Spark Plug Torque

PM sent with the information you requested...

 

For what it's worth, I used the WSM number (15 ft-lbs) and I have actually had a plug back out on me. Not good. Luckily I caught it before it backed all the way out or did any damage. Once a little cylinder pressure leaked by, it popped the spark plug boot out of the hole and I happened to see it.

Not to bog you down sending PM's, but I would also like to know a better number to use.

 

I've tightened them by feel for years and have never had one come loose. I'm sure David hooked him up.

 

My owners manual says 15 then back off, then to 12. Doesn't seem very tight but that's what it says so that's what I did. Wow, your OM spec for your car is vey different, surprised at the spread there, how different could they be?

 

I can't believe you aren't sharing those torque numbers with the rest of the FerrariChat community.

 

I can.



And this MAY be the wave of the future.

 

Seems odd to have so much variation in the torque from the manuals on what seems to be essentially the same cyl head UNLESS they use different size plugs. The service manual for the 328 shows 11.5 ft/lbs for the plugs which is within the usual specs for a 12mm plug on an AL head which is 10-15 lb ft per an NGK chart

Do the earlier cars use an 18mm plug? That 25-27 ft lb figure would be in the range for a 18mm plug/AL head (25-32 on the same chart).

Those torque figures are what I've seen on AL heads/spark plugs from as long as I can remember dealing with AL heads, regardless of what kind of engine is involved.

I would be scared to death to try to torque a 12mm plug to 25 lb/ft on an AL head.

 

My 85 QV owners manual says 18, back off, then 14.

 

He may not want the baggage that comes with sharing information like that....and I can't say that I blame him.

 

No, the 2V and QV heads use a M14x 1.25P threaded spark plug. I quickly scanned ~10 308 OMs, and they all seem to show the 14.4 ft-lb torque value.

Dr. K. -- Do you have a print number XXX/YY or year/model/version description for that OM you are referencing with that 25-27 ft-lb value?

 

I would think both the plugs and the head alloy changed, over time.

I have removed plugs that were installed FAR tighter than I would ever put them in!

Given the difficulty of repair to the head, I would rather stop and pick one up, that had blown out (which has NEVER happened, to me personally, I have seen it once, at a club event, on an older V12....and it was still there on the wire... )

 

Thanks for the information. I was aware that the plug gap dimension had waffled in different OMs (that small value is nuts ) and that the "torque low then high" vs "torque high then low" procedure difference existed, but hadn't seen the final torque value as ever being anything different before.

One thing that comes to mind is that, since the spark plug is a vendor's part, maybe the vendor (wrongly) recommened a torque value assuming a cast iron head, or someone at F used a torque spec chart from the vendor that was (only) for cast iron heads -- just a thought...(but I think that the preponderance of evidence says the 14.4 value is the one to use on a F Aluminum head per Mike's suggestion).

 

I've always wondered about the very narrow gap setting by "normal" standards. Makes me think the ign system is a bit on the marginal side.

Just out of curiosity, any idea what the latest Ferrari engines plug gap specs are?

 

About the 458....

"The engine features a CPU that monitors the currents inside the combustion chamber between the spark plug electrodes. This means, according to Ferrari, that the computer notes every single spark in every chamber, making the process faster and more accurate."

Sooner or later, they'll maybe just design out the plugs

Gap depends on the plug, I suppose....but it looks like the gap for my most recent favorite car (550 Maranello) is .028