Hi, I have a December 1960 build MK2 Jaguar 3.8L with a Lucas DMBZ6A 40240D distributor which I have had rebuilt & an Accuspark Electronic Kit fitted & bench tested. The seal & bearing have been replaced & drive dog tightened up.
My dilemma now is getting 7mm Carbon Leads fitted to the old-style Acorn threaded cap connections. I was hoping to just purchase a push-in style distributor cap & that would make life easy, but apparently no such cap exists for this type of distributor!
The distributor is on route back from the repairer, but I'm told there is not much room inside the acorn connections to fit the 7mm Carbon Core leads (bulky), I'll need to check this when it arrives back but in the interim: -.

Q's:-
1) Is it possible to still run with Copper Core wires & just add Spark Plug Suppressors rated at 5k ohms to get around this or
2) I just make up Carbon leads with new connections & brass spikes pushed up into the core?
3) Do these spikes come out easily?

I did see somewhere where a comment was made that this is the wrong distributor for this model? I hope that's not right!
It has however been used on many brands of UK cars, so I find it strange that no one has made a lead push-on style distributor cap to suit it!

advice appreciated
Peter

 

I would just use solid copper wire and 5k ohm resistor caps from NGK OR forget the resistor caps and use NGK 5k ohm resistor plugs.

Be sure and run a rotor from Distributor Doctor, there's a lot of aftermarket junk out there.

 

Thanks JeffR1, yes that's what I'm thinking too!
Re the rotor, your point is noted & coincidently they had to shave a minuscule of the tip of my new rotor & is now working fine under bench test.
R
Peter

 

I agree with Jeff. So long as there's resistance somewhere, it shouldn't matter much where.
SNG and others sell the DMBZ6A for the Mk2. So long as the advance curve is about right, it should be OK. You could check advance against the value in the service book for a 3.8 with the compression ratio of your car.

 

The continuing saga. Finding the cause of a miss.

The refurbished distributor has had the drive dog fitted incorrectly by the repairer & thrown the timing 180deg out, so I've reversed the plug leads & it now starts & runs with the electronic ignition & copper leads.
Before the distributor was sent away, I had a miss, such that if you put your hand over the end of the exhaust pipes & traced the offending exhaust pipe back the miss was coming from one of the rear 3 cylinders.
Having refitted the refurb distributor & reversed the leads, the miss is now coming from one of the front 3 cylinders!

Assuming the miss is now related to one of the spark plug leads or plugs, I went & checked the resistance of each with a multi-meter with the following results:-
Leads
#1 length 1100mm 32K ohms
#2 length 1000mm 41K ohms
#3 length 910mm 28K ohms
#4 length 740mm 15K ohms
#5 length 760mm 37K ohms
#6 length 650mm 22K ohms

I have a 2150mm length of new7mm copper core ignition cable and the ohm reading is 13K or 6 ohms/mtr ?

So, this would indicate all the original leads are outside a satisfactory ohm range & should be replaced - Yes?
Would this irregular resistance be causing the miss?

Also, should I do away with the old spark plug conduit/shield that slips between the plugs, its seen better days, does it really need to be there?

The non resistor spark plugs NGK BP5ES ohm readings (from top to bottom core tip) are:-
#6 24K ohms
#5 28K ohms
#4 23K ohms
#3 23K ohms
#2 25K ohms
#1 21K ohms

These seem high, as the recommended NGK spec is 1-2K ohms

Your comments appreciated as I'm no auto electrician!
thanks
Peter

 

I just came across an article that states the original Jaguar plug caps have a carbon resistor, which is what I have, & will have a resistance of between 5K-15K Ohms, so why my leads so high?
Peter

 

Try swapping plugs front to back one set at a time to see if miss move to back cylinders as before. 6 & 1, 5 & 2, and 4 & 3... if no change then I think leads would be next.
NGK plugs are from many engines and seldom have correct gap out of the box for older engines.
I would have no concern in shaving or sanding down the 7mm lead installation one half inch from end that goes in the distributors cap nut.
What omh coil are you using with the new electronic trigger ( 3 omh to 1.5 omh would be expected)

