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John Beech
Prolific User
Username: jbeech

Post Number: 280
Registered: 10-2016
Posted on Tuesday, 04 April, 2017 - 05:58 am:   Edit PostDelete PostView Post/Check IP

My new to me 1969 Silver Shadow has a miss. I pulled the plugs and found they were modestly covered with carbon (photo below). The car has 16,000 miles and has never been run much and since plugs are cheap I bought NGK Iridium GR4IX plugs versus the called for Champion N12YC. This, because of their reputed longevity. Anyway, the new plugs seemingly resolved the issue and I was smugly congratulating myself for being so smart when the miss came back . . . within fewer than 100 miles! Now it's like the engine is running on 5 cylinders and because I temporarily resolved the issue by installing new plugs, it has reinforced my belief this is an ignition-related miss. But there's a rub because the plug gap for standard plugs is 0.035" but advice here was to leave the gap alone (e.g. as they came out of the box) at 0.040"). Thus, beyond verifying the gaps were all the same before adding a dab of anti-seize on the threads and torquing them to 15 ft-lbs, I left the gap alone. Anyway, push come to shove I'll pull some spark plugs to check and see if it's misfiring due to carbon build up once again (the engine was running very rich but has now been tuned fairly well). Especially because the NGK website has this to say about gapping Iridium plugs . . .

Q. Do I need to set the gap when installing a new set of Iridium plugs?

A: Maybe. A spark plug part number might fit hundreds of different engines from many different manufacturers. Although the NGK factory will set the gap to a preselected setting, this may not be the right gap for your particular engine. The incorrect plug gap for your engine can contribute to a high rate of misfires, loss of power, plug fouling, poor fuel economy and accelerated plug wear. It is always best to check the gap against the manufacturer's specifications. If adjusting the gap on fine wire or precious metal plugs such as platinum or iridium, be very careful not to apply any pressure or prying force to the fine wire center electrode or insulator as they can be damaged. The gap should be adjusted by only moving the ground electrode.

Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology) you can open the gap from .002-.005".

. . . but frankly, pulling the plugs once again is a pain right now (literally) because of a back injury. And by the way, the forum recommendation wasn't the only thing informing me because at the same time, I also purchased a Pertronix electronic ignition module (with their recommended coil). Frankly, I figured 0.040" would be about right for non-points type ignition because that plus the hotter coil could easily fire the extra 0.050 - but I haven't gotten around to installing this. Initially, this because the points-ignition is working so nicely (seemingly) but now it's because I don't want to introduce another factor/complexity to the equation.

Folks, am I barking up the wrong tree suspecting the spark plug gap? Or is this logically the most likely cause? Last thing, before replacing plugs I replaced the condenser and this didn't affect the issue. Sure, condensers have been known to be bad right out of the box but I'm sticking to the high probability shots, first. Anyway, right now I'm leaning toward replacing the coil because I don't believe the fine wire Iridium plugs would misfire doe to excessive plug gap so quickly. Thoughts?

Carbon fouled Autolite 66 resistor plug - they all look similar
- Note, the shiny threads of the carbon fouled Autolite 66 resistor plug aren't oily

--
John Beech
Tel: 407-302-3361
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1670
Registered: 5-2012
Posted on Tuesday, 04 April, 2017 - 06:25 am:   Edit PostDelete PostView Post/Check IP

Hi John

The handbook states a gap of 0.025". This is because the original coil is 9v and low output. In your situation I would fit the 12v high output coil and replace the ballast resister with a length of wire i.e. 12v all the time. That way you will be sending 40kV down those HT leads, not the original 20kV. The iridium .035" gapped spark plugs will like that. I've been running my car like this for over a year now, through points and with no problems.

Before you fit the pertronix module, make sure you are using the correct HT leads. Zero ohm (copper wire) will destroy it.

