4 one off the Herald, and that won't fit the shaft and the arm is too long. I could shorten the arm if that were the only problem, but I don't think increasing the size of the hole or reducing the shaft diameter are worth the effort.

So does anyone know an alternative rotor arm that fits on the shaft and won't foul the terminals?

Graham

[GrahamFountain]

Bit more research turned up this image of a 44d4 in an 1850/TR7 with the arm I think I'm looking for.

Graham

[Bumpa]

Is that from the Distributor Doctor? http://www.distributordoctor.com/ He sells red ones and his quality is usually excellent.

[sprint95m]

You will be needing a 45D cap to fit over the replacement 45D rotor arm.

If this is for a Sprint, then it will need side HT connections,
so look for an Austin Ambassador cap and ignition leads..



Ian.

[shaunroche]

That's the one I use and it's from Simon BBC, so Accuspark which uses the 45D rotor arm or.....



If memory serves, this is for an Ambassador...

[GrahamFountain]

The rotor arm I thought was for the Herald wasn't - don't know what it is or why I was keeping it. So I took the one out of Herald's spare dissy, and it fits. I checked it didn't catch anything in the spare sprint cap, and then tested it in the distributor with points, under a sprint cap, and it seems fine. I didn't actually drive anywhere but it ticks over and revs off load no props.

But, I can't get the car to run properly with this EI unit. I can get it to just about start, but there's not enough spark to trigger the strobe and it runs like a bag of turds where ever I time it - and I took this dissy out and put the points one back in set that right and put it back timed exactly the same, twice. Perhaps that's why I got it in a boxabits or somert. And yes I powered this EI unit it off the ignition, not the coil. Actually, it runs like a car with points does when the distributor isn't earthed properly cos the set screws holding it down are too slack. Given that, I'm gonna check the earthing to the unit as soon as I stop writing this.

So, for the moment at least, its back to points again. At least I can time them statically.
Todaym, I even found a new way to do that without a multimeter (AVO, for those others that are as chronologically challenged as me) or bulb and wire: Rub the connectors between the coil and distributor together with the ignition on. If they spark, the points are closed. If they don't, the points are open. Mightn't be as accurate as with a bulb&wire, but easier to do roadside in the rain if you haven't got a wire. I used this method trying for 10 before and measured 12 with the strobe.

As a matter of interest, which way does the distributor turn to keep the timing right as the points cam follower wears and the gap has to be opened up again? I'm thinking it must be anti-clockwise. But I aren't sure.
I ask because, with the worn points I have in (new ones on order), the set screws that hold the distributor to the plate are about equally close to one end of the slot or the other, depending on how I engage the drive gears. So when I fit the new set, which I will do with the distributor out, if there's a similar choice, I want to have the most adjustment I can before I have to pull the distributor and turn it round a tooth.

It's not that it's such a bad job in the Dolomite, especially with the engine cold. But it's a right thwaite to do on the TR7 Sprint with the bulkhead so close up to the back of the engine.
Anybody know what access to the 44d4 is like when it's fitted on the Lotus engine?

Graham

[GrahamFountain]

The Herald's dissy is a 25d4 BTW.
Graham

[cleverusername]

I am surprised you're having trouble with that, it is a britpart module and they are pretty bullet proof. I have run one off a 6v supply and it still worked, with 12 v you should have no problem.

In my experience they either don't work or work perfectly.

[GrahamFountain]

I think that rotor arm that's too long could be a 45d4. It turned out that the dissy with the EI unit in had a burr on the shaft that made it too tight, the dolomite and Herald ones weren't so tight a fit on, but the herald one took some getting off till I'd had at the shaft with a file.

I can see how the 45d4 one needs a different cap. But the 25d4 one seems fine under the standard sprint cap - with points in.
As to why the EI unit don't work, I can't say. I can't see that I had it 180 out of alignment cos it ran a bit. And I set the engine to TDC #1 with the rotor arm pointing at the locating lug and swapped the EI unit in so it was the same. Tried it in both positions the points one runs at, and tried the range of adjustment. I've compared the herald arm with the sprint one, and it seems a good match for length and alignment - the conductor is wider than the sprint's, and about centred the same.

But I couldn't get it running anything like right with the EI unit in, and I didn't like the way it did run. And not having any idea how advanced or retarded it was, I didn't feel safe with any of that. Whereas, I know I can get the points set to very close by eye and near cock-on with a meter before I even try to start the car. I might have put one in 180 out before now, ifn' I didn't look at the cam position, but it don't run at all like that.

