11-10-2018, 10:00 AM
From Chris Gould:
I used to measure compression ratios at Ricardo. The clearance volume was measured by resting the cylinder head on V blocks on the level marking off table. This was a large cast iron table with a machined surface. I doubt that anyone reading this has one, but we can manage without it. Make up a board as shown with studs to fit into three of the stud holes in the cylinder head. Put it on a rigid bench and adjust the studs to get the cylinder head level in all directions using a spirit level.
Support a burette with a retort stand and fill it with fusus oil. I don’t know where to obtain this, but diesel oil is a good substitute. If you don’t have a retort stand you can make a substitute with a piece of pipe, a large close peg and a bit of ingenuity a shown.
Put a scribing block onto the head surface and adjust it so that the scriber just touches the head surface.
Fill the burette and let a little of the oil out to remove any air under the tap. Position the burette and the scriber over the combustion chamber and measure the amount of oil to fill it to just touch the scriber. When doing this adjust the tap so that it is just dripping to get the final level. It will cause a ripple that will rise up the scriber. Lift the scribing block and lower it carefully to see if the level is correct. If it doesn’t touch the oil put in another drop, and repeat this until it does.
Measure and calculate the volumes of the valve protrusion and around the piston down to the top piston ring. We used to measure the gasket area with a planimeter. Tracing the shape on graph paper and counting the squares and half squares etc. is a good alternative. Measure the thickness of a gasket that has been compressed. Add or subtract these volumes as necessary to calculate the clearance volume.
The compression ratio = (Swept volume + clearance volume) divided by the clearance volume or 1+ swept volume divided by clearance volume.
I used to measure compression ratios at Ricardo. The clearance volume was measured by resting the cylinder head on V blocks on the level marking off table. This was a large cast iron table with a machined surface. I doubt that anyone reading this has one, but we can manage without it. Make up a board as shown with studs to fit into three of the stud holes in the cylinder head. Put it on a rigid bench and adjust the studs to get the cylinder head level in all directions using a spirit level.
Support a burette with a retort stand and fill it with fusus oil. I don’t know where to obtain this, but diesel oil is a good substitute. If you don’t have a retort stand you can make a substitute with a piece of pipe, a large close peg and a bit of ingenuity a shown.
Put a scribing block onto the head surface and adjust it so that the scriber just touches the head surface.
Fill the burette and let a little of the oil out to remove any air under the tap. Position the burette and the scriber over the combustion chamber and measure the amount of oil to fill it to just touch the scriber. When doing this adjust the tap so that it is just dripping to get the final level. It will cause a ripple that will rise up the scriber. Lift the scribing block and lower it carefully to see if the level is correct. If it doesn’t touch the oil put in another drop, and repeat this until it does.
Measure and calculate the volumes of the valve protrusion and around the piston down to the top piston ring. We used to measure the gasket area with a planimeter. Tracing the shape on graph paper and counting the squares and half squares etc. is a good alternative. Measure the thickness of a gasket that has been compressed. Add or subtract these volumes as necessary to calculate the clearance volume.
The compression ratio = (Swept volume + clearance volume) divided by the clearance volume or 1+ swept volume divided by clearance volume.