MAR8B-JDS are not the only spark plugs that fit the DOHC engine.

It seems the R-series community’s allowed itself to be led down the garden path.

NGK MAR8B-JDS spark plugs are not the only ones that fit the DOHC engine – they just APPEAR to be. The notion that they are the only plugs which ‘can’ be used in the DOHC engine seems to revolve around three dubious ‘facts’:

1. Only BMW are capable of removing and replacing them,
2. There is ‘something special’ about these plugs, and
3. They are the ‘only’ plugs which will physically fit.

C. above is lent credence by the fact that the MAR8B-JDS uses a 14.3mm hex body. Almost all other spark plugs with a 10mm x 1.0 thread diameter and 19mm reach use a 16mm hex body.
But all three ‘facts’ above are just hot air.
I did some poking around inside my ’10 GSA’s engine, and discovered some interesting facts:

1. MAR8B-JDS plugs can be removed and replaced with a common 14mm box wrench or 14mm tube socket.
2. A standard 16mm spark plug socket will fit the DOHC engine’s primary spark plug wells with no problem (provided that it’s outer diameter is no more than 22mm).
3. The point above means that almost any replacement spark plug you want to use is fine, as long as it has the following characteristics:

• M10x1.0 thread diameter/pitch.
• 19mm reach.
• 14mm or 16mm hex body (16mm preferable, as they are far more common).
• A heat range of no hotter than 8 (NGK), 24 (Denso), 6 (Champion) or 4 (Bosch).
• A crush-gasket seat.
• A built-in resistor.
• A solid terminal nut. (However, if you want to use plugs with threaded terminal ends, this is no problem: your friendly local mechanic will normally have a bunch of loose terminal nuts hanging around in his ‘useful spares’ drawer. You will need four.)
• A uniform 10 x 1.0 thread which spans the entire area of the spark plug’s ‘reach’ (this means that ‘half-threaded’ plug types such as NGK CR_EH-9, CPR_EA-9 or CR_EIA-9 can’t be used).
• A non-projected firing-end tip (projected types may have enough reach to contact the piston crown. I need not tell you that this is a very bad thing).

The first attachment shows a MAR8B-JDS (left) side-by-side with a Denso IU27D (a random plug of this size and type, taken from a Suzuki Hayabusa). Note that all vital dimensions except for hex body size are identical.
The second attachment shows the IU27D mounted inside my camhead’s left main spark plug well, with space to spare.

The only tools you will need for the job are a 14mm tube socket to get the old MAR8B-JDS plugs out, and a 16mm tube socket with a maximum outer diameter of 22mm to tighten the new plugs.
If you own a camhead-engined BMW, this clears the way for you to use any regular, platinum-tipped, iridium-tipped or racing plug you want. When my standard plugs are due for replacement, I plan to use NGK CR9EIX (0.6mm iridium-tipped CR9E). I would be using Denso IU27 plugs, but these are unobtainable on an aftermarket basis in SA.

Don’t be fooled by appearances. Just because a spark plug has an unusual-looking firing end with twin earth electrodes doesn’t make it ‘special’ or ‘esoteric’ or ‘irreplaceable’. Engine designers specify this plug configuration for only one reason: it allows them to kill two birds with one stone by squeezing out a somewhat longer lifespan without using (expensive) exotic materials. (To prove my point, the S1000RR uses the LMAR9D-J – a plug which is almost identical in spec to MAR8B-JDS except for having a 26.5mm reach and being one heat range colder.)

Some food for thought: apart from differing hex body sizes, the MAR8B-JDS appears to be closest in overall technical spec and external appearance to the commonly-available CR8EKB (which is simply a CR8EK with a solid terminal nut).

Never occurred to me they might be "special"!!

I just pulled off the cover, eased off the coil pack thing, stuck a couple of long sockets up the hole until one fit, then used an extension to put some pressure on it. Bit of Blu tack in the socket ensures plug comes out. Jobs a good 'un.

What torque does it need doing up to? No idea. Used feel to judge when it was about what I needed to loosen it off.

It's a spark plug FFS!!

From your image of the two plugs side by side I would measure the thread length. You may find that the plug on the right is a bugger to remove at service time because the last couple of threads have been gunged up. A nice technical term there If it knackers the thread in the cylinder head it will be a very expensive money saving tip.

joness7 said:

Never occurred to me they might be "special"!!

What torque does it need doing up to? No idea. Used feel to judge when it was about what I needed to loosen it off.

It's a spark plug FFS!!

