Sulzer RT-flex
Spare Parts Supplier
Supply unit · Rail unit · ICU and FLV · Servo oil filter unit
One family name, several fuel-side designs
RT-flex is the common-rail branch of the Sulzer two-stroke line: RT-flex50, 58T, 60C, 68, 82, 96C and the dual-fuel RT-flex50DF. The diesel types normally carry a design-version letter after a hyphen, and WinGD lists RT-flex50-D and RT-flex58T-E among its legacy engines; the RT-flex50DF is listed without one. The first RT-flex entered service in 2001. Design authority moved to Winterthur Gas & Diesel in 2015, as the Wärtsilä and Sulzer route overview sets out. Below is the narrower question: the four groups a request lands in.
Four assemblies were removed, not redesigned
The maker described the type at launch as based on its mechanical predecessor, and stated that in place of the traditional mechanically driven camshaft with fuel injection pumps, exhaust valve actuator pumps and reversing servomotors it carries electronically controlled common-rail systems for fuel injection and exhaust valve actuation. Read that as a purchasing instruction: an RTA number for anything inside those four assemblies has no counterpart, because the assembly it belonged to is not on the engine.
The letter on the end is a separate book
A type such as RT-flex58T appears with a B, a D or an E behind it, and manuals are published per design version rather than per family. Two engines a decade apart can share everything to the left of that letter and still be documented apart. The letter and the engine number are what turn a design into a machine.
The dual-fuel member reads differently
On the gas-burning member the cylinder group gains gas admission valves and pilot injection valves, and a gas valve unit sits off the engine. The control system is named differently too: the manual for this type gives UNIC where a diesel type in the same family gives WECS-9520. A list written from a diesel RT-flex does not reach the gas side.
Where the successor breaks the rail
The maker's manual is precise about the boundary to the engines that followed: injection control units on the fuel rail apply to X82, X92, RT-flex and the related dual-fuel engines, while flow limiting valves apply to the rest of the X programme. A rail item off an X62 or an X72 is a different device doing the same duty.
Three things about an RT-flex that settle a line before the part number does
None of the three is on the nameplate, all three are visible from the platform, and each changes which catalogue line is the right one.
The first is handedness. The maker's operation manual states that an engine is one of two types: a standard engine has the exhaust side on the right seen from the driving end, a LEFT engine has it on the left. Then comes the sentence a buyer needs, in a note near the front of the book — in the spare parts catalogue, parts carrying the mark LEFT apply only to a LEFT engine, and parts suiting both types carry no mark at all. The absence of a mark is therefore information, and a line copied without it can arrive as the wrong hand of an otherwise correct item.
The second is where positions are counted from. The ends and sides have formal names here — driving end, free end, fuel side, exhaust side — and items are numbered axially from the flywheel and radially from its centre. A cylinder or main bearing counted from the other end names a real position that is not the one the part came out of, and nothing in the request reveals the mistake. The same counting matters for crankshaft deflections: if they are logged by cylinder number, the crankshaft deflection calculator gives the vertical and horizontal deflection for each crank in that order.
The third is the supply unit. On one type in this family the installation manual ties its position to the length of the engine — the shorter builds carry it aft, the longer ones on the exhaust side — and states plainly that the engine performance data are the same either way. The figures will therefore never tell you which arrangement is in front of you, and separate operation manuals are published for the two positions. Here the manual a line is quoted from is chosen by where a large assembly happens to be bolted.
What is ordered off an RT-flex, in the order the engine is grouped
Listed in the maker's own group order: frame and bearings, the cylinder, the running gear, the two groups that exist only on a common-rail engine, then the air side and the instruments.
- Main bearing shells, thrust bearing pads and tie rod items
- Cylinder liners and liner sealing rings
- Lubricating quills and cylinder lubricating pump components
- Piston rod gland boxes, scraper and sealing ring sets
- Injection valves, plus gas admission and pilot injection valves on the dual-fuel member
- Starting valves and cylinder relief valves
- Exhaust valve spindles, seats, housings and complete cages
- Piston crowns, piston skirts and ring sets
- Crosshead, guide shoe and crosshead bearing items
- Connecting rod and connecting rod bearing shells
- Supply unit drive parts, starting air shut-off valve, control air supply items
- Speed pick-ups and crank angle sensor units
- Servo oil pumps and fuel pumps in the supply unit
- Pressure control, pressure retaining and relief valves on the rail
- Injection control units, or flow limiting valves where those are what is fitted
- Exhaust valve control units
- Rail unit accumulator, joint and high-pressure pipe items
- Servo oil filter elements and inserts
- Turbocharger cartridges, nozzle rings and diffusers
- Auxiliary blower, scavenge air cooler and water separator items
- Water-in-oil monitor and oil mist detector consumables
- Overhaul gasket, O-ring and sealing kits
A rail or supply-unit line is written from the engine number and the design version, with the handedness stated alongside. A photograph of the plate, of the supply unit and of the item in place carries further here than a number lifted from an old requisition, because that number may belong to a design version the engine is not. The spare parts supply process sets out how such a request is worked through.
What an RT-flex request has to carry
Half is one photograph of the plate; the rest is handedness, supply unit position and rail hardware, none of which is stamped anywhere.
