Thermal Clearance!!!

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Thermal Clearance!!!

Bài gửi by mercury on 9/3/2009, 07:01

Who has a document a bout Thermal Clearance ? please, share to me know!! I need that document!! Thanks a lot!!!!
I know that the function of the thermal clearance of the valve to preventing expending due to thermal of the valve!! Therefore, it make sure safety for valve and it componence( For exemple: valve seat, rocker arm, push rod...etc..). When that too large,and when engine operation it can changing the position and area open and result to making knock of vavle!!
So what about thermal clearance of piston, xylinder and piston ring??
Please , help me!!

mercury
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Registration date : 02/09/2009

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Some words about clearances

Bài gửi by КЭУ-KMTB on 9/16/2009, 23:30

There is no any specific document about clearances. Depending on each of equipment, we have an individual value of clearance. For example: for bearings, we have oil clearance; for crankshafts, we have longitudinal clearance; for valves (intake and exhaust valves), we have valve clearance and so on.
The oil clearance of bearings permits to form a LO layer on surface of journals. If this clearance is too small, then the bearings will be hot, on the other hand, the LO pressure will be dropped as a result of too large clearance and therefore the lubricating condition of the journals can not be maintained.
The longitudinal clearance allows the crankshaft slightly to expand in the longitudinal direction during operation of the engine.
The valve clearance is the distance between the end of the valve rod and the end of the rocker arm when the roller is on the basic circle of the cam in cool condition (without running) of the engine. The valve clearance permits the valve rod freely to expand due to heat when the engine is working (not prevents the valve from expanding as you had written). If the clearance is too large, then the opening moment of the valve will be late, the opening section as well the total opening angle of the valve will be decreased, besides, it causes a mechanical knock. On the contrary, a too narrow valve clearance is the cause of leakage of the combustion chamber.
For cylinder-piston group, to prevent the piston from seizing, normally the piston is casted with a smaller diameter than that of the cylinder liner, moreover the piston crown is slightly tapered. However, they do not measure the clearance between the cylinder liner and the piston, but check outside diameter of the piston and inside diameter of the cylinder liner to confirm their technical condition.
Lastly, the piston rings have three clearances: the first is the ring end clearance, the second is the ring side clearance and the last is the ring back clearance.
Ring end clearance (ring gap clearance) is the distance between two ends of the piston ring when the piston ring is put into the cylinder (without piston). A large ring end clearance will increase the leakage of compressed air and burned gases from the combustion chamber to the crankcase, while small clearance will cause an excessive wear of the cylinder liner, even seizure of the piston when it is heated.
Ring side clearance is the distance between the top of the piston ring and the bottom of the ring groove land above the piston ring. If the clearance is less than the minimum, so the sealing effect of the piston ring will be decreased. In case of too great clearance, an excessive wear of the ring groove will occur due to the snap of the piston ring to the ring groove when the piston changes the moving direction.
Ring back clearance is the difference between the depth of the ring groove and the thickness of the piston ring. If there is no ring back clearance, the friction wear of the cylinder liner will be increased, even it may cause a seizure of the piston.

КЭУ-KMTB
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Tổng số bài gửi : 15
Registration date : 26/03/2009

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