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Old 01-20-2013, 12:59 PM   #31
danedg
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Here's an aluminum insert, badly welded to the head from the inside, that let loose like a 12 gauge and didn't injure anyone...
The sparkplug is fine!

This was the second time this happened. The head has since been retired...
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Old 01-20-2013, 03:47 PM   #32
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Wow... I had heard of that happening.... luckily you had your safety line attached (i.e. spark plug wire)....!!!...????.....

So, the standard /2 head is always a steel insert into the aluminum head? No wonder they went to long-thread plugs eventually, in aluminum.





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Old 01-20-2013, 04:13 PM   #33
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Quote:
Originally Posted by danedg View Post
Here's an aluminum insert, badly welded to the head from the inside, that let loose like a 12 gauge and didn't injure anyone...
The sparkplug is fine!

This was the second time this happened. The head has since been retired...
Wow!
Did that come from a /2 head? If so, the steel insert was replaced by an aluminum one, then welded in? Details please
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Old 01-20-2013, 05:50 PM   #34
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The remains...



Aluminum insert
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Old 01-21-2013, 09:28 PM   #35
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Originally Posted by Ron Seida View Post
I have to agree Bill, i've never seen a broken plug like the one shown... ever! I think you would need to be a ham-fisted hooligan to do that kind of damage .
Remember that they are talking about a 10 mm plug, ours are 14 mm.
Working on Japanese bikes I've seen my share of broken 10 mm, as well as 8 mm plugs ( those scare me ).
The key is ham fisted mechanics. Especially when they try to re- install a used plug the suggested number of turns and can't because the crush gasket is already crushed.

BTW, it's not just aluminum and steel galling together, more often than not it's the carbon ring that forms on the exposed portion of the plug body inside the combustion chamber. The carbon gets removed by the threads on the way out and some of it stays in the threads making it more difficult the next time around.
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Old 01-21-2013, 10:16 PM   #36
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Originally Posted by danedg View Post
The remains...



Aluminum insert
Look at that cumbustion chamber! That cylinder head had/has more 'issues' than just the plug insert. That botch job was doomed before it started.

I repair the damaged pre-70 1/2 reach head plug threads by welding the hole closed, tapping and then threading in a custom steel insert. A friend also does them w/ the same process w/out any problems. It works great.

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Old 01-21-2013, 10:33 PM   #37
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Quote:
Originally Posted by bpeckm View Post
Wow... I had heard of that happening.... luckily you had your safety line attached (i.e. spark plug wire)....!!!...????.....

So, the standard /2 head is always a steel insert into the aluminum head? No wonder they went to long-thread plugs eventually, in aluminum.





Seems more like the inserts are cast in. Some of them have bodies that are not cylindrical so pressing is not feasible. Also, the thought that there are more than 100,000 pre-70 heads made w/ pressed in inserts is not going to cut it. That is asking for way to much for pressed-in inserts to be subjected to by:
  • Plug insertion and removal
  • A combustion chamber that produces pressure
  • The idea of two dissimilar materials heating and cooling w/out a catastrophe.

With respect to long reach plugs w/out inserts.... if inserts are deleted then 3/4" reach threads are required for stability , it will eliminate a manufacturing process (sort of) and the efficiency of the head is greater by an increase in cooling capability, etc. I usually always build my 55-69 Twins engines w/ the LK heads.

BMW also deleted the lifter bushings out of the late '69 Twins engines. That's for another thread....

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Old 01-21-2013, 10:42 PM   #38
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i wonder if those half inch threads need an insert at all? Tons of dirt bikes have 14mm 1/2 inch deep spark plug threads in aluminum and never have a problem for it.
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Old 01-22-2013, 07:08 AM   #39
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I usually just give my plug threads a rub with the lead of a pencil

I have all the anti-seize stuff available but prefer pencil graphite, quick, clean & easy.
Many years, many vehicles, no problems.
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