MAN L23/30H
Spare Parts Supplier
Mk2 and Mk3 · Two-part piston · Genset auxiliary duty
Four type strings that all sound like this engine
The auxiliary side of the MAN engine route overview carries this frame as one card among eleven. The narrower question is the whole of this page: which of the maker's designations is stamped on the set in front of you.
No Mk is not a missing stamp
The maker's key for engine designation lists this frame three times over: L23/30H, L23/30H-Mk2 and L23/30H-Mk3. The first build carries no suffix on the plate, although the maker's own Mk 3 factsheet refers back to it as Mk 1, so a plate reading nothing after the H is the first build and a requisition saying Mk1 means the same engine. Copy whatever follows the H, including nothing.
Two named changes below the cover
Announcing the Mk3 against its Mk2 predecessor, the maker listed an improved conrod design and a two-part piston among the differences — its factsheet says the crown can be exchanged without changing the entire piston assembly — and put the rod first among new design features: it applies the marine-head design, which allows dismantling of the connecting rod from the crankshaft during overhaul without opening the crankshaft bearing.
Neighbours that are not the H engine
The same programme carries a plain L23/30, an L23/30A, an L23/30S and a dual-fuel L23/30DF, and the maker's current documentation names the S and the DF alongside the H builds under one heading. A line reading L23/30 has not yet named an engine.
The adjacent frame shares the paperwork
Project guide sections for this GenSet programme are issued against a list of types at once, and L23/30H and L28/32H sit in the same heading. A drawing or an instrument code found in the engine file may have been written for both frames, and does not become a part number for yours by being in your folder.
A good part of what arrives against this plate belongs to another catalogue
This machine is sold as a set, and that word does more work in a spares conversation than the designation does: two manufacturers built what is bolted to one frame.
Start with the frame. The maker's project guide puts it plainly: for a GenSet the engine and alternator are fixed on a common base frame, which is flexibly installed, in order to isolate the set vibration-wise from its surroundings. The alternator is not the engine builder's product. Before that base frame can even be drawn, the guide asks the alternator supplier for an outline drawing giving the alternator type and weight, its centre of gravity, direction of rotation, mounting dimensions and the overhaul space needed for rotor and cooler. The electrical end of your set has its own plate, its own drawing and its own spares book. The motor speed calculator checks the pole count on that plate against the engine speed and the board frequency.
Then the pairing between the two ends, which is not free. The guide states that a full finite-element calculation was done for the GenSet design and that, because of it and of experience, some combinations of engine type and alternator type concerning one or two bearings must be avoided; its table marks combinations as standard, as an option or as not recommended, some workable only with top bracing between the engine crankcase and the alternator frame. A coupling or mounting item is answered by the pair, and by whether that bracing is fitted.
Finally the filtration, because here it follows the fuel rather than the type. The guide describes a built-on lubricating oil filter and recommends a built-on centrifugal by-pass filter as an additional one on residual-fuel operation, where it also makes continuous bypass cleaning mandatory — so two sets with the same designation can carry one filter or two. The instrument code list for this programme also carries something a distillate-only machine has no use for: a nozzle cooling system, with its own inlet to and outlet from the fuel valves.
What an L23/30H requisition is usually made of
Ordered the way the set is worked: the cylinder unit, then the running gear where the Mk bites, then the drives and the media systems on the engine.
- Cylinder heads complete, and as valves, seats, guides and rotators
- Cylinder liners, sealing rings and jacket seals
- Pistons — stated by Mk, since one generation is a two-part item
- Piston ring sets, gudgeon pins and small-end bushes
- Connecting rods, rod screws and big-end bearing shells
- Main bearing shells and thrust bearing parts
- Rocker arms, roller guides and push rods
- Camshaft sections, camshaft bearings and cam followers
- Fuel injection pumps and plunger-and-barrel elements
- Injector nozzles, nozzle holders and high-pressure fuel pipes
- Nozzle cooling circuit items where that system is fitted
- Built-on lubricating oil filter elements and inserts
- Centrifugal by-pass filter parts on residual-fuel installations
- Lubricating oil and cooling water pump wet ends and seals
- Charge air cooler elements, covers and O-rings
- Turbocharger cartridges, nozzle rings and diffusers
- Starting air components, stop cylinder and turning gear parts
- Actuator parts and governor linkage
- Resilient mounting elements and top bracing hardware
- Overhaul gasket, O-ring and seal kits
Two of these lines are worth writing out in words. A piston here can mean an assembly, a crown, a skirt or a ring set, and on one generation the crown and skirt are separate order lines by design; a cylinder head can mean the casting, a valve set or the unit ready to fit. Both are read back before a price is attached. What to send is set out in the RFQ evidence guide.
What settles an L23/30H line, and which end of the set it comes from
The engine plate answers the type and the number. The rest is split between the alternator's plate, the actuator's label and the engine file.
