Tap size i need to run tap down spark plug hole to clean up threads, what size tap do i use

Demise, Buy the whole Ford spark plug rethread kit, no guessing involved. You can google search for the kit, to get a good price.
Check the attached links,instruction and guides, Good luck
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Take it back off, Buy a helicoil set. Basically.. Drill the hole out, tap it out to a bigger size. insert the heicoil(which reduces it to the size of the bolt.. A good heicoil set will have the drill bit, helicoils, tap, and the tool to insert the helicoil. Put down rags to catch the metal shavings while drilling and tapping. Then clean the tapped hole(Brake clean and blow it out with air) and use thread lock on the helicoil. Make sure the helicoil sets down below the surface..

If you are lucky, the spark plug was not tightened correctly and worked loose. In this case, you may be able to chase the threads and it will go back in and stay. Make sure the plug is installed correctly this time.

If you are unlucky, the threads will be stripped. In this case, you have 2 choices: thread repair or larger spark plug. Either way, you have to drill and tap the spark plug hole without getting any metal shavings in the cylinder. The main difference is that if you use a thread repair insert, the original spark plug size will fit in your engine; if you tap out the holewithout using an insert you will have to get a different spark plug for the cylinder that was repaired.

The best way is to measure a bolt of the same size and pitch as was fitted in that threaded hole. The specs are the same for both eg M10 x 1.5 or whatever. Then you can take this info, or better, the bolt itself, along and buy a helicoil kit to suit.

If it is for a spark plug hole, they will know immediately on seeing one of your spark plugs (there are 2 main sizes). It is probably also on the back of the kit packet.


The other way is to drill and tap out the hole for a larger size screw or bolt than you had to begin with. Generally you would use a tap drill for the next larger standard size thread.

The Spark Plug hole can be repaired. The professional way is to remove the cylinder head, and use a repair such as a Helicoil.

The spark plug hole is tapped out to a larger thread size, with a special Helicoil tap. Loctite or some other form of thread locker is applied, and the Helicoil is inserted.

Helicoil's are made of Stainless Steel, and are much better than the original material used in the cylinder head. (Be it cast iron or aluminum)
Drag racers use Helicoil's in their engines.

Tapping out the spark plug hole for a Helicoil, or using a special thread chaser, is NOT a good idea, while the cylinder head is still installed on the engine.
The tap creates chips of metal which fall down into the cylinder.
Using a vacuum to try to alleviate the chips, falls short of a good repair job.

You can have the oil pan re-tapped, which mean they can re-thread the oil pan for a slightly over sized oil pan plug. There are different size oil plug and just get one size slightly larger and have a shop re tap the oil pan for the larger oil plug and there you have it, good as new. keep in mind that I would make sure i use lots of grease on the tap tool to ensure i get most of the aluminum filling on the tap and not in the pan. Good luck and this should only cost you 1 hour of the shop rate or you can do it your self if you have to. You can loan out the tap tool from Auto Zone and pick up a larger oil pan plug there too. Be safe friend. 

Quick Tip. Take one old spark plug and saw an X across the threads on the bottom with your hacksaw. Clean away the filings. Oil it and thread it into the spark plug hole. This is called re tapping. Then try the new plug again. Has worked many times for me.

Very, very difficult re-threading an engine block. Not impossible, but very difficult and not usually performed by the DIY. That said take one of your spark plugs down to your nearest hardware store, one that sells loose nuts & bolts. Try screwing the spark plug into nuts of the proper size until you "match" the thread pattern. Do be afraid to ask for assistance from one of the experienced clerks (its free). The matching thread pattern on the nut will tell you the proper thread size. There are at least a couple different thread sizes and patterns. You may or may not be able to get th tool to clean the threads at the same location. My guess is that they will have the smaller sizes, and you may need to find a more specialized store to find the larger size tools.

Carefully inspect the threads it sounds as if you have a crossthreaded hole that isn't allowing the plug to full seat. You'll need to get the proper size threading die and very carefully recut the threads. Best done in a shop as if anything falls into the cylinder your looking at very expensive repairs. It happens quite frequently with aluminium blocks and needs to be fixed as a spark plug popping out lets hot fuel dump into the engine compartment. Here is a description of such a tool at toolmonger.

It can happen to the best of us: one moment of inattention results in a cross-threaded spark plug hole. You can either install a helicoil and hope for the best, or send it out to have the whole shebang re-tapped. Now you have another option. The Back-Tap can fix that cross-threaded hole from the inside — without pulling the head.
The Back-Tap is a tap with expandable threads and a mandrel to catch errant metal shards. Apply a dab of grease to the mandrel, then place the device in the hole past the damaged threads. As you back it out, the cutters expand out to engage the undamaged threads, then gently reshape the damaged ones. The greased mandrel keeps metal filings from ending up in the cylinder.
The result: a task that could potentially take days and cost hundreds of dollars is done in minutes for less than a hundred bucks.
MAC offers a three-piece kit that includes a 10mm, 12mm, and 14mm Back-Tap for $90. You can buy Individual taps from various sources for about $50 each.

Oh, ok. No, they shouldn't be related. The plug cover meaning the spark plug wire boot that goes over the spark plug hole? Why won't it stay in? Is the spark plug missing? Those plug wires snap onto the spaek plug holding the wire on the plug.. There should be a spark plug in the hole. If not, you probably had it blown out. That happens once in a blue moon. If the plug is missing, get a new one and carefully install it by hand, no rachet. If the plug won't start in the hole the first few threads mat be strippe. Do not cross-thread the new plug. Spark plug hole taps are available at parts stores. good luck