JP3384918B2 - Cooling structure of engine for small watercraft - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-cooled engine for a small surface watercraft in which a plurality of cylinders of an engine body are arranged in the front-rear direction of a hull, and more particularly to cooling water handling in such an engine. Regarding the structure.

[0002]

2. Description of the Related Art In a small watercraft for water jet propulsion drive, which is generally called a watercraft, conventionally, as a propulsion drive engine, two or three cylinders are arranged in the longitudinal direction of the hull. A water-cooled two-cycle cylinder engine is used, and in such a small watercraft engine, normally, one side of the engine main body having a plurality of cylinders arranged in the front-rear direction of the hull is used. In addition, an intake passage including an intake silencer, a carburetor, an intake manifold, etc. is arranged on the other side, and exhaust passages such as an exhaust manifold, a muffler (exhaust gas expansion chamber), etc. are arranged along the arrangement direction of each cylinder. ing.

Regarding the circulation of the cooling water to the engine body and the exhaust passage in such an engine, the cooling water pumped by the positive pressure generated by the rotation of the propelling drive propeller is used to exhaust the cooling water located upstream of the exhaust passage. It is sent through the manifold into the cooling water jacket of the engine main body, flows from the lower part of the engine main body to the upper part, and then is sent out to the outside from the cooling water outlet provided in the upper part of the engine main body (upper part of the cylinder head).

A part of the cooling water sent out from the cooling water outlet of the engine body is discharged as pilot water and is sent into the cooling water jacket of the muffler to form the cooling water formed on the peripheral wall of the muffler. After flowing through the jacket to cool the muffler, part of it is discharged as waste water to the downstream end of the exhaust passage, and at the same time it is made to flow from the downstream end of the muffler into the downstream exhaust passage to cool it to exhaust gas. The exhaust gas and the downstream exhaust passage are cooled with water mixed.

[0005]

By the way, in the cooling structure for an engine for a small watercraft as described above, conventionally, the cooling water outlet of the engine body is located either before or after the upper part of the engine body (upper part of the cylinder head). The cooling water outlet of the cooling water jacket of the muffler, which is provided on the side closer to the cooling water inlet, is provided on one side of the upper part of the engine body. It was connected in a state where the water flow path was branched by a three-way valve.

However, in an engine for a small watercraft, since the engine swings up and down in the front-rear direction due to the pitching of the hull, if the cooling water outlet is provided at one of the upper parts of the engine body, It is difficult for the air that has entered the cooling water jacket to escape, and air tends to collect in the cooling water jacket on the side of the engine body opposite to the cooling water outlet.

Further, in an engine for a small watercraft,
The exhaust manifolds are arranged along the arrangement of each cylinder in the engine body, which causes a difference in output due to a difference in exhaust efficiency between cylinders, which in turn causes a cylinder with high output to heat up. However, in that case, if the cooling water outlet is provided on one side of the upper part of the engine body, the flow rate of the cooling water for each cylinder cannot be changed, and the cooling efficiency can be improved for each cylinder with different output. I can't do well.

An object of the present invention is to eliminate the inconvenience of the conventional cooling structure for an engine for a small watercraft as described above, and more specifically, in a cooling water jacket of an oscillating engine body. (EN) It is possible to provide a cooling structure for an engine for a small watercraft that can easily remove the air mixed in the engine and efficiently cool the entire engine body when a part of the cylinders of the engine body becomes highly heated. Has an aim.

[0009]

In order to solve the above-mentioned problems and to achieve the object, the present invention has a plurality of cylinders of an engine body arranged in the longitudinal direction of a hull as described in claim 1 above. In an array of water-cooled engines for small watercraft, cooling water outlets of a cooling water jacket formed in the engine body are provided at the upper front end and the upper rear end of a cylinder head of the engine body. Together with
One of the cooling water outlets has one end opened to the side plate of the ship.
Connected to the pilot pipe, and the other side of the cooling water outlet
However, one end is connected to the cooling water jacket of the exhaust passage.
It is characterized in that it is connected to a wastewater transfer pipe .

Further, in the cooling structure for an engine for a small surface watercraft according to the above-mentioned claim 1, the above-mentioned claim 2 is provided.
As described in , the cooling water flow rate of each cooling water outlet
Pilot piping is connected to the one with less
It is characterized in that the pipe for transferring cooling water is connected to the one with the most water .

