Distributor Rotors

[Splat]

Preamble.....

At a track day last year my car developed a slight misfire. I tried driving through it, but it seemed to become worse. "Not to worry," thought I, as it was at Thruxton (my local circuit), I'd brought the Gallardo along too and rain was threatening. Once cool, the misfire evaporated and I was able to drive home without mishap. I checked what I could and could find nothing amiss.

I undertook several longish drives after that (and quite a few short ones out to Thruxton where we keep our Chipmunk) with no further reoccurrence. But then, on the first drive of this summer, after half an hour of driving I stopped at a local pub for a half in the sunshine and when I started back up again I had a serious misfire. I was only a couple of miles from home, so attempted the drive. I conked out a few hundred yards later, but after a few minutes of cooling I was able to restart and drive (noisily) home. When I came to investigate later, the misfire had disappeared and I could find nothing wrong. At Jan's suggestion I checked my alternator output and found it to be about 19v, but this proved to be my ancient, cheap analog meter (discovered when my replacement alternator also appeared to be producing 19v!!).

About a week later I attempted a further drive. After about fifteen minutes a misfire developed and rapidly became worse. I set about returning home but after a few more minutes the engine died in the middle of nowhere (well OK, a country lane near Highclere). It was obviously not going to restart, so I called the RAC and waited. Shortly before their chap arrived the local farmer/land-owner pulled out of his driveway a couple of hundred yards away and drove over to me. As all Hampshire farmers are wont to do, he showed me photos of his race-prepared Europa twin-cam and his wife's Bristol-engined Ace and we chatted until the orange van was on scene. Courtesy of a pair of well insulated pliers we soon discovered that there was HT from the King lead but not from the plug leads, suggesting that the rotor arm had failed....

I run an Aldon distributor with one of their Hall effect electronic ignition sets (actually a Pertronix unit, I believe). This is based on the Lucas 45D distributor. The RAC man just happened to have a rotor arm for a 25D in his van (commonplace twenty years ago; a minor miracle today!) which got me home. I posted it back to him the following day.

My new friend the farmer, recommended that I look up the "Distributor Doctor" as a source for a new rotor. Whilst on his site I came across an article that perfectly describes the failure mode that I experienced and explains the cause (do read this, it's short but enlightening!):

http://www.distributordoctor.com/rotor_arms.html

I was actually aware of the problems of the modern "Lucas" rotors. (FWIW, Lucas make NO parts for older vehicles. It's all manufactured in the Far East and distributed by Lucas in their green boxes.) Therefore I had deliberately sourced a Bosche rotor arm, which are still made in Germany. But this had failed in exactly the same manor as the pattern Lucas part does.

So I'm now running a DD rotor and everything seems good. It seems to be yet another example of the folly of using pattern parts. I bought two of his rotors together with a NOS Lucas rotor from eBay, all being about the same price as a pattern rotor.

The difference in quality is quite clear to see from the following photos. Here are pattern Lucas (black thermoplastic with the offending rivet), brown Bosche (also riveted), black NOS Lucas (thermoset, no rivet, Lucas script and crest moulded on) and Distributor Doctor (red). Note the difference in both the thickness of the insulating material and of the brass contact on the latter two when compared to the modern replacements:

[Splat]

And a word of warning. The Far Eastern manufacturers are aware of the Distributor Doctors products and now produce rotor arms in red. They even flog them in Lucas boxes! They're all over eBay. Some of the better UK distributors seem to sell the DDs rotors, but they are actually cheaper coming direct from him. I received mine the following day, together with the little felt pad that lives underneath, something that appears in no parts catalogue and that I'd quite forgotten about before he reminded me of it (I remember it from my first car, a "Frogeye" Sprite!).

[Westfield 129]

While I have occasionally (well, once, anyway) had a rotor failure (in the Ducellier distributor of a Renault R5 Turbo with a strange miss... Turned out to be a broken internal locator tab), I have never experienced a rotor failure (so far) on one of my Lucas (or Pertronix replica) distributor equipped cars.

None of my rotors look like the riveted ones that you showed. The one I am running now is a Petronix supplied rotor, with a Pertronix supplied cap. 'Been working for years and 10's of 1000s of miles.

The pictures are interesting, and the information from the Distrubutor Doctor is enlightening, but I have not seen any rotors of that riveted type here in the US. When I don't get the parts direct from Pertronix, I get them from Moss US, from the oritinal store, down the road in Goleta. So far, no problems. I am going to take a look at the rotors I have around (One in a Pertronix equipped Alden that I keep on the shelf as a spare, the one in the car, and another 25D Pertronix triggered spare... I am a firm believer that anything for which one has a spare will never fail. So far, so good...).

You might check the play in your distributor, and the cap as well for any interference or fit problems. I have seen cap fit problems, and found that the cap had to be carefully fitted, mainly pressed firmly home, to ensure that the distributor rotor didnt contact or rub anything that might cause a problem.

While I often time change parts, I have not really paid a lot of attention to the ignition bits since I have eliminated ignition points from my engines. I do check the wires, the cap and rotor, and often put a drop of oil in the felt for my Lucas distributors, but if it is working well, I generally leave the parts alone if they look good. Otherwise, every 5 years or so, maybe.

