I've always steered clear of repairing stripped threads or buying/selling saws that had them. But, I now have two cylinders that I value quite high and they both have questionable threads. Neither is fully stripped - they'll both hold a plug, but the threads aren't 100% - so I'm not comfortable letting them out into the world as-is . . . even considering I subscribe very strictly to a full disclosure policy when selling/trading. So, the opinions I'm seeking with this thread is regarding the type of repair that is better and/or more preferred. I have done a little bit of research and understand there to fundamentally be two approaches; the "helicoil" and the "insert". From my chainsaw dealings over the past few years it seems the overwhelming majority of the repairs I've seen or heard of were helicoil, but I don't want to make assumptions based solely on that. I welcome all input & opinions. Thanks!
If the threads aint too bad u can chase them with a tap...start it straight use lots of lube and go slow....should work fine..not sure ov your thread pitch but u can buy them just about anywhere...good luck..basicaly your just re cutting them..all thats needed is a tap and 1/2" or 3/8 ratchet..proper size is very important and you got 1 shot to get it rite..the proper tap should start just like the plug....i hope the helps..
I touched on this topic awhile back. Inserts are the way to go for sure. Easy and very strong repair. Just make sure you get the tap started straight. http://firewoodhoardersclub.com/forums/index.php?threads/sav-a-thread-spark-plug-hole-repair.3207/
Thanks. I have a good friend who says inserts are the way to to, but in all fairness that's only because someone else told him they were the best. He's like me and stays away from bad threads, but he has used one insert with good success. It's nice to have some reassurance on the insert . . . starting to sound like an easy choice.
I do not like the wire coils for critical threads that will be run in and out periodically, in soft material like aluminum and especially where heat is involved. There are many applications in which they work well, spark plugs ain't one of them.
I'm with the thread insert. Don't do the prep work or start the tap by hand though. Use a mill or drill press.
I've only done it once, but starting the tap by hand was no problem at all for me. The tool that comes with the kit shown in MM's link above has starter threads that fit whatever is left of the original threads in the cylinder, and they really helped get the tap started in the right orientation.
This is the key. The tool I used uses the alignment of the previous threads to set the hole. If you don't cross thread the tool/tap, then your alignment will be perfect. If the hole is really FUBAR'd, requiring drilling, then yes, I would highly recommend using a drill press or vert. mill.
I have done several of the inserts before. Not really a huge deal. Get one of the guided tools like the others have already mentioned.