Further, in the cooling structure for an engine for a small watercraft according to claim 1 or 2 above, as described in claim 3 above , one lateral side of the engine body is provided.
There is an intake passage on the other side and an exhaust passage on the other side of each cylinder.
Cylinders are arranged along the arrangement direction and
Cooling provided on the upper front end and the upper rear end of the head respectively.
The discharge outlet is located approximately on the longitudinal centerline of the hull.
It is characterized in that that.

[0012]

[Operation] With the above configuration, pitching of the hull
Even if the engine swings up and down in the front-back direction,
The air in the cooling water jacket of the engine is
On the front end and the rear end of the head
Is surely drawn out from both cooling water outlets,
Air does not collect in the cooling water jacket of the engine.
Absent.

Also, provided at the front and rear ends of the upper part of the engine body.
One of the cooling water outlets
Connected to the pilot pipe opened on the board,
However, one end is connected to the cooling water jacket of the exhaust passage.
Because it is connected to the wastewater transfer pipe, it can be used to transfer cooling water.
A branch pipe such as a three-way valve is used for the piping and pilot piping.
Without being connected to the cooling water jacket of the engine body
It will be.

Further, since the cooling water outlets are provided at the front and rear ends of the upper part of the engine body, the pipe connected to the cooling water outlet is thinner than in the case where there is only one cooling water outlet. In addition, it is possible to appropriately change the ratio of the outflow amount of cooling water from the front and rear cooling water outlets, which increases the flow rate of the cooling water to each cylinder arranged in the front-rear direction. Since a large amount of air can be made to flow to the side of the cylinder, even if the output of each cylinder varies due to the difference in exhaust efficiency of each cylinder,
It is possible to efficiently cool the entire engine body.

Further, according to the structure described in claim 2, the cooling water jacket of the exhaust passage is provided with a pilot
More cooling than the cooling water that is discharged outboard by piping
Water will be supplied.

Further, according to the above-mentioned structure of the present invention, the engine bodies are arranged separately on the left and right sides.
It is connected to the intake passage and exhaust passage, and each cooling water outlet.
The distance between the two pipes is wide.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cooling structure for an engine for a small watercraft according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a small surface watercraft equipped with an engine to which the cooling structure of the present invention is applied. A small surface watercraft 1 is generally called a watercraft.
The hull 2 is formed in a hollow state by hermetically joining the bathtub-shaped hull 3 and the deck 4, and the deck is designed so that the rider can operate the ship while straddling the seat and holding the handle. A steering handle 5 and a seat 6 are arranged on the upper surface of the engine 4, and an engine 7 is mounted inside the hull 2 at a substantially central portion in the front-rear direction, and a fuel tank 8 is provided in front of the engine 7 (on the bow side). It is stored.

On the lower surface of the rear portion (stern side) of the hull 3, the water injection unit housing space is formed by recessing upward from the bottom surface toward the inside of the hull so as to extend in the front-rear direction in the longitudinal center of the hull. 9 is formed in the water injection unit housing space 9 by a water flow duct 11, a propeller 12 rotating in the water flow duct 11, a nozzle 13 attached to the rear end of the water flow duct 11 so as to be swingable left and right, and the like. The configured water injection unit 10 is installed, the lower side of the water injection unit storage space 9 is closed by the outer edge of the front end opening of the water flow duct 11 and the ship bottom plate 14, and the rear of the water injection unit storage space 9 is a nozzle. An opening is provided to extend 13 outwardly.

The engine 7 is a two-cycle parallel two-cylinder engine in which two cylinders are arranged in the front-rear direction of the hull, and one of the engine main body 15 is formed by sequentially stacking a cylinder block and a cylinder head on a crankcase. An exhaust manifold 16 connected to an exhaust port of each cylinder of the engine body 15 is disposed on the side (port side), and an exhaust gas expansion chamber (expansion chamber) is provided at a front end (downstream end) of the exhaust manifold 16.
The muffler 17 is connected.

