How To Replace Exhaust and U-Joint Bellows in the
Mercruiser Bell Housing
The original tube (#18654A1 or GLM #89100)
is an accordion style rubber hose measuring approximately 5-1/2” in length when not expanded, and an approximate outer
diameter of 2-7/8” and inner diameter of 2-12”. As this is made of rubber, over time the material may become brittle
and could break due to natural wear and tear. When inspecting this piece, look for any cracks or damage and replace if necessary.
You have the option of replacing this with the original style, or the newer open ended tube style. The newer style (#78458A1
or GLM #89150) is approximately 4-3/4” in length, and only uses one clamp for installation into the gimbal housing side.
When the drive is lowered, the flanges will fit into the open ended side of the rubber tube. The main benefit of using the
newer style is it will release some of the back pressure; however this is a trade off with increased exhaust noise. Most people
tend to choose the original accordion style as a replacement.
are 2 ways to perform this job - with or without removing the stern drive
To do this job without removing
the drive – you can simply turn the drive slightly to the port side (left) followed by removal of the clamps on the
bottom of the bell housing. *Please note, this will save time by not having to remove the stern drive, however, installing
the exhaust hose to the transom side will be a challenge. Installing the newer style hose will make installation easier as
you only need to install it into one side. Get a firm grip on the gimbal side of the part and begin to pull it out of the
housing. Since the old piece was likely installed with an adhesive or glue, you’ll need to pull using force; you can
even raise the stern drive to assist with the removal. Before installing the new part, clean the areas of the bell and gimbal
housing where it will sit using a wire brush or course sandpaper, and clean thoroughly with a cleaning agent. This will ensure
the adhesive material will properly seal between the housing flange and rubber piece. New replacement parts will come with
new grounding clips and stainless steel hose clamps – make sure to use the new ones and avoid re-using the old ones
as they may be corroded or damaged. Always make sure to use an adhesive / glue (Sierra #18-9031) when working with these rubber
parts. (This can be purchased above, in the repair tool section. Begin by applying the glue to the inside of both ends of
the tube (only one side for the newer style piece), and around the mounting flanges on both housings. Allow the glue to set
for a few minutes, and proceed to place the hose clamp on the gimbal side of the hose and install – making sure to tighten
the clamp. Next, place the clamp on the other side of the piece and pull open while stretching (using considerable force)
onto the flange on the transom side. This will take a considerable amount of time; if you’re not able to get it on you
will need to remove the stern drive to finish the installation. (See instructions below). Start engine and check for any leaks.
To do this job with the out drive removed, it is recommended you use the expander tool (#91-45497A1 or GLM #90360.
This can be purchased above in the tool section). You'll notice a hole on the side of the bell housing which allows you to
access the screws on the hose clamps using a long screwdriver. This hole is on most models, except for the very old models.
Remove both clamps, and begin to remove the rubber hose from both flanges by pulling / wiggling with force. The adhesive applied
to the part being removed can make this difficult to get off, so be patient. Next, clean the mounting areas on the housing
flanges; and install rubber the hose onto the gimbal housing flange (described in method 1 above). Apply glue on the inside
of the other side of the hose along with the hose clamp. Next, using the expander tool, slide it through the housing into
the exhaust hose and ‘expand’ it. While the tool spreads the rubber open, pull it gently onto the flange on the
transom side. Tighten the clamp using the access hole on the side of the housing. Start the engine and look for any leaks.
Since the above noted
job can be very time consuming (3 - 6 hours), it is recommended to inspect your gimbal bearing while your're at it. To check
the gimbal bearing, spin in in the housing by hand and take note of the feel and sound it makes. When properly functioning,
it should be smooth with no sticking points. If you hear and feel a grinding, or it has some points where it sticks you'll
need to replace it. You can purchase gimbal bearing #21905 here. When installing the new bearing, make sure to align the outer tolerance right so the grease hole is visible - pointed up
and aligned with the grease input in the housing. You may also need to align the coupler with the bearing by using the engine
alignment tool #90050 here.