Just my tuppence worth

Geoff
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Mark Aldridge
Grand Master
Username: mark_aldridge

Post Number: 420
Registered: 10-2008
Posted on Tuesday, 04 April, 2017 - 08:50 am:   Edit PostDelete PostView Post/Check IP

John, were all of the old plugs carbon fouled ? Also it would be useful to compare plugs 1 & 2 on either bank to eliminate a carburettor fault or setup problem.
Mark
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Martin Taylor
Frequent User
Username: martin_taylor

Post Number: 71
Registered: 7-2013
Posted on Tuesday, 04 April, 2017 - 03:06 pm:   Edit PostDelete PostView Post/Check IP

Pull each wire at the dizzy end with the engine idling and see which cylinders you are missing on, are you losing any coolant? If so connect a clear hose to the overflow and look for bubbles. I was hoping my problem was plugs (missing on one sometimes two cylinders) however it appears I have a leaking head gasket! Spark plug gap is not as likely to affect idle, is your miss at high rpm or tickover?
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Jim Walters
Frequent User
Username: jim_walters

Post Number: 100
Registered: 1-2014
Posted on Tuesday, 04 April, 2017 - 05:10 pm:   Edit PostDelete PostView Post/Check IP

Get that coil tester working John. You can also check condensers with it. Condensers can be bad right out of the box, especially if they are old stock or made in China, IME. I think your coil is failing and now working harder to fire the larger gap. Will it rev up smooth in neutral but miss when driving and accelerating under load? Sure sign of an ignition fault and likely coil or condenser. In my experience iridium's do not foul easily even with quite rich mixtures.

SRH8505 SRC18015 SRE22493 NAC-05370
www.bristolmotors.com
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1194
Registered: 9-2004
Posted on Tuesday, 04 April, 2017 - 11:23 pm:   Edit PostDelete PostView Post/Check IP

Or IMO use A OMS tester on the HT resister type leads to check for any failing ones.
The copper core are not affected this way of testing.
To tell the difference The resister type have a single wire pin inserted in the end of the lead.
Pic shows resister type.



Misfire on the Iridium plugs seems highly unlikely
the next easy thing would be a failed distributor cap.
Worse is a sticking valves, low compressions but the most likely cause IMO is the fuelling system judging by the sooted old plugs.
I see the Champion plugs listed for 1969 Shadow are N14Y!
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Jim Walters
Prolific User
Username: jim_walters

Post Number: 101
Registered: 1-2014
Posted on Wednesday, 05 April, 2017 - 04:20 am:   Edit PostDelete PostView Post/Check IP

Further to Patrick's post carbon core resistor leads should have a resistance of 10,000 ohms to 20,000 ohms per foot of lead measured. So for instance if you are measuring a lead that is 2 feet long it should show 20,000 ohms to 40,000 ohms. If outside those parameters replace the leads.

SRH8505 SRC18015 SRE22493 NAC-05370
www.bristolmotors.com
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1198
Registered: 9-2004
Posted on Wednesday, 05 April, 2017 - 05:11 am:   Edit PostDelete PostView Post/Check IP

Thanks Jim for the data.
Reference the NGK plugs that came out of my motor, they just would not fire up with ease on the old petrol.
Have seen worse!



I fitted the LPG iridium plugs and all is well.
This has me thinking is it possible that over time the internal plug resisters break down, I have never checked a plug or if it is possible any thoughts.
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John Beech
Prolific User
Username: jbeech

Post Number: 281
Registered: 10-2016
Posted on Wednesday, 05 April, 2017 - 06:36 am:   Edit PostDelete PostView Post/Check IP

Wow, so many people to thank! In response-order . . .

Geoff, the engine in Tootsie is indeed the 6.25L and since the book calls for an 0.025" gap versus the 0.035" of a 6.75L engine, then obviously the extra 0.015" in the Iridium spark plug's 0.040" gap is definitely looking suspect. My heart sinks at this bit of information because the very reason I used Iridium plugs in the first place was to greatly extend the service interval (due to my back issues). Having to do the job again is not merely a blow to my ego but a heavy price to pay for my hubris of not first, verifying my information . . . heavy sigh. Fitting.

More importantly, nowhere in the Pertronix-instructions do they warn against using solid-conductor spark plug wires but a call to Pertronix confirms what you said. This is presumably related to inductance but I'm rather puzzled why this important bit of information isn't included with the instructions but thank you very much, mate, and because this saves me frying the unit, the beer's on me if we ever meet!

Mark, all 8 spark plugs looked very much the same, e.g. all had a sooty dry-carbon build up exactly like the one in the photo.

