JP3210628B2 - Motorcycle engine - 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 configured to be mounted on a motorcycle and having two exhaust ports per cylinder.

[0002]

2. Description of the Related Art In a motorcycle engine, FIG.
, The upper part of the engine 1, that is, the cylinder head 2
The ignition plug B is attached to the. The mounting hole (spark plug hole) has an upward opening, and it is difficult to perform a complete waterproofing treatment on the upper portion. Therefore, the hole is provided with some water drainage hole. If rainwater accumulates at the bottom of the mounting hole, the spark plug B rusts and becomes difficult to remove,
This is because an electric leak occurs during operation and the output of the engine 1 becomes insufficient.

[0003] In an engine having a plurality of cylinders (cylinders) and the arrangement direction thereof is directed to the left and right sides of the body of the motorcycle, the above-mentioned drain hole is generally provided between the bottom of the plurality of spark plug mounting holes. Are formed to connect.
However, in the case of a multi-cylinder engine, since it is difficult to form a drill hole that is too long, the drain hole is divided into two as shown in FIG. Often, the remaining mounting holes 12 'in half and the drain holes 14' are formed separately by drilling.

In the case where drain holes are separately formed on the left and right sides, usually, one or more downward drain holes 31 'passing near the exhaust port 20' must be formed as shown in FIG. As shown in FIG. 5 (a), depending on the position of the chain tunnel 18 ', the lid 14a'.
14b 'may need to be performed, and for engines in which cylinders are arranged on the left and right sides of the vehicle body (see FIG. 5).
In the case of the engine 1 ′ shown in (a), the left side of the drawing is the left side of the vehicle body), and when the vehicle is parked in a state where the vehicle body is inclined leftward by a side stand (not shown), the drain hole 1 formed on the right side is formed.
This is because no water is discharged from 4 '(even if the end opening is not covered). It should be noted that the engine for a motorcycle generally passes the downward drain hole 31 'through the exhaust port 20' instead of the intake port.
This is because the water drain hole 31 ′ is more easily formed downward when it is mounted on the exhaust side with the exhaust side forward and slightly inclined forward as shown in FIG.

Some high-speed engines are equipped with a pair of exhaust ports (two, but merging one downstream per cylinder) per cylinder. In such a case, the above drain hole provided downward is generally passed between the pair of exhaust ports. JP-A-7-2596
No. 41 (FIGS. 1 and 3) shows such a general case, and FIG. 5B of the present application shows a similar example. On the other hand, depending on the arrangement of the engine, a downward drain hole 31 "may be formed above the exhaust port 20" as shown in FIG. The motorcycle engine 1 "(cylinder head 2") shown in FIG. 6 is described in Japanese Patent Application Laid-Open No. 61-283,752.

[0006]

When each cylinder in a water-cooled engine has a pair of exhaust ports, it is desirable to form a passage for cooling water between the pair of ports. By flowing the cooling water through the passage, the periphery of the exhaust port, which is one of the parts having the highest thermal load in the engine, can be effectively cooled. In the engine 1 'of FIG. 5 as well, as shown in FIG. 5C, a drill hole (a hole formed by machining with a drill) is formed between the ports 20' at a portion of the exhaust port 20 'up to the junction. The cooling water passage 26 'between the exhaust ports 20' is connected to the cooling water passage 25 'in the cylinder head 2' and the cooling water passage (not shown) in the cylinder (not shown). I have.

However, conventionally, when a downward drain hole 31 'is formed between a pair of exhaust ports 20' of a certain cylinder as shown in FIG. 5B, the cylinder is located between the exhaust ports 20 '. The cooling water passage 26 'was not provided. Since the pair of exhaust ports 20 ′ are provided at positions very close to each other because they open into the same cylinder, it is not possible to form both the drain hole 31 ′ and the cooling water passage 26 ′ between both ports 20 ′. The reason is that it is not easy. Therefore, the mounting hole 12 'of a certain spark plug
When a drain hole 31 'as shown in FIG. 5B is formed in the cylinder, the cooling water passage 26' as shown in FIG.
Is not provided, the exhaust port 20 'is not sufficiently cooled, and it is necessary to take measures to cope with the problem. In the case of a water-cooled engine, a measure (such as adjustment of a carburetor) for suppressing the calorific value (and thus output) of the cylinder is taken. The need arises.

