My least favorite part of the project - removing the stubborn head studs. If you are shipping a block to our shop I highly recommend that you remove the studs first - its easier to ship and greatly reduces the chance of damage during shipment.

That begin said - here is how we do it - we tig weld on nuts to the studs - this does two things - 1) gives us a very good grip on the stud and 2) puts some heat into the stud to block interface - where the factory applies lock tite 20 years ago!

Next we have to mount the block to the CNC milling machine. We have made up a custom fixture to mount the 944 block via the crank center line so that the boring will be exactly 90 degrees to the crank. On of the keys to long life of a performance motor is to get everything square. It would be easy to assume the the existing cylinders are true...but they usually aren’t’ - I have measured quite a few.

The CNC machine is programmed with the correct center to center measurements, bore spacing on a seasoned 944 block can be off as much as .004”, this is rectified in the MID installation process. The other key dimension is the depth of the machining - errors here will result in sleeve settling and head gasket failure.

Here the CNC mill is removing the original cylinders - this takes several steps to ensure that the block remains dimensionally stable. If you try to take too much metal off in one pass the bore will distort from the heat and the resulting ‘hole’ will not be accurate.

Note the size of the cutting head - you need this type of machinery so that the cuts remain accurate. Very little flex in that cutting head!

This is what the block looks like after the original cylinders have been machined out and the correct multistep machining required to seat the MID sleeves has been completed. The sharp edges will be dressed before the sleeves are installed.

The MID sleeves before installation - high quality fabrication! The top flange fits in to a machined slot in the side of the top of the block and the bottom third fits into the holes bored into the block webbing. you can see the change in diameter where the sleeves sit on the floor of the block. The grooves in the lower third are for high temp O-rings to ensure the coolant is sealed.

After double checking all the dimension the block is place in the block oven to expanded it so that the sleeves will slip into place easily. This picture is actually from an old dry sleeve project (note that part of the stock cylinders still remain) but the heating process is still the same.

Here is what the MID sleeves look like after they have been dropped into place. The MID sleeves are sealed in to the block with 3 high temp O rings at the base and the upper edges of the block helping to locate the top flange. The red “goo” is a Locktite sleeve locking compound that is specifically designed for this type application

The next step is to machine the bores to match the piston dimensions. It is imperative that the piston clearance be exact so we won’t bore the sleeves until we have the pistons in hand to check the critical dimensions. The use of a toque plate ensures that the bores will be as round as possible. The boring of the sleeves may take several passes so that the sleeves remain dimensionally stable. The 104mm bores require quite a bit of material removal.

BTW - the torque plate is one of many tools that we had to custom make to ensure optimal results

Final step of machining - honing the bore to just the right size and surface. We use a multi step process that creates a Plateau finish. A Plateau ensures quick ring seating and a minimal dimensional change in the bores as the rings wear. Traditional finishes are quite rough and gouged under a microscope - the Plateau finish removes the peaks and rough texture leaving enough valleys to hold the oil in place while allowing a lot of sealing surface.

If you see a shop with a hand drill and hone don’t even ask questions, just go somewhere else!!