Maybe the magnets driving the hall probe in the EI unit are off alignment with the cam lobes. But how would I check that before I get the car running well enough to use the strobe? And if that's so, how will the rotor arm line up with the cap terminals. I've looked at the arm I think is 45d4, and that seems to align with the sprint arm, just longer, and not be offset much.

So I think the fact that it wouldn't trigger the strobe suggests there's a problem with the unit or how it's wired.

Graham

[GrahamFountain]

I been out to the car and wired-up the dissy with the EI unit in, and spun it by hand. I know that's probably not fast enough really, but fast as I can spin it, it gives the weakest spark that could go by that name. I won't hold the plug to measure the voltage by how far up the arm it jolts, but I don't think it would get far past the wrist.

I assume I'm wiring it right and the red wire is +12v, dissy body to earth, black wire to coil. I'm also assuming it works with a ballast resistor in series with the coil.

Another interesting thing is that while the 25d4 arm fits in the 44d4, and at least appears to work, the 44d4 arm catches on the 25d4 cap. I assume it's the conductors catching, but can't physically see. I guess that may weaken the spark at the plug if the gap in the distributor cap is a bit large. But it's still the case that the 25d4 arm works with the points set. I'll look at the cost of these ambasador caps and at shortening a 45d4 arm to fit in the 44d4 cap. I think I can make a jig to show where the 44d4 arm reaches out to.

Graham

[GrahamFountain]

I've measured the rotor arms I have. I measure the Sprint one at 21.6mm centre to edge, the 25d4 one from the Herald at 20.7mm, and the one I'm assuming is 45d4 at 27.6mm. However, they are measured from the centre wear marks made by the carbon brush on the conductor for the sprint and herald ones; where the 45d4 one hasn't been used and has no proper mark to go by.

The question is, whether the 36 thou extra gap between the herald rotor arm and the terminal posts in the sprint cap is enough to stop the EI unit generating a good spark at the plug? If it is, then how does it still spark well with the points driving the coil instead? And that's with everything else the same except the distributor body, i.e. same cap, same leads, same coil and wiring. When/if it stops raining, think I may put the Herald arm in with the points and go for a bit of a drive. I can then see if it affects anything at the higher end of the revs.

I've also thought about the issue, and while I don't mind the dolomite having a 45d4 cap (is one for the Lucas 45d in a Ford, which is cheaper, the same as the Ambassador one, as I assume?), the TR7 Sprint has to stay visually like standard. And I suspect there are others who'd be interested in an EI unit that keeps the car looking standard.

Graham

[GrahamFountain]

Been for a drive and changed to the 25d4 rotor arm under the 44d4 cap, and I can't tell any difference. I also retried the Sprint rotor arm in the herald distributor and can't get it to catch - first time it didn't have a spring in the arm, so I may not have had it on square.
I also found a 25d4 with no guts in it, and looked in through the arched window where the terminal would normally be. There is some clearance between the sprint rotor and the one terminal I cans see, but there's about 40-45 thou between that and the herald's rotor arm.

So I'm down to one of these:

• I put the distributor with the EI in wrongly timed, which I don't think I did every time, and it don't explain not triggering the strobe;

• I'm not running it off the right supply (12v ign switched);

• there's an earth problem I can't find;

• it don't like the ballast resistor with the coil;

• or its got a fault.

[cleverusername]

It could be the magnetic trigger is not located properly. Easy enough to check, rig up a test lamp, like you would with points but one difference. The electronic ignition users a sensor which detects moving magnetic fields, probably some kind of hall sensor. So to test its function you need to rotate the dizzy.

If the test lamp flashes, it is working, if is it isn't, the trigger is incorrectly located or the unit is duff.

[GrahamFountain]

I can see the coil voltage drop with a meter as I turn the dissy. It's not very easy to see though. So I couldn't be sure it happened 4 times a turn properly.
I'll give the bulb and wire test a go.
I can't see a problem with the position of the magnetic ring on the cam. Though there is a bit of scuffing to the top face, presumably because of the rotor being very tight on the burred over shaft and someone's levered it off - I pulled it off with pipe grips, the herald rotor being the cheapest bit.
Graham

[GrahamFountain]

Nothing by the bulb method at all. So I'm taking this unit out, and returning this dissy to points - I like points anyway, and that's despite being an electronics (avionics) engineer by profession. Then again, I remember P110.
Graham