Stripped Drain Plugs on the TRX300

The Honda Fourtrax 300 or TRX300 or any atv for that matter is prone to having the drain plug stripped if too much force is used when re-installing it. This is because the threads are cut directly into the case, which just so happens to be made of cast aluminum.

I have heard of many repairs over the years ranging from over-sized drain plugs with self cutting threads, threaded steel inserts, thread repair coils, and even JB weld.

Never use a 1/2" over-sized self threading drain plug from the automotive shop on the TRX300 or any ATV that utilized a 12mm drain bolt. Why you ask? A 1/2" over-sized drain plug is for exactly what it sounds like. To replace a 1/2" drain plug when the threads have been stripped. Installing one of these in place of a 12mm drain plug can cause a wedge effect essentially splitting the cases cast aluminum. Once this happens you are either going to be shelling out the cash for a good welder to repair the crack (after a complete tear down) or be buying a new case ($$$.)

Threaded inserts do make wonderful repairs. However the cost for one of these repair kits is easily over $100. So it is far from economical.

In my experience heli-coils are alright for most thread repairs but I would never use them in an application such as a plug. I also don't like to use them in applications where the fastener will be removed and installed frequently.

So what do I feel is the best repair. A normal replacement 1/2" drain plug, not an over-sized, nor a self-cutting. Just a replacement drain plug. You will need a couple tools though.

First is a 1/2"-20 Tap. This tap may be a little difficult to find at poorly stocked big chain hardware stores. However smaller hardware stores and automotive shops usually have these for around $5. Pay close attention and make sure it is a 1/2"-20 and not a 1/2"-13.

The next thing you will need which might take some work is a 29/64" drill bit. I managed to find one of these at my local hardware store. It sat me back about $8.

Next is grease. I prefer grease over cutting fluid for this application. Since we will be working with the crankcase and more importantly the area in which the oil is stored in the engine we want to keep as many metal chips out of there as we can. It is advised you keep the old engine oil to flush the engine with after this procedure is complete.

Lastly is your 1/2"-20 drain plug and gasket. Yes I do mean a gasket. If you have ever noticed a spot under your quad where the drain plug is? It probably has to do with this. The gasket will look a lot like an o-ring. Since you are stepping up to a 1/2" drain plug, gaskets will be easy to find. Every auto-store will have an assortment for this size. It is recommended that you replace this gasket at every oil change. After all, it is cheap insurance and only costs a couple cents.

Start by draining the engine of oil. Next you will need to get a drill. I used a hand held cordless when doing mine. Insert the 29/64" bit into the chuck and apply grease to the flutes. Use a relatively low speed on the drill, keep the drill straight while drilling, and don't go too deep. You really shouldn't have to drill through much more than a 1/4". You do not need to apply much pressure, let the drill bit do the work.

Once the hole is drilled you need to get your tap and tap handle. I do recommend using a tap handle so that the tap goes in straight. Once again apply grease to the tap flutes. Insert the tap and begin to turn. Thread the tap in a little bit, then back it out a half turn or so to clean the flutes. Repeat until the tap has cut in to a sufficient depth to thread the hole entirely.

Now you should have shiny new threads cut for your drain plug but you aren't finished yet. Put your oil pan back under your quad and pour the old oil back through the fill hole. Yes the oil is going to run right out the drain, this is what you want. You are flushing any remaining chips out of the engine. You can also use kerosene or diesel to do this but I typically just use the old engine oil.

Now install the gasket on your new drain plug, it works just like a washer. Slide it over and call it a day. Now you can thread your new drain plug in. REMEMBER NOT TO FORCE IT THIS TIME! You only need to get it snug, no tighter. I would recommend using a deep well socket and just using your hand to turn it tight. Then get your ratchet and turn it another 1/8 of a turn.

Fill your quad back up with the recommended oil and check for leaks. If you don't see any you are done and can get back to enjoying your Fourtrax.