If you are very familiar with the Detroit 92/71 series engines, then you will see that there are holes around the sleeves/liners. Many like you have asked why are there holes around the sleeve of this engine. Some years back we have asked similar questions, but after my deep knowledge on these engines, I came to know why. Let me share with you below the reasons for it.
Detroit 92/71 series is a 2-stroke engine. It is an engine without an intake valves. Which means all the valves are exhaust valves. However, you should know by the principle of the engine, that there must be intake air before the engine can run. So how does the engine get the air to run you might ask?
In the other 4-stroke engines, there is an intake valve that opens so that there will be intake air to fill the vacuum when the piston travels downward.
But since there is no intake valve on the 2-stroke engines, the air comes from the air filter to the blower. The blower compresses the air but not similar to the turbo. Then from the blower, the holes around the sleeve allow the air to go into the cylinder. However, the piston’s movement determines when the air will enter the hole. When it is time for a specific cylinder to receive air, the piston will go towards the BDC which allows the hole to remain open for the air to come inside the cylinder. As the piston is traveling upwards, it compresses the trapped air in the cylinder. At this point, the piston serves as the intake valve that opens and closes the air.
When the piston of a specific cylinder is at TDC, it blocks all the holes in the cylinder, so that the trapped air can be compressed. At the end of the power stroke, the exhaust valve will open so that exhaust gases can exit the cylinder.
So the holes in the liner allow the air to get to the cylinder.
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