Spark Plug FAQ

Compiled & edited by Kristian #562
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 13 June 2007, by Winter #1935

• Introduction
• About Spark Plugs
  • Spark Plug Specifications
    • Which plug should I use?
    • What is the spark plug gap on the F650?
    • Decoding NGK plugs
  • Platinum Plugs
    • Do platinum plugs make a difference?
    • Opinions on platinum plugs?
  • Split Fire Spark Plugs
  • Iridium Plugs
  • Autolite Spark Plugs
  • Resistor Spark Plugs
  • General Spark Plug Info
• Procedures
  • General Hints
  • First Plug Change (Spark Plugs for idiots)
  • Plug Chops (and how to do it)
    • For Plug Reads (Colours, Descriptions)
    • Feedback
• Misc Spark Plug Questions
  • Will an extended tip plug cause ill/harm to my GS?
  • What gap should I use on an extended tip plug?
  • What gap should I use on a Iridium plug?
  • My new plugs do not come with a screw-on terminal/cap
  • NGK Plugs in Canada
  • Any hints on accessing the spark plugs?
  • Any hints on removing the plugs on a GS without removing the airbox?
  • My spark plug appears to have corroded
  • Leading causes of dry spark plug fouling, as indicated by dry, black, sooty residue. (NOTE: Not "wet" fouling)
  • DPR9EIX-9 instead of the DPR8EIX-9?
  • Intercom noise after spark plug change?
  • I have a Dual Spark - How would I know if one was not working?
  • What spark plug cap do I use on my FI model bike?

Other related FAQs:

• See also the Plug Caps n Coils FAQ
• Having problems starting your bike? See the Classic Hard Starting / Poor Running FAQ and also the GS Hard Starting / Poor Running FAQ
• Have you seen the Engine Misc. FAQ?
• Experiencing Surging and Stalling on a Fuel Injected Bike? Check the Custom Fixes for S&S

According to BMW service sheets, the spark plug(s) on the F650 should be changed every 10,000kms (6,000miles). Changing your spark plug(s) can be an easy task - it just depends on your model of bike and how easy it is to access to spark plug(s). Spark plugs can also give you an insight into the internal operation of your engine - depending on their condition. I like to keep old plugs around, and write on the packet when they were removed. That way I can check later to see if there have been any changes.

Which Spark Plug Should I Use?

The following table lists the available spark plugs for the F650. If you are aware of a plug that is not listed, please let us know. The OEM plugs are shaded in green.

The Spark Plug Gap is 0.6-0.7mm. The Standard Plug is NGK D8EA or the NGK DR8EB for dual spark FI models (2004 onwards). They are preset from the factory. You can use feeler gauges to check. If your plugs are not gapped properly out of the box, the vehicle should still run fine. But, like having your valves set not-quite-right at the service interval, you would likely encounter problems down the road sooner than you would have if they'd been set right to start. Since the F650 calls for replacing the plugs every 6000 miles, it really isn't all that much of an issue.

Note: Please check the Misc Spark Plug Questions section for comments on the gap for extended tip and Iridium tip spark plugs.

Decoding NGK Spark Plugs

The following table helps to decode NGK spark plugs. Example 1 is the D8EA (12mm thread diam, temp range=8, Long thread, Special) and Example 2 is the DPREIX-9 (12mm thread diam, Projected tip, Resistor Type, temp range=8, Long thread, Iridium, 0.9mm electrode gap).

Platinum plugs are available. NGK D8EVX Platinum. (NGK Racing: R217-9 (retail approx. $19.99))

Do Platinum Plugs make any difference?

The almost overwhelming General Consensus on the F is a resounding "No". Waste of money. They CAN however aid hard starts if you have a fouling problem, but you should look into the cause of that problem first.

Opinions on Platinum Plugs:

