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Second Failed Ignition Rotor in 100 miles????

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RobT

RobT

Jedi Warrior
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I just replaced the second failed distributor rotor on my TR250 in less than 100 miles. The first one went on the road, and this more recent one as I was tinkering with the mixture on the carbs while in the garage. I purchased the rotors several months apart - the first was Lucas and the second one was a Bosh unit from Vic Brit, so is not just a bad batch. Am I unlucky or could there be a problem with my distributor? Alignment or worn shaft perhaps? I have a Lucas sports coil and electronic points, so not sure if that is over-stressing the dialectric insulation.

Any thoughts anyone?

Thanks,

Rob.
 
I just went thru a similar problem with my TR3.

I replaced the system with a petronics (sp?) unit.

I think it may have had something to do with resistance, but I didn't delve into it because the Petronics cleared it up.
 
There is no reason the Pertronix should have changed the life/operation of the rotor as it's still doing the same job, presumably with the same cap and coil.

You didn't mention how the rotor failed. Did the brass melt or burn? Did the bakelite plastic fall apart? Give us a few more details of what happened.
 
[ QUOTE ]

You didn't mention how the rotor failed. Did the brass melt or burn? Did the bakelite plastic fall apart? Give us a few more details of what happened.

[/ QUOTE ]

No visable signs of damage or wear on the rotor - the leading end of the arm that contacts posts on the underside of the distrabutor was still clean (no corrosion or pitting from sparking accross the gap). In fact the only way I figured out it had failed was to replace it. I assumed the insulation failed or the spark was tracking to earth (although cleaning the rotor insullation had no effect).

Its all a bit of a mystery to me.

Rob. /ubbthreads/images/graemlins/confused.gif
 
I wonder if you might have a short that you fix every time you pull the cap off and replace the rotor? Condensor wire? Low Tension wire to the coil? Flaky condensor? Sticky brush thingy in the cap (the thing that connects to the rotor) ???

Just a thought....
 
[ QUOTE ]
I wonder if you might have a short that you fix every time you pull the cap off and replace the rotor? Condensor wire? Low Tension wire to the coil? Flaky condensor? Sticky brush thingy in the cap (the thing that connects to the rotor) ???

Just a thought....

[/ QUOTE ]

Thanks for the suggestion Jim - I thought it could be something odd like that too. But when I swap in the "bad" rotor, the car does not run, put in the "good" one and away she goes! Did this a couple of times to be absolutely sure it was indeed the rotor. And having electronic (sometimes called "pointless")ignition there is not much under the distributor to go wrong.

I think 70% of the problems I have had with Triumphs are related to electrics and a goodly share of those are high-tension ignition issues.

Rob.
 
Could this be a conflict caused by having rotors from different manufacturers, and a cap from still another manufacturer?
Maybe the "good" rotor matches up with the cap better than the other "bad" rotor?

When it comes to caps & rotors, I always make sure I get a matched set ie: both from the same manufacturer. For example I would'nt mix a Bosch rotor with a Beck Arnley Cap.

course that's just me
 
I have had my rotor fail twice for me. All of these came from Moss. I did find that you can go to Auto Zone and they can order rotors. I found this out when I was stuck from home on the first one. It is still in use wtih many miles on it. I will always carry extras with me. I had Petronics installed on the 2nd one. I had the Petronics fail where it would only run on one cly. took it off and installed the points back on and found it ran beter with points than with the Petronics. I found the pickup hand come apart when installed the points back. Found all the magnets and glued the pickup back together reisntalled the electronics and found that it had gone bad and only letting one cly. fire. I was wanting to try to confirm how my car ran with the points and the Petronics. I do not think the car as good with the Petronics installed as with the points installed. I may try one again to find out
 
Hi Rob,

You mentioned in your 1:07 pm response that you have pointless ignition. What type? Has the coil been changed, too? If so, are you using a ballast? Have the plug wires been changed recently?

Some other good ideas and food for thought in the previouis responses.

I agree with Tom, don't like to mix brands. In fact, all my ignition from coil through plug wires is Mallory (currently daul point, but I'll likely change to 100% electronic in the near future). This doesn't absolutely guarantee all will always work as it should, of course, but I figure there's a higher percentage of success likely than if I were to mix a bunch of different manufacturers' parts.

