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Spark plug in an Aluminum Head Questions??
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Posted by: Aaron

04/19/2005, 16:30:42

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I need help in this area since to be honest, I have no clue. With the spark plug diameter of 1/2" and being steel, screwed into an aluminum head that has 5/16" width of threads.(about 3.25 turns till tight) Is this enough threads to hold the spark plug in place, or to not loosen? Any specifications, standards or any other help is appreciated. Thanks, Aaron






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Re: Spark plug in an Aluminum Head Questions??
Re: Spark plug in an Aluminum Head Questions?? -- Aaron Post Reply Top of thread Forum
Posted by: dvbswamy

05/15/2005, 11:54:27

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dear aaron,
in any machine design, the minimum depth to which any threaded part is to go is equal to its diameter. that is D=L. more or less sqaure. that is enough to hold in any ENGG material, including aluminium. the Al used in normal engg. practice is Al alloy and has better strength than pure Al. i am not sure if answered your doubt. let me know if i did not. al the best.
Prof. Swamy.






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Re: Spark plug in an Aluminum Head Questions??
Re: Re: Spark plug in an Aluminum Head Questions?? -- dvbswamy Post Reply Top of thread Forum
Posted by: randykimball
Barney
05/15/2005, 16:23:48

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If you are designing an aluminum head for an internal combustion engine you might consider a steel insert for the spark plug to fit into. There are several on the market. This would settle the problem of strength as the insert would most likely stick out of the head towards the spark plug a couple of more turns. I'm not talking about a coiled type insert, I'm talking about an insert that has male threads on the outside and female theads on the inside. There is often a head area not threaded on the outside or a set of stakes that you push into the thread joint to prevent the insert from coming loose when you remove the bolt, or spark plug in this case.

Search for thread inserts. They are widely used in aircraft applications where the strength per weight properties of aluminum are required with the thread holding properties of steel.

-randy-




The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.


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Re: Spark plug in an Aluminum Head Questions??
Re: Re: Spark plug in an Aluminum Head Questions?? -- randykimball Post Reply Top of thread Forum
Posted by: Daver

07/27/2005, 00:38:11

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Can someone define the minimum thread engagement for a Spark Plug in an Aluminum head without doing a detailed stress analysis? I realize that a best practice might be l/d=1. What I would like to determine is the minimum number of threads based on strength of Aluminum, normal combustion loads and number of cycles. If there is an engineers handbook that takes these type of factors into account it would be a big help.






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Re: Spark plug in an Aluminum Head Questions??
Re: Re: Spark plug in an Aluminum Head Questions?? -- Daver Post Reply Top of thread Forum
Posted by: randykimball
Barney
07/27/2005, 22:42:49

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May I suggest a simple straight forward answer.

Almost all spark plugs seem to have about the same length of threaded barrel on them these days. Many of them fit into alumium engines. It, therefore, would suggest that these engine and spark plug manufactures have clearly concluded together that this is the best length of threaded barrel through experience and testing. I'd save myself the stress and accept their findings and move on to other design problems, it it were me.




The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.


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Re: Spark plug in an Aluminum Head Questions??
Re: Re: Spark plug in an Aluminum Head Questions?? -- randykimball Post Reply Top of thread Forum
Posted by: flexbrite28

08/09/2005, 12:05:58

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I am experimenting with several different types of spark plugs now. I find that by coating the threads the plugs are much easier to insert and remove in the aluminum head and I avoid thread stripping. There seems to be no good reason to attempt to change thread length or size as the whole idea is to position the sparking end of the plug in a specific place within the cylinder, The coating reduced required torque so much that I could easily go past the optimum setting if using the original recommended troque. So, reduce the torque by 30%, leave the thread setup as is and results are pretty much what the manufacturer(s) claim.






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