• I just thought I would share this, although some of you may already know. I recently bought bits from "Motorworks" Web site to do a general service, when on the web site I noticed Platinum plugs, they said that they improved power and fuel consumption so I thought I would try them. I have just gone through the first tank of fuel since fitting them and find the following:
  1. Smoother power delivery, with certainly low/mid power improvement
  2. I used to have a slight roughness at about just under 4,000 rpm under acceleration but this has gone now.
  3. I use the bike for commuting daily and normally get from 50 - 52 mpg, this has not improved with the plugs in fact its about the same.
  Over all, impressed with the smoother more powerful engine, but doesn't give better fuel consumption, well not for commuting perhaps on a long run it might. Grayratg
• I'm not meaning to sound like too much of a nay-sayer, but wouldn't you think that you'd experience the same little joys with new plugs of any flavor? What's the idea behind platinum plugs anyway? That the coating won't foul as much in the heat of the engine? Or that the coating causes better conductivity? I'm thinking it's marketing hype, but I could be wrong. Seacuke #1214
• I am just wondering if your regular plug was old, before you changed to platinum? Could that have caused the differences? It is perhaps a little to soon to draw conclusions on fuel consumption after only one tank...? Spakur #1117
• Platinum plugs do not look like regular plugs. They are NOT like regular plugs. The electrode is a very fine platinum wire. This electrode does not degrade like a regular one. Because it is more or less a point, the spark is a "better" spark due to electric field effects from a point source rather than a "flat surface" like the standard plugs. I ran Bosch platinum's in my R80G/S bikes for about eighty thousand miles or so. They were always still running GREAT at replacement time. Once I had a rather unique platinum plug failure. But Bosch sure did right by me. WARNING! If you change to platinum plugs, make REAL SURE that they are NOT RESISTOR PLUGS unless you go ahead and change your plug caps to NON-resistor type plug caps, too. Running resistor plugs in resistor caps can worsen fuel economy significantly. Flash 412 (CO)
• Platinum plugs have a very thin center electrode that is supposed to provide a better spark that requires less voltage to fire. The platinum may also be more resistant to erosion of the electrode. They have been developed to satisfy the auto manufacturers requirements for longer intervals between tune ups. As you know, that is not a big concern for the BMW motorcycle factory. Now we have Titanium plugs and Iridium plugs. I have no idea what these plugs are supposed to do, besides cost a lot of money and presumably make more profit for everyone involved in their manufacturing and sales. Richard #230

• It's the same marketing gimmick that got people to buy more razor blades by putting two - then three!- in a single razor head. Technical reports (search online) show the V splits really don't have any significant difference for power. Remember: the spark only jumps from one spot - one electrode - at any time. Plus with a split plug, the spark has more opportunity to arc instead of connecting in a straight path to the other (central) electrode.
• I'm not sure if the "platinum" coating helps either because it's really just a very small, very thin coating. You'd have to have a lot more to make it seriously effective.
• Simply cleaning the plug and setting the gap regularly will probably work as well. And check the wires, too.
• And you may want to check the lawsuit against Splitfire here. www.ftc.gov/os/1997/9702/splitfir.htm and here www.miata.net/garage/splitftc.html
• And for a chart of misfires and popular plugs see. www.svt-lightning.com/print.php?sid=16
• Here's an alternative to power boost options... but you'll need to experiment with your jets! www.dragbike.com/news/features/product_directhits.htm. Ichadwick - Canada #1062

Apparently, BMW recommends Iridium for the GS. I picked up my bike from the 20 000 km service today (GS Dakar). The tech said he'd put in a Denso Iridium sparkplug. He said BMW has instructed the dealers to change to this plug when bikes are in for service, and that the OEM plugs are really not that well suited for the engine. And, yes, the bike runs appreciably better with the new plugs. More responsive, and the slight surging or stumbling I've experienced around 3.3k revs is now all but gone. They're perhaps the most expensive sparkplugs out there, but IMHO they seem to be worth it. Oyvind #1052, Norway

On one of my magneto ignition, high compression and kick-start only single cylinder bikes I had to use Champion Gold Palladium plugs. They lasted forever and the bike always started at the second kick. With "normal" plugs the beast was sometimes almost un-startable. I rode it ( on track and road) for +300 000 km so I knew how to start it. Those plugs had a center electrode that was less than half the diameter of "normal" ones. More important, the bike ran better as far as I could appreciate. I can not explain how and why but plug choice seems to be more than just heat range. Design and materials matters also. Haakon #626(Norway-F650GS)

Denso Iridium

BMW F650 97 650 IX24 0.032
BMW F650 ST 97 650 IX24 0.032

About $20, but expect that price to be significantly lower in almost any other country. I think the plug code is IX24M.

Should I install Iridium Spark Plug(s) in my bike?

• If your bike is working fine with the current spark plugs, why waste money.
• Extended tip plugs are suggested more for surging and stalling problems on single spark FI models. Some people perceive an improvement in dual spark bikes using extended tip plugs, however no one really has "factual data" on this mod.
• Iridium tip plugs (not extended tip - e.g. DR8EIX) have also been percieved by some to improve their bikes performance. Again, what this leads to in "factual" performance I have no idea.

