eastmeg2 Posted January 24, 2011 Posted January 24, 2011 Hi Bluey, What about possible oil sludge in the engine or oil lines, that or something else partially blocking one of the lines. Has there ever been a suspect oil filter on the engine or one that went too long between changes. Might be worth removing and flushing out your oil lines and doing another oil and filter change. Actually, just reading your first post again it could be some sludge building up somewhere until a blockage occurs and then the pressure from the oil pump build up enough to flush away the blockage . . . for the time being.
Bluey Posted January 24, 2011 Author Posted January 24, 2011 All oil and filters have been changed within the allotted 100hrly service intervals. Usually services have been performed around the 50 - 60 hr mark. The last service was done at 90hrs. I know many people do services strictly every 50hrs but according to both airborne and rotax that is not necessary if not running on avgas. I am curently at 80hrs since the last service and will now do it to check for particles in the oil filter. I use shell advance vsx 4 oil and only ever use genuine rotax oil filters. It is only my last two services that have gone more than 50hrs. The engine is now at 479hrs. I am beginning to wonder about what possible engine damage may have been done if these oil readings are real????
bones Posted January 24, 2011 Posted January 24, 2011 All oil and filters have been changed within the allotted 100hrly service intervals. Usually services have been performed around the 50 - 60 hr mark. The last service was done at 90hrs. I know many people do services strictly every 50hrs but according to both airborne and rotax that is not necessary if not running on avgas. I am curently at 80hrs since the last service and will now do it to check for particles in the oil filter. I use shell advance vsx 4 oil and only ever use genuine rotax oil filters. It is only my last two services that have gone more than 50hrs. The engine is now at 479hrs. I am beginning to wonder about what possible engine damage may have been done if these oil readings are real???? What is oil like when you change it, my guess would be it is like tar, i do 50 hr services, and the oil is black as the ace of spades at that, i cant believe people who dont do 50hrs services, whats the price of oil and filters, cheap if you have to strip the motor trust me, thats a good 7k worth there. I seriously doubt there be any major trouble from the oil press at start up, though, what i normally do if the motor hasnt been run for a couple of weeks is leave igg switches off and wind it over on the starter for 20-30secs, then flick the switches, and start it. try that and see what happens.
Guest davidh10 Posted January 24, 2011 Posted January 24, 2011 Bluey; You will only need a multimeter to check the timing of the pressure increase at the sender, not some special gauge.
Bluey Posted January 24, 2011 Author Posted January 24, 2011 At oil changes the oil is dark but I have been assured by a number of experienced people as well as airborne themselves that oil changes need only be done every 100hrs. The rotax manual quotes 100hrly services. I have been told that 50hr services are overservicing the engine. I can understand why people do it though. It is an aircraft after all. I was very reluctant to increase the service interval. On another note, a check of my oil filter residue should reveal if any damage is being done to the engine internals and hence confirm whether the pressure issues are a problem or not.
Bluey Posted January 24, 2011 Author Posted January 24, 2011 I forgot to mention that even at the longer service interval, very little oil is consumed by the engine.
Bluey Posted January 24, 2011 Author Posted January 24, 2011 David, where exactly do you hook up the multimeter to get readings? I know one connection (+ve) goes to the VDO sender unit but what about the earth. Exactly where is the earth? (excuse my ignorance).
