Sierra 18-8358 Lower Unit Seal Kit for Volvo Penta 280/290 DP
Sierra 18-8358 Lower Unit Seal Kit for Volvo Penta 280/290 DP — Product description
The Sierra 18-8358 lower unit seal kit reseals the gearcase on Volvo Penta 280 and 290 Duo-Prop sterndrives. You get every O-ring, oil seal, gasket and washer in one box, matched to the drive and built to meet or exceed the original equipment seals. When your gear oil turns milky, this is the kit that gets you back on the water leak-free.
If you run a Volvo Penta 280 or 290 Duo-Prop sterndrive, sooner or later the lower unit starts to weep. Maybe you pulled the drain plug and the gear oil came out milky. Maybe there's a slick on the water behind the drive after a weekend out. Either way, that's your seals telling you it's time. This Sierra 18-8358 lower unit seal kit gives you every O-ring, oil seal, gasket and washer you need to reseal the gearcase and get back on the water leak-free.
Open the box and you'll find the full complement: O-rings, oil seals, gaskets and washers, all matched to the 280/290 Duo-Prop lower unit. It's a complete seal set, not a partial patch, so you're not left hunting for that one odd O-ring halfway through the reassembly.
Sierra builds this kit as a direct replacement for the seals in the 280 and 290 Duo-Prop lower unit. It's the same job the pros do every few seasons. The lower unit is where the driveshaft, gears and prop shafts all live under load, and the seals down there take a beating every hour you run. Water gets past a tired prop shaft seal, mixes with the gear oil, and if you ignore it the gears and bearings pay the price. Reseal it early and you protect the expensive parts inside.
Who's this for? Owners of 280 and 290 Duo-Prop drives, the counter-rotating dual-prop setup you'll find on a lot of 25 to 32 foot express cruisers from the era. If you do your own maintenance and you're comfortable pulling the drive off the transom, this is a weekend job. If you'd rather hand it to your mechanic, the kit is exactly what they'll ask for. Either way, having the right seals on hand means the job goes smoothly instead of stalling out waiting on a back-ordered O-ring.
A few things we've learned watching these jobs go right and go wrong. First, the drive needs to sit dead vertical while you seat the new seals. Let it lean and the O-rings can distort and start weeping again within weeks. Take your time on alignment. Second, don't cheap out on the stuff around the seals. If your bearings feel notchy or the bellows are cracked, do them now while everything's apart. Fresh seals against worn bearings won't last, and old bellows can crack and dump water right back into your clean gear oil.
Model year matters on these drives. The early 280 and 290 units are what this kit is built around. Later drives sometimes moved to updated seal dimensions, so if yours is a late 290 it's worth confirming your part breakdown before you tear in. When in doubt, match the old seals to the new ones on the bench before final assembly. A quick test-fit saves you a second teardown.
When you button it back up, refill with fresh marine gear lube in the grade your drive's manual calls for, and check it again after your first few hours on the water. That first oil change after a reseal tells you everything. Clean oil means you nailed it.
Here's the honest part. This isn't a genuine Volvo Penta box, it's a Sierra kit. And that's fine. Sierra has been supplying OEM engine builders and boat manufacturers for decades, and their parts meet or exceed the original equipment they replace. You're getting the same seal job for a lot less than the dealer counter wants, without gambling on no-name gaskets that ship undersized and never quite fit.
Keep one on the shelf if you run these drives hard. A seal kit is cheap insurance against a milky-oil surprise on a Friday afternoon when nobody has the parts in stock.
Key Features
- Complete lower unit seal kit for Volvo Penta 280 and 290 Duo-Prop sterndrives
- Includes O-rings, oil seals, gaskets and washers in one box for a full gearcase reseal
- Direct replacement that meets or exceeds the original equipment seals it replaces
- Sierra part number 18-8358, the kit your mechanic asks for by name
- Reseals a weeping lower unit before water-contaminated gear oil damages bearings and gears
- Built around the early 280/290 Duo-Prop counter-rotating dual-prop lower unit
- Sierra supplies OEM engine builders and boat manufacturers, so the fit and materials are proven
Why Buy from NVN Marine
- Authorized Sierra Marine reseller, full manufacturer warranty
- NMEA member and ABYC certified, advice from real boat techs
- Same-day shipping before 3 PM ET on in-stock items
- NY headquarters and Fort Lauderdale flagship retail store
Technical specifications
| Title | Sierra 18-8358 Lower Unit Seal Kit |
|---|---|
| Brand | Sierra Marine |
| Manufacturer Part Number | 18-8358 |
| UPC | 808282105525 |
| Product Type | Lower Unit Seal Kit |
| Compatible Engine Models | Volvo Penta 280, 290 Duo-Prop |
| Drive Type | Duo-Prop sterndrive lower unit |
| Application | Lower unit / gearcase reseal |
| O-Rings | Included |
| Oil Seals | Included |
| Gaskets | Included |
| Washers | Included |
| Sold As | Complete seal kit |
Frequently asked questions
Which engines does the Sierra 18-8358 seal kit fit?
It's built for Volvo Penta 280 and 290 Duo-Prop sterndrive lower units, the counter-rotating dual-prop drives common on 25 to 32 foot express cruisers of that era. Check your drive's part breakdown against the seals before final assembly, since late 290 units sometimes used updated seal dimensions.
What comes in the kit?
You get the full seal set for the lower unit: O-rings, oil seals, gaskets and washers. It's a complete kit for the reseal, not a partial patch, so you won't be left hunting for one odd O-ring mid-job.
How do I know my lower unit needs new seals?
The classic sign is milky or foamy gear oil when you pull the drain plug, which means water is getting past a seal. An oil slick behind the drive or a low oil level between services is another tell. Catch it early and you protect the bearings and gears inside.
Do I have to pull the drive to install this kit?
Yes. Resealing the lower unit means removing the drive from the transom and opening the gearcase, so it's a job for someone comfortable with sterndrive service or a marine mechanic. Plan on a weekend if you're doing it yourself.
Should I replace the bellows at the same time?
It's smart to. If the bellows are cracked or aging, replace them while everything's apart. Cracked bellows let water back into your fresh gear oil and undo the reseal you just did.
Can I reuse the old bearings?
Only if they're in good shape. Spin them and feel for roughness or notchiness. New seals running against worn bearings won't last, so if the bearings are tired, do them now while the unit's open.
Is this a genuine Volvo Penta part?
No. It's a Sierra Marine aftermarket kit designed as a direct replacement that meets or exceeds the original equipment seals. Sierra supplies OEM engine builders and boat manufacturers, so the fit and materials are proven.
What's the most common mistake when installing these seals?
Letting the drive lean during assembly. The unit needs to sit dead vertical while you seat the new seals, or the O-rings can distort and start weeping within weeks. Take your time on the alignment.
What gear oil do I use after resealing?
Refill with fresh marine gear lube in the grade your drive's manual specifies. Then recheck the oil after your first few hours back on the water. Clean oil at that first check means the reseal held.
How often should I reseal the lower unit?
There's no fixed interval, but many owners plan a reseal every few seasons or whenever the annual gear oil change shows water. Running the drive hard on a heavier boat tends to wear the seals faster, so inspect the oil at each service.
