Easy Deck Height
Deck Height is the space between the piston dome and the combustion chamber, at top dead center (TDC). When you are building an engine, it
is a good idea to measure the deck height and adjust it as necessary to achieve the proper specs.
It is most critical to check your deck height if your crankcase was surfaced, your heads have been flycut, or if you are changing pistons or cylinders. Even if your machine shop has told you how much they removed during resurfacing, you should check deck height.
There are several ways to make this measurement, but we feel this is a
fast and fairly accurate way.
You will need a pair of Vernier or Dial calipers, some acid core solder
and possibly extra cylinder base shims. The reason we use acid core solder
instead of clay is that clay is too soft to measure. Acid core solder is large
diameter (about 3mm), which will allow for a large range of measurement.
The center of the solder is filled with acid flux. Once you remove the
acid (careful, it is rather corrosive), the hollow solder crushes very easily.
This saves you from damaging your pistons like solid or rosin core solder
can. Also, it is available at most hardware, craft or auto parts stores.
The deck measurement is made after you have completed the assembly
of the crank case or bottom end, prior to installation of your pistons and
Let's start with cylinder #1. Install your piston with both circlips; you won't have to remove it. Then select the cylinder base gasket you are going to start with. The cylinder base gaskets that come in your gasket kit are 0.25mm thick. If you know your heads were surfaced 0.25mm then you must start with two stock shims under your cylinder, or better yet, use one 0.5mm shim. Special shims are available here at C.E. and other true performance shops.
Now place the shim or shims under your cylinder and install the cylinder.
Turn the crank until the piston is a few mm below top dead center. Cut two pieces of acid core solder about one inch long. The solder doesn't have to be this long, but this length is easier to handle. Use a razor blade or sharp knife
to cut the solder, you want nice square ends, not pinched.
Now remove the acid flux in the center of the solder by blowing it out with an air hose, push it out with a piece of wire or spray it out with brake spray. But watch your
eyes! Wear safety glasses! If you want to avoid all this hassle, just use the pre-cut and cleaned solder in your CE Deck Height Kit.
Now glue the solder pieces to the top of your piston as per diagram. The end of the solder should touch the cylinder wall. On high dome pistons you may need to push down
on the solder to conform to the piston dome. This keeps it from rolling off when crushed. I use a dap of curil-T
to hold the solder in place, but anything sticky will do. You just don't want
it rolling around.
If you are building a 356/912 engine, place the solder perpendicular to the crankshaft. If your engine Is a
911/930/964, place the solder parallel to the crank to avoid the valve
pockets. Now place the cylinder head on and tighten the nuts for that cylinder.
If your engine is a 2.0 Liter 911, there is a gasket between the cylinder and head. This gasket must be in place to make your measurement.
After you tighten the head nuts, turn the crankshaft until you feel the solder crush. The solder should crush without much effort. If you feel too much resistance don't push your luck. If you have 0.5mm deck clearance or less you may damage your piston.
We have used this method for over 15 years and never damaged a piston, but it is better to take it easy. If you put a torque wrench on the pulley nut to crush the solder, it should not take more than 25 ft-lbs. of pressure. If it feels like too much pressure
is needed, just remove the cylinder and replace the shim with a thicker one.
After you crush the solder, take off the head and remove the solder pieces. Using a set of
Dial or Vernier calipers, measure the thinnest part of the solder. On most stock Porsche engines, your target deck height is 1.25mm to
On a high performance engine you can run it as tight as 1mm if you are trying for higher compression.
Lets suppose you measure the solder and one piece is .58mm and the opposite piece
is .52mm. This just means the piston was slightly tilted in the clearance between the piston and cylinder. That
is why we are using two pieces. If
we only use one piece, the piston tilts in the cylinder and the reading is wrong. So you have
.58mm and .52mm, just
split the difference, .55mm.
We are shooting for 1.5mm, so lets add a 1mm shim to attain 1.55mm.
If you want a little more compression take out the stock 0.25mm shim and you have 1.3mm. This is about as tight as I ever go on a stock engine.
Now just assemble the engine with the same 1mm shim under each cylinder. There
is no need to measure the
rest because all other factors are equal, cylinder height, rod length, cylinder head height, etc.