Spark Plug shoulder?

I recently changed the spark plugs in my ST. They were the originals by their look. They looked fine (20,000Km) but swapped them anyway.

I fitted Iridium plugs and noticed the original plug removed has a 'shoulder' immediately below the seating washer. This shoulder is larger in diameter than the thread below it and fits snugly into a pocket in the head I could see.

The Iridium plug (CR7EIX) has no such shoulder and this looked like a disadvantage as the pocket in the head was not filled and the long thread of the Iridium plug hovered in 'thin air' down through the pocket space before threading in below. (I hope you can visualise what I'm describing - well done if you can!).

My question is: Is there a problem with the Iridium plug threading way below the seating washer and the pocket in the head not there to lend support to the plug?

Thank you.

That it's the wrong plug. The correct one is an EH, which has the same thread reach but is half threaded and has the shoulder.

This is the (correct) EH plug:


This is the (wrong) E plug:


An E plug will probably put the electrode in the right place but may not seal as well since the threads will run all the way up to the seat.

The correct NGK plug in iridium would be a CR7EHIX-9. Or you could just use the original CR7EH-9, which seem to do just fine.

--Mark

I have removed iridium plugs from at least two ST1300's in the last month, both were using the wrong plugs!
IMHO these bikes really do not need iridium plugs, as the factory ND or NGK plugs in the standard, or cooler heat range work fine.
I have not seen any damage caused by using iridium plugs, however, I have seen a couple posts about damage to bikes that were using them.
Both bikes that I removed them from ran just fine with the factory style plugs put back in them.
NMMV

Thank you for help on this. I have removed the incorrect iridiums. I really have no justification for using them. I have read about Iridium longevity and other possible advantages but I do not know.

For the time being I will find some standard plugs and try to return the incorrect Iridiums to the supplier.

Thanks again

PS. Thanks Mark for plug photos.

I followed up with the supplier of the CR7EIX shoulderless spark plugs and it maintains they are the correct plug! The Co. sent me an NGK link that supports this. I suggested this link is in in error as the plug needs to have the shoulder, I assume Honda engineers put it there for a purpose.

I pointed out there are other websites that show the Iridium plug for the ST is the CR7EHIX-9 with the shoulder.

I decided to write the experience off at my loss. I purchased 8 new std NGK plugs (4 spare) for a 'next to nothing price' confident they will do the job.

I asked the company to remove the ad showing the incorrect Iridium plugs as the correct ST fitment but the ad remains.

So ***Please be aware that some suppliers may be specifying the wrong Iridium spark plug and will happily send these to you***

Duporth said:

So ***Please be aware that some suppliers may be specifying the wrong Iridium spark plug and will happily send these to you***

Click to expand...

What supplier sold you the wrong plug and insists it's the correct one? It sounds like one we might want to avoid.

And if we just order with the correct P/N they should just send what we ordered right?

ST Gui said:

What supplier sold you the wrong plug and insists it's the correct one? It sounds like one we might want to avoid.

And if we just order with the correct P/N they should just send what we ordered right?

Click to expand...

Unless the person on the other end of the phone or keyboard decides to sell you the one THEY think will work
They may believe the link that they see, and believe you are wrong and don't know what your talking about, or just don't care, and want to make a sale.

Igofar said:

Unless the person on the other end of the phone or keyboard decides to sell you the one THEY think will work

Click to expand...

Well anything could happen but if you just order the part with the correct part number how are they going to know what you're ordering for unless you tell them.

99.999% of the people answering phones and working keyboards are worker drones who a) don't have the time to second guess b) don't have the knowledge and c) really don't care.

So I'd easily be willing to take my chances with the correct part number.

The supplier directed me to the following link that specifies the CR7EIX plug with no shoulder. The CR7EIX will fit, tighten, and the engine will run.
As Blrfl says above, "An E plug will probably put the electrode in the right place but may not seal as well since the threads will run all the way up to the seat".

I also think that given the anticipated high longevity of the iridium, there is plenty of time for a problem to arise through the absence of the shoulder. Personally, I would not tolerate this situation.

It is hard to imagine the CR7EIX and CR7EHIX are alternatives that can be used. There are certainly many suppliers, mainly European, that market the shoulderless CR7EIX plug as the correct fitment, presumably based upon the NGK advice in the link above. There are also many suppliers (USA) specifying the CR7EHIX with the shoulder.

I am running the std NGKs at present.

D.