Q & A — November 2002
By Capt. Ken Kreisler
| How to change an exhaust bellows, troubles with an outboard engine’s fuel-bleed recirculation system, and more.
a routine maintenance inspection, I noticed that the exhaust bellows on
my 3.0L four-cylinder stern drive felt hard to the touch and showed some
signs of wear. How difficult is it to install a new one? G.R.,
The first step is to loosen the upper clamps that attach the bellows to the exhaust elbow as shown in the bottom figure. Grab the bellows on top and move it back and forth, twisting it if necessary in preparation for removal. Using the same diagram for reference, remove the fasteners attaching the exhaust elbow to the manifold, and lift the elbow from the manifold and studs. For good preventive maintenance, you should also replace the gaskets and restrictor plate. While they might look okay, it's not worth taking the chance. (Have the new ones ready when you begin reassembly.)
Loosen the lower clamps, and remove the bellows from the exhaust collector. You should be able to free the bellows from the elbow without too much trouble. If you encounter resistance, carefully use a flat-head screwdriver to pry it free.
Next check the exhaust flapper valve. Refer to the top figure for its location. If it is stuck or damaged or has been improperly installed, you must replace it. A faulty one can restrict exhaust flow, allowing water to back up into the system and perhaps even into the engine.
Now drive the pivot shaft (see top diagram) from the valve and bushings using a small-diameter punch. Push the rubber bushings, from the exhaust pipe, being careful not to drop them into the pipe. Apply Scotch Grip rubber adhesive to the new bushings, and insert them into the bores of the exhaust pipe. The flanged side of the bushings must face towards the inside of the pipe.
Position the new exhaust flapper valve in the pipe, with the long side of the valve facing down. Insert the pin through one rubber bushing and valve flange, and align the pin with the second bushing. Once you've done this, push the pin through to the second rubber bushing. Test the valve to ensure free movement. The pin ends should be flush with the exhaust pipe on both sides.
You are now ready to install the new bellows. To make it easier to place them onto the exhaust pipe and elbow, lubricate the insides of the bellows with soapy water and place it and the clamps on the exhaust collector. Position the end of the bellows with one rib (the short end) downward on the exhaust collector pipe. The end of the bellows with two ribs (the long end) must be positioned toward the top.
Place two clamps around the top of the bellows without tightening them, as they must be loose to permit installation of the exhaust elbow. Coat both sides of the new gaskets with sealer, and then position both gaskets and the restrictor plate on the studs of the manifold.
Install the exhaust elbow, and torque down the fasteners according to your engine manufacturer’s recommendation. It should be around 12 to 14 ft./lb., but make sure you check. Take care that the bellows is on straight and not twisted, then tighten the clamp screws. Start your engine, look for leaks, and make sure the operating temperature is within acceptable limits.
This article originally appeared in the October 2002 issue of Power & Motoryacht magazine.