BMW E30 - Removing / Replacing the Front Pipe and Catalytic Converter

The first step is to get the car way up in the air on jack stands. You really are living if you have a lift!

The first step in removing the cat is detaching the rear pipe from the front pipe. Remove the three bolts that connect the front pipe/cat to the rear pipe/muffler. If you are like me, you quickly get frustrated by those three bolts. Unless you used anti-seize compound (I didn't last time), you can spend a lot of time trying to get these three bolts off.

Now you have freed the front pipe/cat from the rear pipe/muffler. The real fun begins when you try to remove those six copper nuts which hold the front pipe to the exhaust headers. You don't want to cut anything here. You can waste your time with penetrating oil, but I have found only one thing that works, and that is a propane torch.

Be careful with your propane torch. The flame is hard to see in daylight and it really will do some damage if you point it in the wrong direction. Keep it the flame far away from anything that is damaged by heat. When you are heating something, remember that the hottest point of the propane flame is right at the tip of the blue flame.

Your mission is to get those nuts so hot that they glow cherry red, then quickly get a wrench or socket on the nut and turn it. The entire nut must be glowing cherry red, or it will not come loose. It may take your propane torch 20 minutes to get the nut completely cherry red. Be patient.

I found that the best setup for getting a socket on these nuts was to use a 1/4 inch drive. If you get the nut and stud completely cherry red, you won't need any more leverage. If the nut won't turn, don't force it and round off the shoulders of the nut. Get the nut cherry red again, then get the wrench on it again. Be prepared to spend hours on this step.

OK, now that you have all six nuts off, the pipe/cat assembly is being held up by one bolt which is connected to the front mounting bracket which is connected to the transmission. Unplug the oxygen sensor from the harness. The plug for my car was securely wrapped with plastic electrical tape. The sensor wire is held in place with clips which are along the rear reinforcement bar (near the rear of the transmission). After the oxygen sensor is unplugged, remove the bolt which connects the front mounting bracket. Watch out: the front pipe/cat assembly is heavy.

Carefully remove the oxygen sensor by turning on the very large hex shaped portion. Don't touch the end of the oxygen sensor! Install the oxygen sensor in the new cat with anti-seize compound. Don't let any of the anti-seize compound get on the end of the sensor!

BMW E30 Installing the Front Pipe and Catalytic Converter

The first step in installing the cat is to loosely bolt it to the front mounting bracket. The hardest part of the installation is to hold the two exhaust manifold gaskets in place while you connect the two pipes on the exhaust manifolds. I used two small bits of duct tape to hold the gaskets steady.

The pipe connecting to the rear exhaust manifold has a bellows in it so that it may be adjusted. My pipe required quite a bit of adjustment (I suspect it may have bent during shipping). You are supposed to tighten the 6 copper nuts to 36-40 ft. lb. I just tightened them as tight as my 1/4 in drive ratchet would allow, given the cramped space.

The rest of the installation is easy. Just use a new gasket, three new copper nuts, and three new bolts to attach the front pipe/cat to the rear pipe/muffler. Tighten up the bolt connecting the front pipe to the front mounting bracket. Plug in the oxygen sensor, wrap the connection with electrical tape, and secure the connector.

Start the car. Check for leaks at the exhaust manifolds before the area gets too hot. Check for leaks at the front/rear pipe union.