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Post by jtl on Nov 23, 2008 17:18:10 GMT -5
I put on a 70cc (Athena) and everything had been going fine. I did a couple of plug chops and on the third one I had a problem. I started the plug buy hand and put it in as tight as I could then I used the plug socket and secured it down to the washer. Good! When I went to take it out it turned a few times and then it seized. I was afraid to crank on the wrench too much so I pulled the head. I finally got it out but in doing so I destroyed the first 2/3 of the treads in the head. After inspecting the plug (NGK) I found that the threads about 1/3 of the way up had some slag in them. Obviously this chewed up the soft aluminum going down and coming up. My first thought was that I cross threaded, but that was not the case because the leading 1/3 went all the way down to the bottom with now issue. Furthermore I am very careful about putting plugs in aluminum heads. Has anyone had this problem. Brent, you of all people may have an opinion on this one. I have pictures but I don't know how to post them on this site.
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Post by 90GTVert on Nov 23, 2008 23:17:09 GMT -5
I had a cylinder head strip out on my stock engine. I think the dealer cross-threaded the plug. I used it as an excuse to get a 70cc kit.
Do you know any sources to get a spare Athena head? If not, you could try to heli-coil the head you have. I'd use anti-sieze on any plugs in the future as well.
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Post by gy6rocket on Nov 24, 2008 13:02:30 GMT -5
perhaps the wrong plug, if the thread pitch in the head was different than the plug pitch it would start out but then strip as it went in. Would be hard to tell using a socket wrench.
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Post by motomech on Nov 26, 2008 15:40:40 GMT -5
I'm not sure Heli Coils are available in that size, but there are spark plug boss repair kits. I used to buy them in auto parts stores. You don't think a partial siezure contributed to the problem? Everything else look OK?
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Post by earlwb on Nov 26, 2008 20:54:31 GMT -5
You can get a helicoil to fix that problem. I always out a drop of motor oil on the plug threads before I screw in the plug. This prevents the galling from occuring. Aluminum and stainless steel both have a notorious tendency to sort of weld themselves to the bolt or plug when you screw it in and then go to remove it later. But like you stated it may have been the defective threading on the spark plug did you in.
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Post by jtl on Dec 1, 2008 8:46:39 GMT -5
Update. I had a local machine shop put in a Helicoil and it works perfect. They person who did it said he thinks they should be SOP on all aluminum parts. Apparently they see lot of auto head probs with galling and cross threading. My prob was a defective plug that I failed to spot ahead of time. NGK asked me to send them the plug, which I did. They may cover my cost of the kit since I cannot purchase a head separately.
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Post by 90GTVert on Dec 1, 2008 9:08:41 GMT -5
Glad it's fixed and good luck with NGK.
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