Martin, your suggestion is what I would have done with a Chevy but for some reason I have a memory of looking at the screw-lock hardware on the distributor-end of the plug wires and deciding not to mess with it (out of for concern about ruining the plug wires where they are secured into the distributor cap). However, I just checked again and there's no problem with unscrewing this bit of plastic and sliding it up and out of the way so that I may try what you suggest for IDing the specific plugs that aren't firing. Good, this will help reduce the number of plugs I clean if fitting a new coil (more later). Anyway, I'm hopeful a new coil will clear the misfire but related to what Geoff said . . .

1. Does anyone know of a specific set of suppressor-core plug wires that will work? In lieu of specific information I figure to simply buy a universal set of resister-type spark plug wires from the local auto parts store and cutting them to fit - but if someone has some words of wisdom I'm definitely all ears.

2. Also, the plugs wires on Tootsie measure about 7mm so I suspect the universal 7mm silicone wire kits I'm finding everywhere will fit within the existing metal loom covers with which the engine is equipped, or am I missing something?

Martin, bubbles and/or a failed head gasket presents different symptoms. In any case, this falls under my philosophy of; "When you hear hooves, think horses not zebras!" and thus, I'm sticking with ignition-issues before going in search of mechanical issues. After all, this car only has 16,000 miles so vacuum hoses or ignition components are nearly a sure bet when sussing out a miss.

Jim, based on Geoff's information regarding the book calling for an 0.025" plug gap, I'm inclined to slip in a new coil to see if the misfire clears up. This, before pulling and regapping the spark plugs because it's much easier job for me (in comparison).

Anyway, with respect to the Pertronix module, I'm inclined to wait and resolve the misfire before worrying about installing it (or the resister-core spark plug wires). Especially since I have one of those super-duper 40KV coils on hand (1.5ohm). A new coil will be very easy for me to try instead of regapping the plugs. Especially because of something I didn't mention earlier. To wit, there's an occasional (and rather muted) backfire, which I can sometimes hear while the engine is idling. This has been in the back of my mind and is the reason I'm thinking 'coil' in the first place. Moreover, considering the plug gap is a bit on the wide side I may get lucky and a 'hot' new coil will sort the misfire (stranger things have happened). In any case, the existing coil is quite likely the OEM unit and after 47 years it owes me nothing.

Meanwhile, I'm still awaiting receipt of the coil/condenser tester (and hoping it arrives this week). Based on your advice in that other thread I'm rather looking forward to attempting a repair because the lunch money investment will result in extraordinary value if I can repair it.

Patrick, what is an OMS tester? And do you mean it 'can' be used with solid-wire strand spark plug wires, or it 'cannot' be used with them? And are you speaking of those little glass case gizmos you can put in-line with a spark plug lead to watch it fire? That's not a bad idea and on the basis that, a) I don't have one, and b) this present as excuse to buy a new tool, I like your thinking ;>)

In any case, while the photo is a little dark on my computer monitor I do know how to identify carbon-impregnated fiberglass core resistance-type spark plug wires (presuming that's the point of the photo). Also, I stand corrected on the Champion plugs being a 14YC instead of a 12YC.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1199
Registered: 9-2004
Posted on Wednesday, 05 April, 2017 - 07:51 am:   Edit PostDelete PostView Post/Check IP

John just my bad on the spelling should be Ohms.
Use ohms tester on the carbon resister leads.

Heck 16,000 miles only in all those years.
Did you carried out a compression test or a cylinder leakage test when the car was recommissioned!
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John Beech
Prolific User
Username: jbeech

Post Number: 283
Registered: 10-2016
Posted on Wednesday, 05 April, 2017 - 09:01 am:   Edit PostDelete PostView Post/Check IP

Compression or leak-down test? I have the tools with which to perform both but frankly, with just 16k miles I'm not especially concerned about anything mechanical with this engine beyond the possibility of valve stem seals. And now that I've begun driving the car this minor concern has evaporated as the telltale puff of blue smoke on cold start is not present. In any case, when it's not missing the car runs sweeeet! Finally, yes I do have a VOM (volt-ohm meter) but of course, it's useless for measuring resistance of solid-conductor wires (beyond showing continuity) because resistance will be zero, or so close as to not matter, e.g. a dead short.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1672
Registered: 5-2012
Posted on Wednesday, 05 April, 2017 - 09:42 am:   Edit PostDelete PostView Post/Check IP

Hi John

Sounds like you have got this all well planned. Don't forget to remove the ballast resister and replace with a short length of wire when you fit the 12v coil.