If you are running an electronic module, you might try swapping points back in just to see if that makes a difference.

Cheers!

Alan
 
When you cleaned the rotor's insulation... you didn't use anything abrasive did you? You didn't wire brush it did you? When I clean a rotor I typically "sand" the brass top surface at the center and the outer tip that approaches the posts in the cap. On the GT6 I have the Delco dizzy and that is different in that it has a blue-tempered spring steel finger on the rotor to contact a fixed carbon brush in the cap. I can't do much with it.

Take a careful look again at the cap and in particular the center contact. As others have mentioned, mixing brands of caps/rotors can cause bad results. It could be that the center contact in the cap doesn't have enough travel OR the rotor isn't sitting "high" enough on the dizzy shaft. Perhaps all you need is a little cardboard disk shim inside the rotor to position it about 1/32" higher?

It's very unlikely that the rotor is providing a path to ground that would keep your engine from running unless it's got a crack or surface scratches that are carrying the current. I can't imagine a situation where the coil voltage was so high that it damaged the rotor. If you have calipers, make some measurements of the cap and rotor to insure that things are where they are supposed to be. In fact, take the "good" rotor and measure it and the "bad" one. Try and determine where their top "contact" surface is relative to the depth of the center bore attaching it to the dizzy shaft.
 
Alan and Doug - thanks for the helpful tips. I did match the rotor and cap (Lucas cap & rotor the first time, then when that rotor failed I swapped out the rotor, cap and leads with Bosh components). Also Lucus sport coil (no bias resistor) and electronic ignition (have to check which brand - but has the optical detector in the distributor and a seperate box for the electronics). I will take a look at the center contact point from the distributor and make sure that is looking good. Shimming it up a tad is a good thought. As for cleaning the rotor - I only wiped it down with a clean cloth - no abrasives.

Anyway I have a new rotor in there now and two spares in the boot (trunk). Isn't that why British cars have boots anyway - to keep the spares.

Thanks for the helpfull advice - I'll let you know if it goes again.

Rob.
 
Rob--It has been my experience that the caps & rotors offered by the big 3 vendors are of questionable quality. After going through many of each, I found the Echlin branded bits from NAPA are excellent. Worth a try.

Also, if you are running high-performance ignition cables (like Magnecor KV85's) with wide plug gaps, you will shortly track the distributor cap, resulting in bad misfiring. Our caps were not designed to deal with the high voltages such cables carry. The only solution is to gap the plugs down to around 0.030.
 
Sounds to me like you have definitely determined the problem to be the rotor itself. Seeing as when you swap it back it doesn't run. You could check the rotor for a ground by checking the continnnnuity between the business end of the rotor and ground when installed. Wiggle it around a bit to see if it changes. Of course that really only confirms what you already know to be true. However, it might give a clue as to what caused two rotors (awefully long odds there) to fail. My guess is internal cracks in the bakolite causing a short. Might be a heat problem.
 
The optical electronic ignition sounds like the Crane/Alison ignition. I ran one for years in my GT6. They work well, but don't get the little black box wet.

Ohming out the bad rotor may not show any problem when using a regular meter. High voltage shorts often involve a "tunneling" failure that is only detectable when high-voltage is present. Think of it the same way you'd think about a cracked dizzy cap. You might see a crack on your dizzy cap and it would still measure OK with a meter... but place it in service and it would short to ground along the crack. (In industry we check for this with what's called a High-Pot tester. Sadly, once you find a problem with a High-Pot tester the test makes the situation worse).

This is just a general question... what condition is your dizzy in? Do you detect a lot of slop or play (wobble) in its shaft?
 
Hard to believe. My TR-7 doesn't have a standard rotor [it's a Delco unit] but my '66 Land Rover runs the Lucas distributor and points/rotor/cap. I've put 300,000 + miles on the car and have replaced the ignitions components often. I've NEVER had a rotor fail that way - one cracked once on a '72 Fiat Spider I owned in the '80's, but that's been it. It's hard for me to believe that that rotor is the problem. If they're not cracked in any way, then you have an electrical problem that's running through the rotor.

Good luck, though.

Jeff
 
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