On the other hand, when a downward water drain hole 31 "is formed at a location as shown in FIG. 6, since the water drain hole 31" does not pass between the exhaust ports 20 ", it is easy to provide a cooling water passage therethrough. However, it is possible to provide the water draining hole 31 "which passes downward while passing above the exhaust port 20" because the engine 1 having the cylinder head 2 "(and the cylinder) whose axis is considerably inclined as shown in FIG. If you have to be mounted in such a tilted state,
The arrangement of the engine 1 "and peripheral devices in the motorcycle is limited to a very special one, and the versatility of the engine 1" and the like is low.

The present invention relates to a motorcycle engine having two exhaust ports per cylinder, which does not require a large inclination of the cylinder as shown in FIG. Is to provide an unnecessary engine.

[0010]

According to a first aspect of the present invention, there is provided a motorcycle engine having a pair (that is, two) of spark plug holes which are located above the center (or substantially the center) of each combustion chamber and are joined downstream. In a motorcycle engine in which the exhaust port of each cylinder is adjacent to the spark plug hole for each cylinder, first, between the pair of exhaust ports for the same cylinder, the cooling water passage and the bottom of the spark plug hole (the mounting screw Upper part) to lower (lower position when mounted on a motorcycle)
(Downward water drainage holes, such as words FIG. 5 (b)) and are formed drainage holes leading to the outside extends. Since the downward drain holes need not be formed in the spark plug holes of all cylinders (see FIG. 5), the above-mentioned "same cylinder portion". Means the same cylinder in one or more cylinders and does not refer to each cylinder in all cylinders. In this specification, "right", "left", "up", "down", "front" and the like indicate directions in an engine mounted on a motorcycle, and the direction of the motorcycle (as viewed in the traveling direction). It matches with right, left, etc. respectively.

[0011] In such a motorcycle engine, since the downward drain hole provided at the bottom of the spark plug hole passes between the exhaust ports as described above, the axial center of the cylinder is set in a mounted state on the motorcycle. You don't have to lean to extremes. That is, since a downward drain hole is not provided through the upper part of the exhaust port as shown in FIG. 6, the engine can be mounted on the motorcycle in various postures that can be considered normally, such as by setting the cylinder upright, In any such state, accumulation of water in the spark plug hole is prevented by the function of the water drain hole. Therefore, it can be said that this engine is a highly versatile engine regardless of arrangement in a motorcycle.

Further, in this engine, since the cooling water passage is provided between the exhaust ports of the same cylinders together with the downward drain holes, the space between the exhaust ports is also cooled for the cylinder having the downward drain holes as described above. And the exhaust ports can be effectively cooled for all cylinders including that cylinder. Therefore, it is not necessary to suppress the heat generation for any of the cylinders, and the output can be maximized.

The motorcycle engine according to the first aspect of the present invention further includes: a) the drain hole extending from the bottom of the spark plug hole in the cylinder head to the lowermost portion of the side wall of the cylinder head (ie, the side wall is connected to the cylinder). position until) formed near the surface, b) the cooling water passage between the exhaust port, is formed above the the water drainage hole and so as not to intersect its drainage hole. Since the cooling water passage in the water-cooled engine is formed vertically and horizontally inside the engine, the "cooling water passage between the exhaust ports" referred to above (and below)
Means a portion of the cooling water passage that passes between the exhaust ports.

In this motorcycle engine, a downward drain hole is first formed from the bottom of the spark plug hole to the lowest portion of the side wall of the cylinder head as described in a) above. In other words, a drain hole is provided in the lowermost portion of the cylinder head as long as a hole that passes through the lowermost joint surface and reaches the cylinder is unnecessary. Since there is no need to provide a hole on the side of the cylinder, a hole required for draining is relatively easily formed.

As described in (b) above, the cooling water passage between the exhaust ports is formed above the downward drain hole.
Since the downward drain hole is provided at the lowermost part of the cylinder head as described above, if the cooling water passage is provided above the same, a portion between the pair of exhaust ports approaching so as not to intersect with the drain hole. It is not difficult to provide a cooling water passage. According to the above a) and b), this engine
It can be said that it is easy to form both a downward drain hole and a cooling water passage between the exhaust ports of the same cylinder.

