Spark Plugs

[the Ferret]

The CB 1100 takes special one off spark plugs designed for this bike. made by NGK they carry the designation LMAR8A-9S Honda part number 31908-MGC-003 and takes QTY 4. The bodies on these plugs are extremely thin as are the threads which are also extremely long at 26.5 MM or just over an inch.

The plugs are expensive at $19.99 each and it's highly unlikely your dealer will stock any so they will probably need to be ordered. A standard spark plug wrench is not going to work well given the small confines of the area to work in. However Motion Pro makes a thin walled 14MM narrow plug wrench that uses a 1/4" ratchet, a 13 mm box end wrench or a 14 mm box end wrench socket or T handle to loosen and tighten. It also has a rubber ceramic gripper up inside. Your dealer can get this from one of his suppliers or you can order it directly from Motion Pro

This pic illustrates just how small these plugs and tool are, On the left is a standard spark plug socket next to the Motion Pro Unit.
On the right is a standard spark plug next to the plug used in the CB 1100. Gap .031-.035 using a wire type feeler gauge is recommended.

L to R std spark plug socket, thin walled 14 mm Motion Pro spark plug socket, std spark plug, LMAR8A-9S spark plug for CB 1100

 

[SanPete_imp]

Thank you ferret for this excellent write up.
How many miles can we expect from the original spark plugs before replacing?

 

[redbirds_imp]

Thanks for the post Ferret, good pics and comparison. Have you done a plug or valve inspection on your DLX?

 

[Novice_imp]

Does motion pro only sell only one 14 mm wrench? I think I found it on their website, but with no part number and our model not listed, I want to be sure I'm ordering the correct one. Where did you order your plugs from?

 

[redbirds_imp]

Here it is.

Motion Pro

 

[the Ferret]

Thanks for the post Ferret, good pics and comparison. Have you done a plug or valve inspection on your DLX?

Neither. Turned over 13,000 miles on todays ride.

Does motion pro only sell only one 14 mm wrench? I think I found it on their website, but with no part number and our model not listed, I want to be sure I'm ordering the correct one. Where did you order your plugs from?

Go by description. I don't know how many they make. my box has a bunch of numbers on it
157174
08-0512
194989

Here's the tool as googled from Motion Pro

Motion Pro

I know I took in the Motion Pro part number in the link above 08-0512 with me and the parts person had to look it up by description from her supplier (not Motion Pro)

I got plugs and tool from local dealer. Tool was $19.99

 

[Novice_imp]

!!!

 

[furious_blue_imp]

yes, thanks for the tip !

there's nothing like setting time aside for a chore only to find that you're hopelessly ill-equipped to carry out the task...

This probably saved me a bit of time and frustration !

 

[ish_imp]

Thank you!!!! Saving me a headache.

 

[the Ferret]

I might mention that a dab of "never-seize" on those plug threads would be a great idea when you replace them

Thank you ferret for this excellent write up.
How many miles can we expect from the original spark plugs before replacing?

San Pete, I don't know we are in uncharted waters on this. I know the Aussies have put enough KMs on their bikes and I believe have had plugs replaced but it is apparently part of their service over there. Not sure if theirs were replaced "just because" or if they actually needed them with wear and tear evident?

Honda calls for an inspection at 8,000 miles. Not sure when they recommend replacement, I will have to look that up.

 

[Randy B]

I haven't touched my plugs at a tick over 18,000 miles, partly due to the EXCESSIVE cost of the plugs. I did find a better price than you did by quite a bit.

#11 in the pick list.

http://www.hondapartshouse.com/oemparts/a/hon/511a8d66f870022e4ccd3236/cylinder-head

 

[the Ferret]

good price! (If $15 for a single spark plug could ever be considered a good price)

 

[Cormanus]

My plugs were replaced, maybe at 24,000 kms. My recollection is that the mechanic thought it probably wasn't necessary.

They were expensive as I recall.

 

[the Ferret]

Ok just looked it up in the service manual

spark plugs: inspect at 4000 replace at 8000 inspect at 12,000 replace at 16,000 ect GADS!

BTW Tighten to 12 ft lbs is spec when replacing.

 

[Redbird_imp]

Hmm, I believe I will take some leeway here. Perhaps replace at a minimum of 12,000.
Back when I had my Valkyrie Honda said replace at 8,000. I replaced them at 24,000 just because. The bike was running fine.
You know, I just replaced the plugs in a 2002 Toyota Highlander at the recommended interval of 120,000 miles. They are iridium tipped and were only eight dollars and change each at Advance Auto Parts. Half the cost of the Honda plugs and 15 times the life before recommended replacement.

 

[Randy B]

The air cooled engine has something to do with it.

 

[flynrider]

The air cooled engine has something to do with it.

I suspect that the absurdly long nose is for better heat transfer from the cylinder head. Honda also put extra oil passages around the plug heads to improve cooling in that area.

Of course, my air cooled CB750 uses $5 standard sized plugs and no special oil passages for cooling, but combustion chamber temperature control was not that critical with the emission standards of 20 years ago.

 

[widude]

Thanks, great info. Plugs at $5 or $20 are till relatively cheap. No issues here, I like to upgrade plugs as called for when it calls for on replacement. That often calls for iridium on replacement.

I had a 2003 GMC truck, I had two upgrades to the original replacement plugs.

 

[Randy B]

The air cooled engine has something to do with it.

I suspect that the absurdly long nose is for better heat transfer from the cylinder head. Honda also put extra oil passages around the plug heads to improve cooling in that area.

Of course, my air cooled CB750 uses $5 standard sized plugs and no special oil passages for cooling, but combustion chamber temperature control was not that critical with the emission standards of 20 years ago.

I suspect that the absurdly long nose is for better heat transfer from the cylinder head. Honda also put extra oil passages around the plug heads to improve cooling in that area.

Of course, my air cooled CB750 uses $5 standard sized plugs and no special oil passages for cooling, but combustion chamber temperature control was not that critical with the emission standards of 20 years ago.
The oil was all about controlling the cylinder head temp to stabilize it for better emission regulation out of the engine. This is the only air cooled engine I have ever seen with a catalytic converter on it, and that is for a reason. The unpredictable and wide ranging head temps would make it so the converter would clog up in short order. With the oil passages in the head it helps keep things much more controlled and allows the bike to pass much tighter emission standards.

Fun stuff.

 

[Cormanus]

Somewhere on this forum there's a discussion about the likelihood that the plugs could be expected to survive much longer than 12,000 miles.