Rough running Silver Shadow

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ecurie
Posts: 31
Joined: Wed Feb 15, 2012 3:23 pm
Location: Belgium

Rough running Silver Shadow

#1 Post by ecurie » Wed Feb 15, 2012 3:27 pm

I own a 1979 Rolls Royce Silver Shadow and am experiencing a very annoying rough running problem. At idling speed the car will rock somewhat and the exhaust makes a burbling noise (like a misfire). At speed performance seems normal but you can feel the engine is slightly rough, certainly not what a Rolls should feel like.

I am now in the middle of replacing the valve stem seals on my Shadow and used the opportunity to inspect the spark plugs.
I installed NGK Irridium GR4IX plugs about 2000 miles ago with an electrode gap of 0,6mm. Imagine my surprise when I remeasured them and found the gap to have grown to 0,8mm on all the spark plugs, as the central electrode had eroded. This kind of wear is of course abnormal, and I suppose it will have contributed to the increasing rough running. The strange thing is, it used to be running slightly better with the standard NGK plugs.

In the past I have had difficulty setting the ignition timing : when setting it at 25°BTDC at 1300rpm, it should be 12°BTDC at 650rpm (according to the workshop manual). However I can not get it under 17°BTDC. Absolutely every ignition component has been replaced (leads, electronic ignition, coil, plugs, cap, rotor, plugs, capacitator), with the exception of the distributor itself. Could it be that the distributor itself is faulty ? The weights and springs seem to be working OK, but look quite rusty to me.

I used a Colourtune kit, just to look at the combustion and found it to be very erratic. Somtimes it fired in quick succession and then nothing for a few seconds.

The fact that the plugs have eroded that much in only 2000 miles and the problem with the ignition timing lead me to believe it is an ignition problem and a new distributor might be needed.

If anyone has any ideas about this, I would very much appreciate them as I am getting increasingly frustrated about this ongoing problem and losing the pleasure the car used to give me.

Maaarrghk
Posts: 254
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Location: Earth

Re: Rough running Silver Shadow

#2 Post by Maaarrghk » Wed Feb 15, 2012 5:11 pm

The fact that you can't get the ignition timing closer than 17 degrees throws up what may be a clue here.

Perhaps the distributer has been out before and replaced one tooth out?

Is the coil connected the right way round?

There was a guy featured in PC a few months back who rebuilds distributors - probably a much cheaper option than a replacement item, even if you can find one off a scrapper (probably "spares vehicle" in RR parlance :D ) which might also be faulty.

I think the chap was called "The Distributor Doctor" or something similar. I'm sure you can get his details off t' net.

If none of that works, you may have a carb' problem also/instead.

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Luxobarge
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Joined: Wed Jan 05, 2011 3:12 pm
Location: Horne, Surreyshire

Re: Rough running Silver Shadow

#3 Post by Luxobarge » Wed Feb 15, 2012 5:16 pm

Maaarrghk wrote:I think the chap was called "The Distributor Doctor" or something similar.
You recall correctly - he's highly recommended:

http://www.distributordoctor.com/

I'd agree with your post and also suggest using him - by the time he's finished with it you will at least know that you have a 100% good dizzy.

Cheers,
Some people are like Slinkies - they serve no useful purpose, but they still bring a smile to your face when you push them downstairs.

ecurie
Posts: 31
Joined: Wed Feb 15, 2012 3:23 pm
Location: Belgium

Re: Rough running Silver Shadow

#4 Post by ecurie » Thu Feb 16, 2012 5:36 pm

Hi,

thanks for your replies.

I'll contact the distributor doctor and see what he can do.

ecurie
Posts: 31
Joined: Wed Feb 15, 2012 3:23 pm
Location: Belgium

Re: Rough running Silver Shadow

#5 Post by ecurie » Fri Feb 17, 2012 8:46 am

I checked the distributor shaft today : how much play is acceptable ?
I can rotate it left to right +/- 1-2 mm (that's +/- 3mm at the rotor tip) and up and down +/- 1 mm.
When turning the rotor and letting it jump back you can see the whole weights/spring assembly moving together with the shaft just that little bit.

