Flathead spark plug torque

[LaSalle5019]

Spark plugs have 10mm threads. The service manual says 35-40 ft lbs. That seems crazy high to me. I quit at 25 ft lbs fearing I’ll be pulling threads out of the head. Does anyone really torque to the specs???
Scott

[39LaSalleDriver]

I torque mine to "feels right"

[Halcyondays]

I wonder what happened to my reply last night.  Where did the text go?
Anyway, a Champion Spark Plug torque guide article which I accessed on the web says 10mm plugs require 8-12 ft-lbs on both cast iron and aluminum heads.






















































A Champion Spark Plug article on torque calls for 8-12 ft-lbs on 10mm plugs.  For both cast iron and aluminum heads.
The article title is "Spark Plug Torque Recommendations | Champion Auto Parts".  I accessed it through Bing but expect Google will work.

[C Gorgas]

Years ago I was instructed never to get carried away tightening the plugs and I guess that was good advice. No problems encountered.

[fishnjim]

check your current plug suppliers documents rather than old manuals.   Check the units.
eg: NGK lists for 10 mm = 10-12 N-m = 7-9 lb-ft.   
Torquing wasn't as well understood then, as it is now.
The "crush ring" supplies the seal and needs to have the proper compression.  Designs vary.
I would not be concerned at ~35 lb-ft for stripping in cast with good threads, but maybe not suitable for aluminum which is not of concern here or with well worn threads.   Some of the "older" plugs had small threaded sections and larger plug body bases, so may need more torq.  ie, not all plugs created equal.
One place I don't use a torq wrench because not easy to get in there but easier on a flattie.  Some of these "break away" socket devices maybe more effective but at this low level, method is proper madness.   Once you've done many you're hands are trained.
More important is not to cross thread.   

[LaSalle5019]

Thank you for the replies.  Well, they shouldn't fall out. I think the next time I remove and install, I'll keep it 10 to 15 ft-lbs.
Scott

[wheikkila]

Good Evening
I checked my 1940 La Salle manuel and it lists the torque for the plugs at 7- 10 ft -b.
Thanks wayne 

[LaSalle5019]

Service manual torque specs

[harry s]

...just to add to the procedure. When using new plug washers tightening should be enough to flatten or crush the washer then tighten or torque to spec.      Harry

[Brad Ipsen CLC #737]

The shop manual had an error in it.  It was corrected with a Service Man note on page 28 in the August 1939 issue.  Correct should be 7 to 10 pounds.

[LaSalle5019]

And all the while I thought Cadillac didn’t make mistakes 
Well, I’m sure my aluminum gaskets are fully crushed! I’ll get some new ones for the next time they come out and and torque to 10 ft lbs. Thanks for the info.
Scott