I did as you have just said and bought a universal wire set from NAPA. You are right to specify 7mm wire. The 8mm gets too tight in the channeling. As a point of interest, I left the channeling off my engine and just routed the wires over the engine with some clips to hold them together. I've kept the channeling just in case I want to put the car back to it's original state, but it's so much easier to not use the channels. They also hold the wires close to the hot engine and at the ends, as the wires emerge to the spark plugs the wires have to be bent through a tight 90 degree bend, not great on high resistance wires.

Geoff
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1200
Registered: 9-2004
Posted on Wednesday, 05 April, 2017 - 10:29 am:   Edit PostDelete PostView Post/Check IP

John I was in fact thinking of more along the lines of some stuck rings on some of the pistons.
As Geoff has said it sounds as though got it all planned.
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Ben Curtis
Experienced User
Username: burgundyben

Post Number: 47
Registered: 12-2015
Posted on Wednesday, 05 April, 2017 - 06:07 pm:   Edit PostDelete PostView Post/Check IP

Where is the thread with the info on the coil and condensor testing?
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Alan Dibley
Frequent User
Username: alsdibley

Post Number: 51
Registered: 10-2009
Posted on Wednesday, 05 April, 2017 - 06:12 pm:   Edit PostDelete PostView Post/Check IP

Hi John, I notice that nobody has suggested ignition timing as a possible source of trouble. Your mention of a backfire brought it to mind.

Also there is a possibility of damaging the ignition system by disconnecting a plug lead to identify misfiring cylinders. The coil has a lot of energy to release at firing time, and it has to go somewhere. The voltage increases till it finds a path to earth, and it tracks across any part of the high-voltage system. Some folk will say that they have been doing it for years with no trouble. That may be true at the time but the problem may show up later - it may be the origin of your current (no joke intended) problem.

Good hunting. Alan D.
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John Beech
Prolific User
Username: jbeech

Post Number: 285
Registered: 10-2016
Posted on Thursday, 06 April, 2017 - 03:06 am:   Edit PostDelete PostView Post/Check IP

Ben, coil-tester chatter within Geoff's thread - "No power on acceleration" - http://au.rrforums.net/forum/messages/17001/17450.html?1491137126

In any case, there's a world of difference between having a plan and executing it because after eyeballing the coil installation, extraction of same is effectively impossible (this, principally due to my back injury even if I were tall enough to reach). Time for Plan B - I recall once reading about a bridge someone built across the shock towers using 2x12 lumber (to give a body where to rest whilst working in the area). Quicker for me to position the fork lift tines across the engine compartment and clamber upon them to try . . . and of course I'll make a stop-rest for the forks using a section of 4x4 post because Mrs. Beech didn't raise a stupid son.
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ross kowalski
Grand Master
Username: cdfpw

Post Number: 352
Registered: 11-2015
Posted on Thursday, 06 April, 2017 - 06:19 am:   Edit PostDelete PostView Post/Check IP

John,

Good on you for working through the back pain. Be careful with the work support.

Here's a thought. A coil's case isn't grounded so just ziptie in the coil for testing and do it right if it's the culprit.
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Jim Walters
Prolific User
Username: jim_walters

Post Number: 102
Registered: 1-2014
Posted on Thursday, 06 April, 2017 - 06:20 am:   Edit PostDelete PostView Post/Check IP

John, if your plug leads are old and are still inside the metal tubes then your backfiring and missing could very well be the leads cross firing or grounding out to the tubes. We see this fairly often on cars with those steel tubes. Have you ever had a look at the engine running in the dark? With poor plug wires you will often see sparks all over the place. Try it tonight with no lights on and observe if there are any stray sparks or not. If so then definitely replace the leads.
To test with another coil it is not necessary to go to the trouble of bolting it in place of the original. We will often use a zap strap to temporarily tie another coil to one of the carb air trumpets and plug the low and high tension leads to it and road test it. If this points to a bad coil (no pun intended) then we'll mount it permanently where the old one is.
And as Alan says you shouldn't pull off plug leads to check firing. Better to slide up the plug boots to expose the connector at the plug, then use a grounded probe to short out the plug instead of pulling off the lead.

