Pistons and Cylinders. How to Rebuild your Air-Cooled Porsche Engine.

Pistons and cylinders on a Porsche air-cooled engine

We are up to putting our pistons and cylinders onto the engine. We like to use the ring compression tool to make this job go smoothly. So we add the piston to the connecting rod, then install the cylinder over this assembly.

Installing the Pistons and Cylinders

If you did not check out our write-up on setting up the piston rings, now would be a good time to review. And if you have only now taken your engine apart you should review how to check your pistons and cylinders.

We start the piston and cylinder install by double-checking the direction of the piston. The cut-outs for the valve guides are one way to check, or your piston may be marked with a front. Remember on this air-cooled engine the front refers to the flywheel side. This is because most air-cooled engines are in the rear of the car and the front of the engine faces the front of the car.

Have you done your math?

We have already done the calculations required to determine this engine’s compression. The shim pack that we are adding is the spot where you can make up for using different parts, machine work, casework, and cylinder head work. If you have not done your engine math, now would be the time to review that module.

Well, really you should have done the math way before this point! But don’t worry, the only number that will be hard for you to get is the case half measurement. You can still calculate case half measurement if your machine shop stamped the case with how much they removed.

How to Calculate Engine Compression

Pistons and cylinders are part of your engine math equation.

Piston Ring Orientation

Before setting the piston ring gaps, make sure to oil the connecting rod and crank area. Next set up your ring gaps, with no gaps on the thrust faces, and no gaps lined up with each other. We can double-check the oil ring assembly at this time.

Taking the wrist pin clip, install it until it clicks into one side of the piston. Think about how you are going to slide in the wrist pin and make sure you put the clip on the correct side. Double-check the intake and exhaust valve cut-outs and work the writs pin through the connecting rod and piston.

Remember that the wrist pin clips should only face up or down, never to the side. Make sure you hear a positive click and check your work before you bring in the cylinder. We oil the rings as a group and twist the whole lot back and forth to move the oil around.

Double check and oil your rings before fitting the cylinders

Sliding on the Cylinders

We like to use the factory ring compressing tool, Hazet 794U-3 as it applies enough pressure but not too much, to get the rings compressed. On a 2 liter motor, you may have to use the Hazet tool band upside down as it is a little thinner for the two-liter sizes.

Do not forget to add your shim pack before you bring in the barrel.

On the cylinder make sure that the largest side faces down, with the flat parts on the sides. Do not force the cylinder down, check it out and remove it if it does not feel right!

Lift up the shim pack as the cylinder comes down. Lightly tap the barrel in place and put on your cylinder head nut tool to hold down the cylinder as you turn over the engine for the next piston.

Work your way methodiccally through the other pistons and cylinders. Repeat the steps each time.

Tools we use to install pistons and cylinders

Hazet 794U-3 Piston Ring Collet
PROLUBE 41431 Steel PT-Type Oil Can, 300ml in Red, includes 5 Rigid and 6 Flexible Spouts
Hazet 794U-3 Piston Ring Collet
PROLUBE 41431 Steel PT-Type Oil Can, 300ml in Red, includes 5 Rigid and 6 Flexible Spouts
Hazet 794U-3 Piston Ring Collet
Hazet 794U-3 Piston Ring Collet
PROLUBE 41431 Steel PT-Type Oil Can, 300ml in Red, includes 5 Rigid and 6 Flexible Spouts
PROLUBE 41431 Steel PT-Type Oil Can, 300ml in Red, includes 5 Rigid and 6 Flexible Spouts

Pistons and cylinders air guides

Porsche issued a TSB about the center air guides. It involves cutting them down to help with cylinder temperatures.

The air guides live up against the cylinders to help direct air to cool the engine. The air guides should have been restored and cut if they have not been yet. The paint or powder coat process can bend the thin guides and a little bit of hand shaping may be necessary. You want them to fit nicely up against the cylinders.

Use the bows to clip the air guides in to place and then you are ready for heads and the cam boxes.

Up Next in your Air-Cooled Porsche Rebuild

If your heads are not checked and restored already, check out our eight part series on the cylinder heads.

If your cam box is not cleaned and inspected check out that too!

Installing Cylinder Heads and Cam Boxes

We are fast approaching the timing lessons, so stay tuned for more!


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