Because the oil drain plug is made of softer metal than the bolt hole in the oil pan, it's a rarer occasion to strip threads in the pan. Stating this fact does not mean the threads in the pan cannot be damaged and sometimes are by novice lube techs who either over-tighten or cross-thread drain plugs severely. Replacing an oil pan can be expensive and labour intensive depending on its position at the bottom of the motor. Rethreading or tapping the oil pan hole is a simpler and much less expensive alternative.
Things you need
- Bolt diameter and thread pitch gauge
- Tap and die set
- Bearing grease
- Replacement drain plug bolt and gasket
- Box-end wrench set
Measure the oil drain plug diameter and pitch size with the thread and diameter gauges. These devices are quite self-explanatory how to use. Insert the plug into the hole it fits best in. Go between metric and Imperial until you've found the tightest fit for the plug. Do the same for the thread pitch gauge.
Try rethreading the oil pan with the original measurements as your first option. If the pan threads are not overly damaged, this may be a viable option. Locate the tap in the tap and die set that matches the measurements of the original drain plug.
Insert the tap into the tap wrench and rub a little bearing grease onto the end of the threads and flutes of the tap. This will help prevent pieces of cut thread from entering the oil pan.
Carefully align the tap to the threads of the pan, making sure the tap is straight and flush. Compromised threads may challenge the direction of the tap, so it's important to make sure the alignment of the tap will allow the replacement plug to tighten straight into the pan.
Turn the tap and wrench one revolution into the threads of the pan once the threads and flutes of the tap have been aligned and are biting into the compromised threads. Back the tap off half a revolution to allow the metal shavings of the pan threads to work their way down the tap.
Repeat Step 5 until the tap is turning freely into the pan. The threads of the pan are only as thick as the pan, so this will not take long.
Remove the tap and wrench from the threads of the oil pan.
Install the new drain plug and gasket making sure the diameter and pitch of the plug match the tap measurement you just cut into the pan.
Tighten the plug with a box-end wrench snugly. Do not over-tighten the plug, but make sure you can tighten it properly. If the plug strips or the threads of the plug will not bite into the female threads of the pan, you're down to one more option before having to replace the pan.
Change the pitch size to the next coarser pitch and repeat this procedure. This will require a different drain plug pitch size and a replacement gasket. If this procedure still does not work, you'll have to have the pan replaced.
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