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According to the NGK identification table, the designation code translates as:

MA: 10mm thread diameter, 19mm thread reach, 14mm hex body
R: 5 Kiloohm resistor
8: Heat range 8
B: Special plug body design (non-ribbed insulator...?)
J: Extended twin earth electrodes
D: Special firing-end design (partially unthreaded near firing end...?)
S: Copper core & 2.5mm centre electrode

For common-or-garden NGK plugs, you never see the word 'special' being used, which means the 'special' features are specified by the vehicle manufacturer.

Still, although I've seen a LOT of forum threads - here and everywhere else - asking for alternatives to MAR8B-JDS, I've not once seen any definitive answers. So I thought I'd check the issue out. In the process, I came up with a definitive answer.

Packer said:

From your image of the two plugs side by side I would measure the thread length. You may find that the plug on the right is a bugger to remove at service time because the last couple of threads have been gunged up. A nice technical term there If it knackers the thread in the cylinder head it will be a very expensive money saving tip.

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I highly doubt it.
If the plug threads on a fully-threaded plug like the IU27D are prone to 'fouling' due to carbon buildup, I see no reason why the threads of a MAR8B-JDS wouldn't do the same. The only difference is that the latter's thread begins approximately 3mm further away from the combustion chamber.

A very sparing amount of heat-resistant copper grease on the plug threads - plus regular maintenance - has worked well for me for eighteen years. The grease does two jobs: it forms a physical barrier against carbon buildup, and an inert chemical barrier against galvanic corrosion (due to the presence of dissimilar metals).

Nick V said:

I did some poking around inside my ’10 GSA’s engine, and discovered some interesting facts:

.

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Do you really think that no other person has managed removed the spark plug from their twin cam engine.

Nick V said:

I would be using Denso IU27 plugs, but these are unobtainable on an aftermarket basis in SA.

.

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Ahhh, you're in S.A. That explains a lot. Take your NGK into any decent motorfactors in the UK and they'll give you a list of replacement options. They may not have them on the shelf but will get them in for you.

Good on you for being curious and it appears diligent in your posting. (I am sure I will be corrected , though). Plugs are not that cheap when you have no alternative. I guess right or wrong...at least you posted all the info and not just a small carp (as is often the case) leaving us even more lost!

Steptoe said:

Do you really think that no other person has managed removed the spark plug from their twin cam engine.

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Nope. But there does seem to be quite a bit of groundless superstition surrounding these plugs in the R-series community.
It's easy to see why: they have a strange designation code, they look funny, they're not available except from BMW parts counters. And NGK.com lists a funny hex body size, too: 14.3mm (even though a regular 14mm socket fits them just fine).

Added to that, the overwhelming majority of plugs featuring an M10x1.0 thread and 19mm reach have a 16mm hex body. So a lot of people will assume that a 16mm hex plug won't fit the plug wells. Even I did, at first.

Steptoe said:

Ahhh, you're in S.A. That explains a lot. Take your NGK into any decent motorfactors in the UK and they'll give you a list of replacement options. They may not have them on the shelf but will get them in for you.

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Compared to the rest of Africa, we actually have it pretty good here on the Southern tip. But having to deal with uneducated salespeople who got their job because they were somebody's nephew really bites it. They know a sum total of three spark plug brands: NGK, Champion and Bosch. Very few people manning parts counters here have access to comparitive spark plug tables, almost none of them have heard the name Denso, and the initiative to take special orders is foreign to them.

adventuredon said:

Good on you for being curious and it appears diligent in your posting. (I am sure I will be corrected , though). Plugs are not that cheap when you have no alternative. I guess right or wrong...at least you posted all the info and not just a small carp (as is often the case) leaving us even more lost!

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Ta, my friend! Much appreciated!

Just for fun, I spent some time last night removing the MAR8B-JDS from my camhead and replacing them with the IU27Ds I snaffled. I was curious as to how they'd perform, so I took the bike out for a quick spin.
I was dumbfounded. The difference in throttle response makes it feel like a totally different bike. Crisp like you cannot believe, and instant pickup even at high engine loads.

Only one bad thing: my displayed average fuel consumption has gone up from 6.1 to 6.6l/100 Km.
However, that may have something to do with the fact that I got so carried away that I was running at 200 Km/h+ for long stretches.

Packer said:

From your image of the two plugs side by side I would measure the thread length. You may find that the plug on the right is a bugger to remove at service time because the last couple of threads have been gunged up. A nice technical term there If it knackers the thread in the cylinder head it will be a very expensive money saving tip.

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Can I just come in here, (Blimey I must be unwell, I have come over all polite!) Anyway, I worked for 30 odd years on Citroen cars and stripped spark plug threads were fairly common. On 2CV's an flat twin like the GS the most common cause was people not knowing how to tighten then, often they were so scared of stripping the threads that they left them little more than finger tight. The plug then blew out taking threads with it. On the Citroen GS model, an air cooled flat 4, the problem was more likely to be cross threading due the the awkward placing of the plugs.

