timing issues
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timing issues
whats up y'all, been awhile since i been on here, but since i always got some good advice, i figured this is the spot. first off, i have a 1975 xlh, bored out 20 over, it has a mallory dual fire ignition. i wrecked it last year, got her running again, and rode from tn. to md., broke down half way. believe it or not i had to put it in the back of a ford escort. anyways, i checked the ignition and somehow my wires got cut by the rotor, i replaced it with a new one and got her fired, but it started spitting fire out of the front cylinder, replaced o rings on the intake, but now i have low compression, my question is. what should the compression stroke be, the rear ia 75, the front is close but lacking. what is the reccomened comression for the front and back. thanks
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Joined: Mar 2008
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From: texas
wow.i want to see pictures of your bike and that escort.thats funny as hell
-----i know it wasnt funny at the time....still funny...
i would say compression should be between 110 and 150.some may be a little more specific but it will be between that.i think anything below 110 is too low.maybe as low as 100 but that is pretty low.
what is the other cyl reading? also have you adjusted your valves? if you have or havnt i would do it again.if there good and youre stiil getting 75 then you got some engine issues.---i noticed you said somthing about it getting hot...how hot and when in relation to your problems?
-----i know it wasnt funny at the time....still funny...i would say compression should be between 110 and 150.some may be a little more specific but it will be between that.i think anything below 110 is too low.maybe as low as 100 but that is pretty low.
what is the other cyl reading? also have you adjusted your valves? if you have or havnt i would do it again.if there good and youre stiil getting 75 then you got some engine issues.---i noticed you said somthing about it getting hot...how hot and when in relation to your problems?
The manual specifies 120 psi, with no more than 10% difference between the two cylinders. A recently re-built engine may show 170 to 180 psi. Note the two requirements for a correct static compression test: engine must be warmed up and both the choke plate and the throttle plate must be wide open [choke full off, throttle full on]. Here's some notes ...
Cylinder Compression And Leakage Tests
A compression test should be done as part of any 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 any 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. Run the engine to get it up to operating temperature
2. Disconnect and remove both spark plugs
3. Screw the compression tester into the spark plug hole for either of the cylinders
4. Lock the throttle open, and ensure the choke plate is also open
5. Crank the engine through several rotations until there is no further increase in reading at the tester guage
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 dammage 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 teardown: 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. The piston must be positioned such that both the intake and exhaust valves are closed. To accomplish this, set the cylinder to be tested precisely at top dead center [TDC] of the compression stroke, as follows:
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 here to have either a shop assistant or a wide "wingspan".
Keep a thumb pressed on the spark plug hole while rotating the back wheel. On the compression stroke you will definitely feel the air pressure working against your thumb.
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.
2. Turn on the compressor, connect the gauge to the air pressure, and adjust the gauge
3. Thread the adapter into the spark plug hole and into the gauge
4. The gauge now shows the amount of leakage
5. Listen at each exhaust pipe. Excessive hissing here indicates the respective exhaust valve is not sealing
6. Listen at the A/C intake. Excessive hissing here indicates intake valve[s] not sealing
7. Listen at the timing plug hole. Excessive hissing here indicates the rings are not sealing
8. Listen around the cylinder/head connection. Excessive hissing here indicates the respective head gasket is not sealing
Notes
The piston must be positioned so that both valves are closed
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.
There are many variables here [engine temperature, precise piston position, whatever] so the test results will not be consistent from one test to the next.
Cylinder Compression And Leakage Tests
A compression test should be done as part of any 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 any 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. Run the engine to get it up to operating temperature
2. Disconnect and remove both spark plugs
3. Screw the compression tester into the spark plug hole for either of the cylinders
4. Lock the throttle open, and ensure the choke plate is also open
5. Crank the engine through several rotations until there is no further increase in reading at the tester guage
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 dammage 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 teardown: 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. The piston must be positioned such that both the intake and exhaust valves are closed. To accomplish this, set the cylinder to be tested precisely at top dead center [TDC] of the compression stroke, as follows:
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 here to have either a shop assistant or a wide "wingspan".
Keep a thumb pressed on the spark plug hole while rotating the back wheel. On the compression stroke you will definitely feel the air pressure working against your thumb.
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.
2. Turn on the compressor, connect the gauge to the air pressure, and adjust the gauge
3. Thread the adapter into the spark plug hole and into the gauge
4. The gauge now shows the amount of leakage
5. Listen at each exhaust pipe. Excessive hissing here indicates the respective exhaust valve is not sealing
6. Listen at the A/C intake. Excessive hissing here indicates intake valve[s] not sealing
7. Listen at the timing plug hole. Excessive hissing here indicates the rings are not sealing
8. Listen around the cylinder/head connection. Excessive hissing here indicates the respective head gasket is not sealing
Notes
The piston must be positioned so that both valves are closed
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.
There are many variables here [engine temperature, precise piston position, whatever] so the test results will not be consistent from one test to the next.
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