Callas Engine Rebuild Measurement Directive

Deck Height:

The goal is to have complete combustion though proper quench, without overdoing it. This is measured by using acid or rosin core solder (start with .050” Solder) on the piston at two places. These must be 180* off from one another and spaced 90* (perpendicular) from valve pockets, must go all the way to the edge of the piston, to cylinder wall. It’s best to have 1.00mm-1.25mm of solder crush. Turn the engine over by hand carefully, don’t force.

Please note: Too much clearance can cause low compression and low power issues. Too little clearance can cause pre-ignition or detonation issues so measure carefully.

Correction can be made with barrel spacers and or piston machining.

Valve to piston clearance:

Measured at valves to piston in valve relief pocket. Minimum .060″ intake and .080″ exhaust.

For Exhaust check for clearance from 15* BTDC to 8*BTDC

For Intake check for clearance from 8*ATDC to 15* ATDC

Please note: The piston chases the exhaust valve closed.

This clearance can be modified slightly by adjusting the camshaft timing, but it’s best to machine or modify the valve pockets. In rare instances, you can modify the valve.

Correction(s) made by machining the piston valve pockets or lowering the valve seats or both. In rare situations you can machine the valves.

Compression ratio:

Measured by filling cylinder head combustion chamber with fluid and measuring CC quantity.

Measured by filling top of cylinder and piston with fluid and measuring CC quantity.

Deduct for piston dome.  If calculations made, you need to perform multiple calculations or use computer program to input all information.  It’s best to do this with the cylinder head bolted to the cylinder before the measurements are made.

Correction made with barrel spacers and by removing material from combustion chamber(s) where necessary to even all. 

Please note: If you really need to match, then it’s done by removing chamber material.

CC’ing volume measurement Tips:

When measuring with the cylinder head installed on the cylinder, the CC volume will include the deck volume; what can be called Deck and or Dome volume.  This should also include the piston crevice (top ring land area above upper piston ring) volume, if carefully sealed with grease and cleaned out of the crevice area to allow fluid intrusion. Fluid must be measured though spark plug hole:

¾” spark plug hole e.g. 911 & 4 Cam engines= 2.0cc

½” spark plug hole e.g. 356 & 912 engines= 1.8cc