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VW engine failure on Take Off

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jamdfingr

Well-Known Member
Joined
Mar 30, 2017
Messages
50
Location
Murray Bridge, South Australia
Hi All,

Went to fly the plane the other day, warmed up on the ground with a few high speed taxis and then hit the throttle to go. Got to about 300ft and power started to fail on the engine. Lowered the nose, hit fuel booster and reduced throttle while managing to turnaround and line up back on the runway. Engine cut about 50ft off he ground and I managed to pull up on the runway before the fence with 30ft to spare. Not fun.

Went out today to check/test the engine and couldn’t fault on the ground. It all felt and looked good so I started it up and it would run up all the way to 3400rpm with temps and pressures in the green. Shut it down and check valve clearances and found a couple a bit tight but nothing to complain about. Ran it back up again trying to see if it would fault and just as I was thinking bad fuel, it suddenly dropped manifold pressure, chts shot up and oil pressure dropped quickly with rising oil temp.

I backed off the throttle and let everything settle down again and was able to then get it back to 3100rpm and watching as the oil pressure was slowly dropping out, then came a point the manifold dropped and the engine began to lose power again.

So am not sure what is going on. I get the feeling that as the oil temp rises, it is losing oil pressure which reduces lubrication film. As this starts to drop away, the engine load from the lack of lube film is then increasing which is dropping out the manifold pressure. This in tern starts to further reduce oil flow around bearings and ultimately the lack of flow to the cylinder heads is causing immediate jump in CHTs.

I thought of icing but it’s a rotec tbi and I doubt I would get the oil temp jump, just a rough running engine.

Anybody have any other ideas on what to test/inspect before I start pulling the engine down for inspection and overhaul? It must be bleeding internally somewhere which escalates as the oil thins out from heat.

For note, it is an Aeropower 2007cc with rotec tbi. Has oil cooler on top and a cooling plenum over the cylinders and cooler. Engine hours are only about 40.

Any thoughts or ideas would be appreciated. Will start with a drain of the oil to see if there is any bearing material in there to identify if they have spun.

Cheers,

Luke
 
I'm not familiar with the Rotec TBI, but I think if the fuel mixture is too lean it could cause the conditions you describe. Cylinder head temperatures could soar, oil pressure could drop, and clearances could open up. I would start by pulling the plugs and inspecting their appearance. Keep us posted on what you find, and thanks for sharing.
 
Ok, so my best guess given what I have seen so far is that something had caused the oil pressure valve to stick and hence it shut off the cooler. This engine has no oil filter so all it would take would be one small piece of something to make it stick and it would remain in place. This would then mean the oil is bypassing the cooler and getting too hot (as was indicated on the temp gauge). At the point it gets really hot, it loses the lubrication layer on the bearings and begins to load up the engine. As the oil is now too thin to circulate properly in the engine, the heads suddenly lose their cooling oil and hence why the CHT's spiked.

My plan now is to run up the engine again and put a thermometer inside of the cooler. If this shows ambient (ish) or at least a discrepancy with what is happening in the oil temp sensor, then it will mean I have no oil cooling occuring on the engine. Then its a case of remove the valve (and if it is difficult to remove, this would confirm the diagnosis) and clean it up properly with a thorough flush of that oil system and gallery.

Aside from a spun bearing (which is unlikely given the run up test I did) this is the only thing I can think of that would have caused the oil to run that hot.

Cheers,

Luke.
 
Bob Hoover wrote a good article on the memory properties of one of the alloys used to make VW engine cases.

https://bobhooversblog.blogspot.com/2006/11/vw-used-crankcase.html
In short, a case that has once been overheated, has a tendency to return to a distorted shape when heated again. The distortion will dump oil from around the main bearings and cause the symptoms described.

If your engine was built on an align-bored case, this could be an issue. If it is a new case (and never overheated), disregard my post.

Good Luck,
Chucker
 
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What fuel are you burning, are you using a gasolator, location?
 
