dual plug head question

[rwfilipowicz1515]

I have an 82 RT100 that has dual plug heads, even has a plug in the bottom. Do these work with out a seperate set of wires and coils or am I missing something? Is this a modification from the original or did they come this way? Is there a reason to add spark to the dual head for general use?
I just got the bike back on the road after buying it and refurbishing. It looks great and runs great.

[GlobalRider]

I have an 82 RT100 that has dual plug heads, even has a plug in the bottom. Is this a modification from the original or did they come this way?

The top plug is original BMW; the bottom is a modification.

Do these work with out a seperate set of wires and coils or am I missing something?

From what I've seen, 2 ignition coils, 4 seperate ignition wires.

Is there a reason to add spark to the dual head for general use?

More complete combustion due to two flame fronts and therefore better gas mileage. A co-worker was getting ten extra miles per Imperial gallon.

You want to make sure you adjust your timing accordingly and limit your ignition advance. You can't set it to the factory specifications.

[20774]

Also allows you to run lower octane fuel without pinging. Mind the way you connect the ignition wires...there's a right way and a not so good way. Some background here: http://home.jps.net/~snowbum/dualplugging.htm

Kurt in S.A.

[rwfilipowicz1515]

Thanks to all who answered. Kurt yours was outstanding. I now have a new project on the board.

[JETHRIDGE]

I have an 83 rt and found two plugs on the bottom of the head. come to find out these were plugs where the smog stuff had been removed. Wonder if that is what you are looking at

[rwfilipowicz1515]

Could be this was smog stuff. this looks to be a California bike. Thanks for the heads up.

[20774]

Pulse air stuff here - http://home.jps.net/~snowbum/pulseair.htm

Kurt in S.A.

[lkchris]

In case you're taking a survey ...

Dual-plugged heads would turn me off from buying a particular bike.

[Braddog]

In case you're taking a survey ...

Dual-plugged heads would turn me off from buying a particular bike.

The R100S that I bought 2 years ago with dual-plugged heads has been "de-converted" to single plug heads, and the coils have been replaced with stock. No difference in performance at all, plus now it starts much easier. The "converted" coils don't do their job very well sometimes.

In my personal experience, dual-plugged heads on an airhead aren't a big improvement, so while it shouldn't necessarily prevent you from buying a bike, it is certainly no option that should be considered a huge plus, either.

[fracture]

Braddog:

Regarding your dual-plugged bike----was dual plugging the only mod?

I can see where dual plugging by itself may not make a difference, but when combined with higher compression and other breathing enhancements, then there may be an improvement. If you have any experience with such mods, I would like to know how it worked out for you.

I have considered the higher compression and dual plugging mods. I still wonder if it is worth the effort for what could be relatively little gain. I have never ridden an airhead with such mods so I have no personal experience to guide me in this matter. The money might be better spent on an oilhead or hexhead.

However, if the airhead is someone's favorite bike, then it may be worth the effort and cost. I like the airheads. Simple, relatively trouble-free, easy to maintain. Would I be giving up these characteristics if I got an oilhead or hexhead? I hear some horror stories of major mechanical failures so for now I am keeping my airhead, mods or no mods.

[GlobalRider]

In case you're taking a survey ...

Dual-plugged heads would turn me off from buying a particular bike.

I feel the same way. My airhead isn't dual plugged and it runs just fine.

[Braddog]

Braddog:

Regarding your dual-plugged bike----was dual plugging the only mod?

I can see where dual plugging by itself may not make a difference, but when combined with higher compression and other breathing enhancements, then there may be an improvement. If you have any experience with such mods, I would like to know how it worked out for you.

I have considered the higher compression and dual plugging mods. I still wonder if it is worth the effort for what could be relatively little gain. I have never ridden an airhead with such mods so I have no personal experience to guide me in this matter. The money might be better spent on an oilhead or hexhead.

However, if the airhead is someone's favorite bike, then it may be worth the effort and cost. I like the airheads. Simple, relatively trouble-free, easy to maintain. Would I be giving up these characteristics if I got an oilhead or hexhead? I hear some horror stories of major mechanical failures so for now I am keeping my airhead, mods or no mods.

Dual plugs were not the only mod. It also has a lighter flywheel, K&N air filter, rejetted carbs, etc. I'm not sure about the pistons, but I do know the valve/valve guides were updated to allow for unleaded gas.

It's a good motorcycle, runs well, looks good. But I think that the 2 previous owners to me put a lot of time and money to try to make this motorcycle into something that it can't quite be.

In comparison, I also have a '77 R100RS, one of the original "big pipe" versions with 40mm carbs and pipes. This bike did have pistons and the valve/valve guides done, and is also geared higher. My bike that previously had the dual-plugged heads and lighter flywheel, etc. isn't even in the same ballpark as my RS.

[lkchris]

There was a period of time--1979-1980--when BMW Airhead owners were in trouble in the USA because premium gasoline simply wasn't available. Pretty much all Airheads through 1979 arrived with either 9.0 or 9.5 compression and required premium fuel.

This was the era of transition from leaded to unleaded gasoline, and there was some confusion as to providing enough octane without lead. So, instead, we could buy two grades of low-test, i.e. leaded and unleaded. There was some talk that a "synergy" could be achieved by mixing the two grades of low test that could provide enough antiknock octane, but this only occurred to best of my knowledge in BMW motorcycle circles. The UOP Shadow was a demonstration at the Formula 1 level that high-octane unleaded was indeed possible, BTW.

Dual plugging, then, became the solution permitting use of regular fuel in these high compression motors, as the better ignition prevented the detonation that could otherwise occur. It was a survival mechanism.

It's only after the high octane fuel shortage was over that dual plugging then became a "performance" enhancement in the minds of those that would promote it as such. The fact that dual plugging kept some highly-tuned bikes on the road does not, of course, make it a performance enhancement--that's like saying front-wheel drive creates fuel economy.

Since all (USA) Airheads from '80 on had 8.2 compression (later 8.5) there was no problem using low-test gasoline and none of these bikes "needed" dual plugging. And, now that premium fuels are again available, there's no problem with the higher compression bikes, either.

There are additionally those that theorize dual-plugging may lengthen cylinder head life of R100 motors. The big-valve versions of the '77-'84 R100 motors had perhaps not enough material left to prevent warping, and "theoretically" dual plugging evens out the heat. All R100 motors after 1984 had smaller valves, like, for example, the R100/7 of '77-'78. But, then, BMW seriously detuned and decontented Airheads in general to try to encourage sales of the slow-selling K-bikes in this era.

Finally, yes, on Oilhead motors, dual-plugging helps with surging caused by lean fuel injecton mixtures. NOT relevant to Airheads.

My conclusion is that Airhead dual-plugging is now an irrelevant anachronism and I'd certainly never look at buying a bike so butchered.

[jbcollier]

Any wide valve angle head will benefit from dual plugs in high performance applications. The high piston dome necessary to raise the compression ratio creates a long thin combustion area which burns faster and more efficiently with twin plugs. There is no need to twin plug a low compression engine.

The most noticed effect of twin plugging is in low rev range. Usually a bike that protests getting throttle at 4500 rpm will accept throttle as low as 4000 rpm after dual plugging. You will notice that I am talking about radically modified engines.

Dual plugging reduces the excess burn time of the long thin combustion area. This means the total timing advance can be decreased. This reduces heat load (important in an air cooled hp engine) and load on the big end (more important in engines with roller big ends).

My experience with dual plugging comes from Ducati singles. Usually dual plugging is not considered unless the engine is almost full race and compression ratios are 10:1 and higher. I have no plans to dual plug my airhead.