Sierra 18-2100
Greasable, Link-Belt heavy duty
Sierra's heavy-duty, grease-serviceable replacement for specified early MerCruiser and other listed drive applications.
Sierra Gimbal Bearings: Greasable vs Non-Greasable by Drive
MerCruiser sterndrives and related assemblies use gimbal bearings that support the driveshaft through the transom assembly. Sierra offers both greasable and non-greasable replacements, and the correct part depends on the original gimbal housing, bearing number and drive serial range. This chart compares four exact Sierra MPNs so that early and late bearing groups are not confused.
Check the installed bearing and drive model
Greasable versus non-greasable18-2100 and 18-21005 are manufacturer-listed greasable bearings. 18-21001 and 18-21006 use non-greasable construction. Match the gimbal housing's grease provision and specified replacement design.
Earlier versus later OEM family18-2100 and 18-21001 share the older Mercury replacement-number group. 18-21005 and 18-21006 belong to a separate later reference group. These are not universal substitute groups.
Serial numbers over general model namesAlpha and Bravo names span multiple years and bearing configurations. Verify the drive model, engine/transom serial number and Sierra replacement reference before ordering.
Application caution: Sierra's catalog lists 18-21001 for MC-1/R/MR/Alpha through 1997 plus certain early Gen II and Bravo drives, while 18-21006 covers later Gen II and Bravo generations. The overlapping drive family names do not establish interchangeability. Follow the exact manufacturer parts breakdown for your serial range.
Sierra gimbal bearing comparison and OEM references
The following selected OEM references come from Sierra's published catalog. A matching reference should be confirmed against the actual transom and gimbal assembly. Differences in lubrication arrangements and housing versions matter.
| MPN | Design | Selected OEM numbers | Published family | Product |
|---|---|---|---|---|
| 18-2100 | Greasable, Link-Belt heavy duty | 30-60794A2 / 30-60794A4 / 30-879194A02 | Earlier MerCruiser generations; verify drive serial number | View |
| 18-21001 | Non-greasable | 30-60794A2 / 30-60794A4 / 30-879194A02 | MC-1, R, MR and Alpha through 1997; earlier Gen II and Bravo by year | View |
| 18-21005 | Greasable | 30-862540A3 / 30-862540T1 / 30-862540A04 / 30-879194A01 | Alpha One Gen II 1998-up; Bravo family per Sierra | View |
| 18-21006 | Non-greasable | 30-862540T1 / 30-862540A3 / 30-862540A04 / 30-879194A01 | Alpha Gen II 1998–2010; Bravo 1996–2010 families per Sierra | View |
Compare four Sierra gimbal bearings
Each product photo and link corresponds to the exact UsedRVParts listing. Use the existing bearing and service manual to distinguish the required part, and check whether any seal or installation components are separately needed.
Sierra 18-21001
Non-greasable
Non-greasable alternate to the older OEM number group. Sierra lists MC-1, R, MR, Alpha (1974–1997), Gen II (1991–1997), and Bravo I/II/III (1988–1995).
Sierra 18-21005
Greasable
Grease-serviceable later-generation design; check whether the gimbal housing and lubrication arrangement support it.
Sierra 18-21006
Non-greasable
Non-greasable alternative in the newer OEM reference group. Confirm the installed drive assembly rather than deciding by model name alone.
Gimbal bearing selection questions
Are Sierra 18-2100 and 18-21001 the same bearing?
Not exactly. They share an older OEM interchange family but Sierra identifies 18-2100 as a greasable heavy-duty Link-Belt design and 18-21001 as non-greasable. Choose the part specified for the exact assembly.
Are 18-21005 and 18-21006 interchangeable?
Both appear in the later OEM reference family, but 18-21005 is greasable while 18-21006 is non-greasable. Compatibility must be checked against the gimbal housing and drive serial number.
Can an Alpha One use any Sierra gimbal bearing?
No. Sierra lists different bearings for earlier Alpha drives, early Alpha One Gen II and later Gen II models. Check the drive serial number and the manufacturer's exploded parts listing.
Does the bearing include an oil seal?
Do not assume so. These are individual bearing listings. Sierra sells specific separate bearing-and-seal kit MPNs, including 18-2100K and 18-21005K, which should be distinguished from individual bearings.
Should I grease a non-greasable bearing?
No. Follow the specified installation and lubrication procedure for the exact bearing and gimbal housing. A non-greasable bearing design must not be treated like a greasable replacement.
Related drive service parts and identification
Replacing the bearing may also require related seals specified by the complete drive service procedure. The shop carries Sierra 18-2094 oil seal, which Sierra identifies as included in selected 18-2100K and 18-21005K seal-and-bearing kits. Verify its relevance to your exact drive rather than assuming every bearing installation requires the same seal.
For another kind of marine-engine service identification, see Sierra Marine Water-Pump Impellers: MPN & Pump-Kit Reference.
Gimbal bearing replacement involves specialized shaft alignment, seal and drive service procedures. Follow the drive manufacturer's current service manual and use the required alignment and installation tools.
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