bones Posted January 24, 2011 Posted January 24, 2011 At oil changes the oil is dark but I have been assured by a number of experienced people as well as airborne themselves that oil changes need only be done every 100hrs. The rotax manual quotes 100hrly services. I have been told that 50hr services are overservicing the engine. I can understand why people do it though. It is an aircraft after all. I was very reluctant to increase the service interval.On another note, a check of my oil filter residue should reveal if any damage is being done to the engine internals and hence confirm whether the pressure issues are a problem or not. I know people who drop the oil/ filter at 25hrs that to me is over serviceing, but damn i know 50 hrs comes around quick when your busy, but its a reason not to get out of bed early one morning out of 5 :)
fly_tornado Posted January 24, 2011 Posted January 24, 2011 David, where exactly do you hook up the multimeter to get readings? I know one connection (+ve) goes to the VDO sender unit but what about the earth. Exactly where is the earth? (excuse my ignorance). the engine block
facthunter Posted January 24, 2011 Posted January 24, 2011 If you are operating under ideal conditions, eg dust free and operating with the oil hot, running to 100 hours would be ok.. Most people don't do this. The darkening of the oil doesn't mean everything. IF the motor is running a bit rich it will darken more. Cutting the filter open is good practice but is mostly an indicator of a larger failure than slightly excess wear. A proper oil analysis would be needed to pick up the finer particles. It is generally suggested that 6 months be the time limit regardless of the hours flown. Short flights in colder climates would be a case for more frequent changes also. Nev
alf jessup Posted January 24, 2011 Posted January 24, 2011 All oil and filters have been changed within the allotted 100hrly service intervals. Usually services have been performed around the 50 - 60 hr mark. The last service was done at 90hrs. I know many people do services strictly every 50hrs but according to both airborne and rotax that is not necessary if not running on avgas. I am curently at 80hrs since the last service and will now do it to check for particles in the oil filter. I use shell advance vsx 4 oil and only ever use genuine rotax oil filters. It is only my last two services that have gone more than 50hrs. The engine is now at 479hrs. I am beginning to wonder about what possible engine damage may have been done if these oil readings are real???? I'm with Bones, Oil is cheap and even though it can go 100hrs why bother as it just means the contaminates the oil has aquired in the 50 hrs just sit there for another 50 doing what they do best. Also 100hrs could take 2 years or more to the average pilot. I have had mine since 287hr and now it has 770hr on it with oil & filter changes every 50 and never had any oil pressure problems other than 1 sender unit crapping itself and then the next one doing it again in a short time. Bluey, I still think your new sender unit might still be half be the problem, whats it hurt buying a spare and putting it on (your only going to do it anyway as they are cheap and nasty VDO units in any case)
Bluey Posted January 25, 2011 Author Posted January 25, 2011 I just picked up an analogue vdo unit and will install it this afternoon to see what is going on. I do more than 200hrs per year so and generally fly for more than 1hr at a time so the oil gets well used during each flight. It doesn't sit around for long between each flight.
Bluey Posted January 25, 2011 Author Posted January 25, 2011 As far as the sender unit is concerned this is with the new sender unit already installed.
Guest davidh10 Posted January 25, 2011 Posted January 25, 2011 David, where exactly do you hook up the multimeter to get readings? I know one connection (+ve) goes to the VDO sender unit but what about the earth. Exactly where is the earth? (excuse my ignorance). You could disconnect the SkyDat connection from the sender and measure resistance of the sender. ie from the sender terminal to ground, which as fly_tornado has said is the engine block (or earthing strap). Keep in mind that if you are using a purchased VDO guage, unless it is designed / calibrated for the specific sender you are using, the reading will not be accurate, but should still give an indication of the presence of pressure. This isn't something I've ever looked into, but I'm sure not all senders have the same resistance to pressure gradient and have different operating ranges depending on the equipment to which they connect. From the "Heavy Maintenance Manual: interpolating from the graph... about 12 ohms at no pressure and 50 ohms at 2 bar, 125 ohms at 6 bar. The relationship is not quite linear.
