Topic: Difference Between NGK DR7EA & D7EA

[jrtruckn]

I would like to start off by saying sorry if this isn't in the right forum. I just got back from the parts store and noticed that they gave me DR7EA spark plugs instead of the normal D7EA. I know the difference between the two is the R - for Construction Type but will they still be alright to run in my CB550?

Jody

[S-Dog]

The R stands for resistor... on the stock cb750 you do NOT want that, however I am unsure about the 550.

[CB500_k2]

I have run the "R" plugs on my CB500 with standard resistor caps as well.  They work just fine.  I was unable to find non R plugs nor non R caps.

[TwoTired]

The resistor plugs will work okay when new.  But, because they require a higher voltage at the coils to fire, and the stock coils are somewhat limited in that regard, you will need to replace them about twice as often as the Non-R plugs.  I'd estimate at 6000 miles instead of 12000 miles.

The non-R plugs are still available.  Just tell the parts store manager that unless they resume stocking the non-R version, you will take your business elsewhere.

Cheers,

[KB02]

The resistor plugs will work okay when new.  But, because they require a higher voltage at the coils to fire, and the stock coils are somewhat limited in that regard, you will need to replace them about twice as often as the Non-R plugs.  I'd estimate at 6000 miles instead of 12000 miles.

Yeah, it bugs me when the guys at the parts counter hand you one instead of the other and say, "yeah.. they're basically the same thing."

With an aftermarket ignition (like a Dyna), you should be fine with the "R's" though, right?

[TwoTired]

The resistor plugs will work okay when new.  But, because they require a higher voltage at the coils to fire, and the stock coils are somewhat limited in that regard, you will need to replace them about twice as often as the Non-R plugs.  I'd estimate at 6000 miles instead of 12000 miles.

With an aftermarket ignition (like a Dyna), you should be fine with the "R's" though, right?

If you use 3 ohm coils, yes.  But, the Dyna ignition unit does not make the coils produce higher spark voltage.  It switches 12v to the coils just like the points do.

Cheers,

[jrtruckn]

Thanks for the help. This bike has been setting for about 10+ years. I just wanted to see if I could get it to run before this winter sets in. The good news is after cleaning the carbs, doing some repairs on the coils/wires and replacing the plugs it ran. Not great (carbs need sync) but it ran. My plan is to tear it down this winter and clean it up and hopefully get it back together before spring. I have about 4 good months before the weather gets good enough to ride. Once again thanks for the help.

[cocinero196]

The resistor plugs will work okay when new.  But, because they require a higher voltage at the coils to fire, and the stock coils are somewhat limited in that regard, you will need to replace them about twice as often as the Non-R plugs.  I'd estimate at 6000 miles instead of 12000 miles.

The non-R plugs are still available.  Just tell the parts store manager that unless they resume stocking the non-R version, you will take your business elsewhere.

Cheers,

Hi, i just installed a Pamco Electronic Ignition, everything else remained stock: coils, spark plug caps & NGK D7EA plugs. Is this okay or should I replace the coils, spark plug caps, wires, etc.?

Btw, i also read that "You must use 5 ohm resistor type spark plug caps or resistor type plugs (not both)". Are the stock CB550k spark plug caps, 5 ohm resistor type spark plug caps or resistor type plugs already?

[TwoTired]

All my Cb550s had non R plugs and 10 K ohm plug caps from the factory.  But, I don't know where you can get 10K ohm plug caps these days.

I was wrong about the voltage effects in previous posts.  I've learned Resistor plugs don't change the voltage requirements, as the spark gap is what determines the voltage needs at the plug.  Resistance change in the spark secondary circuit does change the spark current, and the time it takes to drain the energy from the coils.  Resistors are like water valves in as much as they control the flow rate of power.  If you lower the resistance, the spark current increases.  As the D7 heat range is hotter than other SOHC4 that use D8, the heat plus the increased spark current will erode spark electrodes faster, requiring more frequent replacement.  Sharp edges make an easier point for spark to jump from than rounded edges.  You can make the plugs last longer by filing them back to sharp edges and re-gaping them.  They fire like new again, as long as the center electrode insulator is still clean.

Anyway, to mimic the factory set up, you can use resistor plugs (5K) and the 5K ohm plug caps for the longer plug life it originally had.  The stock wires are steel core stranded.  The plug caps screw into the hard steel core.
The wires only need replacement if the insulation is damaged.  Same is true with the coils.  Unless physically damaged, they pretty much work forever, as the metals used don't degrade unless exposed to the elements.