- Complete type as it appears on the engine, design-version letter included, written after a hyphen as in RT-flex58T-E or RT-flex50-D
- Engine number and the engine builder named on the plate, since these engines are produced under licence by engine builders in several countries
- Standard or LEFT build, because the catalogue marks one hand and leaves the common parts unmarked
- Where the supply unit sits, aft end or exhaust side, as the manual is published per position
- Cylinder, main bearing or crosshead position, and which end you counted it from
- For a rail-mounted line, whether the fuel rail carries injection control units or flow limiting valves
- Crank angle sensor arrangement, on the flywheel or on the intermediate wheel
- Control system designation off its own label, since more than one is in service here
- On the dual-fuel member, whether the line is on the gas admission side, the pilot fuel side or the common engine
- Four-digit material number and the catalogue page it came off, which narrow the search
- Shell bearings: state the undersize already fitted. Ring sets: one set per cylinder, not a count of rings
- Hours on the item itself, apart from hours on the engine, and any earlier reconditioning
- Photographs of the plate, of the supply unit, and of the component before it is disturbed
Why a rail line and a running-gear line are two different enquiries
An RT-flex spares list almost always contains both, and treating it as one enquiry is what makes it slow.
Below the cylinder cover this is the engine it was based on: liners and sealing rings, piston crowns and skirts, ring sets, crosshead and guide shoe items, connecting rod and main bearing shells, gland rings, exhaust valve spindles and seats. Those are ordinary slow-speed overhaul lines with measurable geometry and stated material, and a verified alternative route can be reviewed on them where the buyer's approval requirements allow it, with dimensional and material evidence checked at RFQ stage. An OEM-route review can be asked for on any line inside that half.
Above the cover the enquiry changes shape. Injection control units, exhaust valve control units, supply unit pump elements, rail valves and the electronics behind them are matched to a design version and to a control system, and here the realistic route is often reconditioning of the removed unit rather than replacement — a different kind of request, with the unit itself as the evidence and its own hours as the deciding fact. Those lines go to an OEM-route review by default, and we say so rather than pricing around it. On this family the maker's route has two doors: WinGD sells spare parts directly, and names Wärtsilä Services Switzerland as its global service partner for spare parts and field service. One consumable sits between the halves: the servo oil is the engine's own system oil, filtered on the engine, so servo oil filter elements recur on their own schedule and belong with the fuel-side request. The rating on the old servo oil element, a beta ratio or a micron figure, is read by the filter rating reader. Vessel Core names the route against each line rather than against the order as a whole.
RT-flex parts — questions buyers ask
Will an RTA part number cross to an RT-flex engine?
On the running gear it is worth asking; on the fuel and exhaust actuation side there is nothing to ask. The maker stated at launch that the type replaces the mechanically driven camshaft together with the fuel injection pumps, the exhaust valve actuator pumps and the reversing servomotors. Those assemblies are absent, so their numbers have no counterpart rather than a different one. Send the RTA number anyway — it says which position you mean.
What is the supply unit, and why does its position change your answer?
It is the driven block of pumps feeding the high-pressure fuel rail and the servo oil circuit, in place of the individual injection pumps a camshaft engine carried. Its position is not fixed: on one type the installation manual ties it to the length of the engine, the shorter builds carrying it aft and the longer ones on the exhaust side, with separate operation manuals for the two. Since the performance data are the same either way, the position cannot be inferred from the figures. One photograph settles it.
What does the mark LEFT mean on a catalogue line?
That the part suits only a LEFT engine, the mirrored build with the exhaust side on the left seen from the driving end. The note is worded the other way round as well: parts applicable to both types carry no mark. So an unmarked line is not an unfinished line, and a marked line copied without its mark asks for the opposite hand.
Can Vessel Core review verified alternative routes for RT-flex parts?
On the running gear and on ordinary sealing, gasket and filter items, yes, where your approval requirements permit and the evidence supports it; dimensional data and material documentation are checked at RFQ stage. On injection control units, exhaust valve control units, supply unit pump elements and anything carrying control electronics, an OEM-route review is what we put forward. Vessel Core is an independent spare parts supplier and states the route it proposes against each line before anything is priced.
What does the letter after the type, such as the B, D or E on an RT-flex58T, change?
Which book applies. Manuals for these engines are published per design version rather than per family, so two engines built a decade apart can share everything to the left of that letter and still be documented apart. The letter and the engine number together turn a design into a machine, and a part number lifted from an old requisition may belong to a design version the engine is not.
Is an RT-flex50DF parts list the same as for a diesel RT-flex?
No. On the dual-fuel member the cylinder group gains gas admission valves and pilot injection valves, a gas valve unit sits off the engine, and the manual names the control system UNIC where a diesel type in the same family has WECS-9520. So a list written from a diesel RT-flex does not reach the gas side; say for each line whether it sits on the gas admission side, the pilot fuel side or the common engine.
Is Vessel Core connected to WinGD or Wärtsilä?
No, and there is no agreement of any kind. Vessel Core holds no dealership, distribution, representation or partnership agreement with WinGD or Wärtsilä, and quoting a component against one of their designations implies no approval by the maker and no claim of interchangeability.
Send the type string and the engine number.
Send your RT-flex request — engine designation as plated, and which assembly is needed: common-rail supply unit, rail unit, or the separate injection or exhaust valve control units. RTA numbers for the camshaft, fuel injection pumps, exhaust valve actuator pumps and reversing servomotors have no RT-flex counterpart, and running-gear numbers still have to be checked against the design version, so the exact designation matters.
