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Engine · Exhaust · Pump · UIM
Homologation
2 UIM homologation forms, 40 pages. Most figures carry a tolerance, and 8 numbered calibrated tools are each tied to a measurement; bore, stroke, exhaust ports and pump body name no tool.
- Solid lines carry the throttle cable's pull, fuel, exhaust gas, the turning drive, water . The dotted lines are control links: the control unit's hold over the engine, and the shut-off key's place in the throttle controller.
- Throttle controller (the manual's control handle) to engine: the lever sits at the end of a cable that opens and closes the injector flap on the engine (JetSurf owner manual, 5.1 and 8.16).
- Control unit to engine: after five minutes idle, the ignition control unit switches the electronics off and shuts the board down (JetSurf owner manual, 5.8). Shut-off key: worn on the rider's wrist, it sits in the ignition switch socket on the control handle, and pulled out in a fall it shuts the engine off (JetSurf owner manual, 5.1). Fuel tank to engine: a fuel hose and pump, coupled to the injector (JetSurf owner manual, 6.1). Engine to exhaust: it leaves at the stern, into the water (JetSurf owner manual, 3.3).
- Engine to pump: the jet pump drive shaft (8.9 and 10.6); turning that shaft by hand moves the engine's piston (12.5). The JetSurf owner manual also labels a main gear (freewheel) on every model's engine picture (chapter 4) and lists gears among the parts to lubricate (10.6), but does not say where they sit in the drive, so they are not drawn. The pump reference shared by both forms runs to the driveshaft and gives the intake grate hole the water comes in by.
- The stator's fixed blades sit behind the impeller and take out the water's spin, so its energy goes into thrust, as the held jet pump patent US 8,905,800 B2 describes; the water then leaves through the nozzle, which the patent puts at the pump's outlet and the manual's technical table gives a material (chapter 14). Names in both forms: the pumps Jetpump Titan Stock and Jetpump MSR DFi, the stators Stator Titan Stock and Jetpump stator DFi; the impeller and the control unit are shared.
A key to the forms below, not a drawing of any board: fuel feeds the engine, the engine spins the pump, and the jet of water the pump throws out is what pushes.
How we know: Part names from the homologation forms in Appendices 2 and 3 of the 2026 MotoSurf Rulebook and from the JetSurf owner manual; each link is read from the document the list above names for it.
Not to scale.
Where these figures came from
Pages 74 to 113 of the 2026 MotoSurf Rulebook are scanned images with no text layer, so a text search of the PDF finds none of the figures below. They were read as page images instead, with the small dimension callouts re checked at three to four times magnification.
How to read the figures below
Each tolerance is printed after its figure: a dimension without its band and tool reads as more precise than the form.
The forms mix decimal separators: one stator figure is tabulated with a point and everything else uses a comma, and both stator nozzle figures are printed as tabulated. Figures stored here as numbers print with a point.
Section 1.12 jumps from c to f in both forms; there is no 1.12 d or e.
APPENDIX 2 - JETSURF TITANIUM TECHNICAL SPECIFICATIONS
2026 MotoSurf Rulebook, pages 74 to 94 (21 pages)
APPENDIX 3 - JETSURF RACE DFI TECHNICAL SPECIFICATIONS
2026 MotoSurf Rulebook, pages 95 to 113 (19 pages)
| Field | Appendix 2, MSR_H_B03 | Appendix 3, MSR_H_A03 |
|---|---|---|
| Measured against it | The Titanium DFI is the only board admitted to Stock Men, so this is the homologation a Stock Men powertrain is measured against. | The Race DFI is the eligible board for Elite Women, Masters Women and both Juniors classes, so this is the homologation those powertrains are measured against. |
| Valid from | 2026-02-17 | |
| Manufacturer | MSR Engines s.r.o., craft type PWC | |
| Engine designation | MSR NG100 DFi Ti | MSR NG100 DFi |
| Engine part numbers | A002271, A003635 | A 001090 |
| Cycle | two stroke | |
| Capacity | 97.2 ccm | |
| Block | Aluminium, no sleeves | |
| Bore | 50 mm +/- 2% | |
| Stroke | 49.5 mm +/- 2% | |
| Timing | 0.12 mm +/- 0,04 mm | |
| Exhaust ports | Exhaust port D25: 25 mm at the engine, 25 mm at the flange, +/- 2%; Exhaust port D27: 27 mm at the engine, 27 mm at the flange, +/- 2% | Exhaust port: 25 mm at the engine, 25 mm at the flange, +/- 2% |
| Exhaust system parts | A003614, A000944, POA3876, P007263 | A004200, A003627, A003269, A000064, A001118 |
| Jet pump | Jetpump Titan Stock, part A002293, body 207.5 mm +/- 2% | Jetpump MSR DFi, part A001423, body 187.5 mm +/- 2% |
| Stator | Stator Titan Stock, nozzle 58.8 mm, calibrated tool MSR_ST_A_06 | Jetpump stator DFi, nozzle 61,6 mm, calibrated tool MSR_ST_A_05 |
| Main cable harness | A002341 | A003735, A001271 |
| Also only on this form | Nothing beyond the rows above | Seventeen dimensioned callouts across three orthogonal engine views; The only thread callout in either form, M6 on the mount studs |
A cell across both columns is a figure the forms share.
