Exhaust Tube Assembly – Fits MerCruiser Alpha One, Alpha One Gen II, and Bravo Series (Replaces 78458A1)

$50.49 $80.00

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Product Details

This Exhaust Tube Assembly – Fits MerCruiser Alpha One, Alpha One Gen II, and Bravo Series (Replaces 78458A1) provides a rigid, durable replacement for standard flexible exhaust bellows on a wide range of MerCruiser stern drives from 1978 to present. Designed for a secure, clamp-on installation attached to the transom, it offers a robust alternative to bellows systems, though it may increase audible engine noise and exhaust fumes during operation.

It serves as a direct interchange for MerCruiser 78458A1/78458, Sierra 18-2760, GLM 89150, Mallory 9-72810, and others.

Installs via a simple clamp-on mechanism at the transom.
Constructed from durable neoprene for marine environments.
Includes a marine-grade stainless steel hose clamp and bellows ground clip for a complete installation.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.

Brand	Part Number
MerCruiser	78458A1
MerCruiser	78458
Sierra	18-2760
GLM	89150
Mallory	9-72810
GHmarine	78458A1
YiheoZux	78458A1

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Fits various MerCruiser stern drive models, including R/MR, Alpha, Bravo, and Blackhawk series engines.

Model	Years	Serial Range	OEM Part No.
R / MR / Alpha One	1983–1990	6225577 & Up	78458A1
Alpha One Gen II	1991–2015	All	78458A1
Bravo I, II, III	1988 & Up	0B664190 & Up	78458A1
Blackhawk	1994–1995	0F186717 & Up	78458A1
120/140 (1.98 RATIO)	1978–1982	4893635-6225576	78458A1
165 (1.65 RATIO)	1978–1981	4890460 & Up	78458A1
260/898/228 (1.50 RATIO)	1978–1982	4898730-6225576	78458A1
470/485 (1.84 RATIO)	1978–1982	4893835-6225576	78458A1
454 MAGNUM ALPHA ONE	1986–1988	All	78458A1
4.3L MPI ALPHA/BRAVO(EC)	All	All	78458A1
5.0L, 350, 377 MAG MPI	All	All	78458A1
496 MAG STERNDRIVE(EC)	All	All	78458A1
8.2 MAG / 8.2 MAG HO EC	All	All	78458A1

Technical Specs

Product Type: Exhaust Tube Assembly
Installation: Clamp-On (Attaches to transom only)
Housing Material: Neoprene (CR)
Housing Color: Black
Connection: Stainless Steel Hose Clamp
Dimensions: 16.0" (L) × 12.0" (W) × 12.0" (H)
Weight: 0.17 kg (0.38 lb)
Other Technical Attributes: Includes bellows ground clip (54-86049) and stainless steel hose clamp

What’s in the Box

1 x Exhaust Tube (78458A1)
1 x Bellows Ground Clip (54-86049)
1 x Hose Clamp (54-815504348 or 54-32533)

Installation Notes

Ensure the engine is off and the stern drive is in a safe, accessible position. Work in a well-ventilated area.
Locate and remove the old exhaust bellow or tube from the transom assembly. This may require cutting the old bellow and loosening the existing clamp.
Clean the mounting surfaces on the transom assembly to ensure a clean, debris-free seal.
Slide the included stainless steel hose clamp over the new exhaust tube.
Position the new exhaust tube onto the transom exhaust port. Ensure it is fully seated.
Attach the new bellows ground clip as per the original configuration to maintain proper grounding.
Position the hose clamp over the connection point and tighten securely to prevent exhaust and water leaks. Do not overtighten.
After installation, run the engine and carefully check for any signs of water or exhaust leaks around the new tube.

Troubleshooting & FAQ

What is the difference between this rigid tube and a standard flexible exhaust bellow?

This rigid tube is made of durable neoprene and is less prone to cracking or tearing compared to flexible bellows, especially on higher horsepower engines. However, its rigid design may transmit more engine noise and vibration and could release more exhaust fumes around the transom area, which is less common with sealed bellows.

How can I confirm this tube will fit my specific MerCruiser engine?

Please review the detailed compatibility table provided on this page. Match your engine model, year, and serial number range against the listed applications. It is crucial to verify this information, as fitment is specific.

Is this part difficult to install?

For individuals with mechanical experience, installation is straightforward. It involves removing the old bellow and clamping the new tube onto the transom. However, due to the critical nature of preventing water and exhaust leaks, professional installation is always recommended if you are not completely comfortable with the procedure.

Why might I hear more engine noise after installing this tube?

Unlike flexible bellows that can dampen sound, this rigid tube may transmit more engine and exhaust noise. This is a normal characteristic of this type of exhaust tube and is often considered a trade-off for its increased durability.

What are the signs that my old exhaust tube or bellow needs replacement?

Common signs of failure include visible cracks or tears, water leaking into the bilge, a loud exhaust roar, or excessive exhaust fumes from the back of the boat. A failing bellow can lead to significant water damage, so it should be inspected regularly and replaced at the first sign of wear.

Can I reuse my old hose clamp or ground clip?

This kit includes a new marine-grade stainless steel hose clamp and a bellows ground clip. We strongly recommend using the new hardware provided to ensure a secure, corrosion-resistant installation and proper electrical grounding.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost?

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns?

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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