In the motorcycle engine according to the first aspect of the present invention, the thickness of the pair of exhaust ports (thickness of the metal portion) between the ports near the space where the cooling water passage and the drain hole are formed is further reduced. The opening cross section of each port is made oval to widen, and the cooling water passage between the exhaust ports is formed by casting (therefore, the cooling water passage itself is formed by using a core). Characterized by having a flat opening cross section having a small dimension in the thickness direction.

[0017] In contrast to the drain hole in which the water entering the spark plug hole only needs to be drained slowly, the cooling water passage must have a certain amount of cooling water inside, because the amount of cooling water that provides a sufficient cooling effect must flow inside. It is desirable to have a cross-sectional area.
Therefore, when the cooling water passage between the exhaust ports is formed by drilling a hole as shown in FIG. 5C, the diameter tends to be larger than the diameter of the drainage hole. Specifically, a considerable thickness is required between the two exhaust ports.

However, in this engine, the cooling water passage is formed by casting to make the cooling water passage flat (the opening having a small opening size in the direction of the thickness between the ports) as described above. Even if the area is large, the opening does not spread so much in the direction of the thickness between the ports. In addition, since each port has an oval cross section in the vicinity of the area where the cooling water passage and the water drain hole are formed, the thickness between the ports is widened, so that the cooling water passage between the ports is provided. Is easier to form. In other words, in this engine, it is easier to form a cooling water passage and a downward drain hole between the exhaust ports of the same cylinder than in the above-described engine. It can be said that formation is possible.
As described above, since a large cross-sectional area is not required for the drainage hole, the drainage hole may be formed by a method other than casting (drilling or the like).

The motorcycle engine according to claim 2, wherein
The engine of item 1 is characterized in that the cooling water passage between the exhaust ports is bent including the following a) and b). Explaining with reference to the example of FIG. 1, a) and b) are as follows: a) The lower position p of the exhaust port away from the spark plug hole.
A lower portion extending from the cooling water passage to another portion of the cooling water passage at this position p and approaching the base of the exhaust port and approaching the spark plug hole; and b) an end of the lower portion near the spark plug hole. And-an upper portion extending from the portion Q to a position R above the exhaust port (the other portion of the cooling water passage is connected at this position R). In addition, PQR mentioned here means each part in the example of FIG.

The cooling water passage between the exhaust port, claim 1
It is more preferable that even if it is cast-formed as described above, it is formed as a bent one including the above-mentioned a) and b). The reason is as follows. That is, 1) At first glance, it seems that it is easiest to form the cooling water passage straight from the lower position P of the exhaust port away from the spark plug hole to the upper position R of the exhaust port. It is. However, in fact, as described above, it is easier to form the lower portion through the end Q near the spark plug hole near the base of the exhaust port. Passing through the end Q passes the passage to a position closer to the base of the exhaust port than the positions P and R,
This is because the space between the pair of ports is wider near the base of the exhaust port than near the downstream near the junction, and therefore the wall thickness between them is wide, so that the cooling water passage is easily formed. As described in the first aspect, since there is a drain hole near the lowermost portion of the cylinder head (therefore, a portion near the base of the exhaust port), it is important to provide a cooling water passage at a place where it can be easily formed. Further, as long as the cooling water passage is bent as long as it is formed by casting, there is also a situation that it is not difficult to form the cooling water passage for that reason. In addition, the fact that the cooling water passage extends from the end Q to the upper position R and is connected to the other portion of the cooling water passage at the position R is also a part of the wide gap between the exhaust port and the spark plug hole. This means that a branch point of the cooling water passage is formed at a portion which is easy to form.

2) Since the cooling water flows closer to the base of the exhaust port than when the cooling water passage is provided straight from the lower position P to the upper position R of the exhaust port,
The port can be cooled effectively. The exhaust port has a high temperature throughout the entire region due to the flow of high-temperature exhaust gas. Among them, the temperature near the root at the upstream end is the highest. Therefore, by forming the cooling water passage as described above and flowing the cooling water near the base of the exhaust port, heat transfer from the exhaust port to the cooling water becomes active, and the exhaust port is cooled more effectively. It is.

