spark plugs

[Lumpy]

[quote author=Lumpy link=topic=1349.msg9640#msg9640 date=1326376106]
[quote author=Gnasher link=topic=1349.msg9634#msg9634 date=1326371571]
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  Dont try and remove them when they are hot you will increase the risk of stripping the threads,     

pray tell why? The ally isn't softer at 160 degress C than it is at 0 degrees C and technically the more brittle the metal, that is colder, the more chance of a fracture. Don't mind me I'm just an engineer and an old one at that  :lol

What heating the engine will do is very slightly make the thread larger diameter compared to the steel plug thread which expands at a lower CTE.

Just wondered like.
[/quote]

Because when heated as you say it goes soft and grips the plug threads which makes removal harder and can and does strip threads, plugs should never be removed when an engine is hot.  You being an engineer will know steal and aluminium do strange things when put together one being they tend to seize if the isn't something between them e.g. plug threads have a lacquer on them for that very reason. They also have very different tensile, sheer, wear and surface finish properties as mentioned above plugs mostly seize due to being over tightened i.e. stretched threads, fitting them with crap on the threads (very common on Fazers due to owner/stealers not cleaning the plug wells before/after removing the plugs and fitting a new ones), wet or the lacquer has worn off.

The torque between the collapsible washer isn't what is holding the plugs in it's the the threads in the head gripping the plug threads due to any one or all of the above mentioned.  I've had bike in that the plugs had been done up so tight the washer had been crushed that much so as to be deformed up the sides of the plug body and could be pulled out leaving a gap :eek

I always put a little copper slip on the plug threads always make sure the plugs fully seat BEFORE torgueing, never had one seize yet 

The threads are NOT gas tight the collapsible washer provides the seal once seated against the head and tightened to the correct torque.  Once the seal is broken (undone slightly) the pen oil will do what it's designed to do and penetrate, using the method of undo/do up will further encourage the oil to spread and slowly release the grip of the aluminium.
[/quote]The aluminium does not soften until about 300 degrees more, and NEVER, EVER EVER use copper grease on plug threads, never.


A little knowledge and imagination goes a long way and IF you actually believe the trash you typed we are going to have to agree to disagree on this one.  :rollin ride safe.


I think the fact you torque the plugs properly has more to do with them not seizing. Most people overtighten.


Would agree, to a point, about dirt on the threads though.