The original tube (#18654A1 or GLM #89100) bellows 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 bellows is it
will release some of the back pressure; however this is a trade off with increased noise. Most people tend to choose the original
accordion style as a replacement.
There 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 bellows 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 Mercruiser 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 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 P/N 21905 please look 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 P/N 90050 please look here