Alpha Gen II Three-Bellow Kit Fits MerCruiser Alpha One Gen II Sterndrives 1991+, U-Joint 816431A1 + Exhaust 18654A1 + Shift 74639A2

Three rubber boots, one box — for Compatible with MerCruiser Alpha One Gen II transom work (1991+, check your drive serial). U-joint 816431A1, exhaust 18654A1 (8M0124227 family), shift 74639A2. Rubber only — not a bearing or gasket overhaul.

Why buy all three at once?

Pulling the drive is the hard part. Once it's off, you might as well replace aging rubber while you're in there. All three boots live in the same hot, salty environment — if one's cracked or oily, the other two are usually not far behind.

This kit matches the three Gen II OEM numbers (816431A1 + 18654A1 + 74639A2) so you're not guessing parts or pulling the drive again next season because you left old rubber behind. Wrong generation? Gen I is 60932A4 / 17B1004; Bravo is a different kit.

Only one boot failed? Exhaust leaks are the usual culprit — grab 17B1003 instead. Just replaced the other two? Singles are fine.

What's in the box

Need just one boot? We sell each piece separately.

Component	OEM	Cross-ref	GH single SKU	Qty
U-joint bellow	816431A1	18-2747 / 89180	17B1007	1
Exhaust bellow	18654A1 → 8M0124227	18-2750 / 89100	17B1003	1
Shift cable bellow	74639A2	18-2753-2 / 89080	17B1005	1

 

Which kit is this?

Alpha One Gen II three-bellow rubber kit — the set you want when the drive's off for transom service.

Titles sometimes show 74639Q02 — that's a two-pack catalog number. You get one shift boot (74639A2). Singles: 17B1007 / 17B1003 / 17B1005.

Kit or singles?

Get this kit if:

·       Drive's already off — don't leave two old boots in there

·       Annual check shows two or more boots cracked, soft, or oily

·       Bilge water after running and you're not sure which boot — plan for all three

·       You want all three Gen II part numbers in one shipment

Get a single instead if:

·       Only one boot failed — exhaust is the common one → 17B1003

·       You swapped the other two recently

·       You're filling one gap from shop stock

Sold separately either way: marine bellows adhesive · expander 22ET001 · sleeve driver 21B1001

Signs you're due for all three

·       Water in the bilge after a run — any of the three boots could be the leak.

·       Annual look-see: more than one boot cracked, soft, or shiny with oil — swap the set before season.

·       Drive's off anyway — labor's sunk; old rubber on the other two fails next year if you skip them.

Will it fit my drive?

Brand	Model / Drive	Rated HP	Type	Years	Kit OEM set
MerCruiser	Alpha One Gen II	135–300	Sterndrive	1991+	816431A1+18654A1+74639A2
MerCruiser	Vazer (Gen II context)	Varies	Sterndrive	1991+	Same 3-bellow set
MerCruiser	3.0L / 4.3L / 5.0L / 5.7L on Gen II	135–300	Sterndrive	1991–1998+	Verify S/N

 

Wrong kit? Read before you order

·       NOT for Alpha One Gen I (60932A4 U-joint + exhaust tube family) — see GHMarine 17B3001 / 17B1004.

·       NOT for Bravo three-bellow kit (86840A05 drive boot) — see GHMarine 17B3003 / 18B5001.

·       NOT for full transom seal repair with gimbal bearing + gasket kit 27-94996Q2 — see GHMarine 17B3005 context; this kit is rubber bellows only.

·       NOT for dual shift bellow pack 74639Q02 as two boots — this box contains one shift bellow (74639A2).

·       NOT for 2-pack lower exhaust only — see GHMarine 18BK001.

What ships

·       1 × U-joint bellow (816431A1) with clamps

·       1 × exhaust bellow (18654A1 / 8M0124227 family) with clamps

·       1 × shift cable bellow (74639A2) with clamps

·       Not included: bearing, gasket kit 27-94996Q2, glue, expander 22ET001, driver 21B1001

Photos should show three rubber boots — skip supplier shots labeled gimbal bearing kit.

One boot instead?

·       17B1007 — U-joint Gen II (816431A1)

·       17B1003 — exhaust only (18654A1 / 8M0124227)

·       17B1005 — shift only, one piece (74639A2)

·       Gen I U-joint → 17B1004 (60932A4), not in this kit

Usually ordered with

·       Bellows expander — 22ET001 (tight exhaust/shift)

·       Sleeve install driver — 21B1001 (U-joint ring)

·       Marine bellows adhesive — sold separately

Install order

1. Shift boot, then U-joint, then exhaust last — exhaust is the tight one; use expander 22ET001.

2. Adhesive both ends; let tack before clamps.

3. U-joint retainer sleeve → driver 21B1001 per manual.

4. Drive on, muffs, check bilge for water.

FAQ

What's in the box?

Three rubber boots — U-joint 816431A1, exhaust 18654A1 (8M0124227 family), shift 74639A2. Clamps on each. No bearing, no gasket kit 27-94996Q2, no glue, no tools.

Why buy the kit instead of three singles?

Pulling the drive is the hard part. Once it's off, check all three boots — they age together. One cracked or oily boot usually means the other two aren't far behind. This kit gets you all three Gen II numbers in one box so you're not pulling the drive again next season.

Will this fit my Alpha One Gen II?

Yes — 1991 and newer Gen II sterndrives. Verify serial. Not Gen I (60932A4) and not Bravo (86840A05).

Does this include the gimbal bearing?

No — rubber only. No bearing, no 27-94996Q2 gasket kit. Full transom overhaul hardware is a different story (see 17B3005 context).

74639Q02 on the title — do I get two shift boots?

Q02 is a catalog two-pack number. This kit ships one shift boot (74639A2). Need just shift? 17B1005.

Do I need the expander and sleeve driver?

For a proper install, yeah — marine bellows adhesive, expander 22ET001 (tight exhaust/shift), sleeve driver 21B1001 on the U-joint step. Not in this box.

Please note

Aftermarket replacement kit. Confirm Alpha One Gen II serial before order. Not affiliated with engine manufacturers referenced above.