Hal stated that he uses Autolite spark plugs because they have a longer reach, thereby giving him better performance. I need to verify if this is a safe thing to do? The difference in length is only .041". The gap is also in question:

1. The NGK D8EA is supposed to be .024 to .028 inches.
2. Autolite states a gap of .032 inches.

What are Resistor Plugs? Well by now you might have realised that the major part of the resistance in the F Plug/Coil system is provided by the Plug Cap. Some bikes use Resistor Plugs, so another solution could be to just have a 0kohm Cap and Run Resistor Plugs in your bike, but not both!

• MPG on my R80G/S went up about 10% when I realized I was running resistor plugs AND resistor caps and changed to zero Ohm caps. <DOH!>
• NGK do make a resistor plug, the NGK DR8EA. The OEM cap was 1kohm. Substituting a 5kohm cap is probably OK.  A 0kohm cap without using a resistor plug like the DR8EA is NOT OK. If you use anything (but) more than 5k, you'll probably get less spark than you would with 5k due to impedance mismatch.  But using 10k would probably be just fine in practice.  But for good fuel economy DON'T use both a resistor cap AND a resistor plug. In other words, I don't think it really matters all that much one way or the other as far as making the bike run. Economy might suffer slightly. But would you really notice?
• Resistor Plugs. I've been getting a lot of interference on my helmet comm. lately and one manufacturers website said the cure is to use "R" type plugs. I picked up the "R" version of the D8EA for my classic and have been reluctant to install it as the length of the plug seems to be different from the stock D8EA. Anyone used the NGK DR8EA. Better yet, anyone used on and found it actually cut down on the RF interference? Sean #1015 Ottawa Canada
• I may be way off base, but I thought the resistor in the stock plug caps performed the same function as an "R" type plug. True? If so, adding an "R" plug would simply be adding more resistance to the spark circuit. It probably wouldn't make much difference in how the bike runs if the resistance isn't too high (for a while I used a 5kohm NGK resistor in one of my plug caps when the stock resistor went bad -- and my '99 ran just fine). Bob#550 (Olympia WA)
• What Bob said. On my old Airhead, the mechanics kept replacing my R-plugs with Bosch plugs "to make it run right". Do my own work now, no more arguments...:-) But they were probably right. Consider putting a filter in the 12V power line (s) to the intercom system (assuming it's not strictly dry cell powered). See Radio Shack for options. Marty #436-Chicago-97 F650F.

Links:

• http://www.strappe.com/plugs.html.
• http://www.bmwmotorrad.co.za/bikes/workshop/davidChall.asp?Id=29
• http://www.strappe.com/plugs.html

• I just noticed on the plugs I pulled today that the bottom 4 or 5 threads were black, like they were actually INSIDE the combustion chamber that far (yes they were the right plugs). Anybody had the head off with the plugs in that can confirm this? The reason I bring this up is that any anti-seize (yes, I was taught to use a TINY dab and reduce the torque by about half...I use the touchy feely method after all these years) that is on the threads of the plug COULD get burned and the metallic debris fall into the cylinder Marty #436-Chicago-97 F650F
• You can use a tiny dab of never-seize on the threads (I seldom do). If you have one, you might consider using a torque wrench until you develop the right "feel" for torquing various items like plugs. (Keep in mind that the torque required for a used plug is less, due to gasket crush.) Many will argue, but for me the biggest thing to keep in mind is the different expansion rates of the steel plug vs. the aluminum head. Whenever possible, I try to remove and install plugs only when the engine is dead cold. Overtightening a used cold plug into hot aluminum may eventually result in problems. An experienced mechanic can get away with it for years, but I wouldn't recommend it as a general practice. Todd #389
• Some folks put a bit of anti-seize on the threads of the new plug before installing it. Harl #380
• In my experience, most motorcycle plugs are torqued to 25 NM. Richard #230

by Ted in TO, 01 GS

OK, so this may be just obvious stuff, but I have never dealt with plugs before, and have less mechanical experience than I would like. I decided to do a bunch of routine work on the bike last night (battery, coolant, oil, spark plug, accessory plug).

