OEM spark plug threads
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Joined: Jun 2007
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Well considering Aluminum is softer then steel and how fine the threads are, the head should naturally strip first. If I took a guess, it would be somewhere in the vicinity of 35lb to start over taxing and probably another 10-15lb of applied force before total failure, so roughly 45-50lb.
Do we win a free Billman TCT?
Do we win a free Billman TCT?
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Joined: Jun 2007
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Originally Posted by cosmomiller' timestamp='1445273898' post='23779921
spark plug failed before the head threads stripped
Was able to click off 75 ft-lbs.
When I stepped up to 80, the threads broke off the spark plug in the head.
Was able to spin the broken threaded piece out with pliers from the cylinder side.
Afterwards, I put a new plug in the hole. It went in with slight resistance as the threads were barely deformed.
Was able to torque to spec no problem. It could likely take another 70 ft-lbs.
Good insurance that 24-26 ft-lbs is super safe.
A lose plug will allow combustion gas to torch the threads resulting in stripping. Very safe to say if the threads are stripped, it was followed by torching.
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Joined: Apr 2012
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This. More data points would probably be best in this case. Not that I care much, since the 24-26 lbs is what I go by and I'm miles from that... but at least from a data perspective it might be best to test a couple more. Also, is the condition of that donor head uncompromised in terms of the metallurgy? If an aluminum head is exposed to too much heat, won't it affect the brittleness of some areas?