The Pamco is an electronic switch instead of mechanical point contacts.  It switches the same voltage as the points did.  It doesn't boost any voltages over the points set up.  It does eliminate degradation from points wear.  There is no reason to change coils or wires because of that unit.

If you increase the spark plug gap, or increase he compression in the motor, you may then need higher voltage potential for the spark plugs.  Only then would you need to change coils.  But, beware the electrical budget is rather tight for the stock CB550.  Lower ohm coils will draw more energy from the electrical system.  The effect of this is sometimes issues with keeping the battery charged, as the stock bike won't charge the battery at idle with the lights on.

Cheers,

[cocinero196]

All my Cb550s had non R plugs and 10 K ohm plug caps from the factory.  But, I don't know where you can get 10K ohm plug caps these days.

I was wrong about the voltage effects in previous posts.  I've learned Resistor plugs don't change the voltage requirements, as the spark gap is what determines the voltage needs at the plug.  Resistance change in the spark secondary circuit does change the spark current, and the time it takes to drain the energy from the coils.  Resistors are like water valves in as much as they control the flow rate of power.  If you lower the resistance, the spark current increases.  As the D7 heat range is hotter than other SOHC4 that use D8, the heat plus the increased spark current will erode spark electrodes faster, requiring more frequent replacement.  Sharp edges make an easier point for spark to jump from than rounded edges.  You can make the plugs last longer by filing them back to sharp edges and re-gaping them.  They fire like new again, as long as the center electrode insulator is still clean.

Anyway, to mimic the factory set up, you can use resistor plugs (5K) and the 5K ohm plug caps for the longer plug life it originally had.  The stock wires are steel core stranded.  The plug caps screw into the hard steel core.
The wires only need replacement if the insulation is damaged.  Same is true with the coils.  Unless physically damaged, they pretty much work forever, as the metals used don't degrade unless exposed to the elements.

The Pamco is an electronic switch instead of mechanical point contacts.  It switches the same voltage as the points did.  It doesn't boost any voltages over the points set up.  It does eliminate degradation from points wear.  There is no reason to change coils or wires because of that unit.

If you increase the spark plug gap, or increase he compression in the motor, you may then need higher voltage potential for the spark plugs.  Only then would you need to change coils.  But, beware the electrical budget is rather tight for the stock CB550.  Lower ohm coils will draw more energy from the electrical system.  The effect of this is sometimes issues with keeping the battery charged, as the stock bike won't charge the battery at idle with the lights on.

Cheers,

Thanks for the detailed explanation, I really appreciate it. Btw, I have overhauled and replaced the standard 58.5mm piston to 59.5mm. Does this change my plug requirements? And how does this 59.5mm upgrade affect the bike performance? Will it run faster? Increase gas consumption considerably? etc.

[Don R]

 The overbore will give increased compression due to better bore roundness. Slightly faster maybe, if fuel and spark are optimized for the increase. Sometimes a bigger engine will be more efficient depending on the load it's pulling.

[Don R]

 Oh, and resistance is futile.

[cocinero196]

The overbore will give increased compression due to better bore roundness. Slightly faster maybe, if fuel and spark are optimized for the increase. Sometimes a bigger engine will be more efficient depending on the load it's pulling.

Does this change my plug requirements from stock?

[TwoTired]

Btw, I have overhauled and replaced the standard 58.5mm piston to 59.5mm. Does this change my plug requirements? And how does this 59.5mm upgrade affect the bike performance? Will it run faster? Increase gas consumption considerably? etc.

I would expect no changes in plug requirements.  Might need different carb tuning, as the larger displacement will suck harder on the carbs.
Increasing displacement usually means a bit more torque.  Hot rodders have been increasing engine size for years for speed reasons.  They test their changes on the track or a dynomometer.

However, it is rare to change only one aspect of an engineered machine and not have a ripple effect of needing other things to change to make the most of it.

That said, if it runs fine and makes good spark plug deposit color, enjoy it!

Cheers,

[cocinero196]

Btw, I have overhauled and replaced the standard 58.5mm piston to 59.5mm. Does this change my plug requirements? And how does this 59.5mm upgrade affect the bike performance? Will it run faster? Increase gas consumption considerably? etc.

I would expect no changes in plug requirements.  Might need different carb tuning, as the larger displacement will suck harder on the carbs.
Increasing displacement usually means a bit more torque.  Hot rodders have been increasing engine size for years for speed reasons.  They test their changes on the track or a dynomometer.

However, it is rare to change only one aspect of an engineered machine and not have a ripple effect of needing other things to change to make the most of it.

That said, if it runs fine and makes good spark plug deposit color, enjoy it!

Cheers,

Thanks bud!!