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techtalk:ref:svcproc20 [2018/08/30 20:39] hippysmack [Compression Test Results from XLFORUM Members] |
techtalk:ref:svcproc20 [2020/03/02 05:55] hippysmack [Compression Calculator] |
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[[:techtalk:menu|{{ :techtalk:gototechnicalmenu.jpg|}}]] | [[:techtalk:menu|{{ :techtalk:gototechnicalmenu.jpg|}}]] | ||
- | ====== REF: Troubleshooting - Engine - 03 ====== | + | ====== REF: Service Procedures 20 ====== |
====== Cylinder Compression Test ====== | ====== Cylinder Compression Test ====== | ||
A compression test should be done as part of each tune-up. Record the results and follow any changes over time. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) \\ | A compression test should be done as part of each tune-up. Record the results and follow any changes over time. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) \\ | ||
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* Generally if a compression test shows anything suspect, the next step is a leak down test. ((milmat1 of the XLFORUM http://xlforum.net/forums/showthread.php?t=26208&page=2)) | * Generally if a compression test shows anything suspect, the next step is a leak down test. ((milmat1 of the XLFORUM http://xlforum.net/forums/showthread.php?t=26208&page=2)) | ||
* A leak-down test checks the cylinder's ability to hold pressure (seal) and will reflect where the leak is occuring. | * A leak-down test checks the cylinder's ability to hold pressure (seal) and will reflect where the leak is occuring. | ||
- | * See also [[techtalk:ref:trouble04|Performing a Leak-Down Test]] in the REF section of the Sportsterpedia. | + | * See also [[techtalk:ref:svcproc21|Performing a Leak-Down Test]] in the REF section of the Sportsterpedia. |
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- Ride the bike to get the engine up to operating temperature. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) | - Ride the bike to get the engine up to operating temperature. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) | ||
- Disconnect the power to the coil to prevent it from firing. | - Disconnect the power to the coil to prevent it from firing. | ||
- | * The extra two plugs (on dual plug heads) & wires can remain in place during this test. ((IXL2Relax of the XLFORUM http://xlforum.net/forums/showthread.php?t=2005378)) | + | * The extra two plugs (on dual plug heads) need to remain in place during this test. ((IXL2Relax of the XLFORUM http://xlforum.net/forums/showthread.php?t=2005378)) |
* If you can't disconnect power to the coil, ground out all the plug wires. | * If you can't disconnect power to the coil, ground out all the plug wires. | ||
- | - Clean the area around the spark plugs and remove them. ((79-85 HD XL/XR FSM pg 3-10)) | + | - Clean the area around the spark plugs __BEFORE__ you remove them. ((79-85 HD XL/XR FSM pg 3-10)) |
* If you haven't disconnected the coil, you can insert the plugs into the plug wires and press the plugs against the cylinder heads for grounding. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) | * If you haven't disconnected the coil, you can insert the plugs into the plug wires and press the plugs against the cylinder heads for grounding. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) | ||
- Connect the compression gauge to the first cylinder. | - Connect the compression gauge to the first cylinder. | ||
- | - Make sure the choke and throttle plate is closed before turning over the engine. | + | - Make sure the **throttle plate is fully open** (and the choke, if present) before turning over the engine. |
- | * If using a CV carb, hold the slide up. ((aswracing http://xlforum.net/forums/showthread.php?t=26208&page=2)) | + | * If using a CV carb, **hold the slide up.** ((aswracing http://xlforum.net/forums/showthread.php?t=26208&page=2)) |
- | * If the cylinder can't freely pull in air, the compression reading will be low. | + | * If the cylinder can't freely pull in air, the compression reading will be low. |
+ | * **Do NOT pull the enrichener knob** - The enrichener is mis-named a choke ('86-'06) but it is not a choke plate. | ||
- Crank the engine continuously through 5-7 compression strokes. (until there is no further increase in reading at the gauge) ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) | - Crank the engine continuously through 5-7 compression strokes. (until there is no further increase in reading at the gauge) ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=48311)) | ||
- Record the readings at the end of the first and last strokes for this cylinder. | - Record the readings at the end of the first and last strokes for this cylinder. | ||
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- Repeat for the second cylinder. | - Repeat for the second cylinder. | ||
- | {{:techtalk:ref:tools:checking_compression_1_by_mathormell.jpg?direct&300|}} ((photo by MatHormell of the XLFORUM http://xlforum.net/forums/showthread.php?t=1976997&page=71)) {{:techtalk:ref:tools:checking_compression_2_by_mathormell.jpg?direct&300|}} ((photo by MatHormell of the XLFORUM http://xlforum.net/forums/showthread.php?t=1976997&page=71)) | + | {{techtalk:ref:svcproc:checking_compression_1_by_mathormell.jpg?direct&300|}} ((photo by MatHormell of the XLFORUM http://xlforum.net/forums/showthread.php?t=1976997&page=71)) {{techtalk:ref:svcproc:checking_compression_2_by_mathormell.jpg?direct&300|}} ((photo by MatHormell of the XLFORUM http://xlforum.net/forums/showthread.php?t=1976997&page=71)) |
====== Interpreting the Readings ====== | ====== Interpreting the Readings ====== | ||
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===== Tracking Your Test Results ===== | ===== Tracking Your Test Results ===== | ||
- | {{:techtalk:ref:trouble:sportsterpedia_compression_test_chart.jpg?direct&600|}} | + | {{techtalk:ref:svcproc:sportsterpedia_compression_test_chart.jpg?direct&600|}} |