Note: My Lucas data base shows the correct distributor for you model and year as: DMBZ6 40665 A/B
The 40240D is a D3A4 model is from 1950's not listed for any jaguar model... they may share the same casting, but would have different components inside?
Distributor curve is listed as 700 for 1960 M2 and 475 for the the 1950 distributor.
M2 Advance at RPM targets: 2000 rpm 12*, 1100 rpm 9*, 550 rpm 3.5* (these would be distributor numbers, crankshaft degree numbers would be double (24*, 18*, 7*))
Rgds
David

 

Thanks David, I'll try reversing the plug sets tomorrow & see what happens.

Wow, this Distributor has been in the car since I bought it back in 1976! & no-one has ever told me its incorrect!

The company who refurbished it reset new advance curve specs to:-
Start: 1000 RPM
Intermediate 14 degrees @ 2000RPM
Total 28degrees @ 3000RPM
Vacuum 12 degrees
A test of spark & function to 7000RPM was performed with no issues detected.

The coil is within the correct Ohm range for this electronic unit & spark plug gaps have been checked & set at .025"
regards
Peter

 

This makes no sense, if in deed the plugs are non-resister plugs (no "R" in the series number), then how come the readings are so high, they all should be at zero ohms, or maybe 1 ?

As for your wires, 32 and 41k ohms is pushing it (number "2"), even more so if those plugs are measuring up what you posted here.
Even an electronic ignition with a .8 ohm coil is going to have trouble trying to get a spark through 66K ohms.
Most carbon core resistor wires should be no more then 50K ohms in their longest length.
You should not be running resistor plugs and wires, one or the other.

Use your solid wires with an NGK resistor plugs, that will give you 5000 ohms over-all.
Or use NGK resistor caps with solid wire and non-resistor plugs, that will give you 5000 ohms, and that will be enough to keep the radio quiet and will not interfere with any other electronic gizmos in the area.

Are you measuring the spark plugs with the resistor wire hooked up to the plugs ?

 

I got the new parts to refurbish my '66 S Type's ignition from the Distributor Doctor and he told me the acorn-nut type caps I asked for were not the correct one for my car. They should be push-in, but screw-in would do the job. He supplied two new 'wrong' caps and it's always been fine. It's the same cap as is fitted to my '68 Triumph TR5, that I had to borrow when I broke the Jag's cap when drying it out in bad floods a couple of years ago, The copper leads were fitted to both cars when I bought them many years ago and the Jag is pretty original but the Triumph has an electronic something or other system that the previous owner invested in many years ago. Maybe Lumenition, I think..

I've never worried about ohms and things, any misfire is sorted by inspection or simple substitution of parts until everything is fine again. I'm also a firm believer in old-school Brisk plugs and have them in all my regular users, cars and bikes. They seem to suit this E10 fuel much better, which I run in most bikes and the Jag.

Ray..

 

Note from Moss Motor catalog (for late model M2)
"Please note that some cars may have been converted to a cap with push-in wire connections. Use JLM9524 or JLM9524JAG for these applications. (Other than the wire connections, the caps are interchangeable.)"
You might confirm this with the distributor repair agency you used
Rgds
David

 

David,
I switched #6 front plug with #4 rear plug & the miss/cough switched sides when I placed my hand over the rear exhaust pipes, so I replaced #4 plug & it now idles a lot smoother.
I took the car out for a 5km run and it runs fine albeit for a small miss under load.

When I checked my records, these plugs are 3 years old, so I'll replace all 6 with new & see what impact that has.

Question:- I was running NGK BP5ES (S = std 2.5 copper core CE) plugs put in by the last service tech,
should I go back to BP5EY (Y = V groove CE (14mm only) 2.5mm insulator protection) plugs?
What's everyone else running in their MK2 3.8L with 8:1 compression ratio?


