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Pattern Rotor Arms

I have read recently about problems people have had with arcing on Rotor Arms, but I cannot find a ready reference.

This topic came up at our local "Happy Hour Classic Car Club" this evening, and one of our group has had trouble with both his XK 140 and a Moggy. On both of them there were ignition problems - arcing on the Rotor Arms, the owner swoped over to new (pattern) rotor arms, but still had problems. They then called out the RAC and still there were problems with arcing down the Rotor Arm.

Eventually another member produced a correct Lucas arm and there were no further problems.

It seems the pattern arms are made with a less dense material than the old Lucas ones and for some reason are thus more suseptible to arcing. The above XK tried 3 pattern arms before fitting the Lucas, so you can imagine their frustration.

I seem to recall Malcolm in the Cornwall club had an arcing Rotor Arm, it was in that clubs magazine a month or two ago, I wonder if that was a Pattern model.

Has any of our other contributors had problems with pattern arms.

"Happy Hour Classic Car Club"? well I think that does describe accuratly one aspect of the clubs activities, unfortunatly you have to live within walking distance of the meeting place, to attend.

Naomi

Re: Pattern Rotor Arms

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I wonder if it would be possible to fit a disc of some non conducting plastic immediately below the
rotating contact. From memory there would just be room on most dristributors. This would considerably lengthen the path to earth. Some Bosch rotors have this built in.

Mike

Re: Re: Pattern Rotor Arms

Wasn’t there the same type of problems with repro distributor caps for BLIC mags a few years ago? I think it was put down to damp being able to penetrate into the material that was softer than the original.

Re: Re: Pattern Rotor Arms

Hi all
I don't think an extra disc below the rotor arm would help in this case. Yes it would lengthen the distance to earth, but the problem with the repro rotor arms appears to be low quality bakelite which breaks down under electrical stress and tracks INTERNALLY! A direct conducting line through the material results with no visible effects on the surface.

I've got through eight of these things now on the wifes Triumph TR5, all with the same fault.

Re: Re: Re: Pattern Rotor Arms

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One is down to experience, eight is not fit for purpose - even as a copy part. May I ask who is (has been) your supplier. It would be good to know so that the rest of the stock may be carefully inspected prior to purchase!

Mike

Re: Re: Re: Re: Pattern Rotor Arms

Hi all

I've recently come across an original new old stock Lucas arm so hopefully my problem will be over.

The duff arms I found in various places, mostly unnamed autojumble stalls so I've not been able to take them back. I've also had a word with my local TR specialist (TR Enterprises - Blidworth) who tell me they have had the same trouble - they may (or may not) find one decent arm out of a boxful. These arms last about 1-2000 miles. They also tell me that all these arms are coming out of the same factory no matter what name is on the packaging and where they are bought from. Even those in (new) Lucas branded boxes exhibit the same unreliability.

Unfortunately a visual inspection does not reveal any fault. Even after failure has occured there are still no external signs.

Distributor caps may not have the same trouble since the path through the cap from the HT is much longer. The arm only has the thickness of bakelite from the brass bit through to the spindle.

Martin

Re: Re: Re: Re: Re: Pattern Rotor Arms

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Thanks for that Martin.

I wonder if, as you have so many examples, it might be fun to slice one through to see if that tells anything????

Mike

Re: Pattern Rotor Arms

Thanks for the input lads, there does seem to a serious case of goods not fit for purpose here, both within the A7 movement at the larger Classic car movement in general. I read in the April 2006 edition of Practical Classics today about someone else who had problems, diagnosed originaly as a faulty fuel pump, then eventually the 'new' rotor arm.

Apart from faulty goods and lack of customer service
"... we've never heard of this complaint before...",
".. but I rang you last week about the same thing",
"Oh did you, well it's not on my screen.....".

There's the buggeration factor and the expense such as the Practical Classics Fuel pump (+ labour?) above.

Naomi

Re: Re: Pattern Rotor Arms

Hello everyone,
There was also a reference in "Practical Classics" some time ago (probably 18 months or so ago)which recounted the poor insulation problem in current manufacture Rotor Buttons.I will try and dig the item out because it fairly extensively canvassed the problem, although it was obviously all in vain.

BLR

Re: Pattern Rotor Arms - HT Leads

There appears to be another ignition problem! ---- Chatting at the happy hour session this evening the subject was HT leads. A couple of the lads say they seem to be shorting THROUGH the insulation, rather than along it, all are copper cored HT leads, this was confirmed by our local RAC chap in to watch Sky telly (off duty for the happy hour).

The Jag Owners Club had put them onto Durite HT leads as a way of solving the problem, which worked apparently.

Any views? apart from looking under the bonnet in the dark - hey, rest easy lads.

Naomi

Re: Re: Pattern Rotor Arms - HT Leads

Except as detailed below,I have had no trouble with HT Leads on older cars, but haved had real difficulties with the leads fitted to my "modern" Holden Commodore which has some sort of high energy ignition system, which beggars my understanding, and has what I could best describe as "trunked" HT leads. This gives regular failure and the "disease" is well known to the Service experts as the leads "crossfire" through the insulation. I had trouble during new car warranty with this problem.

Now I know the trouble, I watch for the 'corona display' under the bonnet at night, and the odd 'miss' (I am always on the lookout for an 'odd miss!)

I have used "MagnaCore" leads in my Rover 105S, which was giving trouble at one stage, although anno domini, rather than simple insulation failure would have been the base cause. Plus the fact that the Plug leads are "cooked" in a tube which runs the length of the engine.

Still can't find the Practical Classics item but will keep reading.

BLR