\\ | \\ | ||
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**Possible Cause**: \\ | **Possible Cause**: \\ | ||
Piston ring gap too tight upon installation. ((Jörgen)) \\ | Piston ring gap too tight upon installation. ((Jörgen)) \\ | ||
- | **Pics of the Damage**: ((Photos by sep69 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1567509&page=2)) \\ | + | **Full Article**: http://xlforum.net/forums/showthread.php?t=1567509 \\ |
- | **Full Article**: http://xlforum.net/forums/showthread.php?t=1567509 | + | **Pics of the Damage**: ((Photos by sep69 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1567509&page=2)) |
- | |{{:techtalk:ref:trouble:piston_damage_1_by_sep69.jpg?direct&300|}}|{{:techtalk:ref:trouble:piston_damage_2_by_sep69.jpg?direct&300|}}|{{:techtalk:ref:trouble:piston_damage_3_by_sep69.jpg?direct&300|}}| \\ | + | |{{techtalk:ref:svcproc:piston_damage_1_by_sep69.jpg?direct&300|}}|{{techtalk:ref:svcproc:piston_damage_2_by_sep69.jpg?direct&300|}}|{{techtalk:ref:svcproc:piston_damage_3_by_sep69.jpg?direct&300|}}| \\ |
+ | |||
+ | ====== Compression Calculator ====== | ||
+ | Article by aswracing of the XLFORUM ((http://xlforum.net/forums/showthread.php?t=1441757)) and Hammer Performance site. (( http://hammerperf.com/ttcompression.shtml)) \\ | ||
+ | |||
+ | [[http://hammerperf.com/ttcompression.shtml|Click here to download a free copy of the HAMMER PERFORMANCE Compression Calculator]]. \\ | ||
+ | |||
+ | So how much compression can you run with what cams, and still be able to run pump gas? \\ | ||
+ | This question comes up from time to time on the XLFforum. \\ | ||
+ | And unfortunately, the answers tend to either be inaccurate, incomplete, or just downright vague. \\ | ||
+ | |||
+ | The right answer is that you should figure out your corrected compression ratio. \\ | ||
+ | Which is the compression ratio of the motor considering the intake valve close timing. \\ | ||
+ | In a nutshell, as the piston starts the compression stroke, the intake valve is still hanging open. \\ | ||
+ | Until the intake valve closes, no compression will be built. \\ | ||
+ | What corrected compression ratio tells you is what CR you have after the intake valve closes. \\ | ||
+ | This is the number to look at when deciding if your bike is going to run okay on pump gas. \\ | ||
+ | |||
+ | So how do you figure it out? Well, it's not as simple as it sounds at first. \\ | ||
+ | The big end of the rod travels in an arc and the connecting rod is not infinitely long. \\ | ||
+ | So you end up with a non-linear relationship between piston position and crankshaft rotation. \\ | ||
+ | |||
+ | For example, in the first 10 degrees after bottom dead cylinder, the piston barely moves at all. \\ | ||
+ | By comparison, 10 degrees of crank rotation that happens after the piston is halfway up causes a relatively large amount of piston movement. \\ | ||
+ | It's basically a geometry problem. | ||
+ | |||
+ | To solve the problem, you need to dust off your trigonometry textbook and make right triangles out of it. \\ | ||
+ | Or, you could take the easy way and just download the calculator. \\ | ||
+ | Store the file somewhere on your hard drive where it's easy to find, and then double click on it to execute. \\ | ||
+ | The program is very easy to use, and it will give progressively more info as you enter more data: \\ | ||
+ | * For just displacement, enter the bore and stroke. | ||
+ | * To also get static compression ratio, enter the piston dome, chamber size, piston height, and gasket specs. | ||
+ | * To also get corrected compression ratio, enter the intake close point (.053 lift crankshaft degrees) and connecting rod length. | ||
+ | |||
+ | This program calculates both static and corrected compression ratio. What's the difference? ((http://hammerperf.com/ttcompression.shtml)) \\ | ||
+ | The static compression ratio takes the full compression stroke into account. This is the standard way of doing it. \\ | ||
+ | The corrected compression ratio, however, only counts the portion of the compression stroke after the intake valve closes. \\ | ||
+ | |||
+ | Corrected compression ratios of around 9.2:1 are considered the max you can run on U.S. pump gas, with a reasonably turbulent chamber. \\ | ||
+ | Since no compression builds until after the intake valve closes, \\ | ||
+ | It's the corrected compression ratio that gives the best indication of how pump gas friendly your motor will be. \\ | ||
+ | Premium pump gas in the U.S. will generally tolerate corrected compression ratios of somewhere between 8.8:1 and 9.3:1. \\ | ||
+ | With a poor chamber that has little turbulence ( i.e hemi chambers and no squish band), stay on the low end of that range, maybe even lower. \\ | ||
+ | With a good, turbulent chamber (think squish bands), you can run more toward the high end of the range. \\ | ||
+ | With good chamber turbulence and dual plugs, you can even run it higher, up to 9.5:1 is not unusual. \\ | ||
+ | |||
+ | This is a free tool, independently developed in-house by Hammer Performance ((aswracing of the XLForum)). \\ | ||
+ | Feel free to use it and distribute it as you please. \\ | ||
+ | It's virus-free. \\ | ||
+ | It collects no information about you or phones, home or anything like that. \\ | ||
+ | All it does is perform the calculations and give you the answer. \\ | ||
+ | |||
+ | Note that results given by this program are intended as a guideline only. \\ | ||
+ | HAMMER PERFORMANCE assumes no responsibility for what you do with the information presented. \\ | ||
+ | |||
+ | {{:techtalk:ref:svcproc:compression_calculator_screeenshot_1_by_aswracing.jpg?direct&400|}} ((screenshot by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1441757)) {{:techtalk:ref:svcproc:compression_calculator_screeenshot_2_by_aswracing.jpg?direct&400|}} ((screenshot by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1441757)) \\ | ||
+ | |||