Repair spark plug threads (port)

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  #1  
Old 05-04-16, 05:08 AM
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Repair spark plug threads (port)

I was helping a friend do a tune up on his machine, the spark plug came off as it should, but the new one would not catch. We realized that the first few threads were destroyed and would need to be repaired. I tried my thread chaser tool but it gets hung up after three/four swings of the ratchet. I do not want to force it past that point though.

Also, I noticed that the damaged threads are the first few, what is the best way to correct this issue?
 
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Old 05-04-16, 05:24 AM
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if it's a small engine and you can pull the head without a lot of trouble, take it off and screw the plug in from the inside. Then go to the outside and try it with lubed threads.

If the threads are completely ruined you can put a helicoil in it, but you want to keep track of the costs. Sometimes you can put a different head on it just as cheap.
 
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Old 05-04-16, 06:02 AM
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it is a small engine, I do not know how he would feel about taking things apart...



I was thinking that I should be able to do just enough to get those first few threads cut...or would that not be possible?
 

Last edited by longlegs; 05-04-16 at 06:44 AM.
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Old 05-04-16, 06:39 AM
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You pretty much have to disassemble it with a Spark Plug tapping . . . just to make sure you don't leave any shredded metal fragments inside the Combustion Chamber.

I did my first HeliCoil on a "odd" Muffler Tapping; you'll get much more usage out of the drill, tap, and HeliCoils required for a much more standard Spark Plug Thread.
 
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Old 05-04-16, 10:50 AM
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Oil the thread chaser and run it through. It most likely will fix the problem if you make sure it starts correctly. If not, a helicoil can be installed. the sav-a-thread heli-coil system works well.
 
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Old 05-04-16, 11:53 AM
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so, forcing the thread chaser past the tight spot is not gonna create further issues?
 
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Old 05-05-16, 12:45 AM
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There are no guarantees, but that's pretty much all there is to do unless you remove the head and go from the back side. That's what the thread chaser is for though, to fix up the threads. If it starts and goes in enough turns to feel comfortable and then hits a tight spot, you generally go through the tight spot. If it gets really tight, then there is a point where you have to decide if you want to keep on or not. Lubricate the chaser tap before using it.
 
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Old 05-05-16, 04:25 AM
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Thanks for the help. Using the thread chaser was enough to get the threads repaired. The mower is up and running again. Only thing though, when replacing the plug I found that it required a bit more effort than normal using the wrench.



New question:

this mower is an Ariens 19hp 42in cut automatic trans with BS engine.

Foot pedal type operation... but will not reverse.

what has to be checked to determine the cause of this?
 
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Old 05-05-16, 11:06 AM
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Check linkage operation. Sometimes grass packs up behind the area on the the transmission where the linkage connects and keeps it from traveling back into the reverse position all the way.
 
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