Spark Plug Gap?

[bmw520i]

Hi,

What is the optimum spark plug gap for a 1990 BMW 520i ?

Thanks.
John.

[billB]

BMW520i

Most if not all GOOD new spark plugs come preset by the manufacturers I don't remember when was the last time I had to set a gap on a spark plug. The gap on +4 plug though is 1.6 mm gap.

On the splitfire it is a bit different for example your 520I 2.0L will have 0.9 gap.

regards

billb

[bmw520i]

Originally posted by billB@Nov 8 2004, 04:30 PM
BMW520i

Most if not all GOOD new spark plugs come preset by the manufacturers I don't remember when was the last time I had to set a gap on a spark plug. The gap on +4 plug though is 1.6 mm gap.

On the splitfire it is a bit different for example your 520I 2.0L will have 0.9 gap.

regards

billb

[snapback]226938[/snapback]

I just wondered cos I took them out this afternoon and they looked in pretty good shape but the gaps were anything from .7 - 1.1mm. weird!

The plugs in question are Champion RC8DMC (with built in resister)
funny thing is they measured anything from 200kohms - 800kohms on my multimeter. weird again!

anyway I will get a new set in the morning.

Cheers.
John.

[billB]

BMW520i
I use the Bosch +2 from the dealer and they work fine for me. Also I did use the +4 but did not feel the difference. I guess these 4 little guys fire one by one. As such in terms of power no gain over and beyond the +2. I just could not justify spending the extra money for +4. The Splitfires are different story..again I do stick to what BMW recommend for their car.

The only advantage I can think of for the +4 is they may last longer than other regular spark plugs. this can be argued as follows:

A. less abuse for the threads on the rather fragile head threads (torque, over torque, new plugs in and old ones out etc) because +4 spark plugs may last longer they get changed less frequently. I may be wrong in all this; anyone with a better feed back is greatly appreciated
B. +4 may have a self cleaning effect beacause one electrode is firing at a particular moment since all fours don't fire up simaltanously.

Again on setting the gap some recommend to set them slightly larger to 0.86-0.91mm /0.034-0.036in to get a better idle. I am so sure about that and you may want to ask the dealer when you go for the new ones.

P.S. The above is not written on a stone and open for further discussions/feed backs
regards
billb

[bmw520i]

Hi Bill,
I replaced the old Champions plugs with some Bosch 2-electrodes, the spark gap is set to .7mm, so it just goes to show how the electrodes move apart over time.

The new plugs resistance of 2kohms also goes to show how the resistance value on the champions had crepped up!

The car runs so much better now.
Better exceleration and much smoother.

cheers John.

[frank3]

Originally posted by billB@Nov 8 2004, 03:30 PM
BMW520i

Most if not all GOOD new spark plugs come preset by the manufacturers I don't remember when was the last time I had to set a gap on a spark plug. The gap on +4 plug though is 1.6 mm gap.

On the splitfire it is a bit different for example your 520I 2.0L will have 0.9 gap.

regards

billb

[snapback]226938[/snapback]

Not true. Many plugs are used on many different cars that require different gap settings. On the other hand, the double and quad tip plugs (bosch +2 and +4 for instance) do not require gap settings.

Bottom line, depends on what style of plug you get.

[billB]

Dear FRANK3

While it is true different cars have different gap settings Please read this again:Most if not all GOOD new spark plugs come preset by the manufacturers

The 1.6mm is also the factory preset gap. We talking bimmers
regards
billb