[0022]

1 to 4 show an embodiment of the present invention. FIG. 4 is a side view showing an outline of the engine 1 in a state where it is mounted on the motorcycle A as described above. FIG. 3 is a plan view of the cylinder head 2 of the engine 1 of FIG. FIG. 1A is a sectional view taken along a line II in FIG. 3, and FIGS. 1B to 1E respectively show bb, cc, dd, and e- in FIG.
e is each sectional view. FIG. 2 (a) shows the state in FIG.
It is II-II sectional drawing, Comprising: Each of FIG.2 (b)-(e) is each sectional drawing of bb, cc, dd, and ee in (a).

The illustrated engine 1 is an in-line four-cylinder, water-cooled, DOHC, four-stroke engine, which is a so-called four-valve type having two exhaust valves and two intake valves per cylinder. The main body of the engine 1 including the cylinder head 2 shown in FIGS. 1 to 3 is formed of an aluminum alloy. As shown in FIG. 4, with respect to the motorcycle A, the exhaust side (the side with the exhaust port 20 shown in FIG. 3) is located forward of the vehicle body,
The cylinder is aligned with the left-right direction of the vehicle body and the upper part is inclined slightly forward. The left and right cylinders are named first to fourth cylinders in order from the left (that is, the lower side in FIG. 3). An ignition plug B is attached to the upper cylinder head 2 such that an electrode faces the upper center of the combustion chamber (reference numeral 11 in FIG. 1) of each cylinder.

Since the engine is an in-line four-cylinder four-valve engine, as shown in FIG. 3, four plug holes 12 for a spark plug B (FIG. 4) are formed in the cylinder head 2 in a straight line. Four mounting holes 16 and 17 for a valve (not shown) are provided so as to surround the plug hole 12 (two mounting holes 16 for the intake valve and two mounting holes 17 for the exhaust valve). . The reason why four valves are used in this way is that the illustrated intake port 15 and exhaust port 20
The two parts (a pair) are divided at the base facing each combustion chamber.

As shown in FIG. 3, the engine 1 has a drain hole 31 formed in front (exhaust side) of each spark plug hole 12 of all cylinders. As shown in FIG. 1 (a), each drain hole 31 is formed from the bottom of the front wall surface of the cylinder head 2 by drilling (machining using a drill) into the bottom 12b of the plug hole 12 (plug mounting screw). 12a), and the opening side of the front wall surface is lower than the opening in the plug hole 12 and faces downward. The drain hole 31 has a small diameter (about 4 mm in diameter), and is formed by drilling after the casting of the cylinder head 2 is completed. The water that has entered the plug hole 12 is discharged from each drain hole 31 during the traveling or parking of the motorcycle A (FIG. 4).

Further, similarly to a general water-cooled engine, a cooling water passage 25 is formed in the cylinder head 2 of the engine 1 as shown in FIG. In connection with the fact that the exhaust port 20 is divided into two (one pair) exhaust ports 21 and 22 at the base (upstream side) facing the combustion chamber,
In particular, a cooling water passage 26 is also formed in the partition 23 between the ports 21 and 22. Since the high temperature exhaust gas flows through the exhaust port 20, the space between the ports 21 and 22 is also cooled.
The cooling water passage 26 communicates with other cooling water passages 25 located anywhere in the cylinder head 2.
22 means a passage passing between the two.

The major feature of this engine 1 is that, despite the provision of the downward drain holes 31 for all cylinders as described above, a cooling water passage 26 is formed between the exhaust ports 21 and 22 of each cylinder. Is to be. Therefore, the cooling of the exhaust port 20 is sufficiently performed for any of the cylinders, and it is not necessary to take measures to suppress the amount of generated heat, so that the original output of the engine 1 is maximized. However, since the cooling water passage 26 together with the drain hole 31 is formed in a narrow portion between the exhaust ports 21 and 22 of each cylinder, considerable contrivance is required in taking the configuration.
Hereinafter, the formation of the cooling water passage 26 and the like between the ports 21 and 22 will be described with reference to FIGS.