SRH8505 SRC18015 SRE22493 NAC-05370
www.bristolmotors.com
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Jim Walters
Prolific User
Username: jim_walters

Post Number: 103
Registered: 1-2014
Posted on Thursday, 06 April, 2017 - 06:32 am:   Edit PostDelete PostView Post/Check IP

Patrick, yes plugs do break down. I still have an old spark plug tester, one that shows the spark while under compression pressure. It is amazing to see how a spark will jump easily on a spark plug at atmospheric pressure but when the chamber is pressurized to 120 psi there can be no spark at all, it shorts out through the plug. I used to use it a lot to show clients why they needed new plugs. This was back in the day when we'd have 5 or 6 MG's or TR's in every day for a tune up and they would usually bitch at the cost of a new set of plugs. Back then most of these cars were owned by students with little spare cash and they kept them running on a shoe string.

SRH8505 SRC18015 SRE22493 NAC-05370
www.bristolmotors.com
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John Beech
Prolific User
Username: jbeech

Post Number: 286
Registered: 10-2016
Posted on Thursday, 06 April, 2017 - 09:56 am:   Edit PostDelete PostView Post/Check IP

Not dark yet. While I'm at it I'm going to grab a spray bottle and after starting the car in the dark and looking things over, I'll mist the leads (torture test).

Ross (and Jim), good idea of Zip-tying the new coil in place and moving the leads to vet the idea before going through the hassle of R&R the old coil.

Jim, wise words about shorting the lead with a grounded probe instead of pulling them (Alan made a good point). Here's how mine typically appear. And note how nice and clean everything is (even the small brass disk at the end of the plug wire and inside the well). Believe it or not, there's been nothing special done, this is simply how Tootsie looks after 39 years of air conditioned storage.

Solid-conductor spark plug wires
- Solid-conductor spark plug wires - totaly old-school
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John Beech
Prolific User
Username: jbeech

Post Number: 287
Registered: 10-2016
Posted on Thursday, 06 April, 2017 - 12:10 pm:   Edit PostDelete PostView Post/Check IP

No sparks . . . none! Not sure whether to try the coil next or just bite the bullet and re-gap the plugs. This, because it may actually be easier on me than exchanging the coil. That, and closing the gap to 0.025" from 0.040" is called for, regardless.

Meanwhile, I'm going in for lumbar injections tomorrow. According to the doctor there will be more of them than last time and he recommended I layabout for a week to ten days after. Think I'll follow his advice.

More as it develops.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1673
Registered: 5-2012
Posted on Thursday, 06 April, 2017 - 12:35 pm:   Edit PostDelete PostView Post/Check IP

Best of luck with your back John. Here's hoping you'll be climbing all over that engine in 10 days time.

Geoff
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Ben Curtis
Experienced User
Username: burgundyben

Post Number: 48
Registered: 12-2015
Posted on Thursday, 06 April, 2017 - 05:49 pm:   Edit PostDelete PostView Post/Check IP

I use this timing light.

http://www.drapertools.com/product/52616/Pistol-Grip-Xenon-Timing-Light

If you put it on a plug lead you can see if that plug is sparking, if you put it on the 'king lead' you can see if the points/condensor/coil is working. You can rest it on the engine with the light facing the drivers seat and crank.
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Alan Dibley
Frequent User
Username: alsdibley

Post Number: 52
Registered: 10-2009
Posted on Thursday, 06 April, 2017 - 06:46 pm:   Edit PostDelete PostView Post/Check IP

"If you put it on a plug lead you can see if that plug is sparking,"

Well, I think it tells you that there is current flowing along the wire. Where it's going could be anywhere, including down the side of the insulator or through the wall of the wire (in the gallery, for instance - as above).

Alan D.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1208
Registered: 9-2004
Posted on Thursday, 06 April, 2017 - 08:43 pm:   Edit PostDelete PostView Post/Check IP

Jim of course used one for years, the memory must be failing.
We still have it but where it is who knows, will put a picture up if I find it, will then check out the old plugs if it still works.
My monies on the plug internal resistors breaking down.