Jamdfingr,
Did you every figure out the cause of our high oil temp, low oil pressure and power loss?
Thanks,
Dave
 
I'd do all that Luke, then some more. Install an oil filter. Pull the plugs and borescope the cylinders. You can buy the USB PC variety for less than $10 on Amazon. Your jugs may now look like my $600 Stihl chain saw bore- trashed due to sucking air around the carb mounting gasket in less than 6 hours of use on a new saw! If any doubt about either end, it's rebuild time. Don't bet your life on maybe. Know what you got or rebuild. Your comment about the sudden drop in MAP was interesting but you did not say what was happening to RPM or throttle setting when the sudden drop occurred. This clue would seem to indicate a problem with the intake and carb system. Check your air filter. Here is a good article on MAP. A lot in there on adjustable props, but the concepts regarding MAP apply to fixed as well. Since MAP is based on suction, a sudden drop without any change in throttle means something extraordinary is happening with suction (suction has increased for some reason = drop in manifold pressure = restriction in airflow at some point in the induction); or, perhaps you have a bad MAP sensor or one or more bad gauges. If throttle is open, secure, and fixed, with fixed and secure mixture, MAP should be constant. If MAP suddenly drops at same setting, then it would indicate the throttle body is malfunctioning or perhaps a dirty air filter is restricting airflow and causing the engine to suck against the restriction, dropping the MAP. If using a rubber intake hose, it could cause this symptom due to it collapsing. Essentially, engine is going very lean resulting in spiking temps. Hot enough and your jugs will seize and most certainly score. (Inspect them!). I don't see how an oil flow problem is going to cause your MAP to suddenly drop if RPM is constant. Conversely, if RPM drops due to a lube issue, suction would Decrease and MAP would Rise. Lube and MAP are unrelated issues if RPM is constant. Oil is lubrication, air is MAP. My 2¢, and I'm no hot shot engine mechanic for sure. https://www.advancedpilot.com/downloads/prep.pdf
 
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Wow, Sounds familiar. When I bought my SIILS the engine had quit and wing. Leading edge found a tree. Not that bad to fix.
But found mud daubber nest in Main tank fuel vent. Eventually fabricated vent tubes similar to what the Jabiru J450 has . They are say 3/8"D X 4" long and have maybe 6 tiny holes facing forward. Holes maybe 1/32" . Mounted the vents above the tanks to prevent siphoning fuel out of those vents when located on the belly. Works great No issues since. Fuel vent covers don't fall off now,
BillE

Hi All,

Went to fly the plane the other day, warmed up on the ground with a few high speed taxis and then hit the throttle to go. Got to about 300ft and power started to fail on the engine. Lowered the nose, hit fuel booster and reduced throttle while managing to turnaround and line up back on the runway. Engine cut about 50ft off he ground and I managed to pull up on the runway before the fence with 30ft to spare. Not fun.

Went out today to check/test the engine and couldn’t fault on the ground. It all felt and looked good so I started it up and it would run up all the way to 3400rpm with temps and pressures in the green. Shut it down and check valve clearances and found a couple a bit tight but nothing to complain about. Ran it back up again trying to see if it would fault and just as I was thinking bad fuel, it suddenly dropped manifold pressure, chts shot up and oil pressure dropped quickly with rising oil temp.

I backed off the throttle and let everything settle down again and was able to then get it back to 3100rpm and watching as the oil pressure was slowly dropping out, then came a point the manifold dropped and the engine began to lose power again.

So am not sure what is going on. I get the feeling that as the oil temp rises, it is losing oil pressure which reduces lubrication film. As this starts to drop away, the engine load from the lack of lube film is then increasing which is dropping out the manifold pressure. This in tern starts to further reduce oil flow around bearings and ultimately the lack of flow to the cylinder heads is causing immediate jump in CHTs.

I thought of icing but it’s a rotec tbi and I doubt I would get the oil temp jump, just a rough running engine.

Anybody have any other ideas on what to test/inspect before I start pulling the engine down for inspection and overhaul? It must be bleeding internally somewhere which escalates as the oil thins out from heat.

For note, it is an Aeropower 2007cc with rotec tbi. Has oil cooler on top and a cooling plenum over the cylinders and cooler. Engine hours are only about 40.

Any thoughts or ideas would be appreciated. Will start with a drain of the oil to see if there is any bearing material in there to identify if they have spun.

Cheers,

Luke
 
Congratulations that you managed to bring it back in one piece from just 300ft - on initial climb - with dropping Power (!). These turns tend to end up in a stall. Thrilling experience. Good Job.
 
