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From digest.v6.n65 Wed Jan 15 15:22:51 1997
From: "David J. Kroth" <>
Date: Wed, 15 Jan 1997 09:49:12 -0500
Subject: more NGK plug info

Here's some more NGK plug info...

Forwarded mail from From:
Date: Tue, 14 Jan 1997 17:44:25 -0500 (EST)
Subject: NGK plug info


I am an engineer at NGK Spark Plugs (USA) and I was forwarded a recent post you made in the BMW Digest via a mutual Internet acquaintance (Dave Kroth). He found me on the Talon Digest and has allowed me to see some spark plug questions posted on the BMW Digest.

Okay, enough with the intro, I am writing in reference to a discussion concerning a "platform" plug once produced by NGK for BMW. Now I am an engineer based out of Chicago, IL and have never worked with BMW, but I have seen some of their freaky spark plug design requests. I have seen the "platform" plug (BCPR7ER) you referred to and I may be able to help you with my attempt at an explanation.

> Picture a 3 legged stool in your mind, with the top platform being
triangular with
> 3 holes (I'm guessing for spark travel) in it

The holes have been punched into to the platform for a few reasons. Since I was not involved in the creation of this particular plug, I will pretty much be assuming the reasoning. One reason for the holes is to allow the A/F mixture to pass by the initial spark. Once the flame kernel begins, it is desirable to let it flow to the rest of the combustion chamber and the holes will assist. Again, I have never observed their combustion, but I would think they would get a better "blow-through" than if the holes were not there. The edges of the holes may also allow a possible sharp edge for a spark to travel to.

After all these complications, you may ask why they would ever design such a plug. Well, the Europeans manufactures often use multiple ground electrode spark plugs to allow longer life without using expensive (and longer lasting) precious metals (Pt, Ir, etc.). US automakers ask more of their plugs by claiming 100K mile tune-up intervals vs. the European 100K km (or 60K mile) requirement.

The platform plug was probably a good design early on. The larger ground electrode will give the spark path more options and thus gives the plug longer life by not allowing a large gap growth over time. There are also anti-fouling characteristics gained by this design. The ground electrodes are also able to easily cool themselves into the engine block with 3 different paths.

Here is a second excerpt from your post:

> If you call NGK, you will find out that this plug (BCPR7ER) is now
> discontinued, and the replacement is BKR6EK=85

To begin with, let me give a rundown of what our spark plug numbers mean:

B       Thread Diameter: 14mm
C       Construction: Hex Size =3D 5/8"
P       Construction: Projected insulator type
(K)     Construction: hex size =3D 5/8" projected tip (ISO)
R       Construction: Resistor Type
7(6) Heat Rating Numbers: 2 =3D Hot ->Colder
E       Thread Reach: 19mm (3/4")
R       Firing End Construction: Special Ground Electrode
(K)     Firing End Construction: 2-Ground electrodes for Toyota, BMW

Once again, I have not developed the M50 engine you use, so this is all mere assumption. I don=92t even know if NGK is original equipment in the M50.

Anyway, I have seen programs change plugs after years of using the same plug. This decision to change plugs can be driven by many things, but usually ends up being financial. Then again, there may be performance, emission, or fuel economy reasons as well. Some engines have been known to use four different plugs manufactured by four different suppliers within 12 years. It may so happen that BMW had minor changes that required a different plug design, or they may have been using the wrong plug for years. These are all possibilities that may have required NGK to stop producing the "platform" plugs.

One quick note: You should avoid changing heat ranges of plugs at all costs. A user should not change from the recommended heat ranges unless serious modifications have occurred and problems were observed with a particular heat range. NGK recommends the BKR6EK for the M50. If you go up to a "7," you are risking never reaching the self-cleaning temperature (or region) of that particular plug. A spark plug must reach this temperature to burn off the carbon deposits accumulated at lower speeds. If a plug is too hot (say a "5" for this particular application), you run the risk of pre-ignition under high demand conditions. Pre-ignition can occur if the plug is so hot that it will ignite the A/F mixture before it sparks. I hope you never see pre-ignition because it can rip an engine apart in a hurry.

The difference in heat ranges is simply the cooling rates of the plugs into the cylinder walls. The industry does not have heat range standards, so Bosch does not equal NGK, which does not equal AC, etc. Bosch's equivalent plug to NGK=92s BKR6EK is indeed your F7LDCR, so I assume you are safe.

I hope this helps out a bit, sorry I am not familiar with this particular application. If you feel the need to forward this to the BMW Digest (if it has enough substance), feel free.

Matt Blue
OEM Product Engineer
NGK Spark Plugs (USA), Inc.

End of forwarded mail from

  • -- Dave
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