Guest rocketdriver Posted January 25, 2011 Posted January 25, 2011 Keep in mind that if you are using a purchased VDO guage, unless it is designed / calibrated for the specific sender you are using, the reading will not be accurate, but should still give an indication of the presence of pressure. This isn't something I've ever looked into, but I'm sure not all senders have the same resistance to pressure gradient and have different operating ranges depending on the equipment to which they connect.hi David and others ... I have looked into it and they are all different. I just bought some SPECO engine instruments, not expensive and they all come with senders. The pre existing senders all had an ambient resistance that was different from that of the new ones .... Regards RD
Tracktop Posted January 25, 2011 Posted January 25, 2011 There is a 10mm plug to the rear of the o/p sender that you can remove and install your after market gauge ( transducer / pipe) into. Works fine just need the right adapter. I am also now thinking that some of the intermittent pressure indication problems I have had in the past are cause by the Black box plugs and / or cable terminations. The cable terminations are just a spring loaded connection that to me seems quite poor for the application. Certainly wouldn't be my design choice or even a consideration.
facthunter Posted January 25, 2011 Posted January 25, 2011 just a thought . Where is the oil level in the tank, compared to the engine? Above or below.I'm not familiar with the trike installation.
Guest davidh10 Posted January 25, 2011 Posted January 25, 2011 just a thought . Where is the oil level in the tank, compared to the engine? Above or below.I'm not familiar with the trike installation. The oil tank is below the engine. In the picture in this thread, you can see the engine mounting frame above the oil tank.
facthunter Posted January 25, 2011 Posted January 25, 2011 Well, that would have to be the source of the problem wouldn't it? Try a lightly loaded non return valve in the line and see what happens. Nev
fly_tornado Posted January 25, 2011 Posted January 25, 2011 so is the prognosis just air bubbles in the oil lines?
facthunter Posted January 25, 2011 Posted January 25, 2011 There is every chance that it is draining back due to gravity. You're probably sucking AIR initially. Once air gets in the pump it performs quite poorly at achieving any pressure so it could take quite a while to "prime".. NEW engines should be primed before starting, or they can be quickly damaged. If the suck side of the pump is empty you do indeed have a problem and could have no pressure as indicated, for a while. Although the engine is not highly loaded at idle, it's not good for it. Nev
Guest rocketdriver Posted January 25, 2011 Posted January 25, 2011 If the delay is real, that is likely .... I've also seen it on a high milage car engine with larger than specification big end and / or main bearing clearances. Car still ran fine, but oil pressure took a while to come up. Not sure, but a damaged or dirty oil pressure valve seat can also cause the problem by allowing the oil to back flow (and siphon back) when the pump is stationary (depends on the oil circuit design and I'm not familiar with the rotax ... When that happens, typically the pump unprimes and it takes time for that to fix itself, and then the oil lines need refilling ..... meanwhile the wear goes on! Just a thought .... but this is not the only Rotax with the oil tank below the engine is it? If others are not having the problem, surely this is either a faulty indication or something in the engine is worn or damaged? If it is either, adding another valve has the potential to conceal the problem until, perhaps, it stops the engine?? Just a thought .... Regards RD
facthunter Posted January 25, 2011 Posted January 25, 2011 It's not below the engine in most aircraft and I can't recall any problem with oil pressure rise on start -up with the Rotax then. I even fill the new filter with oil when i install it on a car, to stop a dry start. Trochoidal or gear pumps do not guarantee a seal when stopped. They all have clearance between the parts and oil will pass through them, if the teeth are not in contact. They are only guaranteed contact when one is being driven by the other. Once they are drained they will let air pass through quicker as well, so in my view, the engine would not have to be defective to allow the drain back. Nev
Guest rocketdriver Posted January 25, 2011 Posted January 25, 2011 Except that the pressure valve seal can prevent that if it is properly sealed ..... no oil can drain down the pipe 'cos no air can get in to replace it .... on the other hand, worn bearing allow air to get in one while oil goes out another .....
facthunter Posted January 25, 2011 Posted January 25, 2011 Can get back through any bearing in the motor They all have running clearances and some have squirt holes. When the engine is shut down hot the oil internally is pretty thin. Oil doesn't stay in the galleries. Mostly it drains. Some filters feature anti-drain-back valving to stop some of it draining back through the oil pump. Nev
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