Spark Plug Change and correct size - help needed

[SavMan]

This may seem a stupid question but need some guidance here, I have been advised to change to colder spark plugs due to the power I am running and most US forums recommend NGK LFR7AIX. I ordered some and pulled out an existing one from cylinder 5 and compared with the NGK. The current ones installed are Mercedes branded Champion KC10PYPB4 and the thread length is approx 18mm. The NGK's that arrived are 26mm length so I checked Eurocarparts website and they also suggest a Bosch plug that when I looked up also has a 26mm thread length.

So are the ones I have OK to fit the full part code is NGKLRF7AIX 2309

 

[Benzowner]

That does seem a tad long, 18mm to 26mm. Have a look http://www.sparkplug-crossreference.com/convert/CHAMP_PN/KC10PYPB4that may give a little more info.

 

[brigadier]

Had a quick look on tecdoc. both beru and bosch plugs specified for e55k m113.990 have 26.5mm thread.
edit: looks like the 19mm thread is for e55 without kompressor - m113.980

 

[SavMan]

Thank you I also did some more digging and it seems that Bosch also do a 19mm as well 26mm so it would seem you can fit either, went ahead and fitted them which is a pain in the a@se when it does not go right two plugs just kept spinning. I had to remove the valve cover to get better access and finally get them to loosen all 16 are in now with everything back together and running smoothly. Should hopefully reduce the exhaust gas temperatures supposedly by 100 deg need to dig out a previous run to see if it actually does anything.