Lister and Lister Petter diesels are still found all over the marine and offshore world: as harbour generator sets, emergency and fire pump drives, deck machinery power packs and small propulsion engines. They are simple and long-lived, but they come in several families that look alike from the outside and use different valves. The Sea Keepers approved catalogue now carries two Lister inlet valves: 201-50871 for the air-cooled SR series as SK-00075-AV and 751-40551 for the turbocharged LPWT as SK-00076-AV. This guide explains how to tell which one an engine needs.
SK-00075-AV: inlet valve 201-50871 for Lister SR1 to SR4
SK-00075-AV is Lister part 201-50871, Inlet Valve, for Lister SR1, SR2, SR3 and SR4 air-cooled diesel engines built after 1970, including SR generator sets. Supplier data on the record gives a valve head diameter of 39.6 mm, a stem diameter of 8.7 mm, an overall length of 120.2 mm and a 45-degree valve face. These sizes are useful when an old valve has to be identified without a readable part number. No supersession was found in the sources reviewed.
SK-00076-AV: inlet valve 751-40551 for Lister Petter LPWT
SK-00076-AV is genuine Lister Petter part 751-40551, Inlet Valve LPWT, for the turbocharged water-cooled LPWT2, LPWT3 and LPWT4 engines, including marine and generator-set versions. Online Power Products notes that it is used only in the turbocharged version of the LPW engine. The record also lists it for LPW-series engines and for the Onan DN2M, DN3M and DN4M, which use Lister Petter engines. Aftermarket suppliers list 751-40550 alongside it, so a quotation or an old spares list may show either number; the engine data should decide which one is right. No supersession was found in the sources reviewed.
Why the two valves are not interchangeable
The SR is an older air-cooled family and the LPW and LPWT are a later water-cooled family with a different cylinder head, so the valve length, stem size and head size are not the same. Inside the LPW family the turbocharged LPWT has its own inlet valve, as noted above, so a naturally aspirated LPW valve should not be fitted to an LPWT without confirmation from the parts book. The safe rule is to order from the engine model and serial number on the engine plate, not from the look of the old valve. For an SR engine, the sizes on the record are a good cross-check; for an LPWT, check that the engine is the turbocharged build.
When an inlet valve needs replacing
Inlet valves usually last longer than exhaust valves, because they run cooler, but they still wear. The common signs are hard starting and low compression on one cylinder, a burnt or pitted valve face, a valve stem worn at the guide, a bent valve after a timing fault or a dropped valve, and heavy carbon on the back of the head. On air-cooled SR engines, dirty cooling fins and overheating can speed up valve and seat wear. A worn face can sometimes be refaced, but a valve with a thin margin, a bent stem or a worn stem tip is replaced.
What goes with a Lister valve job
When a valve is replaced, the seat has to be cut or lapped so that the new valve seals, and the valve guide should be checked at the same time, because a new valve in a worn guide will not seat properly for long. Valve springs, collets and stem seals where fitted are checked or renewed, and the cylinder head gasket is replaced. Once the head is back on, the valve clearances are set to the figures in the Lister or Lister Petter manual. For larger engines and for seat insert work, see the valve seat insert and valve guide guide linked below; the same catalogue also carries Volvo Penta D4 / D6 inlet valve 3884010 (SK-00087) and Caterpillar inlet valve seat insert 329-6655 (SK-00082-AV) for other engine families.
What to send with an enquiry
Send the engine model (for example SR2, SR3, LPWT3 or LPWT4), the engine serial number and build number from the engine plate, whether it is a marine, generator-set or industrial build, the part number from the old valve or parts book if you have it, and the number of inlet and exhaust valves needed. Say whether you also want guides, seats, springs, collets and a head gasket. Sea Keepers will confirm the right Lister or Lister Petter number and quote the complete set.
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.
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