1. While it is good to combine work on the bike, combining an oil change and a spark plug change is not a good idea. You want a warm bike to change the oil, and a cold bike to change the plug.
2. I did the whole thing with no special tools other than those in the stock kit, but I had a h*ll of a time getting the plug socket in and turning (not enough room to work in). I recommend buying a good socket.
3. Since I was checking the battery, I had all the plastic ripped off, and this made it easier to get to the plug (well, a bit easier). I ripped off the right hand side plastic, plus the piece that goes over the top. I then removed the snorkel and air box. This gave me access to the top of the plug.
4. The plug itself is on top of the engine, on the right hand side, sort of sticking up and right. Look for the single thick wire that has a 90 degree bend and goes down into the engine. you will see a rubber plug with stainless around it going down into the engine. This is the plug cap. You will not be able to see the plug until you remove this.
5. If you bought the plug already (you should have) it may have a little threaded bit on the very top. Don't worry about the threads. The spark plug cap pushes on, it does not thread on.
6. I found the cap to be very sticky. I could sort of wiggle/twist it back and forth, but I could not pull it off, and was reluctant to really pull too hard on it in case I broke something. Keep wiggling, keep pulling and eventually it will come off.
7. One important detail. Clean the recess (the hole where the spark plug is situated). It often (always) accumulates a lot of sand, grit and dust there, so it is a good advice to use compressed air to blow all the dirt out, before you unscrew the plug. You do not have to do it just prior to the plug change. The day before or something will be sufficient, if you keep to tarmac until the change. If you unscrew the plug with a lot of dirt in the recess, some of it will fall into the engine, NO GOOD. Some will also get stuck on the threads, NO GOOD.
8. Once the cap comes off and you can see the top of the plug, it is pretty obvious. The big socket in the tool roll just fits neatly in there and you can unscrew the old plug. One note: the socket has two holes drilled in it so you can slot a screwdriver (or the pin provided) in there and use it to turn the socket. Unfortunately there is not enough room to turn the socket 90 degrees and use the next hole to turn another 90 degrees. So if your plug is really sticky, you have to turn as far as you can, then remove the socket from the plug and rotate it back one face (60 degrees) then use the screwdriver again. You can get 60 degrees, but not 90 degrees.
9. Check the gap of the *new* plug before installing it, so it's within limits. I've bought some new plugs where the gap was far too wide, so it's best to check. Trevor#999
10. Pull out the plug and pop in the new one. There is a bunch of stuff about looking at the plugs and determining stuff in the faq. I just threw out the old one. Slot the new plug in carefully. If you cross thread it, it will cost more than you can believe to get the hole re-tapped (or so I hear).
11. Shove the plug cap back on there and put all the other bits together and you are good.
12. Hand tighten the plug until it is finger tight, then give it another quarter turn or so. I found several figures for tightness, but the one thing everybody agreed on was that you can do more damage having it too tight rather than too loose. The spec for GS models is 20 Nm.
13. Test the engine. If it doesn't work, bug someone else, mine worked fine. :-)

Plug Chops are what you do to tell which rpm range is rich or lean if you don't have an Oxygen or Gas sensor.

• Basically you run the bike under load, (some do it at a certain rev range e.g. idle, 2000-3500, 3500-4500 etc) however...
• It is MUCH BETTER to make marks on your Kill Switch casing at 1/4, 1/2, 3/4, Full (WFO) and put a pin in your throttle rubber so you can calibrate the throttle position, NOT the rev range)
• Then hit the kill switch, wait for the bike to cool, take out your plugs and "read" them for soot (Rich), Colour, Aluminium Bits (bad).
• Waiting for them to cool is recommended by most people due to Thermal Temp Diff. around plug threads. So it can be a Long term thing and a Royal PITA. An Idle Plug Chop is easy, because you do it every day, when you turn off your engine.
• START with NEW Plugs or you'll fool yourself.
• Hitting the "Kill Switch" is called "chopping" the plugs as you get the colour they are at that range, rather than at idle, which is where you normally turn off your engine (right?).
• Take out your plugs and check the Colour. Generally a nice "Tan" colour in the rpm range you are testing, is what you are looking for. Lamb Chops are tastier though.
• See this very good site http://www.nightrider.com/biketech/spkplghnbook.htm for a guide to Reading Plugs and Plugs in general.
• See the Exhaust Rejetting Spreadsheet for additional performance-related Spark Plug Issues.

For Plug Reads (Colours, Descriptions)

• http://www.nightrider.com/biketech/hdsparkplugs.htm on Spark Plugs and Spark Plug Reading
• http://www.nightrider.com/biketech/spkplghnbook.htm on Reading Spark Plugs, with colours of Plugs
• http://www.strappe.com/plugs.html
• http://verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm
• Or any Clymer or Haynes Manual also has a Plug Chart.

