Spark Plug Shot Out of Your Engine? No Problem!
Its not uncommon for R53 Mini Coopers to have the spark plugs blow out of the cylinder head. This can be a scary event for Mini lovers, but fear not! With the proper tools you can fix your threading and have a new spark plug installed in no time. Okay, so the first thing you will need to do is get your hands on something called an extended reach Time-Sert. With this tool, you can re-tap your spark plug cylinder, cut a new seat, and then install a new insert that you can screw your new spark plug into. Note that an extended reach option is necessary, since the sparkplugs on these mini coopers sit far below the top of the motor. Buying one of these tools may set you back around $200, but this option is much better than a hefty garage bill. If you do some looking around, you may find that you can loan a tool from a Mini Mania forum member and save some money! Or contact TIMCERT for a list of distributors.
Figure 1: Here you can see the long cylinders that house the spark plugs. The plugs are recessed by about 6 inches.
Once you have your tool, you will need to ensure that the piston in the cylinder you are working on is NOT at the top of its stroke. This is important because when you go to tap your new spark plug cylinder, you do not want the tap to come in contact with the top of the piston head. This can cause the entire threading to become ruined if the piston prevents the tap from downward travel. Here is a simple way to determine the distance between the top of the piston, and the bottom of the threads. Take a small rod that will fit into the sparkplug hole, and add a small plastic/foam ring that can slide snug up and down the rod. Ensure that the diameter of the ring is larger than the threading of the spark plug hole. Now, push the metal rod down into the hole until you come in contact with the top of the piston. Now, slide the ring down onto the top of the threading. Once you remove the rod, you now know how far below the piston head is to the bottom of the threads.
Figure 2: A small foam ring was placed onto a metal rod so that it can be slid up and down.
Figure 3: This drawing illustrates a useful way to determine the clearance between the piston and cylinder head.
Now that you have this measurement, you now know how much clearance you have once your tap reaches the bottom of the cylinder head. Ensure that you stay within this clearance as to not hit your piston head. (Note that the tapping instructions vary from tool to tool, make sure you follow the basic instructions outlined in the manual provided with your tool.)
Once you have tapped the new threads, and cut a new seat, some metal chips WILL fall onto the piston head. Here is a trick that will help you vacuum out all the tiny chips with ease! Find a length of flexible plastic tubing that is small enough to fit into the hole that the spark plug sits in. With some taping required, attatch the flexible hose to a shop vac and ensure you have good suction. This next part is extremely helpful. You may find that the plastic tubing is to flimsy, and bends when you try to clean the top of the piston. However, if you take a small metal rod and stick it through the flexible tubing, this will give you more control. At this point, it helps to spray some brake clean into the cylinder to free up any small metal chips. Make sure you do a good job vacuuming up all of the debris and liquid, you wont want this in your car.
Figure 4: A closeup image showing the metal rod dissecting the flexible hose. Note that the rod is small enough to allow the metal chips to pass through.
Figure 5: The flexible plastic tubing fits into the cylinder with ease!
With the cylinder tapped, the new seat cut, and everything cleaned of debris, you can now install the time-sert! This is a small threaded adaptor that allows you to screw in your brand new spark plug. Ensure to reference your tool's manual for this step. And that's it! You have successfully completed this task. There's nothing better than bonding with your Mini! (Note that you can only repair each cylinder once, if your new spark plugs blow out after some time, a new head may be required.)