1) First, as shown in FIG. 1, the location of the downward drain hole 31 is a portion extending from the bottom 12b of the spark plug hole 12 to the lowermost portion of the front surface of the side wall of the cylinder head 2 and a cooling water passage. 26 is provided above the drain hole 31. By doing so, the drain hole 31 can be formed in a simple form without crossing the joint surface 2a with the cylinder (not shown), and the cooling water passage 26 can be formed substantially in parallel with the drain hole 31. By forming the cooling water passage, it is possible to avoid intersecting with the drain hole 31 (when the cooling water passage 26 intersects with the drain hole 31, the cooling water flows out from the drain hole 31, so that the intersection needs to be avoided), and it is easy to form.

2) FIG. 2 shows a cross section of a part of the opening (a cross section cut at right angles to the longitudinal direction) of the exhaust ports 21 and 22.
As shown in FIG. 1 (c), the cooling water passage 26 was formed into a flat shape as shown in FIG. 1 (c). In other words, the exhaust ports 21 and 22 each have a true circular cross section at the opening facing the combustion chamber 11 (FIG. 2B), and they gradually approach and merge downstream (FIG. 2 ( e))
However, the cross section of the exhaust port 20 near the passage of the cooling water passage 26 and the drain hole 31 is shown in FIG.
By making the shape of an ellipse as shown in FIG. At the same time, in the portion of the cooling water passage 26 passing between the ports 21 and 22, FIG.
As shown in FIG. 1, the partition 23 has a flattened cross-sectional shape different from that of the other portions (see FIG. 1D), and the size of the partition wall portion 23 in the thickness direction is reduced. The configuration in which the shape of the opening is changed in this manner is such that the cooling water passage
6 can be formed by casting (simultaneously with the casting of the cylinder head 2), but by adopting such a configuration, the cross-sectional area required for flowing a sufficient amount of cooling water can be reduced by the cooling water passage. Port 21
It is no longer difficult to provide the cooling water passage 26 in the narrow partition 23 between the two.

3) The cooling water passage 26 is connected to the exhaust port 21
-Between 22, as shown in Fig. 1 (a), a path having a "-"-shaped (or vice versa) bent path was provided. That is,
A portion (see FIG. 1E) below the exhaust port 20 apart from the spark plug hole 12 and connected to another cooling water passage 25 in the cylinder head 2 is set to a position P, and the exhaust port 2
Assuming that a portion (see FIG. 1 (b)) that is above R and is also connected to another cooling water passage 25 is a position R, the cooling water passage 26 is located at an end Q near the base of the port 20 from the position P. It is formed so as to include a lower linear portion extending to the spark plug hole 12 and extending from the end Q near the spark plug hole 12 to the above-described position R. The partition wall 23 through which the cooling water passage 26 passes becomes thinner toward the downstream even if the thickness is secured by making the ports 21 and 22 oblong as described above (see FIG. 2 (c)). 2 (d)), the cooling water passage 26 is located at the base (upstream) of the port 20 via the end Q as described above, rather than connecting the positions P and R linearly.
If the partition wall 23 is provided closer, it can be provided in a portion of the partition wall portion 23 where the wall thickness is large and easy to form. And then end Q
, There is also an advantage that the cooling water in the passage 26 can effectively cool a particularly high-temperature base portion of the exhaust port 20 (21/22). While forming the cooling water passage 26 in this way by casting,
Since the drain hole 31 is formed below the cooling water passage 26 as described in 1) by drilling the hole after casting, two holes are passed through the thick portion of the partition wall 23, and both holes are passed. Is considerably easier to form.

If the drain holes 31 are formed in the spark plug holes 12 for all cylinders as in the embodiment shown in FIGS. 1 to 3, there are the following advantages. That is, unlike the example of FIG. 5, there is no need to provide the long drain holes 13 'and 14' extending between the plurality of cylinders, and there is no need to cover the drain holes 14 'before and after the chain tunnel 18'.

Although one embodiment has been described above, it goes without saying that the present invention is not limited to this embodiment. For example, FIGS. 1 to 3 and the like illustrate a four-cylinder engine A, but the invention can be implemented in any number of cylinder engines including a single cylinder engine. Also, as in the example of FIG. 5, only for one of the plurality of cylinders,
It is also possible to implement the invention in a form in which a cooling water passage and a downward drain hole are formed between a pair of exhaust ports.

[0033]

The motorcycle engine according to the first aspect has the following effects.