Peter

 

Good find. I am with you on all new plugs before working on small improvement tweaks... I have use both NGK plugs you mentioned and could not tell the difference. One clean and gap reset on plugs, then new, is what I do. I pull pugs more often to see if mixture from front carb is different than rear carb.

What is your static timing degree? 10* seems to be the book setting. Some distributor re-conditioners that update advance curves to modern fuels that are available, also ask you to set different initial static degree. Missing underload, could be pinging from too much advance at that RPM (my experience is 2500 to 3000 under load is where you get this)
See if it goes away with new plugs. If not, try retarding Static to 8* and see if it goes away.
Rgds
David

 

Thanks guys, for all your feedback, really helpful responses.

JeffR1 - Yes, those Ohms measurements did not make much sense to me at the time either & have led me a merry dance.
Sorry all, I was using my electrician's son-in-law's commercial Fluke multi-meter hoping it would be more accurate than mine & I reckon it's got a flat battery or just stuffed.
Anyhow, I went back & checked a few leads with my cheap multi-meter & they all showed Zero Ohm readings!! So, forget all that resistance data I posted earlier, that's just confused everyone.
Nah, I wasn't measuring the plugs with the resistor wire hooked up Jeff but have re-checked these as well & again are now showing Zero Ohms.
I will now purchase a set of NGK resistor plugs BPR5ES & see how it goes.

David, re the Moss JLM9524 or JLM9524JAG distributor Caps, my repairer & I did research on these & they don't fit my early DMBZ6A distributor.
The current plugs have done 872 miles but most these are short runs. Shouldn't these plugs be good for at least 5000 miles? How often would you pull & check & at what mileage would you replace yours David?
Static timing as recommended by the dizzy repairer was 6-8deg, so I've set it at 7deg.As you suggest I'll recheck this after installing the new plugs.

Ray, Ohms is something I really don't normally get into either but was just trying to eliminate all possibilities & normally do what you do. But this miss has been eluding me for a long time now!
I've never heard of the Brisk Plugs before, looks like they are more for racing & five times the price. What type Brisk are you running in the "S" Type Jaguar Ray?

Once again thanks fellas, I'll report back
regards
Peter

 

Peter,
I actually didn't keep track of miles on plugs, just one re-gap after initial installation ( first re-gap is out of the box, always use correct tool for this) and the second time they need re-gap, I just go new. When they are on sale I get two sets. The fact that you have short trips and one bad plug, makes me think more are suspect. Note: I have run stage 111 Pertronix with low .8 omh coil, allowing NGK plugs to be increased .005" gap over book, this does cause the plug gap to increase faster that normal.
You need to retard ignition to 5-6* based on the recommendations of your distributor shop
Book 10* initial plus 24* mechanical advance = 34* your new curves are 6-8* plus 28* = 34-36*
After plugs are in, if you have mountains near by, a high speed run up the mountain would clear any deposits in cylinders that are causing the pre-ignition.. I would add a can of over the counter octane booster to your gas, just for insurance.

Note from AccuSparkAccuSpark electronic ignition systems require non-copper core ignition leads for proper operation and to prevent interference.
Copper core leads are incompatible: Using solid copper core (non-resistance) spark plug wires can cause electromagnetic interference (EMI) that disrupts the electronic ignition module. This is explicitly warned against by AccuSpark and similar systems like Pertronix.
Recommended leads: Use spiral-wound, low-resistance, shielded HT leads (e.g., AccuSpark Stealth or Triple Ground series). These feature a ferrite core and stainless steel windings to suppress EMI and maintain low resistance (~500 Ohm/m).

