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MG MGF Technical - Dizzy cap & rotor arm again!

Have owned my F from new for about 8 years but cover relatively low mileage. I have just replaced the rotor arm and dizzy cap for the 3rd time - the last time being about 12 months ago. From the archives, this seems to be quite a common failure. Can anybody tell me (or have any thoughts on):
1. Whether there are better quality aftermarket components/modifications to improve the reliability?
2. If failure of the components is related to engine compartment heat build up?
3. If k series engines on other rovers/mg's suffer the same?
4. If there is an underlying issue here?
Thanks people!
P Shuttleworth

The mounting for the rotor arm is glued into the end of the camshaft, which gives potential for misalignment (and the glue can fail), I'm wondering if that could be a contributing factor? Are the caps failing more on one side than the other? If so, it may be worth investigating whether the shaft is absolutely straight in the camshaft hole.

I have to change my rotor arm ,on average,every 2 months, or 400 miles,the engine starts to misfire ,or even worse the engine dies,the last rotor arm ,I bought is different in appearance ,hopefully this mod will may the rotor more robust. see attached picture.


simon connolly


That should read 4000 not 400 miles.

simon connolly

Hi Simon,

something fishy about your distributor failures, my 1997 vvc has done 148,000 kms and never had a cap or rotor arm replaced. Are you sure the miss-firing is'nt due to the effects of rain entering the engine bay via the vents rather than faulty distributor? My car misfires a little after rain (not that we have seen much here in Melbourne lately). Just a thought.

Cheers Alan

P.S. I also have a 1995 K series engined Caterham, no problems there either.
A.J. Mackew

I have changed coil, leads,plugs,cap,rotor arm ,ran another earth lead to chassis.I may have a problem ,but what is it?If you check archives of this site, and other websites,you will see there is a problem with rotor arms,hopefully the new owners have sorted the rotor arm problem .

PS the rotor arm with the orange track is the new type rotor arm.

simon connolly

What make/where are you buying your arms from?
Ralph Gadsby


I have bought from Rover as well as from 'after market' spares suppliers.

simon connolly

I had this problem and the rotor arm kept burning out every 2-5 weeks. A friend of mine who is an old machanic told me it can be caused by the plug gap. I thought he was talking rubbish, but changed the plugs and set the gap and I have not had the problem since. You can look on my threads to see how long it has been without problems. try it and maybe you will be as amazed as I was
B Smith

Thanks for comments guys. My problem is always burnt out carbon bushes on the dizzy cap and burnt insulator on the rotor arm. The last few replacements have been from normal motor equipment shops rather than OE parts (naturally, since Rovers demise). I have however seen unipart dizzy caps on ebay made from blue plastic rather than black. Any difference?
P Shuttleworth

B Smith,
I have checked plug gaps,all ok ,now changed to NGK BCPR7ES.

P Shuttleworth,
RE: burnt out bush on distributor cap,is the splash guard fitted? ,if so?,you could fit a washer behind the cap and in front of the splash guard,on each screw,I have found the dizzy bush lasts longer and the contacts on the dizzy do not burn on the edges.
simon connolly

Maybe the clue is in the term "Burnt out" - I think B Smith might be on the right track - I too had a similar problem and followed his thread with great interest. I was amazed to read that too large a gap causes the HT system to operate at a higher voltage, leading to problems over time - in his case to burn out his rotor arm, in mine to burn out the distributor cap. I put mine down to a cheap cap which only lasted a year (perhaps the 'larger gap' can exist in a poorly made dissy cap, forcing the spark to jump further to each terminal and causing burn out??). I don't really know but I'm sure someone will be along to explain the phenominum. I also noticed that moisture got into the cheap cap far easier than the genuine one.
Mark Clayton

Landrover parts are available, and are OEM quality - and indeed this is what Rimmer Bros do. Fitted a replacement set this summer - although the old dizzy wasn't in too bad condition; however one of the HT leads had been shorting through poor connection.

I have purchased another dizzy and rotor arm off fleabay - whether this was a good idea or not, I guess we'll see.

BTW - the need to replace the rotor arm every couple of months is way too excessive. If the components are burning out this quickly, there must be another problem. If the spark plugs are in good condition, and have the correct gap, then perhaps there is a problem with the HT leads themselves? I have magnecor leads on my car - and they've been absolutely reliable for over 8 years now...
Rob Bell

On Monday,I went to see Dave at Queensway garage Horsham,He found a 3v drop on the 12v feed to the primary side of my coil,the coil was also pulling half an amp more,It is something that I could not test for. Dave's test equipment can test many times a second.I have ran a 'clean' 12v feed from the ignition switch to the coil.The pull away is more smoother with less throttle.Fingers crossed.The other circuits being fed from the existing feed seem to be ok,with no apparent faults.

simon connolly

This thread was discussed between 20/10/2008 and 21/11/2008

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