Every cylinder head overhaul comes down to three small parts that decide whether the head will seal: the valve, the guide its stem runs in and the seat insert it closes against. They wear as a set, and a head that is refitted with a new valve on an old seat or a worn guide will burn the valve again within a few hundred hours. Thirteen valve-train records are now in the Sea Keepers approved catalogue, covering Caterpillar, Cummins, MTU, Volvo Penta, Onan and Lister engines used in propulsion, generator and auxiliary service. This guide explains what each record covers, which numbers have been superseded, and what to confirm before the parts are ordered.
Why seats, guides and valves are replaced together
The valve seat insert is a hard ring pressed into the head. Combustion heat and the hammering of the valve slowly widen and recess the seat, which lowers the valve into the head, changes valve lash and reduces the margin on the valve head. The valve guide controls where the valve lands on that seat; once the stem-to-guide clearance grows, the valve wobbles, the seat wears unevenly and oil is drawn down the stem into the port. Replacing a seat without a guide, or a guide without recutting the seat, wastes the work. When a head is stripped, measure valve recession, stem clearance and seat width, and order all three items for each cylinder that is out of limits.
Caterpillar C15, C16, C18 and C32: inlet seat insert 224-3983
SK-00078-AV is the genuine Caterpillar inlet valve seat insert 224-3983, a 41 mm cast steel-alloy ring for 3406E, 3456, C15, C16, C18 and C32 engines, including C32 generator sets. It is used twelve per head in C32 cylinder head assemblies 357-7398, 431-1153 and 284-2787, and sits alongside exhaust valve insert 226-5561, valve guide 122-7375 and intake valve 490-7199 in the same head. The Cat parts database shows 224-3983 superseded by 280-3979, so a quotation may carry the newer number. For a C18 marine engine this insert belongs with the complete cylinder head group 312-8590 (SK-00049) and head bolts 6I-4025 and 124-1855 (SK-00048).
Caterpillar C9 and C9.3: intake 255-8666 and exhaust 262-2959 seat inserts
SK-00084 is Caterpillar intake valve seat insert 255-8666 for C9 and C9.3 engines, 42.6 mm outside and 36.5 mm inside diameter, superseded by 564-8811. SK-00085 is the matching exhaust seat insert 262-2959, 39.1 mm outside and 32.5 mm inside diameter; the Cat Parts Store shows it as discontinued and the supersession is 564-8812. Both current numbers are used twelve per head in C9.3 cylinder head assembly 491-1831, which is the head that contains basic cylinder head 497-5505 (SK-00050) with its 1.6 swirl ratio. Intake and exhaust inserts on this engine are different sizes and are not interchangeable, so state which seat is needed and how many of each.
Caterpillar 3054C/E, C3.3 and C4.4: inlet seat insert 329-6655
SK-00082-AV covers the smaller Caterpillar engines found in auxiliary generator sets such as the DE33E0 to DE110E and XQP30 and XQP100 ranges. Inlet valve seat insert 329-6655 is used four per head in cylinder head groups 232-7519 and 247-4868 for the 3054C and C4.4, and three per head in C3.3 head assemblies 303-8494 and 303-8483. The related exhaust seat insert is 322-9663 and the inlet valve is 225-5495. No supersession was found in the sources reviewed.
Cummins ISX15 and QSX15: intake 3104445 and exhaust 3683349 / 5614733 seat inserts
SK-00081-AV is Cummins intake valve seat insert 3104445 for the 15-litre ISX15 and QSX15, listed twelve per engine; aftermarket data for the equivalent insert gives 1.640 in inside diameter, 1.953 in outside diameter and 0.195 in depth, with cross-references 3679975, 3681071 and 4059215. SK-00080 is the exhaust insert, carried under both 3683349 and 5614733. The current Cummins number is 5614733: it supersedes 3679659, and the valve train reference lists map 3679659 and 3683349 to the same insert. The engine CPL and serial number decide which head and insert apply. These inserts go into the QSX15 dual-cam cylinder head assembly 4962732 / 5658283 (SK-00046-AV), where the valve crosshead 3086362 (SK-00039-AV) bridges each pair of valves.
