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Finished Liner, Semi Finished Liner or Parent Bore

What is Finished or Semi Finished Liners?


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 needs 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 an engine machine shop, so the cylinder can be machine round without 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 can cause the engine to seize.
Liners basically come in two different flavors – Parallel and Flanged. A description of these are below:

Click here > Perkins Finished Liner 

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.)

Click here >  flanged liner semi finished  

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 run on the cast of the cylinder block bore know as its parent bore. The parent bore can be machined to suits oversized piston. If the parent bore is too damaged a repair liner can be fitted.


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