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The Ford Focus ST Block Mod

Those of you familiar with tuning the Volvo / Ford 5 cylinder engine will know that as we push the power upwards, its not uncommon for them to exhibit failure of the liners in the cylinder head area.

We have a solution for this problem and it can be applied to all the 5 cylinder Duratec ST engines and comes in the form of a set of carefully engineered shims that are used to brace the area around the upper bore area of the block, in between the cylinders. The downside to this solution is that whilst the shims themselves are cheap, to install them, the cylinder head must of course be removed, so its an ideal time to do some other belt and braces servicing while we are in there.

Focus ST 225 Block Mod

The cause of the Focus Duratec ST cracked liners...

This 5 cylinder engine has been cracking liners since long before Ford re-branded it as a Duratec ST and installed it into the Focus ST 225... this problem was already apparent on tuned Volvo's, and whilst most Ford tuners wont admit it, thats where the original fix was first engineered. Volvo tuners.

The problem it seems, is that the open deck design of this engine has a little channel that leaves the upper cylinder area of the block liners free standing. Now, presumably, this was to allow a little heat expansion and coolant flow in the most stressed part of the cylinder bore, the combustion area.

As we increase cylinder pressure, the bore tries to expand outwards and its thinnest part appears to be the weak link and it can crack here. Heat will play a great part in this, but its mainly the cylinder pressure itself which causes the expansion.


Its worth noting that cylinder pressure can be translated as torque. Torque is a measure of force. BHP is not, so it is not brake horse power that will do this, but torque, and torque cant be measured in boost pressure either. For example, 18psi and 20 degrees of timing can create the same torque and cylinder pressure as 24 psi and 10 degrees of timing, so its not easy to know when this issue will occur, but it seems safe to assume that over and above a stage 1 tune, if you drive it hard enough and often enough, you are likely already on borrowed time.

Symptoms of a Focus ST cracked block liner.

The symptoms of a cracked block liner are:

  • Misfiring
  • Loss of engine coolant
  • White smoke from the exhaust

Cracked Focus St Block

This image shows a standard block. Notice how there is a nice even groove running in between the cylinders?

Focus St cracked liner

This shows you a totally failed and cracked block. You can see the liner has distorted and gone oval by looking at how the groove is thinner in the middle than at the ends. If you look carefully you can also see the crack.

The solution to the Focus Duratec ST cracked liner problem...

As you can see from the images above, the issues seems to be confined to this area between the cylinders, and all thats needed to strengthen this area significantly is the correct installation of some bracing material to fill the gap. Whist this part of the solution is quite easy to do, the engine does of course have to come apart to do it. So we strongly recommend the job is done as follows:

  • Genuine Ford Head Gasket
  • Genuine Ford Head Bolts
  • Genuine Ford Camshaft Seals (x2)
  • Genuine Ford Camshaft VVT seals (x2)
  • Genuine Ford Cambelt
  • Cambelt Tensioner
  • Cambelt Pulley
  • Both Auxiliary Drive Belts
  • Turbocharger oil/water supply washers
  • Turbocharger manifold gasket
  • Spark Plug Seals (x5)
  • Coolant change
  • Oil and filter change (Castrol Edge 0w40)

A full diagnostic test will then be performed to ensure everything is running as it should be and the report will form part of your work report.

The Cost:
£800 all in, including all parts, labour and VAT.

(A new water pump can also be installed while we are in there at additional cost if required)

Block Mod Done... Lets Tune!

Once your block mod is done, you are free to enjoy more power and torque. Here is a customers Focus ST 225 on the dyno after coming in for converting to the RS Map Sensor, RS Injectors, RS MAF and our MSD340 calibration to suit plus power runs on our 4wd Dyno Dynamics Dyno. This one made 522NM and 350PS.