Engine Compression
“Compression pressure is the value when the engine is simulated rotating at low speed. When this value is low, it means that the engine starts poorly.”
Standards and Service Limits - Honda S2000 Service Manual
Standard Pressure: 228 psi (16 kgf/cm^2, 1,570 kPa)
Maximum Variation: 28 psi (2 kgf/cm^2, 200 kPa)
Minimum Pressure: 135 psi (9.5 kgf/cm^2, 930 kPa)
WHY YOU NEED TO KNOW THE COMPRESSION?
Just as blood pressure measurement provides clues to the condition of the human body, measuring engine compression (i.e. compression pressure) can provide information about the condition of the engine. Just like human blood pressure, whether engine compression is too low or too high, there is a problem lurking somewhere.
You can easily measure it with a commercially available professional gauge, so you can use it not only when you experience unusual behavior in your car but also on a regular basis. Regular tests can help you find an issue earlier or make it easier to schedule repairs and overhauls.
ENGINE COMPRESSION INSPECTION
Warm up the engine to normal operating temperature (i.e. 80°C or the cooling fan comes on) and turn off.
Operate to cut the fuel supply system.
00-05 UK Model: Remove the fuse No.12 (15A) for the fuel pump
06-09 UK Model: Use the HDS to turn all the injectors OFF
Remove all the ingnition coils.
Remove all the spark plugs.
Attach a commercially available compression gauge to the spark plug hole No.1.
Open the throttle fully, then crank the engine with the starter motor. The value of compression pressure is small when the piston first passes top dead center, and as the piston repeats its stroke, the value gradually increases until it reaches a certain point and no longer increases.
Repeat the process on the remaining cylinders.
Reinstall all the spark plugs and ingnition coils in reverse order.
Reconnect the fuel supply system.
Conduct the ECU RESET procedures.
Complete the ECU idle learning procedure.
Fig 1. Under Dash Fuse Box (05 UK Model)
Fig 2. Preparation
Fig 3. Cranking
You can watch an example of how to crank the engine to measure the compression here. This link will direct you to our YouTube channel.
TEST RESULTS
Our demonstration car is the Honda S2000 AP1 2005 UK RH Model with the second generation head and its mileage was 83,000 miles. Engine oil at the time of the test was 3,000 miles old.
Cylinder No.1: 225 psi
Cylinder No.2: 218 psi
Cylinder No.3: 226 psi
Cylinder No.4: 237 psi
The average is 226.5 psi with a maximum variation of 19 psi. When the standard expectation is 228 psi with a maximum variation of 28 psi, the outcome is within the specifications.
Test Results
NOT WITHIN SPECIFICATIONS
If the compression is not within the specifications, check the procedure and test again. If the second test failed again, you should consult with your garage or engineer. Probable issues may be from the following items.
The valves and seats are worn or damaged.
The cylinder gasket is damaged.
The piston lings are worn or damaged.
The pistons and cylinder bore are worn or damaged.
If the compression pressure exceeds the upper limit, it is likely that the combustion chamber volume is smaller than the standard state, and specifically, carbon deposits on the top of the piston are often the cause.
In this case, if the deposited carbon is soft, cleaner chemicals that clean the inside of the combustion chamber may be effective.
If it is hardened, you may need to take drastic measures such as removing the cylinder head and removing carbon from the top of the piston and combustion chamber.
When the compression pressure falls below the lower limit, more specific symptoms such as a lack of engine power and white smoke will occur.
If the compression doesn't rise, it means that even if the piston moves up, the air-fuel mixture still escapes somewhere.
Specific causes include piston ring wear, carbon jamming on the intake and exhaust valve faces, and too narrow valve clearance.
These are symptoms that appear as deterioration over time that have been driven for a long time, but on custom vehicles that are driven with a funnel without the air cleaner, compression pressure may drop due to physical damage caused by inhaled foreign objects.
Neither the upper limit nor the lower limit of the standard value is a good condition for the engine, but the important role of a compression gauge is to be able to visualize this.
DRAPER Expert
8 PIECE DIGITAL
PETROL COMPRESSION
TEST KIT
35885