Feedback

• Reading Plugs. I have an old see through plug thing that lets you see the combustion colour. Useful on Urals, but I can't be bothered on the F (put petrol in & ride & don't worry). The plug thing is called a colour tune. David Angel at F2 motorcycles in the UK is the source. Andy Leeds UK #982

There have been reports of older (pre fuel injected models) bikes having corroded spark plugs / caused by the plug caps. Please check the Plug Caps and Coils FAQ for more information.

Leading causes of dry spark plug fouling, as indicated by dry, black, sooty residue. (NOTE: Not "wet" fouling)

In my search for wisdom regarding fouled plugs I have plowed through the faq, NGK's spark plug guide, and too many Google searches to count. After reading acres of verbiage, and sifting our the contradictory data, here is what I have boiled it down to: (robert in TX #959)

1. Too "cold" of a spark plug, resulting in the plug operating at a non-self-cleaning temperature.
2. Too rich of a mixture.
3. Excessive idling (including stop-and-go driving).
4. Retarded timing. -- robert in TX #959
5. Crap Beru spark plug caps allowing intermittant firing. (They allow plugs to wet-foul when they're totally dead) Flash 412 (CO)
6. If you have a sick oil burning donk, then the plug will oil foul. The solution is a re-ring and cyl hone and/or valve guide job for a permanent fix. Otherwise go 2 grades hotter than recommended for spark plug, this will keep oil deposits burnt off the plug tip. Keep pouring oil in to the engine, so it does not run low. IF you run hard miles like this, you COULD bash a hole in the piston, but it will probably run out of oil first! jack

DPR9EIX-9 instead of the DPR8EIX-9?

So, I'm reading that the Denso IX24 is the better plug for the GS for many reasons. Problem is...that particular plug is difficult to come by locally. However, many shops offer the NGK DPR9EIX-9 instead of the DPR8EIX-9, the 8 being the exact equivalent and the 9 being slightly different with regard to temperature? The guy on the phone said it was a little cooler but should work. I also read of some people using the 9, but no followup...which is probably a good thing. rob feature

• It'll ultimately depend on what the true compression ratio you are getting on your bike is, the octane level of the fuel you are using, how fast (and therefore how hot your engine is getting) and the spark advance that your computer is producing... But the pragmatic way to evaluate it is to try it and then look at the plug afterwards (soot on the plug means it's too cold, tarnished ceramic insulation casing indicates its too hot). The NGK website has a pretty extensive explanation of the science behind selecting plugs.
• I think I'm gonna try the DR8EIX. I can get it locally and it's an exact match to the recommended IX24. rob feature
• Actually, I think what makes the bike run better is the "P" which stands for projected tip. It puts the spark a little deeper in the cyclinder. I've had both the iridium and regular projected tip plugs, and they both worked better than the iridium dr8xxxx non projected tip. gsatlanta

Intercom noise after spark plug change?

Intercom noise is sometimes caused by RF noise. The RF noise can be generated by spark plugs / plug caps with no resistors. Take a look at the table below... If you replace the plug caps on the earlier models with a non-resistor type plug cap, you may experience noise. If you replace the spark plugs on later models with a non-resistor spark plug, you may experience noise... In other words: either your spark plugs or plug caps should be a resistor type.

Where can I find a supplier for the NGK DR8EB?

• The DR8EB was a specially made plug for BMW from what I can find out - and in theory is only available through your BMW dealer. Winter #1935
• I just ran into this for the first time recently as well, and my discovery was the same: that plug is made special for BMW by NGK, and is only available from BMW dealers. It is not in the NGK parts catalog. charleshmosesii
• My BMW dealers (stealers) don't use them don't stock them. they use the D8EA. Anyway I bought the DR8EA today, and the noise has gone from my helmut in the autocom unit. (on a decent ride to work tonight will really tell). liddell

I have a Dual Spark - How would I know if one was not working?

• Note: It is NOT a good idea to just disconnect one plug cap. This could lead to damage to the coils.
• The suggestion in the Clymer (for Funduros) is to remove one plug and ground it against the engine (somewhere away from the open plug hole) and then attempt to start the bike. If the plug works, you'll see the spark. Then just swap the plugs and repeat. I've used this method in the past and it is fairly easy to tell whether or not the plugs are working properly. [Ed note: This should work on both the Carb and FI dual spark models] banner #1750

What spark plug cap do I use on my FI model bike?

• NGK XD 05FP works on an '01 F650GS according to cdnabn49