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spark plug threads messed up

breakingorbit's Avatar

Join Date: May 2006
Posts: 23

05-13-06, 05:21 PM   #1  
spark plug threads messed up

I have a 97 mtd yard machine mower that I was cleaning up while changing the spark plug my ratchet did not turn "true" so it really screwed the threads up.Can I tap this out or am I just out of luck. My plug is a briggs and stratton 694385. What kind of tap do I use?
Thanks for the help

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repair_guy's Avatar
New Member

Join Date: Apr 2004
Posts: 539

05-13-06, 05:38 PM   #2  
There is a tool that you can buy at any auto parts store,it can be used to straighten threads or heli-coil the head.Which ever is needed.When I got mine a few they was $29.50.A lot for one time use,but it's worth every penny.

It comes with a 14mm tap and 3 heli-coils.just ask for a spark plug tap.

mla2ofus's Avatar

Join Date: Jan 2005
Posts: 478

05-13-06, 07:18 PM   #3  
Just some advice for next time. Start the plug with your fingers to be certain it screws in a couple of turns before using ratchet.

JLOpower's Avatar

Join Date: Dec 2005
Posts: 106

05-14-06, 04:23 AM   #4  
There are more than one kind of thread repair tool on the market:

There is a spark plug tap designed to 'chase' or reform the original threads. This tap has cutter teeth that produce the same size threads that are on the spark plug. After you use it, you simply screw in the new spark plug into the original hole. Since you have deformed the original metal, this type of tap leaves a weak repair and you will have to be extremely careful not to overtighten or cross-thread the plug when you reinstall it. If you really destroyed the original threads, this type of tap may not work.This tap is less expensive, probably in the $10-$18 range.

The second type of tap is the insert type. This kind of repair kit comes with a tap that cuts larger threads in the cylinder head. Once the new threads are cut, you thread in an insert that comes with the tap. This resizes the hole back down to the original threads required by the spark plug. There are a couple of different type of inserts depending on which brand of kit the parts store sells. [Solid inserts or helical spring type inserts.] There are differing ways to secure the inserts to the head. Just follow the instructions that come with the kit. This type of repair, if installed correctly, will provide you with new strong threads to install the plug in. You must follow the instructions carefully so that the insert will stay in the head the next time you change the plug. If you don't, the insert will come out with the plug, possibly ruining the oversize threads. If the oversize threads are damaged you would be forced to replace the head since 'double oversize' thread repair kits are not available. This type of kit will cost $32-$46 and you can purchase additional inserts seperatly if needed for other repairs.

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