What does it mean to resleeve an engine and what’s the difference between the engine head and block?
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Inside your engine are chambers called “cylinders” and moving within the cylinders are parts called “pistons”. The pistons move up and down with furious speed and force constantly and that’s what produces the energy in your engine.
Overtime those moving pistons can damage the lining of the cylinder and that’s no good. A “sleeve” in this case is a lining you can put around the cylinder. It varies from car to car, but you can consider the lining of the cylinder “consumable” meaning it’s going to damaged over time and eventual repair should be expected. The sleeve just a replacement “cylinder wall lining”.
Sometime you need to get *into* the cylinder to do work (like replacing a sleeve) so you can’t just make an engine out of a massive single chuck of hollowed out metal, you need it to come apart.
So engines come in 2 basic pieces like a sandwich, the top piece is called a “head” and the bottom piece is called a “block” (because it’s bigger). The two are mechanically fastened using bolts and there is a layer of compressible material between the two called a “Gasket” that seals the joint so gasses can’t escape.
The block is the main body of the engine, and contains the cylinders in which the pistons will move. Those cylinders are open on the top. The head is the part that bolts onto the block and “tops” the cylinders – it also has the (complex) valves in it, holds either the camshaft (in an overhead cam engine) or the rockers (when the cam is down below), and the spark plugs and fuel injectors. Between the two (block and head) is the “head gasket” to seal them. Lining the cylinders are the sleeves – those provide a bearing surface for the pistons, which are sealed against them with the piston rings. Re-sleeving is replacing those sleeves, which can be worn or scored by the movement of the pistons.
Sleeving is taking metal tubes that fit inside of the cylinder walls and pushing them down into the engine block, which is the larger hollow metal structure around the rotating parts. It’s job is really to hold everything in place. The cylinder head, bolts down onto the top of the engine block, or deck surface. It controls the airflow in and out of the cylinder as it cycles from intake to exhaust.
If you take the ‘head’ off the engine then when you look down you are going to see where the cylinder articulates. Inside the head are the injectors and the valves that let the air in and out. So, for that reason, it is a critical component and it must be removeable because you will have to eventually service the parts in there or replace the gasket that goes between the cylinder head and block.
You typically don’t replace a cylinder on a car engine but the process is common on aircraft piston engines which are of a similar design. After a period of time and use, the surface of the wall that surrounds the piston can get pitted and damaged with use. Resleeving it means to replace that wall with a new one. Not all engines can do this, the sleeve is built into the block so to get that done you need to send the engine block back to the manufacturer for a rebuild. Typically you wouldn’t do that either, you would just buy a rebuilt block and sell yours back to the manufacturer so they can rebuild it and sell it back to someone else.
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