816431A1 U-Joint Bellow Fits MerCruiser Alpha One Gen II and Vazer sterndrives

816431A1 U-Joint Bellow — Fits MerCruiser Alpha One Gen II and Vazer sterndrives, Replaces 18-2747, 89180, 64431P

GHMarine U-joint bellow (universal joint grease boot) for the drive shaft inside the bell housing on compatible MerCruiser Alpha One Gen II and Vazer sterndrives. Replaces OEM 816431A1 and cross-ref 18-2747, 89180, 64431P. Match your drive serial in the table below.

Ships as one U-joint bellow; clamps and sleeve when shown in product photos. Marine bellows adhesive and expander tool (ref 91-45497A1) sold separately.

Which bellow is this?

This is the U-joint / drive-shaft bellow inside the bell housing — it wraps the universal joint. It is not the large exhaust bellow at the transom, the shift cable bellow, or exhaust tubes in the engine bay.

If you are not sure, pull the drive and inspect the accordion boot on the universal joint — match the part number stamped on the old boot and your drive serial tag.

Signs yours is due

·       Water in the bellows cavity after running — cracks or soft rubber on the U-joint boot let salt water reach the universal joint and gimbal area.

·       Every drive-off service — inspect the accordion boot for splits, pinholes, or hardened ribs; replace on sight before U-joint or gimbal damage.

·       Grease weeping or rusty U-joint caps under a torn boot — the boot keeps grease in and water out; re-grease alone will not fix a compromised seal.

Will it fit my drive?

This U-joint bellow is Compatible with MerCruiser Alpha One Gen II (1991–current) and Vazer sterndrives that use OEM 816431A1. NOT Alpha One Gen I (S/N thru 0D469858) — see GHMarine 17B1004. NOT Bravo — see GHMarine 17B1006. Confirm drive serial before you order.

OEM & swap numbers

Primary OEM is 816431A1. Common interchange refs: 18-2747, 89180, 64431P.

Wrong part? Read before you order

·       NOT for Alpha One Gen I (S/N 06225577 thru 0D469858) — different U-joint boot; see GHMarine 17B1004 (60932A4 family).

·       NOT for Bravo I / II / III sterndrive — GHMarine 17B1006 (86840A05 family).

·       NOT for bell-housing exhaust bellow 8M0124227 / 18654A1 — that is GHMarine 17B1003.

·       NOT for shift cable bellow 74639A2 — that is GHMarine 17B1005.

·       NOT for exhaust riser or upper tubes (32-14358T / 32-44348T) — engine-bay exhaust, not drive shaft.

What ships in the box

·       1 × U-joint bellow (816431A1 family)

·       Clamps and sleeve when shown in product photos

·       Not included: bellows adhesive, expander tool 91-45497A1 (unless shown)

Often ordered with the other transom boots

·       Exhaust bellow (bell housing) — GH SKU 17B1003 (ref 8M0124227 family).

·       Shift cable bellow — GH SKU 17B1005 (ref 74639A2).

·       Alpha Gen I U-joint — GH SKU 17B1004 (ref 60932A4) — different boot, not this listing.

·       Bravo U-joint — GH SKU 17B1006 if your drive is Bravo.

·       Many shops install shift and U-joint boots first; put the exhaust bellow on last — it is the tightest fit.

Install tips while the drive is off

Remove the sterndrive per your service manual. Work in a ventilated area. Professional install recommended if you are not comfortable with drive removal.

1. Inspect U-joints, gimbal bearing, and input shaft before installing new rubber.

2. Remove old boot; clean bell housing flange and drive shaft landing areas.

3. Apply marine bellows adhesive to both boot ends; let dry until not tacky (often 10–20 minutes).

4. Install large end on bell housing first; tighten clamps through access holes.

5. Use bellows expander tool (OEM ref 91-45497A1) on the drive-shaft end; tighten clamp securely.

6. Reinstall drive; run on muffs; check for water intrusion at the U-joint cavity after a heat cycle.

FAQ

Will this fit my Alpha One or Bravo?

U-joint bellow for Alpha One Gen II and Vazer only (816431A1). NOT Alpha Gen I (see GHMarine 17B1004). NOT Bravo (see GHMarine 17B1006). Match drive serial on the sterndrive tag — horsepower alone is not enough.

What is in the box?

One U-joint bellow (816431A1 family). Clamps and sleeve when shown in product photos. Marine bellows adhesive and expander tool 91-45497A1 sold separately unless shown.

How is this different from the exhaust or shift bellow?

This boot wraps the universal joint on the drive shaft inside the bell housing (816431A1). Exhaust bellow = 8M0124227 (GH SKU 17B1003). Shift cable bellow = 74639A2 (GH SKU 17B1005). Three different locations, three SKUs.

Do I need adhesive and expander tool 91-45497A1?

Yes for a proper U-joint bellow job — adhesive on both boot ends, and an expander tool to stretch the small end over the drive shaft flange. Typically requires removing the sterndrive for access.

Please note

Aftermarket replacement part. Not affiliated with engine manufacturers named above. "Compatible with", "Replaces", and cross-ref numbers mean this part is built to work like the originals listed — always confirm fit with your drive serial number.