Spark plugs for ST1300

Don B

I just changed the spark plugs in my '03 ST1300 yesterday afternoon, at 26,250 mi. on the clock. I installed the standard factory-recommended NGK CR7EH-9 plugs. The ones that were in the motor were NGK CR9EHIX-9 Iridium plugs. I have no idea how long they had been in there, but they looked clean, nice tan color on the porcelain tip, although one of them appeared to have a slight leak, judging by the discoloration around the circumference of the porcelain insulator where it meets the shell. My question for the forum is, which plug should I use if I decide to switch back to Iridium the next time I change plugs (probably a year or two away:) )? The shop manual only recommends CR7EH-9 or CR8EH-9 (optional), or the DENSO equivalents; it has no recommended Iridium plugs in the manual. I have to assume the plugs I took out of the bike were 1 or 2 heat ranges too hot; apparently the "HIX" in the NGK designation signifies an Iridium plug, and the rest of the designation for reach, thread size and heat range. The closest that I've found in NGK's plug type listing would be either the CR7HIX (with no -9 at the end) or the CR8EHIX-9. Since I don't know the significance of the "EH" or the -9 in NGK's plug type designations, I'm left at a loss as to which plug to choose.

Any ideas?

Don B.
 
Bob, the 9s are actually a colder plug than standard. They would be used in an ST11 for extended high speed riding. The safest bet would be to use the 8s that Jeff has suggested. I don't know why Honda would give standard and optional plugs without some sort of explanation. For the ST11 no hotter plug is listed for cold conditions.

It is probably a testament to the plugs that thay looked ok, as colder plugs have only caused me trouble with missfiring after a while in older bikes. The ST13 may also run pretty clean combustion wise
 
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Mine had the non-iridium 7 heat range installed from the factory. I could not find the matching heat range in the iridium plug so went with the 8 which is just slightly cooler. Precious metal plugs have a wider heat range than standard ones, so some manufacturers don't supply them in as many ranges.

There hasn't been a problem in my case and I've gone over 25,000 miles since installation. If you run through the application guide on NGK's site for the ST1300, it specifies the 8 heat range plug as available at Tucmoto.
 
I just installed 8 range Iridium's from Tucmoto. First plug change with 34K on the clock. I was surprised by how small the center electrode was. Don't remember them being this small the last time I changed some on my ST1100.

Phil
 
Just choose btw what the Honda Manual recommends as they work to the teeth & you get the bike up & running. No use worrying about the Iridium equivalents at this point in time.
 
NoBull not sure how long they go in bikes but in my SO honda van std replacement interval is 100k miles and they were clean and still in good shape then. I will put them in my ST and pull them at valve adj time and judge accordingly. Most iridium plugs in cages are 100k mile replacement items
 
I don't know what the ultimate life is, but on the ST11 they are 28,000kms on and working like new. I have read that the standard plugs can easily last that long or more as well.
 
I thought all Iridium plugs are rated at 100k miles...
Does someone have different information?

Mark
 
I know that on the website normal IX iridiums are rated for 60,000kms and laser ones for 100,000kms (for cars), but when you check the tech info they revert back to the manufacturers replacement period or when an experinced mechanic says so. As Honda does not specifiy them from new its a bit hard to say what the life should be.

This site seems to indicate that bikes could be as low as 20,000 miles http://www.spark-plugs.co.uk/pages/technical/iridium_spark_plugs.htm
 
I put the CR8EHIX-9 Iridium plugs in my ST1100 and have almost 60,000 miles on them now. I have not seen any change in performance or gas mileage so they must still be working :) And, they looked great last time I checked the gap etc.
I may change them when I do the 100,000 mile service in a few months but I’m not sure yet.

Rick
 
The iridium material is MUCH denser, 6 times, than iron, therefore it erodes less in the combustion event. This maintains the gap for a longer period of time. The real benefits are that they require less voltage and fire a hotter spark than standard plugs. This reduces the stress on the ignition system and at the same time improves combustion stability. They are the state of the spark art presently. That is until they start making depleted uranium spark plugs. wooha
btw, the smaller the electrode is the better. Nipon Denson, the IUH24 for the ST1300, is 0.4 mm wire while the NGK is a .6 mm. The IUH24 could be a better plug. I am going to try a set. I won't get to compare the NGKs but I would use either in a hearbeat over "standard." The leaner they make these bike run (for emission reasons) the harder it is to ignite the mixture. Any help is help, I say. The IUH24 is the colder option of plug, probably what we need here in HOT HOUSTON TEXAS.
 
I found a good price on the iridium plugs at NGK wholesale. They are $6.95 each. I used USPS shipping ($6.40) so thought that was good. Don't tell me I could get a better price at my local auto zone, please.

JDP
 
Being aluminum heads, and given the life of the iridium plugs do you guys use anti seize on the threads. I understood this is a good idea with aluminum heads.
 
You should be pulling the plugs when you do the 16K, 32K, etc. service so there shouldn't be a problem with them not coming out. I do put a dab of anti-sieze on them provided I can find my tube. :)
 
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