The Timing value is the distance offset of the piston top from the TDC position. Measured with calibrated tool POA1928.
Appendix 2. Two exhaust port sizes are homologated as separate numbered variants, which the Race DFI form does not do. A 35 mm diameter appears on both flange drawings and is not carried into the tabulated list on either page. A metal tapered resonator with a separate CFRP knee and a carbon silencer. The knee is homologated as its own section, which the Race DFI form has no equivalent of. A cooling nozzle is specified at four separately numbered positions.
Appendix 3. One port size only. Unlike the Titanium form, this one does tabulate the 35 mm flange dimension, along with a third figure of 14 mm. A visibly different design from the Titanium system, photographed as a large black composite canister, with five part numbers none of which is shared. No CFRP knee section. The cooling nozzle is given as a single range rather than four positions.
One impeller, with the same geometry, tolerance and tool, serves both the Titanium and the Race DFI.
- Impeller, Propeller 15-19
- Outer shape R46 mm +/- 1%, rotor length 35,75 mm +/- 1%, blade spacing 120 degrees, R17,70. Three blades, which is unambiguous on the drawing and is nowhere stated in words. Measured with calibrated tool MSR_ST_A_07. No part number is given: it is a named designation only.
- Crankshaft assembly, A000040 and A003403
- Both homologated in both forms. Minimum weight 1195 g +/- 5% for each. The shaft retaining key is included in the weighing, which the form states and a photograph calls out. This is the only mass figure in all forty pages, and it is a component mass in grams, not a craft mass.
- Reed valve assembly, P004698, P004699, P004700, P011764
- Identical bill of materials in both forms, itemised in Czech. Cage, two reed petals in Thornel Mat VMA, two stopper plates, four DIN 7049 2,2x6,5 screws. Overall 41,40 mm and 22 mm, both to plus 0,1 and minus zero.
- Injector, BOSCH 0 280 158 251, MSR number P009523
- Both forms carry a red callout pointing at the body marking and reading the Bosch code, which makes it an explicit scrutineering identification point rather than just a part number.
- Connection rod
- Big end interior diameter 22 mm +/- 0,5% without shell bearings, length between the axes 91 mm +/- 0,5%. The tightest tolerances in either form.
- Piston
- Gudgeon pin centre line to highest point of crown 22,44 mm +/- 1%, maximum length 52,74 mm +/- 1%. Squish band lower value 0,8 mm with no upper value stated, measured in the gudgeon pin axis direction with calibrated tool MSR_ST_A_02.
- Ignition control unit, A001058
- Common to both forms.
- Starter cable harness, A000456
- Common to both forms.
- Spark plug, NGK BPR7HS 6422
- Common to both forms, and the same plug the owner manual specifies. The one component on the board side named identically by the sanctioning body and the manufacturer, and it is an ordinary catalogue part.
- Throttle body
- Inlet dimension 22 mm +/- 2,5%, calibrated tool MSR_ST_A_01.
- Jet pump, shared dimensions
- 140 mm +/- 1,5%, 120 mm +/- 2%, an 8 mm +/- 2% intake grate hole, and a 586,3 mm overall reference including the driveshaft. Only the pump body length and the stator nozzle differ between the two forms.
- Silencer non return valve
- Both forms carry the same explicit permission: the use of the silencer without the non-return valve, the ball, is permitted. The owner manual separately notes the ball can fall out during a ride.
Each tool is named by number and tied to the measurement it serves.
- POA1928
- Timing, the piston top offset from top dead centre
- MSR_ST_A_01
- Throttle body inlet dimension
- MSR_ST_A_02
- Piston at top dead centre to the gasket plane, the squish band
- MSR_ST_A_03
- Cooling nozzle inlet diameter
- MSR_ST_A_04
- Cooling nozzle inlet diameter
- MSR_ST_A_05
- Jet pump stator dimensions, Race DFI
- MSR_ST_A_06
- Stator dimensions, Titan Stock
- MSR_ST_A_07
- Impeller outer shape
Engine displacement: the forms and the manual disagree
Engine displacement as the homologation forms and the JetSurf owner manual state it, beside the Art. 501.02 a) ceiling for Elite Men and Masters Men, drawn from zero.
How we know: The forms' capacity and the two stroke ceiling are both from the 2026 MotoSurf Rulebook: the forms are its Appendix 2 and 3, the ceiling Art. 501.02 a). The engine figure is from the JetSurf owner manual. A ceiling is a rule's upper limit, not an engine's displacement.
The list classes, Elite Women, Stock Men, Masters Women, Juniors Boys and Juniors Girls, have no ceiling: Art. 502.02 b), 503.02 b) and 504.02 b) hold the engine to its form. Neither document says which displacement is right, so both are printed and neither is used as the figure.
Read from 2026 MotoSurf Rulebook, published by Union Internationale Motonautique, accessed 2026-09-10. Appendices 2 and 3 were read as page images on that date, because the text layer for them does not exist.