For a number of reasons, exhaust system work can be the most dangerous type of work you can do on your car. Always observe the following precautions:
- Support the car extra securely. Not only will you often be working directly under it, but you'll frequently be using a lot of force, say, heavy hammer blows, to dislodge rusted parts. This can cause a car that's improperly supported to shift and possibly fall.
- Wear goggles. Exhaust system parts are always rusty. Metal chips can be dislodged, even when you're only turning rusted bolts. Attempting to pry pipes apart with a chisel makes the chips fly even more frequently.
- If you're using a cutting torch, keep it a great distance from either the fuel tank or lines. Stop what you're doing and feel the temperature of the fuel bearing pipes on the tank frequently. Even slight heat can expand and/or vaporize fuel, resulting in accumulated vapor, or even a liquid leak, near your torch.
- Watch where your hammer blows fall and make sure you hit squarely. You could easily tap a brake or fuel line when you hit an exhaust system part with a glancing blow. Inspect all lines and hoses in the area where you've been working.
A number of special exhaust system tools can be rented from auto supply houses or local stores that rent special equipment. A common one is a tail pipe expander, designed to enable you to join pipes of identical diameter.
It may also be quite helpful to use solvents designed to loosen rusted bolts or flanges. Soaking rusted parts the night before you do the job can speed the work of freeing rusted parts considerably. Remember that these solvents are often flammable. Apply only to parts after they are cool!
See Figure 1
System components may be welded or clamped together. The system consists of a head pipe, catalytic converter, intermediate pipe, muffler and tail pipe, in that order from the engine to the back of the car.
The head pipe is bolted to the exhaust manifold. Various hangers suspend the system from the floor pan. When assembling exhaust system parts, the relative clearances around all system parts is extremely critical. In the event that the system is welded, the various parts will have to be cut apart for removal. In these cases, the cut parts may not be reused. To cut the parts, a hacksaw is the best choice. An oxy-acetylene cutting torch may be faster but the sparks are DANGEROUS near the fuel tank, and, at the very least, accidents could happen, resulting in damage to other under-car parts, not to mention yourself!
The following replacement steps relate to clamped parts:
- Raise and support the car on jackstands. It's much easier on you if you can get the car up on 4 stands. Some pipes need lots of clearance for removal and installation. If the system has been in the car for a long time, spray the clamped joints with a rust dissolving solutions such as WD-40® or Liquid Wrench®, and let it set according to the instructions on the can.
- Remove the nuts from the U-bolts; don't be surprised if the U-bolts break while removing the nuts. Age and rust account for this. Besides, you shouldn't reuse old U-bolts. When unbolting the headpipe from the exhaust manifold, make sure that the bolts are free before trying to remove them. If you snap a stud in the exhaust manifold, the stud will have to be removed with a bolt extractor, which often necessitates the removal of the manifold itself. The headpipe uses a necked collar for sealing purposes at the manifold, eliminating the need for a gasket.
- After the clamps are removed from the joints, first twist the parts at the joints to break loose rust and scale, then pull the components apart with a twisting motion. If the parts twist freely but won't pull apart, check the joint. The clamp may have been installed so tightly that it has caused a slight crushing of the joint. In this event, the best thing to do is secure a chisel designed for the purpose and, using the chisel and a hammer, peel back the female pipe end until the parts are freed.
- Once the parts are freed, check the condition of the pipes which you had intended keeping. If their condition is at all in doubt, replace them too. You went to a lot of work to get one or more components out. You don't want to have to go through that again in the near future. If you are retaining a pipe, check the pipe end. If it was crushed by a clamp, it can be restored to its original diameter using a pipe expander, which can be rented at many auto parts stores. Check, also, the condition of the exhaust system hangers. If ANY deterioration is noted, replace them. Oh, and one note about parts: use only parts designed for your car. Don't use fits-all parts or flex pipes. The fits-all parts never fit and the flex pipes don't last very long.
- When installing the new parts, coat the pipe ends with exhaust system lubricant. It makes fitting the parts much easier. It's also a good idea to assemble all the parts in position before clamping them. This will ensure a good fit, detect any problems and allow you to check all clearances between the parts and surrounding frame and floor members. See the accompanying illustrations for the proper clearances.
- When you are satisfied with all fits and clearances, install the clamps. The headpipe-to-manifold nuts should be torqued to 20 ft. lbs. (27 Nm). If the studs were rusty, wire-brush them clean and spray them with WD-40® or Liquid Wrench®. This will ensure a proper torque reading. Position the clamps on the slip points as illustrated. The slits in the female pipe ends should be under the U-bolts, not under the clamp end. Tighten the U-bolt nuts securely, without crushing the pipe. The pipe fit should be tight, so that you can't swivel the pipe by hand. Don't forget: always use new clamps. When the system is tight, recheck all clearances. Start the engine and check the joints for leaks. A leak can be felt by hand. MAKE CERTAIN THAT THE CAR IS SECURE ON THE JACKSTANDS BEFORE GETTING UNDER IT WITH THE ENGINE RUNNING!! If any leaks are detected, tighten the clamp until the leak stops. If the pipe starts to deform before the leak stops, reposition the clamp and tighten it. If that still doesn't stop the leak, it may be that you don't have enough overlap on the pipe fit. Shut off the engine and try pushing the pipe together further. Be careful; the pipe gets hot quickly.
- When everything is tight and secure, lower the car and take it for a road test. Make sure there are no unusual sounds or vibration. Most new pipes are coated with a preservative, so the system will be pretty smelly for a day or two while the coating burns off.