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Ignition Rotor...WTF?!

- - - - - Defender D90 NAS 3.9L ignition

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11 replies to this topic

#1
TigerDan

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I was working on a D90 the last couple of days, a '94 NAS truck so 3.9 V8-powered. I noticed right off that it had the cheap aftermarket blue plastic distributor cap so we yanked that off and reinstalled the old Lucas cap that he had fortunately kept as a spare, as it was still in good shape and just need a little cleaning/de-carbonizing of the contacts. He had tossed the rotor and I didn't have any spares with me, so I pulled the genuine Lucas rotor off my RRC, gave it a quick cleaning and swapped him.

 

Drove my RRC about 8 or 9 miles around the are where he lives, and then last night headed for home in the pouring rain. Got about 6 miles from his house when my engine shut off as if I'd just turned off the key. Worked on it for a bit and then threw in the towel, he came down and towed me back to his house where I worked on it again this morning. Checked (again) for spark from the coil, looked good, had fuel, could hear the pump running, checked all wires and even pulled the distributor, checked timing chain as well as I could to see if it had jumped time (didn't really think so as it has a double-roller timing chain with all steel gears, not the stock chain with the fiber cam gear.)

 

Even tried to start it with ether. wouldn't even pop so it had to be ignition-related. Finally, out of desperation I swapped his old rotor back into his D90 and took out my Lucas unit, and his 90 suddenly wouldn't start. Put my Lucas back into my RRC and lo and behold, it fired right up! Ran a crappy at first as it was pretty flooded from all my attempts to start it, but it settled down and smoothed out to it's usual purr after a bit.

 

So here's the question for you electrical engineer types (and other people who are way smarter than me!)...how can a part as simple as a rotor, with no moving parts and consisting of a piece of plastic (or is it Bakelite?) and a simple strip of brass who's only job is to conduct spark from the center electrode of the distributor cap out to the various terminals leading to the plugs, suddenly fail and lose all conductivity? I can see it getting dirty and building up resistance, but this one was freshly cleaned. There's no visible reason for it not to work...I'm still scratching my head in wonder and frustration.


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#2
GraemeWare

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So here's the question for you electrical engineer types (and other people who are way smarter than me!)...how can a part as simple as a rotor, with no moving parts and consisting of a piece of plastic (or is it Bakelite?) and a simple strip of brass who's only job is to conduct spark from the center electrode of the distributor cap out to the various terminals leading to the plugs, suddenly fail and lose all conductivity? I can see it getting dirty and building up resistance, but this one was freshly cleaned. There's no visible reason for it not to work...I'm still scratching my head in wonder and frustration.

 

Dan,

 

I'm one of those electrical engineer types ...

 

The failure mode is not the failure of the piece of brass to conduct, it is the failure of the inside of the rotor arm which causes a short to ground (or 'earth' if you're working on a Land Rover!).  The spark is therefore grounded through the rotor shaft.  In other makes, there can be a built-in resistor in the rotor arm, but not in this case.

 

Regards,

 

Graeme


Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#3
dcproven

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You should be able to measure that with the engine off and an ohm-meter... but sounds about right



#4
GraemeWare

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You should be able to measure that with the engine off and an ohm-meter... but sounds about right

 

Only if it is a direct short.  Even a tiny gap will measure open to low voltage dc, but to HV it can be low impedance.  A mega tester (insulation resistance tester) could be used though.  I always carry one ....

 

Graeme


  • dcproven and RedRover like this

Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#5
DHappel

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This is exactly what happened to Paul's RRC at Sedona last year. We searched and searched before borrowing another rotor from Bill Burke to test with. Paul had just put in new components prior to that trip as PM only to grt burned by aftermarket!

Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#6
Timbo

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I've read that there are some very bad cheep rotors floating about for rover v8's. the story I heard was that to get the same color as the genuine they impregnated the plastic with graphite.

If true, then could it be that the graphites causing a short ? Pretty intense spark going through there that's going to find the path of least résistance

#7
GraemeWare

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I've read that there are some very bad cheep rotors floating about for rover v8's. the story I heard was that to get the same color as the genuine they impregnated the plastic with graphite.

If true, then could it be that the graphites causing a short ? Pretty intense spark going through there that's going to find the path of least résistance

 

Another urban legend.  The black pigment is "carbon black" which is an insulator (it is used in rubber, for example, and rubber gloves are used when working on high voltage electricity).

 

Regards,

 

Graeme


Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#8
GraemeWare

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..... Finally, out of desperation I swapped his old rotor back into his D90 and took out my Lucas unit, and his 90 suddenly wouldn't start. Put my Lucas back into my RRC and lo and behold, it fired right up! Ran a crappy at first as it was pretty flooded from all my attempts to start it, but it settled down and smoothed out to it's usual purr after a bit.

 

Dan,

 

Did I mention that RoverWare.US normally stock genuine Lucas items for $9 each?  We have had a bit of a run on these today .... could you start posting about bad drive shafts, or ball joints, or drag links?

 

Regards,

 

Graeme


  • dcproven and Jethro like this

Graeme Ware -- San Carlos, CA

1990 Range Rover Classic - LT230 Transfer box, Warn winch, 2" lift, 235/85-16 Dunlop MUD Rovers, "Blue Submarine"
1996 Discovery 1 (R380 Manual Transmission, Ashcroft under-drive, RoverWare rear bumper, 33x12.5-15 BFG ATs) -- we call her "Katrina" -- Fordyce 7.5 mile survivor
1999 Discovery 2 (D1 CDL Linkage, 265/75-16 BFG A/T KO, RoverWare front and rear bumper)
1993 Jaguar XJS convertible; 1971 Triumph GT6; 1959 Morris Minor convertible
other assorted British pot metal ...


#9
TigerDan

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 Sure. And how much is my commission? :P


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#10
lithium1330

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So, lesson learned is genuine parts for anything fuel and electrical related. Got it.


Chris

#11
DHappel

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And anything with a CV joint, at least on the newer rigs. Or OEM anyway....Kinda like that Roverware place has.

Don
'07 LR3 HSE/HD - slightly non-stock

'96 D1 - even more non-stock


#12
JFuller

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Roverware also supplies top shelf P38 parts like door handles (if you own one you know why they are needed), gas struts (even for the center cubby!!) and other hard to find bits on this side of the pond.  Thanks for a good customer service!







Also tagged with one or more of these keywords: Defender, D90, NAS, 3.9L, ignition

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