Topic: Ignition coil compatibility (750->550?)

[cb544]

I've searched- but maybe I just haven't used the proper search terms.

I've read the FAQ- but maybe I just haven't read closely enough.

I've done my own research- but don't trust myself.


My friend picked up a set of coils from a 750 and is convinced they will work on my 550. I rebuilt my coils and they seem to be fine, and I really don't want to burn out my bike just so I'm not the ungrateful jerk.

Will stock 750 coils work on a stock 550?

[69modelj]

The wires are shorter on the 750, and probably not reach the plugs on a 550.

[cb544]

The wires are shorter on the 750, and probably not reach the plugs on a 550.

Suppose they did... are they the same internally?

[mlinder]

More or less, yeah. They're coils. I've used a cb750 coil on cb350f.
They're fine, if they will reach.

What do you mean you rebuilt your coils?

[cb544]

More or less, yeah. They're coils. I've used a cb750 coil on cb350f.
They're fine, if they will reach.

What do you mean you rebuilt your coils?

I mean soldered in some new plug wires...

[HondaMan]

More or less, yeah. They're coils. I've used a cb750 coil on cb350f.
They're fine, if they will reach.

What do you mean you rebuilt your coils?

I mean soldered in some new plug wires...

That's scary. Can you show a close up picture? The Honda coils have a junction deep inside the coil body that is made before the epoxy shell is cast in place. The wires are not removable, nor replaceable. Those that have been "spliced" somehow usually end up building electrical trace arcs along the joint surface which lets the spark escape to the nearest metal surface.

Like the gas tank. 

[cb544]

More or less, yeah. They're coils. I've used a cb750 coil on cb350f.
They're fine, if they will reach.

What do you mean you rebuilt your coils?

I mean soldered in some new plug wires...

That's scary. Can you show a close up picture? The Honda coils have a junction deep inside the coil body that is made before the epoxy shell is cast in place. The wires are not removable, nor replaceable. Those that have been "spliced" somehow usually end up building electrical trace arcs along the joint surface which lets the spark escape to the nearest metal surface.

Like the gas tank. 

  Sounds like I've got a bad day waiting to happen... I'll get a picture asap. I was planning on using an epoxy to seal up the casing, but I'd rather buy a replacement set if you aren't confident in a hodge-podge'd repair... If the 750 coils my friend picked up don't fit, are the Dyna replacements sufficient or should I look for a Honda OEM set first?

[HondaMan]

More or less, yeah. They're coils. I've used a cb750 coil on cb350f.
They're fine, if they will reach.

What do you mean you rebuilt your coils?

I mean soldered in some new plug wires...

That's scary. Can you show a close up picture? The Honda coils have a junction deep inside the coil body that is made before the epoxy shell is cast in place. The wires are not removable, nor replaceable. Those that have been "spliced" somehow usually end up building electrical trace arcs along the joint surface which lets the spark escape to the nearest metal surface.

Like the gas tank. 

  Sounds like I've got a bad day waiting to happen... I'll get a picture asap. I was planning on using an epoxy to seal up the casing, but I'd rather buy a replacement set if you aren't confident in a hodge-podge'd repair... If the 750 coils my friend picked up don't fit, are the Dyna replacements sufficient or should I look for a Honda OEM set first?

The dynas have the advantage of removable wires. They have the disadvantage of shorter spark duration. The 5-ohm coils are pretty close to Honda's stock units, while the 3-ohm coils have only about 1mS of spark (20% less than the Honda, 10% less or so than the 5-ohm coils). The 3-ohm can be hard on wiring and alternator loads unless you have a 750 with stock headlight (not halogen). I do make (on request) a Resistor Pack for those 3-ohm coils to help improve on the situation, and it extends the spark a tiny bit more on the 3-ohm discharge (about 5%-7% longer than Dyna stock). This spark duration is much more important in the CB750K0-K6 and the CB500 than in the other engines. (Long story, covered elsewhere here at the forums...  ).