The muffler 17 is formed by connecting a plurality of parts, one end of a communication hose 18 is connected to the downstream end of the muffler 17, and the other end of the communication hose 18 is a water lock. The exhaust pipe 20 is introduced into the front of the water lock 19, and the downstream exhaust pipe 20 is led out from the rear of the water lock 19. The downstream exhaust pipe 20 is once extended so as to bypass the water surface. Therefore, the terminal opening 21 is opened in the water injection unit housing space 9.

The water lock 19 is provided to prevent water from flowing backward from the end opening 21 of the downstream exhaust pipe 20 to the muffler 17 when the small watercraft 1 is capsized. It has a structure that can store a certain amount of water inside, and the water injection unit storage space 9
Is arranged inside the hull 2 located on the side (port side) of the.

From the engine body 15 to which the above-mentioned exhaust passage is connected, the engine output shaft 22 which is interlocked with the crank shaft via the gear in the crank case is projected rearward (stern side). A propeller rotating shaft 24 is connected to the engine output shaft 22 via a coupling 23.

The propeller rotating shaft 24 is supported by a bearing member 26 fixed to a partition wall 25 provided in the width direction of the hull 2, and although not shown in FIG.
It passes through the inside, penetrates the middle part of the water flow duct 11, and is projected into the water flow duct 11 so that its rear end is located in the horizontal rear part of the water flow duct 11, and the propeller 12 is integrally formed at the rear end. Is attached to.

The water flow duct 11 of the water injection unit 10 is
A shaft accommodating cylinder 27 accommodating the propeller rotating shaft 24 is integrally molded, and is installed in the water injection unit accommodating space 9 so as to extend in the front-rear direction at the approximate center of the hull 2 in the width direction. A propeller 12 is arranged inside the rear end of the member 11 extending substantially horizontally.

The front end opening of the water flow duct 11 is a water intake port 11.
The front end of the water flow duct 11 is opened toward the lower front as a.
The water flow duct 1 has a rearward opening 1b.
The front end of the nozzle 13 is externally fitted to the rear end of the nozzle 1 while being pivotally supported to the left and right, and the rear end of the nozzle 13 is opened rearward of the hull.

In the small watercraft 1 having the above-mentioned structure, the propeller rotating shaft 24 is rotated from the output shaft 22 via the coupling 23 by the drive of the engine 7 to rotate the propeller 12 of the water injection unit 10. Due to
From below the hull 2 through the water intake 11a, the water flow duct 11
Water is sucked into the inside, and the water that is sucked and pressurized is the water injection port 1
Injecting from 1b to the rear of the hull 2 through the nozzle 13,
With the jet reaction force of this jet water, the hull 2 is moved forward,
When the rider on board rotates the steering handle 5 to the left and right, the nozzle 13 is rotated to the left and right in conjunction with the rotation of a steering shaft (not shown) following the steering handle 5 to change the jet direction of the jet water. Instead, the traveling direction of the hull 2 is controlled.

2 to 4 show an engine 7 mounted in the hull 2 of the above-mentioned small watercraft 1, and FIG. 2 shows the engine 7 from the side (port side) (muffler 17).
FIG. 3 shows a state in which a part of the engine 7 is seen.
Is viewed from the front (that is, the direction of arrow A in FIG. 2), and FIG. 4 is a view that illustrates the engine 7 from above (that is, the direction of arrow B in FIG. 2).

The engine body 15 is, as shown in FIG.
This is a two-cycle engine in which a cylinder block 32 and a cylinder head 33 are sequentially stacked on a crankcase 31 and connected by bolts. As shown in FIG.
a and 15b are arranged in the front-rear direction of the hull and are fixed to the hull 2 via the vibration absorbing member 34.

On the side of the intake side of the engine body 15 (on the starboard side, that is, on the left side when viewed from the front), an intake silencer 36 having an air intake port which is arranged above and is opened downward at the front thereof. A carburetor 37 whose upper end (upstream side) is connected to the intake silencer 36, an intake manifold 38 which connects a lower end (downstream side) of the carburetor 37, and a crank chamber in the crankcase 31 are arranged.

FIG. 5 shows the intake silencer 36, the carburetor 37, and the intake manifold 38 as seen from the intake side (starboard side, that is, the direction of arrow C in FIG. 3).
Of each cylinder 1 of the engine body 15
Carburettors 37a and 37b for 5a and 15b respectively
Are arranged side by side in the front-back direction of the hull.

