Liners

  • Leaking Liners?
  • How Do We Check For Leaking Liners?
  • The Remedy

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!

It's a good question! Unfortunately it is not the easiest of things to accurately diagnose 'in the car'.
The first problem is that the leak is often only noticeable when the engine is warm. We can check the water system for the presence of Hydrocarbons, which does identify a problem, but could equally be attributed to a blown head gasket which shows almost exactly the same symptoms as a leaking liner.
We can run a 'leak-down' test which is a little more definitive. Because the only connection point between the cylinders and water jacket is on the end cylinders (1, 2, 7 and 8) a leak-down test that shows leakage into the water system on a central cylinder (3,4,5 or 6) can only be a liner problem.
The leak-down test needs to be performed with the engine at normal running temperature and with the engine rotated to the correct position to have both valves closed during pressurisation.
The only absolutely definitive test is a pressure test of the block alone. This involves a completely removed and stripped engine, a number of blanking plates, an oven and 130 psi air pressure!
Obviously this testing requires time, effort and subsequently cost. The best advice we can give is that if the symptoms are there, run the first three checks and hope that something definitive is found, if it is not then I am afraid the bottom line is it is almost certainly a liner issue and you need to start making a decision as to which route to take next.

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.