In almost all case the cure was relatively simple and involved very little dismantling. A product call Timesert , made by Wurth allows the cutting of new threads and the fitting of an insert in the head simple by removing the plug. These inserts are a far better solution than such as a helicoil as they are designed for something like a spark plug that will be replaced from time to time. I have done literally hundreds over the years and never had a problem, often getting repeat business for servicing etc because we had solved the problem quickly and cheaply whereas the dealer had wanted to fit a new cylinder head

A little care is needed but any competent person should be able to do it. So yes a real pain if the threads are damaged but not the end of the world both in terms of cost and work involved.

John

The Grey One said:

Can I just come in here, (Blimey I must be unwell, I have come over all polite!) Anyway, I worked for 30 odd years on Citroen cars and stripped spark plug threads were fairly common. On 2CV's an flat twin like the GS the most common cause was people not knowing how to tighten then, often they were so scared of stripping the threads that they left them little more than finger tight. The plug then blew out taking threads with it. On the Citroen GS model, an air cooled flat 4, the problem was more likely to be cross threading due the the awkward placing of the plugs.

In almost all case the cure was relatively simple and involved very little dismantling. A product call Timesert , made by Wurth allows the cutting of new threads and the fitting of an insert in the head simple by removing the plug. These inserts are a far better solution than such as a helicoil as they are designed for something like a spark plug that will be replaced from time to time. I have done literally hundreds over the years and never had a problem, often getting repeat business for servicing etc because we had solved the problem quickly and cheaply whereas the dealer had wanted to fit a new cylinder head

A little care is needed but any competent person should be able to do it. So yes a real pain if the threads are damaged but not the end of the world both in terms of cost and work involved.

John

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Timesert sounds like a great variation on the Helicoil concept - but surely you'd still have to remove the head in order to guard against swarf getting into the combustion chamber? Or is there a way around this?

These days, I believe there really is no excuse for anyone to strip spark plug threads. Torque values and approved procedures are readily available on the internet, and anti-sieze lubricants are common and cheap.
The secondary plugs on hex/cam heads are also located at a funny angle, but it's still a straightforward task - IF the enthusiast removing and replacing them tackles the job with due care and attention. If these attributes are absent, said enthusiast probably needs their tools confiscated anyway...

NickV, Jpburg riding sounds a bit like Riyadh (180 - 200 for looong stretches), and I recall threads about valves etc getting cooked there. I cooked mine last summer here, rebuilt with new pistons and 2nd hand heads. Fitted boosterplug to richen the mixture (but I read it only works while accelerating and not steadystate). Do you get pinging there due to low octane fuel? Bin

Bin Ridin said:

NickV, Jpburg riding sounds a bit like Riyadh (180 - 200 for looong stretches), and I recall threads about valves etc getting cooked there. I cooked mine last summer here, rebuilt with new pistons and 2nd hand heads. Fitted boosterplug to richen the mixture (but I read it only works while accelerating and not steadystate). Do you get pinging there due to low octane fuel? Bin

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Bin, I've noticed both the blue bike (R1200S engine, 12.5 compression) and green bike (standard GS camhead engine, 12.0 compression) pinging - but only under full-throttle acceleration and/or high-load, high-speed conditions, and then only when using 93-octane. But it doesn't always happen, even running twice under exactly the same circumstances. And they don't do it regularly.

BMWs sold here carry a warning sticker on the fuel filler cap, stating that only 98-octane should be used - but 98-octane petrol doesn't exist here. At altitude, you have three choices: 93 lead-replacement, 93 unleaded and 95 unleaded. At and close to sea level, you have 95 lead-replacement and 95 unleaded.
If you want to go higher, you have to make a jump to 100-octane racing fuel at more than twice the price.

One thing I do with all my bikes is replace the standard spark plugs with ones a single heat range colder. A little extra insurance against pinging. To date, I've had no problems with fouling or hard starting because of this.

Booster plug, accelerator module etc. are simply a resistor placed in line with the intake air temperature circuit in order to 'fool' the ECU into thinking the air being breathed in is colder than it actually is. This effectively shifts the entire management map up (or down) the enrichment scale.
Since the resistor is there all the time, it works all the time - from 0% to 100% throttle. In order to have something that enriches the mixture only under acceleration, you need something sophisticated enough to detect a 'load' condition by processing throttle position, engine speed and preferably also vehicle-speed inputs.
That means getting into piggyback systems, such as Power Commander.

Nick V said:

Timesert sounds like a great variation on the Helicoil concept - but surely you'd still have to remove the head in order to guard against swarf getting into the combustion chamber? Or is there a way around this?

