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MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - rotor arms

Who is it makes those hi-quality distributor rotor arms - blue or red in colour or something?
Daniel Thirteen-Twelve

I think his name is Jeff Sclemmer at Advanced distributors here

http://www.advanceddistributors.com/
Robert (Bob) Midget Turbo

Mini Spares stock them.
But isn't it time you went crank fired ignition Daniel?
Brad (Sprite IV 1380)


My red one came from the Distributor Doctor. Excellent quality and service...

http://www.distributordoctor.com/
MarkH1

I just got a load from Nick Swift... I also bought some of his external condensors too, they are just fantastic....!

http://www.swiftune.com/

Mark.
M T Boldry

Mine also came from the distributor doctor

http://www.distributordoctor.com/

very pleased with both the rotor arm and the condensor which I bought from him.


John Collins

I bought 2 blue ones from Mini Spares (the car has run a 45 series distributor body for at least 15 years).

There are things much higher up on my wish list than a crank fired ignition system though I might do this one day.

I'll probably buy a couple of red rotor arms in due course.

Daniel Thirteen-Twelve

Heard somewhere that you can get a rotor arm that doubles as a rev limiter. Does it work? Whats the part number?
S.A. Jones

I did a little research on the subject of rotor arms a while back and put an article in Masc magazine 'Mascot'. A member who experienced the problem, and whose car I fixed, then passed the article on to West Sussex MG owners Club for their magazine 'Main Gear'.
Apparantly recently manufactured rotor arms have been failing because the typical 'mix' used in the moulding process, nowadays, contains more carbon blacking and is therefore more conductive. It has been found that the rivet which holds the brass contact inlay into the moulding is slightly longer than original bringing it too close to the spring clip on the underside. The high tension current averaging 30000 volts is always looking for the easiest route to earth and shorts out from the tip of the overlength rivet through the reduced thickness of the more conductive plastic and the spring clip on the underside of the rotor arm to earth out down the dizzy shaft. This results in no spark at the spark plugs. This problem sometimes rectifies itself on cooling but then re occurs with increasing frequency until the rotor permanently short circuits.
Aldon & Moss can supply good rotors maybe you were unlucky with the Bosch item. Distributor Doctor now makes a rotor arm without the rivet. www.distributordoctor.com
Alan.
Alan Anstead

"a rotor arm that doubles as a rev limiter"..sounds like one that's breaking down!! Check out my thread, missfire cured!

If you want a rev limiter, buy a rev limiter! They are not expensive and work well, and are adjustable.

The rotor arm that failed on me was a Bosch one, supplied by Aldon very recently. I have to say though, Addon were fantastic to deal with, so I have no complaints at all with those guys.
Robin Cohen

Actually Robin, I was refering to this book
http://books.google.com/books?id=V3STrysMNjQC&pg=PA59&lpg=PA59&dq=lucas+rev+limiter&source=bl&ots=p5HQZgg0na&sig=Mt2mkzojrZ58r86NLHnXXpdzpKA&hl=en&ei=z_-QS9W-N4_UM6jC_fcM&sa=X&oi=book_result&ct=result&resnum=5&ved=0CBAQ6AEwBA#v=onepage&q=lucas%20rev%20limiter&f=false
S.A. Jones

Seth,

The author of that book is the person who posted just before your previous post.
Gary Lazarus

Yes they do exist - albeit I haven't seen one for years - I'm not sure/don't recall whether they were ever produced for Lucas dizzy's

The means of operation is that centrifugal force would appear to cause the spark to be cut at high revs... however I don't know how you can guarantee that a consistent rev limit would be applied - I suspect that cheap micro electronics has rendered these devices obsolete (along with points and condensors on race engines...)

Personally I certainly wouldn't use one as a means of protecting an expensive tuned engine from overevving...

JB
James Bilsland

I think rev-limiter rotor arms were used by Lucas before being used on other cars. They are not very adjustable as the cut out point varies according to the weight of what I'll call the bob weight (possibly 3 settings). I first saw one while working at a Classic Jag garage in the 1970s (while still at school).

Photo attached for anyone YET to buy a copy of the Spridget book from www.veloce.co.uk






Daniel Thirteen-Twelve

There was one of those in my ignition when I bought my midget. Took it out immediately and was planning to replace someone else's rotor with it just for laughs. Never came to it, kinda lost it.
Alex G Matla

The rotor arm you want that has a revlimiter on it is in the Lucas distributor on the 1558cc Lotus engine on the Lotus Elan and Lotus Cortina. Off hand I could not tell you what the rev limit was but it was like turning the ignition off when it cut in . Modern technology will give you a smoother cut off.
R Mcknight

As mentioned by R McKnight, the rev limiter was fitted to the Lotus Twin Cam engines with the Lucas 25D distributor, the rev limit was 6500 rpm although this could be changed by the addition or removal of a little screw on the counter weight of the rotor. I used to have loads of them that I had taken out of Twin Cams (they worked better to 8k), but the Lotus originality guys loved them so they went on ebay over a period of time.

Mark.
M T Boldry

Bosch also made rev limiting rotors for Porsches back in the 70's.

We used them in 356 race cars back in the day.

Dave
Dave Rhine ('78 1500)

This thread was discussed between 28/02/2010 and 07/03/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.