Harley firing sequence
#11
12-15-2010, 11:36 PM
Outstanding HDF Member
Wait a minute thats a bogus part number? Dangit I been tricked
#13
12-16-2010, 02:15 AM
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#14
12-16-2010, 05:01 AM
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Last edited by CrustyAngel; 12-16-2010 at 05:08 AM.
#15
12-16-2010, 08:08 AM
[QUOTE=parts eeter;7661058]
Thanks for the reply, but the thing that is kinda confusing me is it seems that the dual fire in the rear cylinder when it's about to begin the intake stroke would cause problems (not the alternate 405 degree fire when it's on the exhaust stroke).
I realize Harleys don't dual fire anymore but when they did it seems it would interfere with the intake since I remember some cams actually open up the intake valve while the exhaust is still closing but maybe thats only in cars where the intake manifold maintains flow pressure and actually helps blow out the remaining exhaust gas. But at any case I would think a spark occuring while the intake was opening would cause a backfire.
That would be part # zero as in never made. So then now it's your turn to comment on the sequence.
Well I said that as you answered your own question. A "dual fire" ignition is just that when either hole needs lit both plugs get zapped. So in essence there truly is no firing order on that particular engine. Like there is no radiator on a VW Bug. One hole is always firing 45 degrees off. Here is the basics from 8541Hogs link.
Well I said that as you answered your own question. A "dual fire" ignition is just that when either hole needs lit both plugs get zapped. So in essence there truly is no firing order on that particular engine. Like there is no radiator on a VW Bug. One hole is always firing 45 degrees off. Here is the basics from 8541Hogs link.
I realize Harleys don't dual fire anymore but when they did it seems it would interfere with the intake since I remember some cams actually open up the intake valve while the exhaust is still closing but maybe thats only in cars where the intake manifold maintains flow pressure and actually helps blow out the remaining exhaust gas. But at any case I would think a spark occuring while the intake was opening would cause a backfire.
#17
12-16-2010, 09:11 AM
Cruiser
#18
12-16-2010, 09:13 AM
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[quote=R_W_B;7661810]
Thanks for the reply, but the thing that is kinda confusing me is it seems that the dual fire in the rear cylinder when it's about to begin the intake stroke would cause problems (not the alternate 405 degree fire when it's on the exhaust stroke).
I realize Harleys don't dual fire anymore but when they did it seems it would interfere with the intake since I remember some cams actually open up the intake valve while the exhaust is still closing but maybe thats only in cars where the intake manifold maintains flow pressure and actually helps blow out the remaining exhaust gas. But at any case I would think a spark occuring while the intake was opening would cause a backfire.
both cylinders fired at the same time every 360 degrees. That is why the early engines never maximized power because you had to adjust timing to a best fit for both cylinders, so obviously optimum performance could never be obtained. One firing was always with the exhaust valve open, hence the unique sound. Some aftermarket companies did offer dual point/dual coil setups, but they never really worked right.
Thanks for the reply, but the thing that is kinda confusing me is it seems that the dual fire in the rear cylinder when it's about to begin the intake stroke would cause problems (not the alternate 405 degree fire when it's on the exhaust stroke).
I realize Harleys don't dual fire anymore but when they did it seems it would interfere with the intake since I remember some cams actually open up the intake valve while the exhaust is still closing but maybe thats only in cars where the intake manifold maintains flow pressure and actually helps blow out the remaining exhaust gas. But at any case I would think a spark occuring while the intake was opening would cause a backfire.
#19
12-16-2010, 09:35 AM
[QUOTE=fchava;7662068]
Ok thanks, that really addressed what I was after. I surmize they had to bump the spark ahead on the front cylinder to keep it while the exhaust was still open on the rear, course some of that I've read actually is better for performance but with a 45 degree lead of the back cylinder it had my curiousity going as to how it did?
My next confusing item is this: if both single fire and dual fire, "fire" approximately every revolution, why do some tachs require a single fire adapter. It seems there would be the same number of "pulses" being counted at the coil for either scenario?
I know my cobra tach is wired into the coil with one wire connected to the Blue-Red coil wire.
But I'm going to be buying another tach when I put my new bars on since they are T-bars and the my mini apes are mounted with the cobra tach riser bar clamp cover.
both cylinders fired at the same time every 360 degrees. That is why the early engines never maximized power because you had to adjust timing to a best fit for both cylinders, so obviously optimum performance could never be obtained. One firing was always with the exhaust valve open, hence the unique sound. Some aftermarket companies did offer dual point/dual coil setups, but they never really worked right.
My next confusing item is this: if both single fire and dual fire, "fire" approximately every revolution, why do some tachs require a single fire adapter. It seems there would be the same number of "pulses" being counted at the coil for either scenario?
I know my cobra tach is wired into the coil with one wire connected to the Blue-Red coil wire.
But I'm going to be buying another tach when I put my new bars on since they are T-bars and the my mini apes are mounted with the cobra tach riser bar clamp cover.
#20
12-16-2010, 12:17 PM
Road Master
[QUOTE=fchava;7662068]
Sorry but this is wrong. Parts eeter has it right. Both pistons connect to the crank at the same position. There is a 45 degree difference in the crank rotation between the two TDC. That is what causes the "lump" in a Harley. One rotation will be 45 degrees less than a full rotation, and one will be 45 degrees more than a full rotation between power strokes.
I have no idea if both plugs fire at the same time but I would bet not. The manual shows that the rear spark wire most be connected to the top terminal on the coil. If you wanted to find out, just switch them around and see if the bike runs.
both cylinders fired at the same time every 360 degrees. That is why the early engines never maximized power because you had to adjust timing to a best fit for both cylinders, so obviously optimum performance could never be obtained. One firing was always with the exhaust valve open, hence the unique sound. Some aftermarket companies did offer dual point/dual coil setups, but they never really worked right.
I have no idea if both plugs fire at the same time but I would bet not. The manual shows that the rear spark wire most be connected to the top terminal on the coil. If you wanted to find out, just switch them around and see if the bike runs.