Spark Plug Gap

[Bob_Roller]

There is a thread on an oilhead forum I belong to .
The question is, should you leave the spark plug gap as it is set at the spark plug manufacturer, or use the recommended gap that BMW states in their repair manual .
I've always set it to what the vehicle manufacturer states .

[donbmw]

I have always used them right out of the box. Don’t remember ever needing to set the gap when I was checking.

[Justin B.]

I have seen plugs with the gap noticeably "off,", probably due to mishandling so if it is a standard plug I usually check.  The newer ones with plat and irid electrodes is another thing...

[Barry]

I always check the gap on new plugs and in necessary set to the spec of 0.024"

Our spark plug gaps are narrow by modern standards. Electronic ignitions usually use bigger gaps, typically up to 0.0040"  If the ignition system can cope a bigger gap is a good thing because it increases spark energy.  Pushing the gap up increases spark energy by 56% at 0.030" and 178% at 0.040" so I've always been puzzled that BMW kept the same gap when they introduced electronic ignition.

[Tony Smith]

There is a thread on an oilhead forum I belong to .
The question is, should you leave the spark plug gap as it is set at the spark plug manufacturer, or use the recommended gap that BMW states in their repair manual

I have an oilhead - 2002 GSA. As far as I am concerned it simply is not possible to accurately adjust the setting on the weird specified plug. The two ground electrodes end with a concave "scallop' out of them which means that the only way to measure the true gap would be a form gauge or calibrated wire (held very carefully).

I intend to simply change them out every year at the yearly major service, the cost of a couple of plugs isn't going to worry me overly much.

Fun fact, When I fitted the "weird" twin ground plugs a significant amount of the rough running when cold and cutting out went away (fully cured with removal of the additional "tuning" chip and cleaning injectors and replacing O-Rings).

The specified plugs do not seem to be available in Australia and most people use the single ground alternative, I bought a box of the specified plugs from Motobins, so I am sorted for some time to come.

[Bob_Roller]

I've got the owners manual from my '81 R65 and '84 LS and they have .024 in., .61 mm plug gap on my '81 R65 .
I questioned this the first time I removed the plugs .
Called the dealer I bought the bike from was and told to use  .030 -.032 in., .76 -.81 mm .

That's interesting Tony, my '02 R1150R came with Autolite 3923 copper core plugs .

[Tony Smith]

That's interesting Tony, my '02 R1150R came with Autolite 3923 copper core plugs .

Not the best photo - but you get the idea

https://www.ngk.com/product.aspx?zpid=9354

[Bob_Roller]

OK, multi ground electrode plug !!!
I  used Bosch +4 plugs, four ground electrode plug in my '81 R65, I think they recommended not trying to adjust the gap, more likely to do damage in the process .

[Tony Smith]

OK, multi ground electrode plug !!!
I  used Bosch +4 plugs, four ground electrode plug in my '81 R65, I think they recommended not trying to adjust the gap, more likely to do damage in the process .

I agree, hence my earlier post. Hey I found something  a few weeks ago. Some time int he early 80s the former British spark plug concern of Golden Lodge was bought out by the italians, this made sense as I think that Alpha Romeo was the only car manufacturer to specify them as OEM. Anyway, the (then local to me) European car parts place in Townsville had them on display when I was there buying an oil pressure switch and I bought a box of 12 of them, A few days ago I found the box which still contains 12 Golden Lodge plugs.

Given the silly prices these are currently getting on eBay I may just make a large windfall profit.


P.S. It's a long time ago but I seem to recall that the GL plugs made no difference to performance on the R100RS and I simply never bothered to use the rest of the plugs - for once I may just have some luck.

[Bob_Roller]

I have used a few different type plugs, claimed to be better for performance, fuel economy and in the end, it's all marketing hype !!!!!!!!
I have not seen any difference in the different type plugs .
The vehicle operator and basic vehicle maintenance  is the biggest factor in this !!!!!!!!

[Tony Smith]

I have used a few different type plugs, claimed to be better for performance, fuel economy and in the end, it's all marketing hype !!!!!!!!
I have not seen any difference in the different type plugs .
The vehicle operator and basic vehicle maintenance  is the biggest factor in this !!!!!!!!

I could not agree more - the "trick: is to install the correct plug from both an electrical and combustion chamber point of view.

I have lost track of the number of "my motorcycle doesn't run right" investigations that have found things like the wrong reach plug or the wrong type of plug (eg extended nose or twin ground etc). But my all time favourites are where the plug specification has changed in the course of a model's lifespan - e.g. XS750 Yamaha and KLE500 Kawasaki both started life with unshielded, plain wire conductor ignition leads with non-resistor caps. In both cases the specifications changed (and in the case of the yamaha, more than once) I have seen every possible wrong combination - resistor plugs with resistor caps, resistor caps fitted to wrong coils (require non-resistor). My all time favourite was on a Yamaha XS750 whose owner spent a lot of time touring and had fitted a car type  radio cassette player into their tank bag. In an effort to reduce  what he thought was ignition interference (it was partially) he had fitted carbon ignition leads, resistor caps and used resistor spark plugs.

And he wondered why it ran badly (the coils he had were the original ones that needed plain wire leads and no resistor).

I cured the "doesn't run properly" fault by the obvious means and then cured the "ignition noise" by fitting capacitors to both the coils and the alternator.

[Barry]

The one thing that exotic spark plugs whether multi electrode or precious metal do deliver is very long life. I ran the Bosch  +4's in my old 190e for 60,000 miles without any need to attempt at adjustment.

The down side of plugs that last a long time is I live in fear that they will be seized in when I come to replace them.  I keep meaning to take them out and put them back in my current car but it's not a 2 minute job like the bike.