confusing spark plugs numbers

simon

simon

Famous Member
spark plug reference lists are driving me nuts…

What is the difference between motorcraft BF42C and BSF42C ?
The NGK replacement for both is WR5, so I guess BF42 and BSF42 are equal, more or less. Then again, the cross reference list shows differences on the Bosch plugs - like this:

Motorcraft BF42C – Bosch D9BC

Motorcraft BF82C – Bosch D10BC

Motorcraft BSF42C – Bosch D8BC, Bosch DR8BC, Bosch DR9BC

Motorcraft BSF82C – Bosch DR10BC

Then, autolite ap35 and ap46 are both recommended to replace the motorcraft BSF42C.

Even more confusing, Champion RF11YC alone seems to be suitable to cover ALL of the plugs above, plus a dozen more.
thats too much for me, how can one manufacturer make a spark plug that covers several different heat ranges of other competitors?

Guess what… yeah, I´m lost.
 
Ford has a simple corporate policy on using plugs. They grab some-one elses, and then either have it reclasified in the own system, or reworked as a Motorcraft part. Then they just give it a sequential number.

Back in the 1990's Ford used a Volvo spark plug in the XR6 Falcons, and it took 9 months the get it reclassified to the Autolite/Motorcraft scale.

Ford really do a bucket load of work on plugs, and they run whole engine combinations to run standard off the shelf parts. They cost out the value of running an oddball plug, and if its worth it, they'll regrade someone elses plug to there scale and just add another number. In most cases, it's not, and they prize pool the plugs to save on cost. Unlike Rober Bosch, Motorcraft don't make plugs for everyones European machine, so they mainstream the choices. It may be that the subtle changes trade a half hp or so, but when your servicing the cars you sell, you make a tidy mark-up on having just the one Motorcraft plug insted of 5!
 
thanks Dean.

So, basically I could use every spark plug thats been listed in the same range as the Champion RF11YC, or NGK WR5. That´d cover all the plugs for SBF engine family as well - 18mm, tapered seat, .460 reach, .8125 hex size.

Gives me something to play with... what could possibly happen? Either they run fine, or gum up with residue and deposits, or promote pinging when the tip gets too hot.

Now on to the next obstacle in my way... BOSCH has different numbers for their plugs in US and Europe. :shock:
my parts dealer says motorcraft plugs aren´t listed in his cataloge anymore, but he offers me Accel plugs Ive never seen listed before, and the local bosch dealer won´t sell me platinums for the ford six over here, because DR9BPX are for the US market only.
Ahhh, the joy of re-importing stuff... :wink:
 
I'm pretty sure we have the Euro spec plugs here, also. Certainly can't get the Platinum series as spec'd for the US Fords.

The Bosch cattledog is quite clear though in explaining the part numbers, and you can look at the duty descriptions/choices and reasonably guess at the first trial set, and which way to go following that point. It seemed to be constructed with competent mechanics in mind.

Balance that against a cynical parts marketing machine which pitches products at - specifically - DIY types who may well not have the years of experience or evaluation capabilities of a regular mechanic. I'll trust the catalogue. The grass is not always greener.
 
It does get confusing doesn't it :shock:

OK first, the NGK WR5 is made to cover a few different heat ranges. This is so they only have to make one plug to cover a few cars. They usually go about five steps up or down. IF you want to go 5 steps colder than a WR5 than you can use a AP7FS (2127)

Now, Bosch. The DR10BC is a resistor plug. That is what the "R" stands for. The lower the number the colder the plug. For the US 6 cyl. Bosch says to use a DR10BC. For the OZ 250 Bosch says to use a DR8BC the DR8BC is colder. Which is the one I am currently using. To make things more confusing most part stores go by the numbers Bosch 7551 (DR10BC) & 7550 (DR8BC) BTW, these are both copper plugs. The 6200 is a plat plug and is equal to the DR10BC and a 4226 plat. is equal to the DR8BC

Now Autolite AP35 is a lot colder than the AP45 and I would not use it.

The Champ RF11YC is the same as the NGK covering different heat ranges.

Thanks to CobraSix I have also found out that the Bosch plugs are a tad bit shorter (reach) than the Autolites. Which helps me because the plugs hit my piston and I always have to index them. (Don't over mill your head or you might have this problem also :lol: )

Hope this helps.

Also, don't use too hot of a plug or you might damage the engine with prolonged use.
 
Thanks a bunch.

My only problems now are counter kids who won´t let me use their catalogue, and old stubborn bosch dealers who insist there are "no plugs available, never have been".
 
Marco, If you don't mind, I'm going to use your sparkplug research numbers to post on my website in the future (when I get around to doing the major updates required). It's good information for us 6'rs. I'm probably using the 10C platinums and if Bosch recommends the 8C for the Oz, I may change out next time around.

Slade
 
Slade, go ahead. I will be updating my webpage sometime soon also. I havn't in a long time.

Simon, the 7550 & 7551 copper plugs are only $1.09. The plats. are $1.89 I think. If you need some sent to you just let me know.
 
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