tonymax2

My '89 GM 'vette service manual calls for 22 ft-lb torque on the spark plugs in the aluminum heads. So does my '89 GM Caprice manual for 305 cu.in. iron heads. I would have thought the alum torque would have been lower. Any wisdom on this out there??

C4driver99

Follow the GM service manual. It comes from the engineers who built it.

Corvette Kid

With anti-sieze on the threads, 15 lbs. will be enough.

tonymax2

Yea, I generally do but one never knows weather the book has a misprint or not! I've searched the forum but didn't find anything specific. I tried a google search and it seems several other outfits say 18-22 ft.-lb. for alum, some show slightly higher for iron heads. I generally compression check 2 or 3 cylinders (the easy ones) on '89s I'm checking out looking for "mine" and I sure don't want to over torque someone else' heads and strip a thread! I think I'll hedge my bet and use 18. Thanks for the input!

tonymax2

Makes sense, and it's within the range of my small torque wrench. Thanks for the input.

1987C4

Hmmm... My Haynes manual (got it early on before I got the factory manual) says 22 ft/lbs for iron heads and 12 fl/lbs for aluminum heads. I set mine to 12 lbs with anti-seize for my aluminum headed 1987 and they haven't seemed to have any problems, but now I'm worried. I may pull and check a couple. My factory manual (bought it after the tuneup) says 22 lbs...seems a bit high for an aluminum head!
Brad

parafrog

if you're questionable about the torque, then you definitely need to be aware that with enough time, the plugs will fuse into aluminum heads without anti-seize. BIG DEAL.

i would think that a general consensus of torques would be a good bet since everyone is basiclly talking about the max abilities of aluminum threads to hold steel without stripping. it's essientially more a concept and less a detail.

i understand what you mean about misprints in your year service manual. i just found a major misprint in the 85 manual that might make the rear wheels fall off. just cause a manual is approved, that doesn't mean it doesn't have mistakes in it. thems full of a lot of words.

"there is no such thing as a dumb question--just dumb answers"--Poppa Frog.

"god bless the enlightened and the tolerant"--Bubba Rumraisin.


frog.

rick lambert

I've never used a torque wrench doing plugs-and I've never had a problem-knock on wood

Mike_88Z51

I was concerned about overtorquing the plugs also. I know that the Factory Shop Manual is not written by GM Engineers, but by Tech Writers who sometimes misinterpret or make mistakes writing down what the Engineers say. Since my Kawasaki uses the same size and thread pitch spark plug as my 88 Vette, and both the bike and the Vette have aluminum heads, I looked at the my FSM from big K. Both shop manuals specify 18~22 ft.lb. torque. I use anti-seize and torque both to 19 ft.lb.

dlmeyers

With aluminum fittings, low range torque is perfectly acceptable to me.

As a note, those advertising 100,000 mile spark plugs in aluminum engines may have a 50,000 mile inspection requirement. Keeping a spark plug in an aluminum head for 100K may not be a good idea.

I don't hate aluminum, just seems to do its own thing.

dlmeyers 90 coupe zf6 3pseed shocks