A) Since a downward drain hole from the spark plug hole is provided so as to pass between the exhaust ports, even if the engine is not mounted on the motorcycle with the cylinder axis extremely inclined, Drainage from the spark plug hole can be performed through the hole. Therefore, this engine can be mounted on many types of motorcycles in various postures.

B) The exhaust ports can be effectively cooled for all the cylinders including the cylinder having the downward drain hole, so that the output can be maximized.

[0036] Then, c) between the exhaust port of the same cylinder, that is formed respectively to facilitate the downward water drainage hole and the cooling water passage.

[0037] If the motorcycle engine according to claim 1, d) as well as the ones flat cooling water passage in the vicinity of the cooling water passage passes between the exhaust port, the opening cross section of each port oval By doing so, the thickness between the ports is widened, so that it is easier to form the cooling water passage between the ports while having a sufficient cross-sectional area.

E) Even in a small-sized (for example, small-displacement) engine in which a pair of exhaust ports tend to approach each other, a drain hole and a cooling water passage are formed between the exhaust ports to form the above a).
The effect of b) can be obtained.

Particularly, in the case of the motorcycle engine according to claim 2 , f) the cooling water passage is passed through a portion near the base of the exhaust port, where the thickness between the ports is as large as possible.
The formation of the passage is further facilitated.

G) Since the cooling water flows to the portion near the base of the exhaust port, the exhaust port can be cooled more effectively.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention,
FIG. 1A is a longitudinal sectional view (II sectional view in FIG. 3) of a cylinder head 2 of the motorcycle engine 1 shown in FIG. FIGS. 1B to 1E are cross-sectional views of bb, cc, dd, and ee in FIG.

FIG. 2A is a longitudinal sectional view (a sectional view taken along the line II-II in FIG. 3) of the cylinder head 2 of FIG. 1 cut along another surface. FIGS. 2B to 2E are cross-sectional views of bb, cc, dd, and ee in FIG.

FIG. 3 is a plan view of a cylinder head 2 in the engine 1 of FIGS. 1, 2, and 4;

FIG. 4 is an overall side view showing a motorcycle A and an engine 1 mounted thereon.

FIG. 5 (a) is a front sectional view of a cylinder head 2 'in a conventional motorcycle engine 1'. FIGS. 5B and 5C are cross-sectional views of bb and cc in FIG. 5A, respectively.

FIG. 6 is another conventional motorcycle engine 1 ″ different from FIG.
13 is a side sectional view of the cylinder head 2 ″ in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Motorcycle engine 2 Cylinder head 12 Spark plug hole 20 ・ 21 ・ 22 Exhaust port 26 Cooling water passage 31 Drain hole

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-259641 (JP, A) JP-A-9-280104 (JP, A) JP-A-61-283752 (JP, A) 64849 (JP, U) Fully open 1-114950 (JP, U) Fully open Showa 61-99605 (JP, U) Fully open Showa 61-178049 (JP, U) Fully open, Showa 55-54542 (JP, U) Hira 3-65837 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02F 1/00-1/42 F01P 3/02-3/16 F02P 13/00

Claims (2)

(57) [Claims] 1. A motorcycle engine in which a spark plug hole is provided above the center of each combustion chamber, and a pair of exhaust ports converging downstream exist adjacent to the spark plug hole for each cylinder. between a pair of exhaust ports minute, and cooling water passage is formed with water drainage holes leading to the outside extends to the lower than the bottom of the spark plug holes, drainage holes of that of the spark plug hole in a cylinder head The motorcycle engine is formed from the bottom to the lowermost portion of the side wall of the cylinder head, and the cooling water passage between the exhaust ports is formed above the drain hole so as not to intersect the drain hole.
In addition, the pair of exhaust ports has a cooling water passage and a drain hole between them.
In order to increase the thickness between ports near the formed area,
The opening cross section of the port is oval, and the cooling water passage between the exhaust ports is formed by casting.
Between the ports, a flat plate with a small dimension in the thickness direction
It has a flat opening cross section.
Motorcycle engine . 2. The cooling water passage between exhaust ports,
Exhaust port from a position below the exhaust port away from the spark plug hole.
Lower part that extends near the base of the heat sink and approaches the spark plug hole
Minute and the lower part of the lower part close to the spark plug hole
An upper portion extending to a position above the exhaust port.
2. The self-timer according to claim 1, wherein
Motorcycle engine .