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Hot running - points/dizzy cap/rotor arm issues & checks
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welshrover



Joined: 09 Aug 2011
Posts: 326

PostPosted: Thu Feb 21, 2013 11:27 pm    Post subject: Reply with quote

ive heard no end of these new so called lucas rotor arms being problematic .its the carbon /plastic theyre made of today (cheap) the red ones are no problem at all .the dizzy doctor sells very good original lucas condensors the historic rally boys use them .. Cool
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Fri Feb 22, 2013 8:54 am    Post subject: Reply with quote

trampintransit wrote:
BTW..never heard about black rotor arms being problematic...anybody else heard of this?


Its not a problem with all black rotor arms, and equally just because a rotor arm is red is not guarantee its good!

However as demand for rotor arms has plummeted over the last 25 years, firms like TRW (Lucas) sub out to firms who can handle low volume at lower cost. Modern injection moulding mixes tend to favour a higher carbon content as this adds physical strength but increases the chance of potential electrical conductivity; ironically its not cheaper! . These arms can electrically break down and this is emphasised when they get hot, the HT leak, presents very similar symptoms to fuel starvation. The new "red" arms also dispense of the brass rivet that attached the conducting arm to the body, and use less carbon in the mix. The rivet acted as an electrical bridge accelerating HT leak.

About 15 years ago I was convinced that modern petrol was causing fuel evaporation in my Morris 8; the car would always start fine from cold, I could drive for about 10 miles and then it would misfire, eventually it would get so bad it was un-drivable. I would have to leave it for over an hour before it would start Shocked

I put an insulator on the carb, re-routed fuel pipes, used different petrol all to no avail.....it was the rotor arm...

A get you home fix; can be to reduce the plug gaps, the plugs will now fire at a lower voltage, thus reduce the chance of an electrical breakdown of the arm.

Dave
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Fri Feb 22, 2013 10:08 am    Post subject: Reply with quote

trampintransit wrote:
BTW..never heard about black rotor arms being problematic...anybody else heard of this?


http://www.oldclassiccar.co.uk/forum/phpbb/phpBB2/viewtopic.php?t=8225&highlight=red+rotor
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Fri Feb 22, 2013 10:16 am    Post subject: Reply with quote

I knew there was a problem with loads of poor quality rotor arms ( had a dud on a Peugeot 504 coupe about three years ago , which I also wasted ages on having diagnosed as a rich running whilst hot problem )
What I didn't realise was that colour was a clue to the crap ones. Certainly Ill take the tip above and source only from the Distributor Doctor.

Anyway....I'll do this head off and decoke, and throw a few quid at the ignition system when it goes back together........
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Fri Feb 22, 2013 11:12 am    Post subject: Reply with quote

The insulation deterioration of HT components is to be expected and the norm;as with anything the better ones will last longer. Rotor arms, distributor caps, HT leads even coils should be considered as consumable.

Many faults are due to the cumulative effect of a number of ignition components being less than perfect;and so the vehicle may be running less than perfectly long before a misfire or poor starting is noticed by the driver. Often the carburettor is wrongly blamed and adjusted in an attempt correct the problem.

The challenge we have, is that unlike a mechanical component where we can measure wear, a leaky distributor cap, rotor arm or HT lead can appear perfect, yet they all may only be performing at 80% with a resulting misfire, changing any one of them may get rid of the misfire, but the vehicle will still not be running optimality.

I am an advocate of the adage if it ain't broke don't fix it however I treat the dizzy cap, rotor arm and leads like oil, filters and plugs; they don't need changing as frequently as the latter, but should be part of routine maintenance.


Dave
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Fri Feb 22, 2013 1:01 pm    Post subject: Reply with quote

I have adopted a habit of testing the rotor arm if I ever need the distributor cap off.
Very simple and obvious, but it seems not a well known procedure.
Perhaps procedure is the wrong word.
Just in case. Remove the centre HT lead from the cap. Hold the end close to the rotor arm (without removing same) and making sure the points are closed, flick them open. If any trace of a spark jumps to the rotor arm - scrap it!
Probably everyone on here knows, but then a lot of people think a "healthy" spark at the points says the condenser is fine!
Jim.
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Rick
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Joined: 27 Apr 2005
Posts: 22429
Location: UK

PostPosted: Fri Feb 22, 2013 1:06 pm    Post subject: Reply with quote

Jim.Walker wrote:
I have adopted a habit of testing the rotor arm if I ever need the distributor cap off.
Very simple and obvious, but it seems not a well known procedure.
Perhaps procedure is the wrong word.
Just in case. Remove the centre HT lead from the cap. Hold the end close to the rotor arm (without removing same) and making sure the points are closed, flick them open. If any trace of a spark jumps to the rotor arm - scrap it!
Probably everyone on here knows, but then a lot of people think a "healthy" spark at the points says the condenser is fine!
Jim.


I don't think I've ever tried that, thanks for the reminder Smile

RJ
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Rick
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PostPosted: Fri Feb 22, 2013 1:07 pm    Post subject: Reply with quote

I think I'll move this to the electrical category, and tweak the title, as there's some handy info in this thread - thanks all

RJ
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Jim.Walker



Joined: 27 Dec 2008
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Location: Chesterfield

PostPosted: Fri Feb 22, 2013 2:35 pm    Post subject: Reply with quote

I think the brilliant on is reducing spark plug gap. So obvious as a possible "get you home", but how many people would think of it?

Another Not very obvious one is to scrape insulation material (such as distributor caps and rotor arms) where "tracking" is visible. Usually identified as a crack it is often a carbonised track made by escaping electricity which looks like a crack, scraping the tracking off with a pen knife or similar sometimes/often gets things working again. At least for a while.
I have "recovered" quite a few vehicles by this treatment and once completed an entire shift with a taxi after I had been stranded miles from anywhere (before mobile phones and out of radio range).
Jim.
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trampintransit



Joined: 09 Aug 2010
Posts: 166
Location: Edinburgh

PostPosted: Thu Jul 04, 2013 5:06 pm    Post subject: Reply with quote

It was the rotor arm.....!!!!!
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