Lubricating structure for an internal combustion engine

1. An internal combustion engine wherein a transmission case which accommodates a transmission is provided on one side of a crankcase which supports a crankshaft and a crank side oil chamber is provided at a lower portion of said crankcase comprising:

a transmission side oil chamber partitioned from a transmission accommodation section is provided at a lower portion of said transmission case such that oil is circulated through said transmission side oil chamber,

wherein said crank side oil chamber has a first oil chamber and a second oil chamber separate from each other, and

a first opening is in constant flow communication with said transmission side oil chamber provided in said first oil chamber while a second opening is in constant flow communication with said second oil chamber provided in said transmission side oil chamber.

2. The internal combustion engine according to claim 1 , wherein a third opening communicating with a strainer of an oil pump is provided in said second oil chamber.

3. The internal combustion engine according to claim 2 , wherein said first oil chamber is provided at a position to which returning oil from a cylinder section of said internal combustion engine drops and said second oil chamber is provided rearwardly of said first oil chamber while said strainer chamber is provided forwardly of said second oil chamber below said first oil chamber.

4. The internal combustion engine according to claim 2 , wherein said second opening is positioned lower than said first opening and said third opening is positioned lower than said second opening.

5. The internal combustion engine according to claim 3 , wherein said second opening is positioned lower than said first opening and said third opening is positioned lower than said second opening.

6. The internal combustion engine according to claim 1 , wherein said transmission side oil chamber is positioned below said transmission chamber of said transmission case in which said transmission is accommodated.

7. An internal combustion engine

according to claim 1 ,

wherein a guide member for guiding returning oil from a cylinder section of said internal combustion engine to said transmission side oil chamber is provided on the inner side of said crankcase.

8. The internal combustion engine according to claim 7 , wherein said guide member is provided so as to extend between left and right walls of said crankcase.

9. The internal combustion engine according to claim 1 , wherein oil flows outwardly from a first oil path to enter the crankcase past an oil passage groove formed between a right bearing and the crankshaft to an end portion of a connecting rod and along a second oil path formed in a crank pin.

10. An internal combustion engine including a transmission case for accommodating a transmission is provided on one side of a crankcase which supports a crankshaft comprising:

a crank side oil chamber formed at a lower portion of said crankcase; and

a transmission side oil chamber formed from a transmission accommodation section, said transmission side oil chamber being provided at a lower portion of said transmission case;

wherein oil is circulated through said transmission side oil chamber,

wherein said crank side oil chamber has a first oil chamber and a second oil chamber separate from each other, and

a first opening is in constant flow communication with said transmission side oil chamber provided in said first oil chamber while a second opening is in constant flow communication with said second oil chamber provided in said transmission side oil chamber.

11. The internal combustion engine according to claim 10 , wherein a third opening communicating with a strainer of an oil pump is provided in said second oil chamber.

12. The internal combustion engine according to claim 11 , wherein said first oil chamber is provided at a position to which returning oil from a cylinder section of said internal combustion engine drops and said second oil chamber is provided rearwardly of said first oil chamber while said strainer chamber is provided forwardly of said second oil chamber below said first oil chamber.

13. The internal combustion engine according to claim 11 , wherein said second opening is positioned lower than said first opening and said third opening is positioned lower than said second opening

14. The internal combustion engine according to claim 12 , wherein said second opening is positioned lower than said first opening and said third opening is positioned lower than said second opening.

15. The internal combustion engine according to claim 10 , wherein said transmission side oil chamber is positioned below said transmission chamber of said transmission case in which said transmission is accommodated.

16. The internal combustion engine according to claim 10 , wherein a guide member for guiding returning oil from a cylinder section of said internal combustion engine to said transmission side oil chamber is provided on the inner side of said crankcase.

17. The internal combustion engine according to claim 16 , wherein said guide member is provided so as to extend between left and right walls of said crankcase.

18. The internal combustion engine according to claim 10 , wherein oil flows outwardly from a first oil path to enter the crankcase past an oil passage groove formed between a right bearing and the crankshaft to an end portion of a connecting rod and along a second oil path formed in a crank pin.