- Type as stamped, with the cylinder count in front and whatever follows the H — nothing, Mk2 or Mk3 — plus any further suffix, such as the ECR the maker's Mk 3 factsheet lists for one five-cylinder variant
- Engine number and the works that built it, since these sets have been built under licence as well as by the maker
- Whether the plate reads MAN B&W, MAN Diesel & Turbo, MAN Energy Solutions or Everllence, which dates the paperwork
- Cylinder position for any cylinder-unit or running-gear item
- Connecting rod and bearing arrangement as recorded in the engine file, since more than one is documented on this frame
- Undersize already in the journal for any bearing shell, and ring sets counted per cylinder
- Fuel actually burned in service, and whether the set has been moved onto low sulphur fuel
- Whether a centrifugal by-pass filter is fitted alongside the built-on filter
- Whether the set has a nozzle cooling circuit
- Turbocharger designation from its own plate
- Actuator make and type, and the control system designation from its own label
- Alternator make, type and serial for anything past the coupling
- Whether the alternator sits on one bearing or two, and whether top bracing is fitted
- Hours since the item's last overhaul, separately from hours on the set
- Photographs of the engine plate, the alternator plate and the item in place
Three generations in one fleet, and a fuel that changed underneath them
The Mk boundary is where a route decision usually starts, because a fleet can hold all three builds and be tempted to treat them as one line item. It cannot. The maker announced the Mk3 against the Mk2 as carrying an improved conrod design and a two-part piston whose crown can be exchanged without changing the whole assembly, and put the rod first among new design features: the marine-head rod can be dismantled from the crankshaft during overhaul without opening the crankshaft bearing. That is two consequences, not one. A piston line becomes a different number of order lines by generation, and an overhaul planned around the older rod books work the newer one does not need. The maker presents the Mk3 as its build for the 2020 sulphur cap, so one generation is young in service and the others are not. Where the vessel's papers do not settle which is in front of you, a photograph of the rod and cap does more than a search through the engine file. If the crankshaft deflections are taken during that overhaul, the crankshaft deflection calculator turns the dial gauge readings into the vertical and horizontal deflection of each crank.
The fuel is the second thing. This frame was drawn for residual operation and much of the installed population has since been moved onto low sulphur fuel oils, which the maker addressed on the new build by designing it with coated fuel oil pumps to account for the poorer lubricating properties of those fuels. That is a statement about pumps, not about fuel. On a set built before it the pumps were not made that way, and plunger, barrel and nozzle wear is where the change shows up first. The marine fuel grade reader tells residual, distillate and low sulphur grades apart by their ISO 8217 names. From there the split is clean. Liners and sealing rings, piston rings, valves and seat inserts, guides and rotators, bearing shells, gaskets, O-rings, filter elements and mounting elements have measurable geometry and stated material, and a verified alternative can be reviewed on them where your approval requirements allow, against dimensional records and material documentation supplied with the offer. Cylinder heads, injection pumps and plunger elements, camshaft sections, turbocharger internals, the actuator and anything belonging to the control system go to an OEM-route review, and so does any scope a surveyor will look at. Everything past the coupling leaves this page and is priced from the alternator maker's book. The route is written beside each line; the OEM or verified alternative comparison sets out what evidence each needs.
L23/30H parts — what buyers ask first
There is nothing after the H on my plate. Which generation is it?
The first one. The maker's key for engine designation lists L23/30H, L23/30H-Mk2 and L23/30H-Mk3; the earliest build carries no suffix on the plate, and the maker's Mk 3 factsheet refers back to it as Mk 1. A bare L23/30H is therefore a complete answer, not a partial one, and a requisition reading Mk1 means the same engine. Photograph the plate anyway: the engine number beside the type is what opens the book.
Is a Mk2 piston the same item as a Mk3 piston?
No, and the maker is the source for that rather than a supplier's guess. In announcing the Mk3 against its Mk2 predecessor it named a two-part piston design among the differences, and its factsheet says the crown can be exchanged without changing the entire piston assembly. The same word therefore covers a different item, and a different number of order lines, on the two generations.
Why ask about the alternator when I am ordering engine parts?
Because the machine is a set, and the maker's own project guide treats the alternator as somebody else's product: it asks the alternator supplier for the outline drawing, type and weight before the common base frame can be designed. Requests reaching us against an L23/30H plate regularly concern bearings, diodes or a voltage regulator at the electrical end, which are in a different book. Naming both plates saves the round trip.
Can Vessel Core review verified alternatives for L23/30H parts?
On wear items with measurable geometry and documented material, yes, where your approval requirements permit — liners, rings, valves and seats, bearing shells, gaskets, seals and filter elements. On cylinder heads, injection equipment, camshaft sections, turbocharger internals and control hardware we put an OEM-route review forward instead, and say which before anything is priced.
Is Vessel Core connected to MAN?
No, and there is no agreement of any kind. Vessel Core holds no dealership, distribution, representation or partnership agreement with MAN, and quoting a component against the L23/30H, L23/30 or L28/32H designations implies no approval by the maker and no claim of interchangeability.
