Triumph Sports Cars

engine swaps and other performance upgrades, plus "factory" V8s (Stag and TR8)

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rtope
M. Ray Tope

(9 posts)

Registered:
08/08/2010 01:35AM

Main British Car:


Distrbutor Rotor failer
Posted by: rtope
Date: May 14, 2013 06:51PM

Has anyone had this problem with their TR-8 (1981)?? During some testing of the system after the car went dead it was found that no spark was going through the distributor to the plugs, We installed another rotor & the motor came back to life. I got the car home and it sat in the garage for a couple of days and as I was heading out to a photo shoot of the car it did the same thing again. This time I removed the rotor, witch after about 45 minutes was still very warm, and just reinstalled it and the motor fired right up but sounded like the RPMs were fluctuating. It also acted like the cylinders were being mixed up in the order. The distributor was installed new out of the box about a year ago and had not given me any problem.

Could their be a problem with the ECU unit or one of the three control modules be hind the glove box???

I'm very open to suggestions since I want to use the car this year since it went though a round of refurbishing most of last year. Anyone can contact me directly at the attached email address.

Regards
Ray Tope


mdale8
Mike Dale
Milan, Mi/Oshkosh, Wi
(1 posts)

Registered:
10/06/2010 09:49PM

Main British Car:
1974.5 MGB GT V-8 Buick 266 (215 stroker)

Re: Distrbutor Rotor failer
Posted by: mdale8
Date: May 15, 2013 10:14PM

Ray,

Some guesses for you, as I do ignition systems for a living. None of this is specific to the TR, but is generally true for ignition systems.

It sounds to me as though you have arcing under the distributor cap. That is the logical answer for both the failed rotor and the seeming misfire, out of sequence fire. I am betting if you look at your cap you will see spider webs on the underside where the high voltage has been arcing. The cause of this is likely to be a bad plug or bad spark plug wire. Most plugs will fire in the 8Kv to 22 Kv range, sometimes higher depending on compression ratio and vehicle/engine loading. When the plug cannot fire (because the wire is bad, the wire fell off, there is something really really wrong with the terminals on the ends of the wires) the high voltage wants to find a way home. This can sometimes result in an arc through the rotor to the distributor housing (common on GM HEI systems) or it can arc to a tower it is not supposed to go to inside the cap.

This whole problem can be made worse by the very common aftermarket mega spark blaster coils that produce really high voltages (or at least claim to). All that voltage needs to get home and the rotor, cap and wires are the weak points in the system that are likely to fail when there is a system problem. Generally caps/rotors and wire systems are good for 25 to 30 Kv. Really high voltages don't help much in the first place as the voltage across the plug will only rise to the required amount to fire it. Usually less than 30 Kv in all but extreme cases.

The classic solution for this is to get this engine hooked to an oscilloscope that will display for you the firing KV. You'll see in a minute which cylinder is asking for all the zap.

One other specific thing to think of. The distributor of course connects via the jack shaft to the camshaft. If you have excessive pressure in the crankcase, it can cause gasses to vent up into the distributor. This can be anything from excessive blowby, an oily exhaust gas like material, water vapor etc. This can coat the rotor and the underside of the cap to get coated resulting in the arcing you describe. Not as likely as a bad wire, but do look under the cap for unusual contamination as well as the spider webs. Good luck

Mike Dale


rficalora
Rob Ficalora
Willis, TX
(2764 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Distrbutor Rotor failer
Posted by: rficalora
Date: May 15, 2013 11:46PM

Great answer and welcome Mike!


88v8
Ivor Duarte
Gloucestershire UK
(1041 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Distrbutor Rotor failer
Posted by: 88v8
Date: May 16, 2013 04:04AM

There has been a lot of problem with sub-standard rotor arms in the UK. I only know of this in the TR6 but it could also affect the V8. Good arms available from Distributor Doc
[www.distributordoctor.com]

You might also check the little furry wire inside the distributor that carries the 12V to the points. This can fracture or come loose with advance/retard baseplate movement.

More likely to be the sort of problem Mike has highlighted though. Sometimes when HT is tracking where it shouldn't, you can see it by running the engine in the dark.

Ivor


roverman
Art Gertz
Winchester, CA.
(3188 posts)

Registered:
04/24/2009 11:02AM

Main British Car:
74' Jensen Healy, 79 Huff. GT 1, 74 MGB Lotus 907,2L

Re: Distrbutor Rotor failer
Posted by: roverman
Date: May 16, 2013 11:46AM

Since this "seems" to be breaking rotors now, I would change brands,(better), and check very closely for distributor shaft end and side play. Either one will break a rotor. Good Luck, roverman.


glenc
glen crawford

(1 posts)

Registered:
02/12/2011 07:53PM

Main British Car:


Re: Distrbutor Rotor failer
Posted by: glenc
Date: June 28, 2013 09:19PM

another other possibility: the rotors are fine but the Lumenition is cooked.

I had similar symptoms and replaced the Lumenition with the Crane replacement ($170 or so) and all is good since 2007.

Just for fun, try one of the 'bad' rotors while the car is running right.

Probably not the ECU - once they go bad, its lights out (but the problem is usually just a bad solder joint somewhere in the metal box...)

ps my car is an 81 tr8 as well...great drive



Edited 1 time(s). Last edit at 06/28/2013 09:22PM by glenc.


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