Cummins QST30 Inlet Valve Seat Insert 3094159: Pack Quantities, Seat Wear Checks and Cylinder Head Rebuild Parts

The Cummins QST30 is a 30-litre V12 diesel used in large generator sets, emergency and harbour power, and marine and industrial drives. It has separate cylinder heads and a large number of valves, so a top-end overhaul on a QST30 is a big parts list. One of the most important lines on it is the valve seat insert, the hard ring in the head that the valve closes on. The Sea Keepers approved catalogue now carries Cummins inlet valve seat insert 3094159 for the QST30 as SK-00079-AV. An earlier group guide mentioned it in one line; this guide covers it on its own.

What SK-00079-AV is

SK-00079-AV is genuine Cummins part 3094159, Valve Insert, Inlet, supplied as a package of six. It is pressed into the cylinder head to form the seat on which the inlet valve closes. It is listed for Cummins QST30 V12 engines in generator-set, industrial and marine use. No supersession was found in the sources reviewed, but Cummins numbers change over time, so the current number should always be checked against the engine serial number before the order is placed.

Why the pack of six matters

Because 3094159 is sold as a pack of six, the order quantity is a number of packs, not a number of inserts. A buyer who orders 24 thinking of single inserts may receive 24 packs, or 144 inserts. Before ordering, count how many inlet seats are being renewed, from the parts book or from the inspection report, and divide by six. On a full top-end overhaul of a QST30 the count is large, because there are twelve cylinders; on a repair of one or two heads it is much smaller. Write both the number of packs and the number of inserts on the purchase order, so the supplier and the receiving engineer read it the same way.

Signs that the inlet seats are worn

Inlet seats run cooler than exhaust seats, but on a generator set that runs long hours at steady load they still wear. The signs are low compression on one or more cylinders, a valve that has sunk into the head (valve recession) so that the valve lash closes up, a seat that is pitted or burnt, a cracked or loose insert, and fuel or oil residue around a seat that no longer seals. Valve recession is checked by measuring the valve head depth below the head face and comparing it with the Cummins limit. A loose or cracked insert is serious: if it comes out, it can wreck the valve, the piston and the head.

Re-cut or replace?

A seat that is only lightly worn can be cut or ground back to the correct angle and width, as long as the valve depth stays within the limit after cutting. Once the seat is too wide, too deep, cracked, loose or badly pitted, the insert is replaced. Many workshops replace all the inserts on a head when it is overhauled, because the head is already stripped and the cost of the inserts is small compared with the labour. When inserts are replaced, the valve guides should be checked or renewed first, because the new seat is cut true to the guide. For the general method, see the valve seat insert and valve guide replacement guide linked below.

How inserts are replaced

The old insert is removed without damaging the counterbore, usually by running a weld bead around the inside so that it shrinks and lifts out, or with a puller. The counterbore is cleaned and measured; if it is damaged or oversize, it is machined for an oversize insert where Cummins offers one. The new insert is chilled, often in dry ice or liquid nitrogen, and the head may be warmed, so that the insert goes in with an interference fit without being hammered. After fitting, the seat is cut to the angle and width in the Cummins manual, the valve is lapped or checked with marking compound, and the valve depth is measured. Inlet and exhaust inserts are different parts and must not be mixed up.

What else goes with a QST30 head job

A QST30 cylinder head overhaul usually needs inlet and exhaust valve seat inserts, inlet and exhaust valves if the faces or stems are worn, valve guides, valve stem seals, springs if they fail the free-length or load test, collets and retainers, cylinder head gaskets and the head bolts if they are single-use. Injector sleeves and seals are often renewed with the heads. Order from the engine serial number so that all these lines match the same build. The approved catalogue also carries Cummins valve stem guide 3202210 for KTA19, KTA38, KTA50, QSK19 and QSK38 engines (SK-00069-AV), which is a useful reference when the same fleet runs older K-series engines.

The other seat inserts in the catalogue

SK-00079-AV fits the QST30 only. The Sea Keepers catalogue also carries Cummins ISX15 / QSX15 intake insert 3104445 (SK-00081-AV) and exhaust insert 3683349 / 5614733 (SK-00080), Caterpillar inlet insert 224-3983 for the 3406E, C15, C18 and C32 (SK-00078-AV), Caterpillar inlet insert 329-6655 for the 3054 and C4.4 (SK-00082-AV) and MTU Series 396 inlet insert 5500531831 (SK-00083-AV). These are different sizes for different heads, so none of them should be offered as an alternative to 3094159.

What to send with an enquiry

Send the engine model (QST30), the engine serial number (ESN) and CPL number from the engine dataplate, the generator set or vessel the engine is in, the number of inlet inserts needed and how many packs that makes, and whether you also need exhaust inserts, valves, guides, seals, gaskets and head bolts. Add the delivery port and any documentation the buyer needs. Sea Keepers will check the Cummins number against the ESN and quote the complete head kit.

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

Compare alternatives on certified performance, compatibility, installation requirements, inspection interval, spares availability and total life-cycle cost. A lower unit price is not a like-for-like comparison when approval documents or service support differ.