---------------------------------------------------------- RotaxEngines-List Digest Archive --- Total Messages Posted Sat 08/08/09: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:50 AM - loss of compression (Catz631@aol.com) 2. 07:12 AM - Re: loss of compression (Roger Lee) 3. 12:22 PM - Worn piston ring grooves (rparigor@suffolk.lib.ny.us) 4. 07:52 PM - Re: loss of compression (dashwood) ________________________________ Message 1 _____________________________________ Time: 05:50:18 AM PST US From: Catz631@aol.com Subject: RotaxEngines-List: loss of compression Well, it has finally happened to me. I have read about this problem happening to a few members and now I witnessed it. My Kitfox had not flown in about two weeks so I decided to fly it yesterday. I checked the oil quantity and of course it was below the dipstick (as usually happens when the aircraft sits for a while) I started turning the prop thru its normal ritual when I noticed one of the cylinders had no compression. Great, now what do I do. Well, the tank had not "burped " so I continued turning the prop and eventually the compression came back on the one cylinder and I flew the aircraft. The engine performed fine. I am assuming I had a stuck valve and it "unstuck" itself. I have been using 87 auto fuel with no alcohol. No avgas has been in the engine. The 912 UL has 210 hrs since new. The only thing I have done differently recently (I know this is sacrilege) is added Marvel to the fuel, along with fuel stabilizer. I have read and talked to people that have had this problem in the 912 and they have indicated that Marvel seemed to help with sticking valves and that is why I started adding it to the fuel. I used it in my Pacer and prior aircraft with no problems. I have had problems in the past with sticking valves until I used the Marvel (specifically a Cessna 120 which ended up with a stuck valve and bent pushrod) My plan of attack now, is to try and rotate the prop every day whether I fly or not in order to move the offending valve. If this happens again and the compression loss does not "fix itself" should I run the engine or not? Did the addition of Marvel loosen carbon sticking it in the valve guide? Should I not use it? I personally think it probably had no effect at all on the valve sticking. Any ideas would be greatly appreciated. I know this has happened quite a few times to other guys with there 912's. My oil temp has been running about 190-200 in cruise and coolant temp about 185. Dick Maddux Kitfox 4 912 UL Milton,Fl **************A Good Credit Score is 700 or Above. See yours in just 2 easy steps! =JulystepsfooterNO115) ________________________________ Message 2 _____________________________________ Time: 07:12:32 AM PST US Subject: RotaxEngines-List: Re: loss of compression From: "Roger Lee" Hi Dick, Why do you think you have a stuck valve? Many Rotax engines will feel less compression or none at all when they have sat a while and or they are cold. (I have experienced the same thing. Run the engine like you normally would up to operating temps and then after that see if it feels the same. My guess it will be back to normal. If the plane has sat a while a lot of the oil has drained away from the areas that help seal some of that compression, plus the cylinder walls and pistons are not at their optimal diameter because they are cold and different metals. Go taxi it around or just park it and run it up to 4000 rpm on the ground to temp. bet it goes back to normal. I know some people swear by Marvel Mystery Oil and it may not cause an issue, but it may not help either. No one really knows in a Rotax. We don't know for sure if it may have a odd burn with one of the engine oils or leave a burnt deposit where you really don't want it. We just don't know for sure. 5 million Rotax's running out there and the majority don't use Marvel Mystery oil and they have never had any issues and some are in the 3000 hr range. I'm not saying don't use it, but more or less, why? Sticky valves aren't very common and is usually caused by something we did to the engine or didn't do. Using a good fuel has cleaners already in them. -------- Roger Lee Tucson, Az. Light Sport Repairman - Maintenance Rated Rotax Service Center 520-574-1080 Read this topic online here: http://forums.matronics.com/viewtopic.php?p=256637#256637 ________________________________ Message 3 _____________________________________ Time: 12:22:13 PM PST US Subject: RotaxEngines-List: Worn piston ring grooves From: rparigor@suffolk.lib.ny.us I was looking at O-300 Continential torn apart at 600 hours since major with brand new Superior cylinders and pistonswith low compression and cracked crankcase. Anyway 2 pistons had worn piston ring groves where the portion near the end gap of the rings was about twice the thickness of the rings??? Anyone ever have such a problem with a Rotax 91X? Anyone know what would cause such wear? (perhaps wrong choke?) Ron Parigoris ________________________________ Message 4 _____________________________________ Time: 07:52:41 PM PST US Subject: RotaxEngines-List: Re: loss of compression From: "dashwood" I may not be understanding your plane but if i had no oil on the dipstick i would add some first before hand prop to ensure i didn't just pump air into the system from an empty reservoir. ???? 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