Topic: CB400F Plug Wrench Question

[Senna27]

What size plug wrench do I need to remove the plugs on my '75 CB400F?

[Deltarider]

I strongly advise you to use the original Honda plug wrench (toolset). The wrench has a rubber part deep inside that prevents damaging the sparkplug.

[Senna27]

I strongly advise you to use the original Honda plug wrench (toolset). The wrench has a rubber part deep inside that prevents damaging the sparkplug.

I can purchase a plug socket with the rubber grommet inside but I need to know the size!

[Sporkfly]

It also depends on the brand of plug. I have a set of Champions and a set of NGK for my bike (it's a 550 however) and the Champion is a 5/8" and the NGK is an 18mm.

[Deltarider]

18mm hex but.... not every plug wrench can make it through the hole.

[Senna27]

It also depends on the brand of plug. I have a set of Champions and a set of NGK for my bike (it's a 550 however) and the Champion is a 5/8" and the NGK is an 18mm.

They are NGK DR8ES-L

[Senna27]

18mm hex but.... not every plug wrench can make it through the hole.

OK... I'll make sure I measure it so that it fits.

[dave400]

If you have resistor type spark plug caps (It's an original Honda part)....... are you? Then you should be using NGK D8EA plugs. I have 5KΩ NGK caps on my bike and it's direct replcement for the honda part.

[dave m]

IIRC it should be 18mm.

You still got those alloys on your 400F Dave?

[Senna27]

If you have resistor type spark plug caps (It's an original Honda part)....... are you? Then you should be using NGK D8EA plugs. I have 5KΩ NGK caps on my bike and it's direct replcement for the honda part.

I have a Dyna S Ignition System and aftermarket plug wires w/o resistors. That's why I need the DR8ES-L.

[Gordon]

I have a cheap, long reach, thin walled 18mm that I use for spark plugs.  Works great and fits easily into the plug recesses for the difficult #2 and #3 plugs.  It doesn't have the rubber grommet, but I've been using it for several years and never once damaged a spark plug.  I always thought those were put in spark plug sockets to hold onto the plug to keep it from falling down into an engine bay.  Not something you need to worry much about with a bike. 

[Senna27]

I have a cheap, long reach, thin walled 18mm that I use for spark plugs.  Works great and fits easily into the plug recesses for the difficult #2 and #3 plugs.  It doesn't have the rubber grommet, but I've been using it for several years and never once damaged a spark plug.  I always thought those were put in spark plug sockets to hold onto the plug to keep it from falling down into an engine bay.  Not something you need to worry much about with a bike. 

Yeah, the grommet helps hold the plug in place. Just bought an 18mm spark plug socket and changed my plugs. All good, thanks for the help guys!