Tinus89 Posted October 6, 2017 Author Share Posted October 6, 2017 Did you have the throttle wide open during the comp test? Was the engine at operating temp? 108psi is very low and 130 isnt exactly up there either. Of equal importance is also how the engine makes its final compression numbers. A good engine should give you the maximum reading in 2 or maybe 3 steps, if it creeps up there in 4 or more steps thats not great. Pleased you found the rattling ball cause....great info that. Ciao I may have rushed this one a little bit. Engine was cold when I did the test. I was holding the gauge, not the one starting, so I'm not sure whether the throttle was WO when I did them... Should the engine be warm? I've never heard about that. Throttle should be WO indeed, forgot to check that. As I mentioned a while back, it's time for a leak down test. . I'd love to see a tutorial for that! Pressure, hot or cold engine, how to keep the engine from spinning due to the pressure... Link to comment Share on other sites More sharing options...
coreytrevor Posted October 6, 2017 Share Posted October 6, 2017 I'd love to see a tutorial for that! Pressure, hot or cold engine, how to keep the engine from spinning due to the pressure... That's always a problem, potentially dangerous. On the Guzzi, I would pull the rocker arms, then do the leakdown test at BDC. 1 Link to comment Share on other sites More sharing options...
Scud Posted October 6, 2017 Share Posted October 6, 2017 Seems like a lot of extra work to pull the arms for that test. I did this test recently, but at TDC following these steps: raise the rear wheel (using factory stand) put bike in gear, turn rear wheel to find TDC (spark plugs out). lower bike (still in gear) then pressurize cylinder with tester The wheel on the ground eliminates the risk of piston movement. You don't even have to take the valve covers off to do it this way - because if piston is at top, you either get some pressure (valves closed) or no pressure (valves open). You can put light pressure into the cylinder at step 2 above to verity that it's at TDC. If you guessed wrong, spin the wheel again. There are plenty of videos of leakdown tests on YouTube. If you buy a leak down tester, it will probably come with useful instructions. I got the OTC Cylinder Leakage Tester. https://www.amazon.com/gp/product/B0030EVL60/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 Link to comment Share on other sites More sharing options...
Chuck Posted October 6, 2017 Share Posted October 6, 2017 If the piston is exactly at TDC it wont move. Hissing at throttle body, intake valve.exhaust valve will hiss at the muffler. Rings at crankcase breather. Sorry for the cryptic posts, I'm pecking on a tablet. Link to comment Share on other sites More sharing options...
68C Posted October 7, 2017 Share Posted October 7, 2017 I agree with all you are saying Chuck as far as diagnostics goes. One must be carefull however, it is a routine operation on a piston aircraft engine with a strong chap holding the prop, much more awkward on a motorcycle engine. as it is difficult to hold the engine at tdc, if it moves just a few degrees either way there will be a lot of force kicking the crank round. Typically 90psi on a 3 inch piston is around 640 lbs pushing down on the piston! Link to comment Share on other sites More sharing options...
Chuck Posted October 7, 2017 Share Posted October 7, 2017 I agree with all you are saying Chuck as far as diagnostics goes. One must be carefull however, it is a routine operation on a piston aircraft engine with a strong chap holding the prop, much more awkward on a motorcycle engine. as it is difficult to hold the engine at tdc, if it moves just a few degrees either way there will be a lot of force kicking the crank round. Typically 90psi on a 3 inch piston is around 640 lbs pushing down on the piston! True..but all that happens isthe piston goes down. Crank it around to TDC ready to fire and try again. Leak down tests are done at 80 psi. A good used cylinder will be about 5 % leakage. Over 10 % is suspect. Link to comment Share on other sites More sharing options...
coreytrevor Posted October 7, 2017 Share Posted October 7, 2017 I don't think you could hold the crank with the drivetrain and rear wheel if the crank started to turn. There is so much slop and 2 cush drives in the drivetrain. If it started to turn, there is more and more force with each degree of rotation, it's just going to keep going. I agree that if you are EXACTLY at TDC, it shouldn't turn. Just make sure you don't leave a wrench on the crank nut! Link to comment Share on other sites More sharing options...
68C Posted October 7, 2017 Share Posted October 7, 2017 Having reread the topic I think I agree with Coretrevor. "That's always a problem, potentially dangerous. On the Guzzi, I would pull the rocker arms, then do the leakdown test at BDC". It looks like a far safer way to check the valves although may not show a worn bore as that tends to be at the upper end of the stroke. Link to comment Share on other sites More sharing options...
luhbo Posted October 7, 2017 Share Posted October 7, 2017 What is unsafe here? What will happen in case the piston suddenly snaps down? Does anyone have his fingers inside the engine during a leak test? 1 Link to comment Share on other sites More sharing options...
coreytrevor Posted October 7, 2017 Share Posted October 7, 2017 Only unsafe if you are trying to hold the crank from moving. If not, no problem. Link to comment Share on other sites More sharing options...
68C Posted October 7, 2017 Share Posted October 7, 2017 True. Link to comment Share on other sites More sharing options...
Chuck Posted October 8, 2017 Share Posted October 8, 2017 All I can say is it doesn't go down that fast, but don't try to hold it. Put it right on TDC.. I've done it *many* times. Link to comment Share on other sites More sharing options...
Tinus89 Posted October 8, 2017 Author Share Posted October 8, 2017 So I re-did the compression test, this time correctly: warm engine, WO throttle. Values after 3 compressions strokes: Left: 145 PSI Right: 135 PSI I still have to go and find the correct value. Also put my finger on the crankcase vent for a while during running, but she does not seem to build any pressure really. Link to comment Share on other sites More sharing options...
luhbo Posted October 8, 2017 Share Posted October 8, 2017 I opened my first engine after 125.000 km, pistons and sleeves looked nearly as new, alas I didn't measure the ring gaps. I put in new ones while the engine was open. Can't say whether that was due, but I don't think so. In your case I definitely wouldn't change anything. To me the measured values seem reasonable. That's about 10 and 9.3 bar. Geometric compression is about 9,5:1, so 10 isn't bad (compression starts not before the inlet valve has closed). From a Beemer forum: ...Gemessen habe ich bei meiner 1043ccm GS mit ca. 60.000km Laufleistung 9,0 (links) und 9,5 bar (rechts), Motor warm, Gashahn aufgezogen, Stecker vom Zündsteuergerät ab...sollte eigentlich ok sein. ... Could you perhaps post a picture of where you found that rattling valve on your bike? Link to comment Share on other sites More sharing options...
docc Posted October 9, 2017 Share Posted October 9, 2017 Hey all, Took out the check valve, ran the engine: silence. The rattle was the little ball jumping up and down on the crankcase pressure. I looked back at the 1999-2001 parts diagram, and no "check valve" ball. Tinus89, how about a brief video of how she runs and idles without this thing? Photos of what you found and where? Are we thinking it was fitted between the [metal] "breather pipe" #14 and the [rubber] "breather pipe" #18? Link to comment Share on other sites More sharing options...
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