Congratulations that you managed to bring it back in one piece from just 300ft - on initial climb - with dropping Power (!). These turns tend to end up in a stall. Thrilling experience. Good Job.
Amen! I HIGHLY recommend EVERYONE (that hasn't already & several times) read the timeless and always relevant classic by Wolfgang Langewische: Stick and Rudder...and to do so before your next flight! I am currently on my 2nd time through it and book marking and taking cockpit notes and logging memory items like a 'mad-dog'! The knowledge in this book could and just might save your life AND your "ship" some day. Regs and Happy Holidays to all of you.
John
 
Good that you got back safe. Read this Don’t fly that motor again!! Tear it down inspect everything for damage be very careful about reusing parts that are near heat damage like rods crank heads. Before you tare it down try to find why it lost MAP. You may have two problems that are unrelated or one caused the other. Because of the oil pressure issue I suspect internal damage probably a rod bearing they are the first to go on low oil pressure. Any damage there I personally would get a new rods and possibly a crank. Any heat damage for sure trash them both. On rebuild check all oil passages and clean clean them machining leaves loads of stuff in there. Vw cases need carful inspection of oil casting area for correct casting drill passages sometimes don’t line up. Oil plungers don’t slide we’ll need a polish on and on.
 
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Amen! I HIGHLY recommend EVERYONE (that hasn't already & several times) read the timeless and always relevant classic by Wolfgang Langewische: Stick and Rudder...and to do so before your next flight! I am currently on my 2nd time through it and book marking and taking cockpit notes and logging memory items like a 'mad-dog'! The knowledge in this book could and just might save your life AND your "ship" some day. Regs and Happy Holidays to all of you.
John
I have a signed copy somewhere????
 
Amen! I HIGHLY recommend EVERYONE (that hasn't already & several times) read the timeless and always relevant classic by Wolfgang Langewische: Stick and Rudder...and to do so before your next flight! I am currently on my 2nd time through it and book marking and taking cockpit notes and logging memory items like a 'mad-dog'! The knowledge in this book could and just might save your life AND your "ship" some day. Regs and Happy Holidays to all of you.
John
Here's the Cliff notes version: https://www.mastery-flight-training.com/stickandruddernotes.pdf
 
Wow, Sounds familiar. When I bought my SIILS the engine had quit and wing. Leading edge found a tree. Not that bad to fix.
But found mud daubber nest in Main tank fuel vent. Eventually fabricated vent tubes similar to what the Jabiru J450 has . They are say 3/8"D X 4" long and have maybe 6 tiny holes facing forward. Holes maybe 1/32" . Mounted the vents above the tanks to prevent siphoning fuel out of those vents when located on the belly. Works great No issues since. Fuel vent covers don't fall off now,
BillE
I like that vent design, Bill. Do you have one to keep birds from nesting on the engine?
 
Kind of like this? Can’t find any real pic and don’t know how the ball works. Sorry for the screen shot.
 

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Ever try using a fuel cap vent from an ATV? They have a spring-loaded ball to prevent fuel coming out from negative g or inversion. Very cheap, billet aluminum and work great. Try teeing off from the fuel level indicator hose at the back of the tank. You can get a brass 1/4" tee from all over the place. No insect infiltration either. I'll send you a drawing if you're interested.1607705424338.png
 
Amen! I HIGHLY recommend EVERYONE (that hasn't already & several times) read the timeless and always relevant classic by Wolfgang Langewische: Stick and Rudder...and to do so before your next flight! I am currently on my 2nd time through it and book marking and taking cockpit notes and logging memory items like a 'mad-dog'! The knowledge in this book could and just might save your life AND your "ship" some day. Regs and Happy Holidays to all of you.
John
Shocktropper thanks for the recommendation. Purchased the book. It is a great book.
 
Luke, Your failure on takeoff with an unability to repeat the problem on the ground is typical of a fuel delivery failure caused by acceleration, rotation and fuel covering the vent in the fuel tank. If you have a gravity feed fuel system, the vent is most likely the problem. Try a simple, temporary forward facing pitot vent on fuel cap. The vent system shown in the plans will fill with fuel and siphon the pressure out of the tank.
 
Further to my previous post, here's the unit installed at a tee junction I created with the fuel sight gauge tubing. My aircraft previously had a periscope looking unit at the front of the tank but even that prevented filling the tank.
 

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