These days, I believe there really is no excuse for anyone to strip spark plug threads. Torque values and approved procedures are readily available on the internet, and anti-sieze lubricants are common and cheap.
The secondary plugs on hex/cam heads are also located at a funny angle, but it's still a straightforward task - IF the enthusiast removing and replacing them tackles the job with due care and attention. If these attributes are absent, said enthusiast probably needs their tools confiscated anyway...

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No excuse maybe but you can't legislate against stupidity, it knows no bounds.

The inserts are, as I said, far superior to helicoils for this application. They are designed to go in and stay in with the inserting tool rolling the bottom of the tube out to hold it in place. There really is no problem with swarf, put a good blob of sticky grease on the cutting tool and it will collect most of it, spin the engine over on the starter with no plugs in for a few seconds and you are ready. We are talking about ali heads here, any tiny residue will do no harm. I am sure we will get comments from those with lots theoretical knowledge but out there in the real world it works.

As I said I have fitted hundreds and never had a problem. Some were fitted when the vehicle was nearly new (careless owners usually!) and went on to run for over 100,000 miles with an insert in place.

The Grey One said:

No excuse maybe but you can't legislate against stupidity, it knows no bounds.

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You forget, you're telling this to a South African.
With erections coming up this year, the latest catch-phrase is: "You can't fix stupid. But you can vote him out of office."

Nick V said:

You forget, you're telling this to a South African.
With erections coming up this year, the latest catch-phrase is: "You can't fix stupid. But you can vote him out of office."

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If only we could do that in the UK!

John

thanks for taking the trouble to pass on the information Nick. I cant imagine I will ever replace a plug - I never do in any of our cars - but if I do get a rush of blood to the head I will use the info you have given us. Thanks.

The Grey One said:

If only we could do that in the UK!

John

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(Thread-hijack alert)

Admittedly, that outlook is optimistic even here. As I've been telling people, Jacob Zuma is an uneducated, denialist fool.
However, this hasn't prevented him cultivating the low cunning that enables the ANC to manipulate elections and play 'Yes sir, no sir' with the large corporations which fund it's election campaigns.

He may not be able to correctly recite numbers totalling hundreds of thousands or give a speech without looking up from his crib notes, but he knows what side his bread is buttered on.

(Political rant over)

Booster plug explanation from Jens at: http://www.boosterplug.com/shop/cms-24.html

On Open Loop bikes you will add 6% of fuel to the entire fuel map (6% is just the example from above - it can be something else with another resistor). This means that if your current fuel consumption is 5.0 liters per 100 km, it will be raised to 5.3 liters. A small fee to pay for an improvement you will enjoy every minute on your ride.

If your bike is Closed Loop, the resistor tuning idea is even smarter. The lambda sensor will try to adjust the mixture back to the preprogrammed level, but the time delay mentioned earlier will work to our advantage.

In conditions where you maintain constant RPM and throttle opening, the feedback from the lambda sensor will adjust the mixture back to original level, and our small tuning device will sit idle and wait for something to happen. This is fine – you don't need the richer mixture at level speed.

As soon as RPM or throttle opening moves, the fuel map will shift horizontally or vertically on the 15 x 15 grid, and the lambda sensor feedback will be temporary disabled. This means that the ECU runs open loop for a short period every time we change RPM or throttle, and the enrichment from the AIT sensor modification kicks in exactly at this point.

As the enrichment will only be effective under these conditions, the extra fuel consumption will only be aprox. One third of the 6%, so if your usual fuel consumption was 5.0 liter / 100 km, it will now be 5.1 liter. Still while maintaining all the positive effects.

Bloody marvelous job for a small resistor

The rest is worth reading...

The Grey One said:

If only we could do that in the UK!

John

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But here in the UK we do have " erections coming up this year" ! Sometimes we have them more often!

If I can just switch to old man talk for a moment ( some will say I did that above !) it is very noticeable these days how much more seriously young riders ( and thats anyone below 40)take issues like servicing. I reckon its because they havent had to learn on old knackered machines as their parent did and indeed many have never taken an engine to bits in their lives. The result is that they have no option but to take the manufacturers schedules as gospel. If the manufacturer says change the plugs every 10k miles or whatever, the bike falls to bits if you dont do so. Well its all a load of bollocks. Its good to give a bike a regular oil and filter change but if you miss one there will be no real consequences. And as for the plugs - forget it. They'll likely do the life of the bike.

Look after it but treat what the makers say with a cellar of salt.

Here I have had a Dodge and now a Jeep both with a 5.7L V8 Hemi, and they want to change the oil every 10K kms (a pain but it is very dusty) on t'other hand they won't change the plugs til 100K !!

So.................has anyone gone down this route and tried the Denso IU27 plugs ?