I would try to use the 7mm wires and fit them (modify them as needed) to the acorn nuts.
Rgds
David

 

Brisk plugs are made in Eastern Europe, Czech Republic, I think, and are still glazed by the old method using lead. All other manufacturers, NGK, Bosch, Champion etc changed to a new method several years ago that didn't involve lead and this is what causes them to fail permanently if they get wetted up inside. On my bikes, if a plug gets wet for any reason, it's very unlikely to work well again so has to be replaced however few miles it's done. Any of us who run old bikes will have found this out.

I've got an old BSA B31 that I use throughout the year that I can easily over-flood if it hasn't been used for a week or three and a few kicks with open throttle and the valve lifter pulled will clear a Brisk plug. This then works quite happily again indefinitely. I recently replaced the Brisk plug in this bike because it had done over six thousand miles but it didn't need it. I only fit Brisk -plugs if the NGKs are due for replacement, about 6000 miles, and so far have them in BSAs, Triumph Twins and Laverda Triples and also the.'66 3.8 S Type.

The Brisk UK main importer is, I think, in Ireland but I get mine from the motorcycle agent for them in Lincolnshire. He's a CZ/Jawa agent, a very helpful chap and just supplied me with the Brisk equivalent to the NGK number I gave him becausehe has no informatioin on cars. Mr Google knows all about them if more info is needed.

Ray, in Dull and Dank South Norfolk.

 

David, I'm always running 98 Octane fuel, so do you think I should still add a can of Octane Booster on a full tank as well?
Your point re retarding timing back to 5-6deg is noted & I'll adjust that once I fit new NGK Resistor Plugs and can borrow a strobe timing light which is a must now with an electronic unit.
I know Accuspark's policy & I've spoken to them about it, naturally they want to sell their complete kit. They do know of customers who are running copper core cables with their kits & have never heard of any complaints.
I will run with what I have for now and look into your suggestion re adapting the 7mm carbon leads.

Ray, thanks for that information on the Brisk plugs, very interesting re the use of lead still in their manufacturing process.
So, the way I'm reading your previous post is that your '68 Triumph TR5 has copper leads & an electronic ignition, that right Ray?

thanks fellas
Peter in hot Adelaide

 

That's correct, Peter, I'll check later but it's a common brand of magic ignition fitted by a previous owner - I've had the car about twenty years. It's always started well, hot or cold, and doesn't miss a beat. We haven't used it a huge amount because I mostly use bikes daily and the S Type for carting folk about.The only problem I can remember having with the TR5 Triumph is a plastic clip disintegrating in the rotary petrol pump, which caused the cold start device to stick. It used about four gallons of best E5 to get the Far Better Half the ten miles home from work. The advantage of this problem was that I could properly get my head around Joe Lucas's antique Petrol Injection system to fix it.

The TR's ignition has been fine and it's still on NGK plugs because they are not due for a change yet. It will go onto Brisk when the day comes because I like them for their forgiving nature. These plugs have wider bands in their heat range so my 1980 Laverda Mirage uses the same plugs as my '66 and '71 650 Triumphs. They were two or three grades apart in NGK and Champion.

I've always run 98 Octane E5 in the TR5 car with lead additive because the previous owner did and it may be addicted to it. I use cheap E10 fuel in the Jag, also with lead replacement additive. just in case. The 8:1 pistons run fine on low grade fuel and I did a head job about three years ago, with new valves and springs, so it doesn't actually need the additive. It's just an extra bit of insurance. I've only ever used octane booster in race bikes, never needed it on the road, in spite of having some funny old bikes in my time.

Ray, in warming-up Old Blighty

 

Peter, doing one low cost fix at a time to see if the problem reoccurs is what I try. New plugs, still getting issue under power (note RPM when this occurs), high speed run up a hill, add octane booster, re-time distributor, if you still have the issue, I would suspect ignition wires.
Just be glad you can do all this yourself, and not have it being done by an expensive shop.
Rgds
David
PS: Looks like a spirited run up the M1 is just the ticket in your area.

 

This thread is turning into a guessing game.