Zero Knievel Posted November 27, 2010 Share Posted November 27, 2010 Did a cylinder head compression test on the XX. Yes, the manual (and test kit) says to test with a warm motor. Not possible. Tank is off and bike is where exhaust can't vent. Never mind that by the time I got the tank off, drained it, pulled off the airbox, got the plugs out, etc. the motor would be cold again at the speed I work. So, the manual calls for (on a warmed-up motor) 185 psi. No upper or lower end...just that number. This is the result I got on a COLD motor. Tested each cylinder twice...just to be sure there were no loose connections costing me PSI. LEFT -------> RIGHT of motor 1. 170-175 psi (needle was between these two readings) 2. 175-180 psi (needle was between these two readings) 3. 160 psi 4. 165 psi It is my hope that a cold motor costs PSI when doing this test, but I don't know that. Anyone more experienced with stuff like this know what the actual numbers would likely have been on a warmed-up motor? Also, is lower than spec compression something a valve clearance adjustment would correct? I don't think it would. Quote Link to comment Share on other sites More sharing options...
ironmike Posted November 27, 2010 Share Posted November 27, 2010 Was the bike level (centerstand) or tilted (sidestand)? Pooling residual oil (rings/cylinder wall/valve seals) can impact the readings. As I recall, the reason a warm engine (normal operating temp) was recommended was so that the oil had been thoroughly cycled, and the heat retained in the rings/cylinder walls assured a good (or at least the best possible) seal. Compression readings would then reflect conditions as close to "running" as possible. Then we'd let the engine cool to the ambient temp and conduct a leak down test (compressed air). Evaluating the results of both tests could give us the best data, a sort of conceptual x-ray - short of a complete tear down and getting busy with the micrometers. I wouldn't be overly concerned with a cold compression differential of approx 11%... assuming you feel the bike is running okay. You could most likely find that differential significantly diminishing with a warm motor. Quote Link to comment Share on other sites More sharing options...
blackhawkxx Posted November 27, 2010 Share Posted November 27, 2010 Why are you testing it? Quote Link to comment Share on other sites More sharing options...
Zero Knievel Posted November 27, 2010 Author Share Posted November 27, 2010 I wouldn't be overly concerned with a cold compression differential of approx 11%... assuming you feel the bike is running okay. You could most likely find that differential significantly diminishing with a warm motor. Bike was on the centerstand. Had not been run in a while (couple weeks at least). Bike seems to run fine. Only testing compression because I really need to check the valve clearances (70K) and since I have it down to the plugs, why not? Adding 11% to the lowest value would put the test near spec....probably nothing to worry about. Quote Link to comment Share on other sites More sharing options...
cbrxxquad Posted November 27, 2010 Share Posted November 27, 2010 I WOULD SQUIRT SOME OIL IN AND DO IT AGAIN. Tells rings. So if they are the problem will show the difference. As in cold and piston shrunk. Make sure that you have the throttle open. Quote Link to comment Share on other sites More sharing options...
Zero Knievel Posted November 28, 2010 Author Share Posted November 28, 2010 I WOULD SQUIRT SOME OIL IN AND DO IT AGAIN. Tells rings. So if they are the problem will show the difference. As in cold and piston shrunk. Make sure that you have the throttle open. Thanks. I'll try that. Didn't have a way to "squirt" so I used a funnel and tube to dribble a little bit of oil down the plug hole. Tested only the last two...which shot up over 250 in a few cranks. Not sure if that makes a better result or not. Quote Link to comment Share on other sites More sharing options...
cbrxxquad Posted November 29, 2010 Share Posted November 29, 2010 Yah might have be a little to much...LOL. Quote Link to comment Share on other sites More sharing options...
Zero Knievel Posted November 29, 2010 Author Share Posted November 29, 2010 Yah might have be a little to much...LOL. Try again tomorrow? Dribble and wait an hour? Quote Link to comment Share on other sites More sharing options...
jon haney Posted November 29, 2010 Share Posted November 29, 2010 Yah might have be a little to much...LOL. Try again tomorrow? Dribble and wait an hour? I concur with Stan, but I wouldn't bother putting in any more oil. Just test it again. Quote Link to comment Share on other sites More sharing options...
cbrxxquad Posted November 30, 2010 Share Posted November 30, 2010 Yah might have be a little to much...LOL. Try again tomorrow? Dribble and wait an hour? I concur with Stan, but I wouldn't bother putting in any more oil. Just test it again. Is it ok to +1 yourself... Quote Link to comment Share on other sites More sharing options...