Cummins QST30: inlet seat insert 3094159
SK-00079-AV is Cummins inlet valve seat insert 3094159 for the QST30 V12, supplied by Cummins as a package of six. A full set for one bank or the complete engine should be ordered in multiples of that pack. No supersession was found in the sources reviewed.
Cummins K-series: valve stem guide 3202210
SK-00069-AV is Cummins valve stem guide 3202210 with a 45-degree tapered top, used for both intake and exhaust valves on the K19, KT19, KTA19, KTA38, KTA50, QSK19 and QSK38 engines in industrial, marine and generator service. IPD's K19 parts list shows the same guide in the standard, improved standard and premium cylinder heads, and it replaces the old numbers 3021693 and 3201311. Because the guide serves both ports, the order quantity is simply the total number of valves being renewed.
Onan HDKBB and HDKBC: inlet valve guide 185-5500
SK-00065-AV is the Onan (Cummins) inlet valve guide 185-5500 for the HDKBB 5.0 and 5.5 kW and HDKBC diesel generator sets. The HDKBB parts manual lists two per cylinder head, paired with exhaust valve guide 185-5501, in both the Spec A-B and the Spec C-and-later heads, and the part carries NATO stock number 2805-01-619-8005. When the guides are changed, valve spring collet 185-5541 (SK-00022) from the same parts family is normally renewed at the same time.
MTU Series 396: inlet seat insert 5500531831
SK-00083-AV is the MTU inlet valve seat insert 5500531831 for Series 396 engines such as the 8V, 12V and 16V 396 TE and TB, listed next to exhaust seat 5500530232 in an 8V396TE94 parts list. MTU superseded it by 5500531231 on 30 November 2001, and that number also replaces 5370530131, 5500530131 and 5500530531. An MTU quotation will therefore show 5500531231; the record is kept under the old number so that older parts lists still match.
Inlet valves: Volvo Penta D4/D6, Lister SR and Lister Petter LPWT
SK-00087 is Volvo Penta intake valve 3884010 for the D4 and D6 marine engines from the D4-150 to D4-320 and the D6-280 to D6-480, cross-referenced with Volvo 3581886 and the aftermarket Recmar RM3884010. SK-00075-AV is Lister inlet valve 201-50871 for the post-1970 SR1 to SR4 air-cooled engines, with a 39.6 mm head, 8.7 mm stem, 120.2 mm overall length and a 45-degree face. SK-00076-AV is Lister Petter inlet valve 751-40551 for the turbocharged LPWT2, LPWT3 and LPWT4; it is used only in the turbocharged version of the LPW engine, is also listed for LPW-series and Onan DN2M, DN3M and DN4M sets, and suppliers list 751-40550 alongside it. No supersession was found for any of the three.
Fitting notes
Seat inserts are an interference fit. The old insert is cut out or pulled, the counterbore is measured and cleaned, and the new insert is chilled or the head warmed before it is pressed home square. The seat is then cut to the engine's face angle and width, and the valve is lapped and its recession checked against the limit. Guides are pressed to the specified height and reamed or honed to the stem clearance in the manual; a guide that is driven in dry or out of square will seize the valve. After the head goes back on with new head bolts, valve lash is set with the rocker gear; a worn rocker arm button such as Cat 258-8721 (SK-00009-AV) will make the lash impossible to hold.
What to send with an enquiry
To match the right insert, guide or valve, send the engine make and model, the engine serial number or Cummins CPL, the cylinder head part number if known, whether the part is for the intake or exhaust side, the quantity per head and the number of heads, and whether a standard or oversize outside diameter is required. Sea Keepers will check the current manufacturer number, confirm the supersession and quote delivery to the port or yard.
For the business buyer
Confirm the intended vessel or facility, operating environment, quantity and required approval before requesting a quotation. Capacity, coverage and service interval should be matched to the risk rather than selected by headline price.
For technical experts
Verify the delivered model against the maker reference, rating, dimensions, materials, operating limits and certification scope. Record the serial or batch number and retain the manufacturer datasheet, declaration, test report and maintenance instructions in the vessel file.
Product comparison
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