Hey--

I'm trying to figure out what torque to apply when reinstalling my spark plugs. I checked out the NGK torque guide and they say for an 18mm thread (that's what the GS500 has, yeah? I just know I'm using an 18mm wrench here. same thing?), aluminum heads, flat seat with gasket, 25.3-28.9 lb-ft.

Does that sound right? I'm not clear on what cast iron vs. aluminum heads refers to, and I'm a little shady on "flat seat with gasket." Is that referring to the surface that the outer edge of the spark plug rests on? Either gasket, or metal?

Thanks in advance!

Hmm, I have a copy of the suzuki factory manual and they don't specify... All their references to spark plugs just tell you to make sure and get the right kind and tell you what the gap should be...

NGK DPR8EA9 plug takes 18 mm wrench but the thread is 12 mm.  Torque is about 10-15 ft lbs in aluminum head:

http://www.ngksparkplugs.com/tech_support/spark_plugs/installation/index.asp?mode=nml

http://www.ngksparkplugs.com/docs/tech/partnumberkey.pdf

I've always used this rule of thumb:

First time the plug is installed (crush washer is new): 1/4 turn from seated
Any time a used plug is installed (crush washer has been... crushed) 1/8 turn from seated

Great, thank you.

Yeah, when I tried doing the 1/2-2/3 turn I got about an 1/8 of the way and then felt like it was too much.