Think it had Champion wrote on it.
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Martin Taylor
Frequent User
Username: martin_taylor

Post Number: 72
Registered: 7-2013
Posted on Thursday, 06 April, 2017 - 09:21 pm:   Edit PostDelete PostView Post/Check IP

With 16k on the clock it is probably worth pulling the dizzy cap and twisting the rotor to check the weights are not seized
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Ben Curtis
Experienced User
Username: burgundyben

Post Number: 49
Registered: 12-2015
Posted on Friday, 07 April, 2017 - 07:07 am:   Edit PostDelete PostView Post/Check IP

@ Alan Dibley.

Fair point, well made!

I have been running daft old cars for too long, at the first sign of misfire, I bin the points and condenser and fit a powerspark. Along with new coil, leads, cap, arm and plugs. They are all relatively low cost consumables.
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John Beech
Grand Master
Username: jbeech

Post Number: 301
Registered: 10-2016
Posted on Sunday, 09 April, 2017 - 03:48 am:   Edit PostDelete PostView Post/Check IP

Geoff, thanks for the well wished. Moving a bit better already following 4 injections in the lumbar region. They put me under for these and after seeing the photo Lynn took of my back side I know why. Fairly well bruised to say the least. Anyway, if it pays dividends I'll be happy enough.

Martin, already checked the weights are free. Surprised there's no vacuum advance.

Ben, good advice, thanks. I wonder this, when you switched out the points/condenser, there's a small piece of nylon in the side of the distributor where the wire feeds through the side; did you clip the lead and fish the Powerspark wire through it?
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1677
Registered: 5-2012
Posted on Sunday, 09 April, 2017 - 07:09 am:   Edit PostDelete PostView Post/Check IP

John

The powerspark comes with it's own grommet of the correct size. I managed to free the existing one by heating it up and pushing it out. It was made of rubber however, not nylon.

There are some pics and lots of great advice in this thread:

http://au.rrforums.net/forum/messages/17001/16753.html

Geoff
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John Beech
Grand Master
Username: jbeech

Post Number: 306
Registered: 10-2016
Posted on Monday, 10 April, 2017 - 01:45 pm:   Edit PostDelete PostView Post/Check IP

Geoff, you mention Powerspark but I have a Pertronix and that name is not mentioned anywhere on the box. What the unit says is Ignitor (as a trademark), instead. In any case, I checked and indeed it does have a rectangular black rubber molded piece that looks like it will be perfect fit for the slot in the distributor of my car (dual points Lucas 20D8) where the coil wire fits (which has a similar appearing nylon block. Anyway, my bad for not looking more closely at what I purchased. Last thing, while looking at it just now I noticed the manufacturer used expensive (and über flexible) silicone jacket 20 AWG wire - well done! This is a small detail that I notice, which makes me feel better about forking over more than USD$200 for the unit as compared to another brand, which is less than half price.
Pertronix-Ignitor-module
- Pertronix-Ignitor-module

Lucas 20D8 dual point distributor (inner workings)
- Lucas 20D8 dual point distributor (inner workings)
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Alan Dibley
Frequent User
Username: alsdibley

Post Number: 54
Registered: 10-2009
Posted on Thursday, 13 April, 2017 - 06:27 pm:   Edit PostDelete PostView Post/Check IP

By coincidence the "T" had a misfire yesterday which seemed like one plug not firing, so I "invented" a new tool.

Solder a yard of wire to the blunt end of a long pin and attach a crocodile clip on the other end of the wire. Clip the clip onto a good earth near the distributor. Start the engine on idle. Grip the pin with a pair of narrow-nose pliers and insert it vertically, through the rubber hat, down the side of one of the distributor sockets till it reaches the connector and earths the spark. If the engine falters even more that cylinder/plug is OK, if not, not.

This method avoids starting and stopping the engine. It avoids damage to the ignition leads by disconnecting and reconnecting to plug or distributor. It avoids burning your fingers on hot bits or high-tension bits. It avoids unnecessary removing and re-installing plugs, which is a job to be avoided, especially on the "B" side.

It worked - B2 was whiskered. I fitted an Iridium plug because I had just bought eight after reading this thread.

Bingo.

Regards from Alan D. (SBH10630) who knows that there are probably some reasons why this may not be a perfect method, but it works.

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