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Hex Heads...Literally


Koop

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Anyone have a photo of the hex head combustion chamber? Looking at the spark plug orientation I'm having a difficult time understanding the secondary plugs relationship to the combustion chamber. With the CR of this engine, there shouldn't be much room to have a plug introduced from the side. How'd they do that??

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This is the best I could find. If you look at the closest cylinder you can see the tip of the secondary spark plug in the lower part of the cylinder.

 

r12gs_motor.jpg

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Thanks for the illustration. I wish the service manual (CD) had system overviews and iilustrations. Now I'm wondering why there's a gear drive and chain on the front of the crank. Kind of like wearing a belt and suspenders!

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Koop, gears drive the balance shaft & the chain(s) drive the cam intermediate shaft & pumps.. The balance shaft runs backwards to engine rotation..

 

Twisty

 

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Here's a picture of a head, taken while I had it off to repair a crashed piston. You can see both the center and lower (angled in) spark plug holes:

 

217462838_edQSK-M.jpg

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Wasn't the 2nd plug added to reduce the infamous "surging" caused by tightened emission controls (hunting for the perfect fuel:air mix)?

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Wasn't the 2nd plug added to reduce the infamous "surging" caused by tightened emission controls (hunting for the perfect fuel:air mix)?

 

It was not added to cure surging, though it did have that effect. It was added to allow the boxer to meet the newest European emissions regulations. Essentially, not all of the mixture was getting burnt - possibly due to the spare-squirt FI that fires on the fiting stroke as well as the induction stroke. The second plug burns all of the fuel leading to less surging, more power and lower fuel consumption as well as lower emissions.

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IIRC, a number of airheads were fitted with dual plug heads back in the late 1970's to alleviate the detonation caused by lower octane gas as lead was phased out in U.S. The alternative was thicker base gaskets to effectively lower compression (and power).

Tom

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