Each of the carburetors 37a and 37b has an intake upstream side (upper side) connected to the intake silencer 36, and an intake downstream side (lower side) of the carburetors 37a and 37b located below the engine body 15 via an intake manifold 38. The air holes are installed so as to extend in the vertical direction so as to be connected to the respective crank chambers in the crankcase 31 located, and are of a so-called floatless type that does not have a float chamber or a float.

On the other hand, on the side of the exhaust side of the engine body 15 (the port side, that is, the right side when viewed from the front), as described above, the cylinder block 32 of the engine body 15 is provided.
An exhaust manifold 16 connected to the exhaust port of each cylinder and a muffler 17 connected to the exhaust manifold 16 are arranged.

Each cylinder 15a, 15b of the engine body 15
Exhaust gas exhausted from the exhaust is collected into one muffler 17
The exhaust manifold 16 for feeding to the engine is extended in the front-rear direction of the hull along the arrangement of the cylinders 15a and 15b of the engine body 15, and its front end is connected to the muffler 17.

Therefore, the exhaust manifold 16
Inside the cylinders 15a, 15 the length and shape of the exhaust flow path from the connection (exhaust gas inlet) with each cylinder 15a, 15b to the connection (exhaust gas outlet) with the muffler 17 are
It depends on b.

The muffler 17 is connected to the exhaust manifold 16 and folded upstream so as to be an upstream portion 17.
a, a central portion 17b serving as an expansion chamber, a downstream portion 17c having a gradually reduced diameter, a connecting portion cover member 17d for covering the outside of the connecting portion between the upstream portion 17a and the central portion 17b, the downstream portion 1
Ring-shaped lid 17 attached to the end of 7c with a bolt
The muffler 1 is formed by a plurality of parts such as e.
A communication hose 18 extending to the downstream side of the exhaust passage is connected to the end portion of the downstream portion 17c of 7.

The muffler 17 has, on the respective wall portions of its upstream portion 17a, central portion 17b and downstream portion 17c,
A cooling water jacket 17g is formed in a state of communicating with each other via a space between the connecting portion of the upstream portion 17a and the central portion 17b and the connecting portion cover member 17d. A cooling water drain port 17f for draining the cooling water as waste water is provided, and a ring-shaped lid 17e provided at the end of the downstream portion 17c has a cooling water jacket 1f as shown in FIG.
A cooling water discharge hole 17h for discharging the cooling water in 7g into the communication hose 18 is provided.

By the way, as described above, the engine body 15
Regarding the cooling structure of the engine 7 in which the intake passage and the exhaust passage are arranged on both the left and right sides of the cooling water supply pipe 41, the rear end of which is opened downstream of the propeller 12 of the water injection unit 10.
Of the exhaust manifold 16 is connected to the cooling water inlet 16a of the exhaust manifold 16, so that the positive pressure generated by the rotation of the propeller 12 causes the cooling water pumped through the cooling water supply pipe 41 to flow into the exhaust manifold 16a. It is sent into the cooling water jacket.

Although not shown, the exhaust manifold 16 and the engine body 15 are respectively formed with cooling water jackets which communicate with each other, and the cooling water sent to the cooling water jacket of the exhaust manifold 16 receives the cooling water jacket. After cooling both through the cooling water jacket of the engine body 15, from the cooling water outlet 33b provided in the upper rear end of the cylinder head 33 above the engine body 15 via the cooling water transfer pipe 42, Muffler 17 cooling water jacket 1
It is sent to 7g.

The engine body 15 is further provided with a cooling water outlet 33a above the front end of the cylinder head 33 together with the cooling water outlet 33b, and both of the cooling water outlets 33a and 33b are provided. The engine main body 15 is arranged substantially on the longitudinal centerline of the hull, and the engine main body 1
The cooling water that has passed through the cooling water jacket 5 is sent out from both the cooling water outlet 33a and the cooling water outlet 33b, and the cooling water sent out from the cooling water outlet 33a passes through the pilot pipe 43, The pilot water is sprayed from the port side plate on the port side where it can be seen by the driver.

