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| - | #REDIRECT [[Truncated Engine compression test]] | + | A '''compression test''' will check the condition of the engine cylinder sealing -- how well the compression rings are working. The exact compression reading you get will vary depending. Among many variables, the reading depends upon your camshaft, static compression ration, and (most importantly) the accuracy of the gauge. Some guages will read higher or lower than others. '''What is important is that the reading of each cylinder is close to that of the others'''. |
| + | |||
| + | = Overview = | ||
| + | To perform an Engine compression test: | ||
| + | # Perform Dry Test. Ensure all four cylinders are within 20% of each other | ||
| + | # Perform Wet Test. Squirt a bit motor oil into each spark plug hole. Spin engine a couple of revolutions. Check compression on each cylinder. | ||
| + | #* If the compression reading doesn't rise with the wet test, it's all good. | ||
| + | #* If it does rise, the rings are bad. | ||
| + | |||
| + | Details: | ||
| + | # Put transmission in nuetral and block the wheels | ||
| + | # Remove the spark plugs | ||
| + | # Disconnect distributor wire | ||
| + | # Block throtle open | ||
| + | # Connect [[Tools|compression tester]] (according to its directions) to spark plug hole for cylinder #1 | ||
| + | # Crank engine 3-4 revolutions (or until the gauge reading won't go any higher) | ||
| + | |||
| + | As a rough guide, each cylinder should be between 110-150 lbs pressure (depending on your gauge, etc). Some variation is OK, but all cylinders should be within 25 lbs of each other. '''If one cylinder is 90 psi or below''' suspect bad rings or a burnt valve. | ||
| + | |||
| + | = Factory Service Manual = | ||
| + | The 1973 B110 [[Factory Service Manual]] says: | ||
| + | <blockquote><hr>'''Checking Engine Compression''' | ||
| + | |||
| + | ''Compression pressure test'' | ||
| + | <br>NOTE: To test cylinder pressure, remove all spark plugs and hold tester fitting tightly in spark plug hole of a cylinder. | ||
| + | The tester is used to determine whether cylinder can hold compression, or whether there is excessive leakage past rings, etc. | ||
| + | |||
| + | Test compression with engine warm, all spark plugs removed and throttle and choke valve opened. No cylinder compression should be less than 80% of highest cylinder's. Excessive variation between cylinders, accompanied by low speed missing of the cylinder, usually indicates a valve not properly seating or a broken piston ring. Low pressures, even though uniform, may indicate worn rings. This may be accompanied by excessive oil consumption. | ||
| + | |||
| + | '''Test conclusion''' | ||
| + | <br>If one or more cylinders read low, inject about one tablespoon of enigne oil on top of the piston in low readubg cylinders through spark plug hole. Repeat compression check on these cylinders. | ||
| + | # If compression improves considerably, piston rings are defective. | ||
| + | # If compression does not improve, valves are sticking or seating improperly | ||
| + | # If two adjacent cylinders indicate low compression and injecting oil on pistons does not increase compression, the cause may be a cylinder [[Head Gasket|head gasket]] leak between the cylinders. Engine oil and coolant in cylinder could result from this problem. | ||
| + | |||
| + | Combustion pressure | ||
| + | 12.5 to 14.5 kg/cm² | ||
| + | (178 to 206 psi) at 350 rpm | ||
| + | <hr></blockquote>Reference: Section ET (Emission Control and Tune-up), 1973 | ||
| + | |||
| + | [[Category:Emission Control And Tune-Up]] | ||
Revision as of 04:29, 15 January 2012
A compression test will check the condition of the engine cylinder sealing -- how well the compression rings are working. The exact compression reading you get will vary depending. Among many variables, the reading depends upon your camshaft, static compression ration, and (most importantly) the accuracy of the gauge. Some guages will read higher or lower than others. What is important is that the reading of each cylinder is close to that of the others.
Overview
To perform an Engine compression test:
- Perform Dry Test. Ensure all four cylinders are within 20% of each other
- Perform Wet Test. Squirt a bit motor oil into each spark plug hole. Spin engine a couple of revolutions. Check compression on each cylinder.
- If the compression reading doesn't rise with the wet test, it's all good.
- If it does rise, the rings are bad.
Details:
- Put transmission in nuetral and block the wheels
- Remove the spark plugs
- Disconnect distributor wire
- Block throtle open
- Connect compression tester (according to its directions) to spark plug hole for cylinder #1
- Crank engine 3-4 revolutions (or until the gauge reading won't go any higher)
As a rough guide, each cylinder should be between 110-150 lbs pressure (depending on your gauge, etc). Some variation is OK, but all cylinders should be within 25 lbs of each other. If one cylinder is 90 psi or below suspect bad rings or a burnt valve.
Factory Service Manual
The 1973 B110 Factory Service Manual says:
Reference: Section ET (Emission Control and Tune-up), 1973
Checking Engine CompressionCompression pressure test
NOTE: To test cylinder pressure, remove all spark plugs and hold tester fitting tightly in spark plug hole of a cylinder. The tester is used to determine whether cylinder can hold compression, or whether there is excessive leakage past rings, etc.Test compression with engine warm, all spark plugs removed and throttle and choke valve opened. No cylinder compression should be less than 80% of highest cylinder's. Excessive variation between cylinders, accompanied by low speed missing of the cylinder, usually indicates a valve not properly seating or a broken piston ring. Low pressures, even though uniform, may indicate worn rings. This may be accompanied by excessive oil consumption.
Test conclusion
If one or more cylinders read low, inject about one tablespoon of enigne oil on top of the piston in low readubg cylinders through spark plug hole. Repeat compression check on these cylinders.
- If compression improves considerably, piston rings are defective.
- If compression does not improve, valves are sticking or seating improperly
- If two adjacent cylinders indicate low compression and injecting oil on pistons does not increase compression, the cause may be a cylinder head gasket leak between the cylinders. Engine oil and coolant in cylinder could result from this problem.
Combustion pressure 12.5 to 14.5 kg/cm² (178 to 206 psi) at 350 rpm