BerndM Posted February 9, 2012 Share Posted February 9, 2012 Will a 1200 Hex run with the 2 lower plugs out of action? What do they actually do? IIRC, someone mentioned that all 4 plugs fire at exactly the same time all the time. This is a hard concept for me to wrap my head around. Link to comment
dirtrider Posted February 9, 2012 Share Posted February 9, 2012 Evening Bernd Yes, no maybe so… Unlike the 1100/1150 with a lost spark system that sparks all plugs on every piston up the 1200 hexhead only sparks each side on top of compression stroke. On the 1200 RT hexhead both coils on a SIDE do spark at the same time at idle & low RPM's, but as the RPM's increase the lower spark plugs are phase shifted & spark at a slightly different time until at higher RPM's they really do nothing as their spark comes too far off the top of compression stroke. Those lower spark plugs light off the lower edge of the combustion chamber to promote a more even flame front & better (more complete) combustion. It (the 1200 hexhead) will run on only the upper plugs but it won't idle every good or at all & the low RPM performance will be very poor. At higher (re hi-way) speeds you probably wouldn't be able to tell the lower plugs were not working. Link to comment
BerndM Posted February 10, 2012 Author Share Posted February 10, 2012 Thanks for that info D.R. Link to comment
Clive Liddell Posted February 10, 2012 Share Posted February 10, 2012 Hi DR, As I recall I read somewhere that there was a variable timing change on the bottom plug wrt the side plug presumably to control detonation or incomplete combustion. I may have dreamed this but I don't think so :>) Edit: Sorry, Re-read your post above and see you comprehensively cover my rambling thoughts on this... Link to comment
lkchris Posted February 10, 2012 Share Posted February 10, 2012 It will nevertheless be pretty difficult to disable the bottom plugs without damaging coils. Plus, wouldn't this generate a "code" that a dealer would need to reset? In any event, doesn't seem like a viable course of action. Link to comment
roger 04 rt Posted February 13, 2012 Share Posted February 13, 2012 Evening Bernd Yes, no maybe so… Unlike the 1100/1150 with a lost spark system that sparks all plugs on every piston up the 1200 hexhead only sparks each side on top of compression stroke. On the 1200 RT hexhead both coils on a SIDE do spark at the same time at idle & low RPM's, but as the RPM's increase the lower spark plugs are phase shifted & spark at a slightly different time until at higher RPM's they really do nothing as their spark comes too far off the top of compression stroke. Those lower spark plugs light off the lower edge of the combustion chamber to promote a more even flame front & better (more complete) combustion. It (the 1200 hexhead) will run on only the upper plugs but it won't idle every good or at all & the low RPM performance will be very poor. At higher (re hi-way) speeds you probably wouldn't be able to tell the lower plugs were not working. Hi DR, By promoting a better flame-front, didn't this also reduce lean-surging in the earlier Oilheads? Might a 1200 have some surge if the second plug were removed? Link to comment
dirtrider Posted February 13, 2012 Share Posted February 13, 2012 Morning Roger Probably so, I've never ridden a 1200 hexhead with both bottom plugs disabled at the same time but they run poorly enough with just one lower plug disabled that I doubt surging would be the biggest concern. Link to comment
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