In the present embodiment, the flow rate of the cooling water passing through the cooling water outlet 33b connected to the cooling water jacket 17g of the muffler 17 becomes the pilot water from the ship side plate through the cooling water outlet 33a. The cooling water outlets 33a and 33b are arranged so that the flow rate of the cooling water is greater than the flow rate of the cooling water.
There is a difference in the outflow amount of cooling water from the.

The cooling water sent from the cooling water outlet 33b of the engine body 15 to the cooling water jacket 17g of the muffler 17 through the cooling water transfer pipe 42 is the muffler 1
7 upstream portion 17a, central portion 17b and downstream portion 17c
Cooling water jacket 1 formed to communicate with each other
After cooling the muffler 17 through 7g, the muffler 17 is discharged into the communication hose 18 through the cooling water discharge hole 17h of the ring-shaped lid e, and the discharged cooling water is mixed with the exhaust gas. The communication hose 18 made of a rubber material or the like is cooled.

At this time, if the amount of the cooling water mixed is too large, the resistance to the exhaust gas is generated. Therefore, the cooling water passing through the cooling water jacket 17g of the muffler 17 is partially discarded as the upstream water 17a. And the connecting part of the central part 17b,
Cooling water drain port 1 formed in the cover member 17d of the connection portion
It is discharged from 7f and discharged to the downstream end of the downstream side exhaust pipe 20 by the drainage pipe 44 connected to the cooling water drainage port 17f.

As described above, according to the engine for a small watercraft of this embodiment, which has the cooling structure in which the cooling water outlet 33a and the cooling water outlet 33b are provided in front of and behind the cylinder head 33 of the engine body 15, respectively, Compared with the case where a single cooling water outlet is provided, each cooling water outlet 33a,
Each of the pipes 42 and 43 connected to 33b can be made thin.

Even if the engine 7 swings up and down in the front-rear direction due to the pitching of the hull 2, the engine body 1
The air that has entered the cooling water jacket 5 is reliably extracted by the cooling water outlet ports 33a and 33b provided on the front end upper part and the rear end upper part of the cylinder head 33, respectively. Air does not collect in the cooling water jacket.

By the way, in the engine 7 for a small watercraft, each cylinder 15 in the exhaust manifold 16 is
Since the exhaust passages have different lengths and shapes with respect to a and 15b, the exhaust efficiency of the exhaust gas discharged from each of the cylinders 15a and 15b is different (in the present embodiment, the exhaust flow in the exhaust manifold 16). Under the influence of the exhaust gas discharged from the cylinder 15b on the rear side of the long road,
Since the exhaust gas discharged from the cylinder 15a is prevented from flowing to the muffler 17 side, the exhaust efficiency of the rear cylinder 15b is better than that of the front cylinder 15a having a short exhaust passage. ), The output of one cylinder 15b is the other cylinder 15a
The output of the cylinder 15b is higher than that of the cylinder 15b, and the one cylinder 15b is highly heated.

On the other hand, in the present embodiment, the flow rate of the cooling water sent out from the cooling water outlet 33b provided at the rear end of the cylinder head 33, that is, the cylinder 15b side, is larger than that of the cylinder head 33. Is larger than the flow rate of the cooling water sent out from the cooling water outlet 33a provided on the front end of the cylinder 15a, that is, from the cooling water jacket of the exhaust manifold 16 to the engine main body 15. The cooling water supplied to the cooling water outlets 33a and 33b by the cooling water jacket flows more in the engine body 15 toward the cylinder 15b than to the cylinder 15a. Is cooled better and the engine body 15
The overall cooling efficiency will be good.

In connection with the above point, the cooling water sent to the cooling water jacket of the exhaust manifold 16 by the cooling water supply pipe 41 is located inside the engine body 15 on the cylinder 15b side rather than the cylinder 15a side. The cooling water inlet 16a is provided on the side close to the cylinder 15b so that the cooling water can flow easily, and although not shown, for example, the cooling water passage in the exhaust manifold 16 following the cooling water inlet 16a is 15a and a flow path toward the cylinder 15b are branched into a flow path toward the cylinder 15b.
The diameter may be larger than that of the flow path toward 5a.