jon haney Posted November 30, 2010 Share Posted November 30, 2010 Yah might have be a little to much...LOL. Try again tomorrow? Dribble and wait an hour? I concur with Stan, but I wouldn't bother putting in any more oil. Just test it again. Is it ok to +1 yourself... Well, only if you're absolutely sure. Quote Link to comment Share on other sites More sharing options...
cbrxxquad Posted December 1, 2010 Share Posted December 1, 2010 Yah might have be a little to much...LOL. Try again tomorrow? Dribble and wait an hour? I concur with Stan, but I wouldn't bother putting in any more oil. Just test it again. Is it ok to +1 yourself... Well, only if you're absolutely sure. Well now that I have slept on it...I think that I have done this and spun the motor with the plugs out to get the excess out, and blew my hat off and took a while to clean my glasses, and hair..of the oil.. Quote Link to comment Share on other sites More sharing options...
Zero Knievel Posted December 1, 2010 Author Share Posted December 1, 2010 Checked again today (without adding more oil). Worst cylinder was still pumping out 250 psi+ after a few seconds of cranking. Quote Link to comment Share on other sites More sharing options...
jon haney Posted December 2, 2010 Share Posted December 2, 2010 Checked again today (without adding more oil). Worst cylinder was still pumping out 250 psi+ after a few seconds of cranking. There is something wrong with your pistons and probably your head. Send them to me and I will send you some replacements that are sure to yield smaller numbers. Seriously, have you ever had the bike on a dyno? I would love to know the numbers. Have you had the bike since new? It sounds like someone has bumped the compression a bit. Quote Link to comment Share on other sites More sharing options...
cbrxxquad Posted December 2, 2010 Share Posted December 2, 2010 Na I am thinking it has to much oil in it. And can't get out. Taking up compressed volume. A tea spoon of oil would yield those numbers. Now getting it out, well that can be fun. Cranking with the plugs out will get some, but not enough. Another fluid would work if it mixed,,,and did not catch fire, when you spin it to blow it out, and then evaporated..like gas, or alcohol. Or run it to burn it. But, that is going to be some work, to get back to the testing point, and put some DROPS in it this time.. Sorry, I should have been more clear..My bad. Quote Link to comment Share on other sites More sharing options...
Zero Knievel Posted December 2, 2010 Author Share Posted December 2, 2010 Or run it to burn it. But, that is going to be some work, to get back to the testing point, and put some DROPS in it this time.. Sorry, I should have been more clear..My bad. Well, if you think drops when you say "spray", I have to wonder.... Honestly, I don't know why Honda doesn't give a range. Is 180 the "minimum?" Is there a maximum? Nothing in the manual. Quote Link to comment Share on other sites More sharing options...
cbrxxquad Posted December 2, 2010 Share Posted December 2, 2010 Or run it to burn it. But, that is going to be some work, to get back to the testing point, and put some DROPS in it this time.. Sorry, I should have been more clear..My bad. Well, if you think drops when you say "spray", I have to wonder.... Honestly, I don't know why Honda doesn't give a range. Is 180 the "minimum?" Is there a maximum? Nothing in the manual. some give a acceptable %. I do a ratio calc with the local baro pressure and compression ratio. I am at 3000 foot and normal baro is 13.2, so 10 to 1 would be 132# 12 to 1 would be 158.4# 180 would be 13.63 to one for me. sea level is 14.65, so 12.28 at 180 Quote Link to comment Share on other sites More sharing options...
tomek Posted December 3, 2010 Share Posted December 3, 2010 some give a acceptable %. I do a ratio calc with the local baro pressure and compression ratio. I am at 3000 foot and normal baro is 13.2, so 10 to 1 would be 132# 12 to 1 would be 158.4# 180 would be 13.63 to one for me. sea level is 14.65, so 12.28 at 180 Sorry, but that is rather unacceptable way of thinking.How about couple of rules of thermodynamics ?. Temperature of the gas increases when is compressed,so real pressure when cranking is higher then what would you get from simply comparing geometry,plus there is influence of intake valve closing past BDC. I`m looking at R1 specs,12.4 CR,fairly long duration cams and standard cranking pressure is 210 psi. You would get "your" numbers if the gas,air in this case, could be cooled down on the compression stroke so there would be no temp increase,but in reality it does not work like that. Quote Link to comment Share on other sites More sharing options...
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