Compression
#1
09-18-2012, 10:44 PM
Join Date: Jul 2012
Location: Anchorage
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#2
09-19-2012, 07:35 AM
The Factory Service Manual 99484-78 says that at less then 120 psi the top end should be re-built. We usually leave that for a Winter project if the bike is running reasonably well. A little smoke at start-up is not a big deal.
Mine are at 150 and have been consistant since the last top end about 12000 miles ago [January this year]. In the past i have had 160 to 180 after a fresh top end.
In the following procedure it is very important that the engine be at full operating temperature and that the throttle be fully open during cranking ...
Cylinder Compression And Leakage Tests
A compression test should be done as part of each tuneup. Record the results and follow any changes over time.
A cylinder leakage test should be done any time you are considering taking down the top end. This test gives you useful information regarding what you should look for when you have it apart.
Each of these requires a tester which you can buy at an auto parts store. A compression tester could be found for about $40.00 more or less, and a clyinder leakage tester for somewhat more than that amount. With the cylinder leakage tester you will also need a small air compressor. Should be able to find a small sausage style for under $100.00.
Use these tools once and they have paid for themselves, compared to paying $50.00 to $100.00 per hour at a shop. Buy a slightly larger air compressor [look for about 5 CFM @ 90 PSI] and you will be able to use it with air tools.
Compression Test
1. Ride the bike to get the engine to get it up to operating temperature
2. Disconnect and remove both spark plugs; insert them into the leads and place them on the cylinder heads for grounding
3. Screw the compression tester into the spark plug hole for either of the cylinders
4. Hold the throttle open, and ensure the choke plate is also open [choke **** pushed in]
5. Crank the engine through several rotations until there is no further increase in reading at the tester gauge
6. Record the final reading
7. Repeat for the other cylinder
The difference between the two readings should not be more than 10 psi. A low reading on one cylinder indicates possible valve or ring damage to that cylinder. To determine which, pour about 1/2 oz of oil into that cylinder through the spark plug hole and repeat the test. If the reading returns to normal then valves are good, rings may be defective. If compression does not return to normal then valves may require service.
Cylinder Leakage Test
This test will tell you what to look for at the top end tear down: worn exhaust valves, worn intake valves, leaky head gaskets, or worn rings.
This test is usually done immediately following a compression test. So the engine is at or close to normal operating temperature, and the spark plugs have been removed.
1. Remove the pushrods to ensure that the valves are closed.
2. Set the cylinder to be tested at or near top dead center [TDC] as this is the wear area for the rings ...
a] rear wheel off the ground, shift to 2nd gear, rotate wheel until it clicks, repeat until you get to 4th gear. Now by rotating the rear wheel you are rotating the engine. Almost impossible with the plugs in; very difficult in lower gears. For the following it helps to have either a shop assistant or a wide "wingspan".
b] you can see in thru the spark plug hole, especially with a flash light. You can also try inserting something soft like a pencil and watch it rise and fall as you rotate the engine with the back wheel; but be careful it does not break or get stuck! You will have to hang on to the pencil with left hand while rotating the rear wheel with the right.
3. Turn on the compressor, connect the gauge to the air pressure, and adjust the gauge
4. Thread the adapter into the spark plug hole and attach to the gauge
5. The gauge now shows the amount of leakage
6. Listen at each exhaust pipe. Excessive hissing here indicates the respective exhaust valve is not sealing
7. Listen at the A/C intake. Excessive hissing here indicates intake valve[s] not sealing
8. Listen at the timing plug hole. Excessive hissing here indicates the rings are not sealing
9. Listen around the cylinder/head connection. Excessive hissing here indicates the respective head gasket is not sealing
Notes
A mechanics stethoscope [with the probe removed for this test] makes a good listening device, as does a length of oil line hose.
Greater leakage results in a sound of lower pitch.
There will always be some leakage, especially past the rings.
Mine are at 150 and have been consistant since the last top end about 12000 miles ago [January this year]. In the past i have had 160 to 180 after a fresh top end.
In the following procedure it is very important that the engine be at full operating temperature and that the throttle be fully open during cranking ...
Cylinder Compression And Leakage Tests
A compression test should be done as part of each tuneup. Record the results and follow any changes over time.
A cylinder leakage test should be done any time you are considering taking down the top end. This test gives you useful information regarding what you should look for when you have it apart.
Each of these requires a tester which you can buy at an auto parts store. A compression tester could be found for about $40.00 more or less, and a clyinder leakage tester for somewhat more than that amount. With the cylinder leakage tester you will also need a small air compressor. Should be able to find a small sausage style for under $100.00.
Use these tools once and they have paid for themselves, compared to paying $50.00 to $100.00 per hour at a shop. Buy a slightly larger air compressor [look for about 5 CFM @ 90 PSI] and you will be able to use it with air tools.
Compression Test
1. Ride the bike to get the engine to get it up to operating temperature
2. Disconnect and remove both spark plugs; insert them into the leads and place them on the cylinder heads for grounding
3. Screw the compression tester into the spark plug hole for either of the cylinders
4. Hold the throttle open, and ensure the choke plate is also open [choke **** pushed in]
5. Crank the engine through several rotations until there is no further increase in reading at the tester gauge
6. Record the final reading
7. Repeat for the other cylinder
The difference between the two readings should not be more than 10 psi. A low reading on one cylinder indicates possible valve or ring damage to that cylinder. To determine which, pour about 1/2 oz of oil into that cylinder through the spark plug hole and repeat the test. If the reading returns to normal then valves are good, rings may be defective. If compression does not return to normal then valves may require service.
Cylinder Leakage Test
This test will tell you what to look for at the top end tear down: worn exhaust valves, worn intake valves, leaky head gaskets, or worn rings.
This test is usually done immediately following a compression test. So the engine is at or close to normal operating temperature, and the spark plugs have been removed.
1. Remove the pushrods to ensure that the valves are closed.
2. Set the cylinder to be tested at or near top dead center [TDC] as this is the wear area for the rings ...
a] rear wheel off the ground, shift to 2nd gear, rotate wheel until it clicks, repeat until you get to 4th gear. Now by rotating the rear wheel you are rotating the engine. Almost impossible with the plugs in; very difficult in lower gears. For the following it helps to have either a shop assistant or a wide "wingspan".
b] you can see in thru the spark plug hole, especially with a flash light. You can also try inserting something soft like a pencil and watch it rise and fall as you rotate the engine with the back wheel; but be careful it does not break or get stuck! You will have to hang on to the pencil with left hand while rotating the rear wheel with the right.
3. Turn on the compressor, connect the gauge to the air pressure, and adjust the gauge
4. Thread the adapter into the spark plug hole and attach to the gauge
5. The gauge now shows the amount of leakage
6. Listen at each exhaust pipe. Excessive hissing here indicates the respective exhaust valve is not sealing
7. Listen at the A/C intake. Excessive hissing here indicates intake valve[s] not sealing
8. Listen at the timing plug hole. Excessive hissing here indicates the rings are not sealing
9. Listen around the cylinder/head connection. Excessive hissing here indicates the respective head gasket is not sealing
Notes
A mechanics stethoscope [with the probe removed for this test] makes a good listening device, as does a length of oil line hose.
Greater leakage results in a sound of lower pitch.
There will always be some leakage, especially past the rings.
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