Is such play in the shaft acceptable or can it cause enough variation in the timing for it to result in the rough running problem ?

Wicksy
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Re: Rough running Silver Shadow

#6 Post by Wicksy » Fri Feb 17, 2012 9:44 am

Speaking for Lucas dizzys you should be able to twist the shaft as you say and end float is always present but how much end float and how far you can twist can only be determined from the data sheet for a particular dizzy.
Because you can feel the spring action suggests that the mechanism is working but the spring tension may now be weak or the weight pivots worn or partially siezed - only a full strip and reference to design data will tell the full story.
I was under the impression that the R-R V8 has a duplex contact set, i.e two breakers - if I am right they need a fairly complex set up.
I also remeber, at one stage, R-R used an anti Knock pick up like a microphone to retard ignition and prevent detonation, does your Shadow have this? - all clever stuff but needing a marque expert to diagnose and fettle IMHO
:D

ecurie
Posts: 31
Joined: Wed Feb 15, 2012 3:23 pm
Location: Belgium

Re: Rough running Silver Shadow

#7 Post by ecurie » Fri Mar 16, 2012 8:52 pm

Yesterday I checked the combustion in 2 cylinders (both fed by a different carb) with a Colourtune. The colour of the spark was ok, so the mixture should be about right. However, on both cylinders the combustion was very irregular. Sometimes nothing for 1-2 seconds, then 3 explosions in quick succession, etc... There was no pattern in this, all very erratic.
Could this misfire be due to a worn distributor (all other ignition components have been replaced) ?

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JPB
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Re: Rough running Silver Shadow

#8 Post by JPB » Fri Mar 16, 2012 9:27 pm

More likely to be an ignition amplifier fault, probably a bad capacitor. Check every discrete one in the amp. Eliminating those, then the trouble must be related to one of the caps in the amplifier chip itself, but at least that's standard stuff so shouldn't be too hard to find. Are Rodley Motors still doing stuff for American V8s?

Distributor wear could cause timing scatter but that in itself wouldn't be likely to create the symptom you described.
J
"Home is where you park it", so the saying goes. That may yet come true.. :oops:

ecurie
Posts: 31
Joined: Wed Feb 15, 2012 3:23 pm
Location: Belgium

Re: Rough running Silver Shadow

#9 Post by ecurie » Sat Mar 17, 2012 4:56 pm

Hi John,

I am not sure I fully understand. I aready replaced the original electronic ignition (Lucas Opus) with a Lumenition one, with no improvement.
I just rebuild the carbs and the idle was much smoother. However, when the engine is at full operating temperature, it began to idle roughly again, the exhaust making very noticeable plopping sounds.
Also, at idle, the revs vary between 600-750 rpm. When revving it hard to 1500rpm and the letting go of the accelerator, the revs drop to 400rpm, almost stalling, before going up again to 650rpm.

As I replaced all ignition components, rebuild the carbs and have trouble adjusting the timing, I'm left with the distributor.

Unless somebody has a better idea (which is very probable).

alfaSleep
Posts: 119
Joined: Mon Nov 21, 2011 7:10 pm
Location: Wallsend-on-Tyne

Re: Rough running Silver Shadow

#10 Post by alfaSleep » Sun Mar 18, 2012 10:01 am

this isn't a Carb/Mixture... (having a wobbly) issue, is it?

Dunno... yrr description seems to have the motor reving up - then droppping off a cliff and fluffing (but not when COLD... starting out RICH???)

You have listed all the 'hard' swap out parts... but 'happy carbs/mixture' can be a movable feast.... oh, for a modern.. they either go or not ;)

Back in the Day..... SunTune agents were in every back lane (ah yes...points/timing/mixture) and would wire you up...and y'd get a print out (usually sold you 4 plugs..lol)

alfaSleep
'the french will always be there when they need you'...Monty ;<)

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