Further, in this embodiment, each cooling water outlet 33 is provided.
Since a and 33b are arranged substantially on the longitudinal centerline of the engine body 15, the intake and exhaust passages and the cooling water outlets 33a and 33b are separately arranged on the left and right sides of the engine body 15. Both pipes 42, 43 connected
Since the interval between the cooling water transfer pipe 42 and the pilot pipe 43 can be easily performed with respect to the engine body 15 without being interfered by each member of the intake and exhaust passages.

Furthermore, since the cooling water transfer pipe 42 and the pilot pipe 43 are connected to the cooling water jacket of the engine body 15 without using a branch pipe such as a three-way valve, both pipes 42 and 43 are cooled respectively. Water outlet 33a, 33b
To the exhaust passage because the cooling water jacket 17g of the muffler 17 is sufficiently supplied with more cooling water than the cooling water discharged to the outboard by the pilot pipe 43. Can be sufficiently cooled.

[0051]

As described above, according to the cooling structure for an engine for a small watercraft according to the present invention as described above, a pipe connected to the cooling water outlet is provided as compared with the case where a single cooling water outlet is provided. It is possible to make it thin, and it is easy to remove the air mixed in the cooling water jacket of the swinging engine body, and efficiently cool the entire engine body when some cylinders of the engine body become highly heated. Can be done with
The cooling water transfer pipe and pilot pipe are attached to the three-way valve, etc.
Easily connect to the cooling water outlet without using a branch pipe
You can

Further, according to the structure as described in claim 2, the cooling water jacket of the exhaust passage is sufficiently cooled.
Can supply effluent to sufficiently cool the exhaust passage
Moreover, according to the configuration as described in claim 3 above , it is distributed to the left and right sides of the engine body.
Intake and exhaust passages and cooling water outlets
The space between both pipes connected to the
Piping for cooling water can be easily provided to the main body .

[Brief description of drawings]

FIG. 1 is a partial sectional side view schematically showing a small watercraft (watercraft) equipped with an engine to which a cooling structure of the present invention is applied.

FIG. 2 is a partial cross-sectional side view showing a port side (exhaust side) of an engine mounted on the small watercraft shown in FIG.

3 is a front view of the engine shown in FIG. 2 as viewed in the direction of arrow A in FIG.

FIG. 4 is a top view of the engine shown in FIG. 2 as viewed in the direction of arrow B in FIG.

5 is a side view of the carburetor-related portion of the engine shown in FIG. 2 as viewed in the direction of arrow C in FIG. 3 (starboard side).

6 is a rear view showing a downstream side portion of the muffler of the engine shown in FIG.

[Explanation of symbols]

1 Small watercraft 2 hull 7 engine 15 engine body 16 Exhaust manifold (exhaust passage) 17 Muffler (exhaust passage) 33 cylinder head 33a Cooling water outlet 33b Cooling water outlet 36 Intake silencer (intake passage) 37 Carburetor (intake passage) 38 Intake manifold (intake passage) 42 Cooling water transfer pipe 43 Pilot piping

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01P 11/04 F01P 11/04 F (58) Fields investigated (Int.Cl. ⁷ , DB name) F01P 3/20 F01P 3 / 02 F01P 11/04 B63B 35/73

Claims (3)

(57) [Claims] 1. In a water-cooled engine for a small watercraft in which a plurality of cylinders of an engine body are arranged in the longitudinal direction of a hull, a cooling water outlet of a cooling water jacket formed in the engine body has an engine body. The cylinder head is provided on the upper front end and the upper rear end, respectively ,
One of the cooling water outlets has a port with one end open to the side plate of the ship.
It is connected to the pilot pipe, and the other side of the cooling water outlet is
Cooling water with one end communicating with the cooling water jacket in the exhaust passage
An engine cooling structure for a small watercraft, which is connected to a transfer pipe . 2. The cooling water flow rate is the smallest among the cooling water outlets.
The pilot pipe is connected to the one that does not
The cooling structure for the engine for a small watercraft according to claim 1 , wherein a cooling water transfer pipe is connected to the other side . 3. An intake passage on one side of the engine body on the left and right sides.
However, there is an exhaust passage on the other side in the arrangement direction of each cylinder.
It is arranged along the front of the cylinder head.
Cooling water outlets at the upper end and the rear end
Is arranged substantially on the center line in the longitudinal direction of the hull, and the cooling structure for an engine for a small watercraft according to claim 1 or 2, characterized in that.