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Finished Liner , Semi finished Liner or Parent bore

Posted by Ashley Wilson on

What are Finished  or Semi Finished Liners?

Semi-finished liners once fitted to the cylinder block require boring and honing to size the cylinder liner is very rough and the piston will not fit inside the semi finished liner , this is why it need to be bored. A semi finished liner can be flanged and all parallel liners are semi finished. this is the preferred liner to use by a engine machine shop, so the cylinder can be machine round with out any taper or ovality.
Finished liners are supplied pre-bored and once fitted may only require a light hone. the finished liner follows the contour or the old worn parent bore and can have taper and ovality which cans cause engine seize. ( i will talk about bore distortion in a later blog.
Liners basically come in two different flavours: Parallel and Flanged. A description of these are below:
Parallel Liner: As it says, the parallel liner is flat on all edges. These are held in the block by an ‘interference’ or ‘press fit’. Meaning the liner is marginally bigger than the parent bore of the motor. When these are pressed into place, they may distort and conform to the shape of the parent bore. Available only in semi-finished. (needs to be bored to size)
Flanged Liner: Yet again, as the name implies, these liners have a flange at the top. This flange locates into a counter bore cut into the top of the parent bore. These liners can be either ‘press’ or slip’ fit. Available in either; finished (pre-sized) or semi-finished. (needs to be bored to size)
Parent Bore: this means the cylinder block does not have any liners fitted at all. The cylinder block is machined so the piston and rings runs on the cast of the cylinder block bore know as its parent bore. the parent bore can be machined to suit s oversize piston. if the parent bore is too damaged a repair liner can be fitted.

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