The Mercury Upper End Cap Assembly 1159-858521T 1 is a genuine Mercury Marine OEM part used in the cylinder block and end caps section of many legacy Mercury, Mariner, and Mercury Racing V6 two-stroke powerheads. In older Mercury parts systems, this same upper end cap family also appears as 1156-9642-C and 9642A1, both superseded to the current number 1159-858521 T1.
If you are rebuilding a classic Mercury V6, this is a complete top cap assembly kit and includes one (1) upper O-ring, one (1) x top bearing, and one (1) x oil seal in the block/end-cap assembly. Mercury parts diagrams commonly show it used with O-ring 25-54029, roller bearing 31-16756A4, and oil seal 26-41953.
What the upper end cap assembly does
The upper end cap assembly forms part of the upper crank/block end-cap structure of the powerhead. Correct fit matters because the cap must align properly with the upper bearing and sealing surfaces.
When the powerhead is apart, this is the time to inspect the upper end cap, the bearing pocket, the O-ring groove, and the seal condition so the block goes back together with the correct OEM parts.
Genuine Mercury OEM quality
This is not a generic aftermarket substitute. 1159-858521T1 is sold as a genuine Mercury Marine factory OEM part, which is important on internal engine components where machining, fit, and sealing need to match the original Mercury design.
Fitment: 2.0L, 2.4L, and 2.5L V6 families
This top cap is commonly associated with Mercury and Mariner 2.0L, 2.4L, and 2.5L V6 engines that use the upper top-cap bearing for a 1-3/8" journal, including the Mercury Racing SST 120, SST-200, 200XS and S2000 among the racing engines that use it.
Mercury model-family listings for 1159-858521T1 also show broad fitment across legacy V6 applications, including 105 Jet, 135 HP, 140 Jet, 150 HP, 175 HP, 200 HP, XR6 / Magnum III, 150/200 EFI (2.5L), 200 EFI Pro Max / Super Magnum, 150 EFI Pro Max / Super Mag, 225 EFI Pro Max / Super Magnum, 225X EFI Pro Max, 225 Sport XS, 250 Sport XS, 250XS, and 200XS DFI (2.5L).
It is also fits Sport Jet / Jet Drive applications, including 175 HP Sport Jet and other V6 Sport Jet families tied to the same upper end cap part family.
Why the 1-3/8" journal note matters
That 1-3/8" upper journal detail is important because it ties the end cap to the correct upper bearing/crankshaft arrangement. If your 2.0L, 2.4L, or 2.5L V6 is running the crankshaft and top-cap bearing combination that uses the Mercury upper main bearing 31-16756A4 for a 1-3/8" journal, this upper end cap assembly is the correct OEM family to confirm against your parts diagram.
Helpful ordering note
The safest way to avoid ordering the wrong cap is to confirm four things before purchase: your engine is a Mercury/Mariner/Mercury Racing V6 two-stroke, your block diagram calls for an upper end cap assembly, your listing matches 1159-858521T1 or the superseded numbers 9642T1 / 9642A1, and your build uses the 1-3/8" upper journal / 31-16756A4 bearing combination when applicable.
Our Mercury Upper End Cap Assembly 1159-858521T1 (MSRP $342.99) is the genuine OEM upper end cap family for a wide range of legacy Mercury V6 engines, including many 2.0L, 2.4L, and 2.5L applications and race engines like SST 120 that use the 1-3/8" upper journal / top-cap bearing setup. If your parts diagram calls for 858521T 1, 1156-9642-C, 9642T1, or 9642A1, this is the correct upper end cap assembly family to use.
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.