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--- techtalk:ref:svcproc20 [2019/10/16 22:18]
ixl2relax [Test Each Cylinder for Compression]
+++ techtalk:ref:svcproc20 [2024/01/21 23:17]
hippysmack
@@ Line 2: / Line 2: @@
 ====== REF: Service Procedures 20 ======
 ====== 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 https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/29105-cylinder-compression-and-leakage-tests-for-your-ironhead?t=48311)) \\
   * The compression tester has a one-way valve in it's hose, allowing it to see the pressure of the compression stroke\\ but not relieve it on the other strokes. Additional strokes that produce higher pressures will increase the\\ reading of the gauge.
-  * Always look for a compression tester that has it's check valve as near to the chamber as possible. Otherwise, you're\\ adding the volume of the hose (up to the check valve) to the chamber volume which causes the compression reading\\ to be lower, because the piston is trying to fill that hose space as well as the chamber. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=26208&page=2))
+  * Always look for a compression tester that has it's check valve as near to the chamber as possible. Otherwise, you're\\ adding the volume of the hose (up to the check valve) to the chamber volume which causes the compression reading\\ to be lower, because the piston is trying to fill that hose space as well as the chamber. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/15672-four-strokes-and-leak-down-compression-tests-how-they-work/page2?t=26208&page=2))
   * A proper compression test should be done with the engine close to normal operating temperature, when possible. ((79-85 HD XL/XR FSM pg 3-10))
 ===== Compression Test vs Leak-Down Test =====
+  * These are both fancy names for a deceptively simple process (installing an air gauge in the spark plug hole and noting the results). ((GOTWA of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/15672-four-strokes-and-leak-down-compression-tests-how-they-work?t=26208))
-  * These are both fancy names for a deceptively simple process (installing an air gauge in the spark plug hole and noting the results). ((GOTWA of the XLFORUM http://xlforum.net/forums/showthread.php?t=26208))
   * A compression test checks the cylinder's maximum pressure ability. A low reading reflects poor sealing of the chamber.
-    * 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 https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/15672-four-strokes-and-leak-down-compression-tests-how-they-work/page2?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.
     * See also [[techtalk:ref:svcproc21|Performing a Leak-Down Test]] in the REF section of the Sportsterpedia.
 ====== Test Each Cylinder for Compression ======
@@ Line 91: / Line 88: @@
 **Pics of the Damage**: ((Photos by sep69 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1567509&page=2))
 |{{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)) \\

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