Cylinder Compression Check

[pandora63]

Engine: Cylinder compression check (for 1996-2000 Civics)

A compression check will tell you what mechanical condition the upper end (pistons, rings, valves, head gaskets) of the engine is in. Specifically, it can tell you if the compression is down due to leakage caused by worn piston rings, defective valves and seats or a blown head gasket. Note: The engine must be at a normal operating temperature and the battery must be fully charged for this check.

Tools needed:
Socket Wrench
Sparkplug Socket
Long Extension
Compression Gauge (Available at any parts store for about 20 bucks)

Begin by cleaning the area around the spark plugs before you remove them. Compressed air should be used, if available, otherwise a small brush or even a bicycle tire pump will work. The idea is to prevent dirt from getting into the cylinders as the compression check is being done.

This check is pretty much the same on any car. Although the pressure specs may vary depending on the type of engine, the most important thing you?re looking for is that all cylinders are consistent (+ or - 10-20psi).

Start off by removing the plug wires and plugs. Note which wires go where (label them if you have to), some aftermarket wires may have one or two that are the same length and you don't want to switch them around.

Next, remove the 15A FI (Fuel Injector)/PGM-FI fuse so that you don't have fuel spraying into the cylinders. It should be located in the same place on most Hondas, right side of the cowl under the glove compartment. Lower the glove compartment to access it. Disable the ignition system by detaching the primary connectors at the distributor. (Pictures available at sources below)

Install the compression gauge in the number one spark plug hole. To use a compression gauge, you must have a gauge with an adapter long enough to reach down the spark plug tubes. Be sure to open the throttle as far as possible during the compression check. (Pictures available at sources below)

Crank the engine over at least seven compression strokes and watch the gauge. The compression should build up quickly in a healthy engine. Low compression on the first stroke, followed by gradually increasing pressure on successive strokes, indicates worn piston rings. A low compression reading on the first stroke, which doesn?t build up during successive strokes, indicates leaking valves or a blown head gasket (a cracked head could also be the cause). Deposits on the undersides of the valve heads can also cause low compression. Record the highest gauge reading obtained.

Repeat the procedure for the remaining cylinders and compare the results to your car?s specifications.

SOHC engines - Cylinder compression pressure
Standard??..184 psi
Minimum??..135 psi
Maximum variation between cylinders??.28 psi

DOHC engines ? Cylinder compression pressure
B16A2
Standard??184 psi
Minimum??135 psi
Maximum variation between cylinders??.28 psi

B18B1
Standard??199 psi
Minimum??135 psi
Maximum variation between cylinders??.28 psi

B18C1, B18C5
Standard??270 psi
Minimum??135 psi
Maximum variation between cylinders??..28 psi

B20B4, B20Z2
Standard??178 psi
Minimum??135 psi
Maximum variation between cylinders??..28 psi

If the readings are below normal, add some engine oil (about three squirts from a plunger-type oil can) to each cylinder, through the spark plug hole, and repeat the test.

Replace the plugs and wires along with the fuel injector fuse when finished with test.

If the compression increases significantly after the oil is added, the piston rings are definitely worn. If the compression doesn?t increase significantly, the leakage is occurring at the valves or head gasket. Leakage past the valves may be caused by burned valve seats and/or faces or warped, cracked or bent valves.

If two adjacent cylinders have equally low compression, there?s a strong possibility the head gasket between them is blown. The appearance of coolant in the combustion chambers or the crankcase would verify this condition. If one cylinder is about 20% lower than the others, and the engine has a slightly rough idle, a worn exhaust lobe on the camshaft could be the cause. If the compression is unusually high, the combustion chambers are probably coated with carbon deposits. If that?s the case, the cylinder head(s) should be removed and decarbonized. If compression is way down or varies greatly between cylinders, it would be a good idea to have a leak-down test performed by an automotive repair shop. This test will pinpoint exactly where the leakage is occurring and how severe it is.


Sources: Haynes Repair Manual, #42025
HAzone.com - http://www.hazone.com/hb18ccomptest.htm


~*~Jenn
pandora63
2/25/04