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boxertwinjeff wrote:So being a mechanical dumby, how do I know if it's a dual plugged model?

Second plug at 6 0'clock, or under the cylinder. Done after purchase. It's not a factory option.

Ahh, a guy on another forum says Bmw released some S models dual plugged So what's the advantages
in dual plugging anyway?

boxertwinjeff wrote:Ahh, a guy on another forum says Bmw released some S models dual plugged So what's the advantages
in dual plugging anyway?

Not in the airhead version of BMW. Some oilheads after 2000 were.

http://rubberchickenracinggarage.com/Do ... nition.pdf

Interesting reading Steve, thanks.

boxertwinjeff wrote:. . . So what's the advantages in dual plugging anyway?

In short, twin plugs ignite the fuel air mixture in two places rather than one. Among other things this promotes a faster and more complete combustion. The ignition will usually needed to be retarded because less time is required to complete the combustion "event". There is correspondingly less likelihood for "knock" or "ping" and theoretically, at least, lower octane fuel can be used.

One potential disadvantage is that there is less thickness in the head where the second plug goes. That means you need to use a plug with half inch thread length as opposed to the 3/4 inch thread length for the top plug. It's a little easier to strip the 1/2" threads unless you're careful. It is also usually recommended to use a smaller diameter plug, such as a 12mm, to forestall any cracking in the head between the plug and the valves.

It's a judgment call if the work and cost of twin plugging it worth it. My '77 R100S came to me twin plugged. I like it, but I reckon I'd be just about as happy without it.




Ken

Dual plugging was developed in the US when the high compression sports models started pinging on the new fangled unleaded gas.

The main advantage is to allow highish compression ratios. 10:1 without problems on today's crappy gas. As a side advantage you will get a smoother engine and easier starting. It is best done as one part of a total tuning package, if done by the right person, you can get a decent amount of extra useable performance. It's much easier to do nowadays in that there are some ignitions available that have the right ignition maps available out of the box.

902 by boxertwinjeff, on Flickr


914 by boxertwinjeff, on Flickr


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915 by boxertwinjeff, on Flickr


913 by boxertwinjeff, on Flickr
Looks fairly clean to me.

This is the new bike.

Very nice Jeff!

For some reason, I just visualised you standing at Darwin Harbour with binoculars.

SteveD wrote:Without knowing the R90S that closely, it looks the goods. I've seen 2valves schmick version a few years back but other than that not much idea. When is your ship due in

Are you developing a collection? I have a mate that wants a 75/5 desperately! He just needs to sell his 1935 side valve Triumph first.

She's still sitting in Cal, just waiting on Import approval cetificate, then Shipping Co. will pick it up, do their
thing, then ship. I wouldn't expect to see it for aleast 2 months or more.. lucky I'm patient ..
No Collecting!!, 2 bikes in the loungeroom is enough... looks like I'm building that shed earlier than I expected!