17-2-08 Top Hat liner with block cut in half
What the Rover V8 block looks like when sliced in 2, with demo of the top hat liner. I found this on the internet
Although there is little definitive information as to why the cylinder liners on some Rover V8 blocks appear to become 'porous' or start leaking, the most popular theory revolves around a flaw in the block casting.
It is thought that some blocks, particularly those used for the 4.0 litre and 4.6 litre engines, have a small casting defect behind the liners. This defect is between the water jacket in the cylinder block and the back of the liner. Over a period of time, water seems to cross the defect and end up on the back of the liner. This then works its way up the side of the liner and eventually causes a leak pathway all the way up to the block face.
This pathway allows the hot gasses from the cylinder to pass into the water jacket, pressurising the system and adding extra heat to the coolant.
Although at this point the problem is a minor one and may only appear from time to time, it does worsen over a period of time and eventually causes the engine to overheat and expel its coolant on a regular basis.
The worst case scenario is that the engine is stopped with substantial pressure in the water system and the water then is pushed back into the cylinder. If the water is still there when the engine is re-started it cannot be compressed and a 'hydraulic lock' occurs which tends to bend connecting rods, warp heads, lift head gaskets and is generally not very pleasant!
The Remedy:- The only real 'repair' is to bore out the old liners and fit new 'Top Hat' flanged liners to the block.
There is no real point in replacing them with standard liners as the block flaw is unlikely to be completely solved and you may end up back where you started in a very short time (this has happened to a number of people in the past!).
The top hat liners negate the problem at source. Because the liners use a stepped construction into the block face, the cylinder head actually presses the liner down onto the block when fitted so there is no possible pathway through to the cylinder from the water jacket. Added to this the gasket actually seals inside the outer edge of the liner and therefore the gasket seals better on the block face.
Essentially, we have fitted top hat liners to many hundreds of blocks over the past years and, touch wood, we have never had one fail yet! The fitting procedure is very precise, the blocks are bored to remove the old liners and any imperfections are repaired. The blocks are then heated, the new liners cooled in liquid nitrogen and the two mated. The fitted block is then allowed to cool naturally for a number of hours before the machining processes are carried out to create a finished bore. The liners can be bored to any size from 94mm to 97mm and this allows for a variety of engine configurations to be used. (my engine is 94.04mm with 77mm stroke)
17-2-08 Top Hat liner with block cut in half
What the Rover V8 block looks like when sliced in 2, with demo of the top hat liner. I found this on the internet
Although there is little definitive information as to why the cylinder liners on some Rover V8 blocks appear to become 'porous' or start leaking, the most popular theory revolves around a flaw in the block casting.
It is thought that some blocks, particularly those used for the 4.0 litre and 4.6 litre engines, have a small casting defect behind the liners. This defect is between the water jacket in the cylinder block and the back of the liner. Over a period of time, water seems to cross the defect and end up on the back of the liner. This then works its way up the side of the liner and eventually causes a leak pathway all the way up to the block face.
This pathway allows the hot gasses from the cylinder to pass into the water jacket, pressurising the system and adding extra heat to the coolant.
Although at this point the problem is a minor one and may only appear from time to time, it does worsen over a period of time and eventually causes the engine to overheat and expel its coolant on a regular basis.
The worst case scenario is that the engine is stopped with substantial pressure in the water system and the water then is pushed back into the cylinder. If the water is still there when the engine is re-started it cannot be compressed and a 'hydraulic lock' occurs which tends to bend connecting rods, warp heads, lift head gaskets and is generally not very pleasant!
The Remedy:- The only real 'repair' is to bore out the old liners and fit new 'Top Hat' flanged liners to the block.
There is no real point in replacing them with standard liners as the block flaw is unlikely to be completely solved and you may end up back where you started in a very short time (this has happened to a number of people in the past!).
The top hat liners negate the problem at source. Because the liners use a stepped construction into the block face, the cylinder head actually presses the liner down onto the block when fitted so there is no possible pathway through to the cylinder from the water jacket. Added to this the gasket actually seals inside the outer edge of the liner and therefore the gasket seals better on the block face.
Essentially, we have fitted top hat liners to many hundreds of blocks over the past years and, touch wood, we have never had one fail yet! The fitting procedure is very precise, the blocks are bored to remove the old liners and any imperfections are repaired. The blocks are then heated, the new liners cooled in liquid nitrogen and the two mated. The fitted block is then allowed to cool naturally for a number of hours before the machining processes are carried out to create a finished bore. The liners can be bored to any size from 94mm to 97mm and this allows for a variety of engine configurations to be used. (my engine is 94.04mm with 77mm stroke)