If your cheap Chinese voltmeter reads high, change the battery inside (probably 9V) and the accuracy will improve, if not return to OE accuracy. I had the same problem with mine recently, when it said that my Mercedes alternator was putting out 14.6 V, but was really doing only 13.2 (after changing the battery in the volt meter)... Not enough to hold up the battery on a hot day with the A/C and the fans running. New alternator going in this weekend. And I believed that thing for months, thinking that I had a bad battery or two.

And, while your voltage problem was not alternator related (nor was your miss), I would still get rid of the Lucas alterntor. Those I have had LOTS of problems with, replacing more than 7 in a two year period, all with failure of the rectifier (vibrating apart) or the regulator (simple failure). Fortunatly, I only had to pay for one unit, with the rest covered under the warranty, or rebuilt when I finally gave up... And each alternator came from a different rebuilder. My Chinese Hitachi has been flawless, for $70 USD.

[jonclancy]

I was enjoying a twilight run in SKK on empty Cotswolds roads last night. A quick blast to blow out he cobwebs before bed.

On the return leg, and after around 40 mins of driving, I had the same momentary power loss I had on the M27 going to the ferry last month.

I dead-sticked into a lay by and checked everything in the fading light. I now know my phone flash/torch is kaput!!

Turned over fine, but no start. Waited 15 mins with the bonnet removed to aid cooling, got her restarted, and proceeded home making most of high gears and light throttle. Home in time for supper, rather than wait for recovery in the pitch black!!

Two Dist Doc rotor arms now ordered, and added felt pads. If you need advance springs, you need to supply the serial number on the dizzy body. A full recon on a dizzy is about £190 plus VAT.

I'll let you know how I get on. Hopefully problem cured!

[Simon Marks]

I recently had a long term misfire (when warm and under load) on my Talbot Sunbeam Lotus. This eventually turned into the car not starting after a hillclimb (on a particularly hot day) and I needed recovery home. A new rotor arm sorted the job the following morning. I used to be the co-ordinator for the British Historic Rally Championship and could not count the times that high-revving BDAs retired due to rotor arm failure. The quality of the easily obtainable parts is truly hit or miss so this is one spare item that is best carried (particularly as is is such an easy thing to replace - on the A Series anyway).

Simon

[jonclancy]

Hmm...

I whipped off my distributor cap last light, ready to install my shiny new DD rotor. Insert of finding some tat with a nail in it, I found what looks suspiciously like an older DD rotor arm. Martin did think my name rang a bell, but I thought it was because we had spoken on the phone a few weeks earlier. Maybe correct, and this was the original rotor TonyL fitted some 4000+ miles ago.

Funnily, the symptoms of ignition failure when hot, and recovery when cool, just pointed to the rotor. The old one looks worn anyway, so it has been swapped. Could be that the problem lies elsewhere. Need to replace a T10 sidelight holder and connectors before I can do an extended road test next week.

Here are a couple of pics...

[jonclancy]

I forgot to mention that I am running a Lumenition optical electronic ignition. Seems to have been reliable, apart from when the optical chopper part severed a wire inside!

When I have the momentary loss of power, the RPM gauge drops to zero, too. I'll look into the RVC feeds. Maybe it's a coil problem... Maybe the Tach has an intermittent fault interfering with the coil.

[Westfield 129]

Hot short problems can be in the coil, or the condenser if you are using one.

If the electronic tach drops to zero when the failure occurs, then it's igntion. Fortunately, not too many parts to replace.

[jonclancy]

I remembered that I fitted some Accuspark plugs and leads a while ago. They sell a red rotor that is made to the original DD specs. Might explain that one.

I have a ballast system on my car. This was probably because the Lumenition coil demanded it, rather than saving points from arcing. I initially ordered a DLB105, then checked and ordered the 110. It came the next day, which was just amazing!

During the fitting process, I Contralubed every connection in the underbonnet wiring. Started fine, and when the weather is suitable, I'll road test her. I have a standard solenoid fitted, though. Thus I don't get the benefit of full 12V blast into a 1R5 coil while cranking. In other words, the tag on the opposite side to the ignition switch feed is blank. On a ballast solenoid, there is a lucar connector here that feeds the positive side of the coil.

Being (a) too tight to change a perfectly decent solenoid, and, (b), worried I may buy the poor quality tat that caused Splat's XI to have our hand prints on the back at CLM, I reckon a feed from the starter motor side of the solenoid could do the job. Any reason why this would be a bad idea before I get the crimp tool out?

[Westfield 129]

I connect the coil to the ignitino switch when I wire the car, which should be the way yours is wired. The solenoid gets its power from a momentary section of the ignition switch, or a separate momentary switch.

Your ignition circuit should not be going through the solenoid at all. At least I never wired a car that way. I use a Lotus 7 Series 2 wiring scheme, or a Painless box with a separate igintion circuit with its own fuse, closed by the key switch, or master off/ignition/momentary start switch.

You should be getting 12V or so at the coil, ignition on, engine running or not, equal to voltage measured at the battery.

Some of the cars I wire have two solenoids, one with the start button on the firewall for setting the valves or other engine rotation chores.

In that case, I bridge the solenoid on the starter (Usually a British Starters Hitachi/Honda unit) that engages the pinion during starting. This is covered in British Starters installation documentation.

Anyway, if you connect the ignition circuit to the 12V main starter power, you will only have momentary ignition voltage. What you need is a continuous 12~13V at the coil through your switched power circuit.