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09-04-2006 08:26 PM  14 years ago
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w.pasman

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Netherlands

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Help! engine problem
Sorry, long post, I'm really puzzled and I am giving much details about the problem (excerpt from the logbook), as I don't know which detail may be relevant...

Raptor 50 w/ OS50 (non-hyper) I have been flying all season with it, no special problems except for the "occasional" rear bearing issue (once every 50 flights....). But since the last bearing replacement I have problems with it, OK let me tell the history of this problem

August 6. My engine kept running hot and the muffler kept getting loose. Could not find any problem so I decided to replace the engine rear bearing that had lasted 115 runs. Bearing was notchy but not worse than some other rear bearings that I replaced and had not even started rattling. This time I placed a C3 SKF bearing instead of the normal SKF bearing I used previous times. Placed new glow plug.

August 9. I flew 1 day (7 flights) with it, worked fine.
August 24. I flew another day (5 flights), worked fine.
August 25. I flew a third day, engine was running hot all the time. First flight, tuning a few clicks leaner seemed to cool down the engine. But then the second flight it was running hot again and I could not get it tuned properly anymore, neither tuning richer nor leaner did change anything.

Checked glow plug, seemed slightly hot but at same time a very small piece of carbon near root of glow wire is developing (that indicates running slightly rich if I understand it right?).
I again pulled the rear bearing. It seemed just slightly notchy, don't think it's causing the problem but I replaced it with a brand new, normal SKF bearings that I used before I switched to the C3 bearing.

I also replaced the main clunk line. I pressurized the whole main tank and held it under water with all lines attached. No air bubbles.

SURPRISE during re-installation: the governor sensor does not reach the magnet anymore! Now I needed to sand the governor mount bracket hole larger to get it at the right position! I'm really puzzled at this one, how is it possible that the governor sensor was at the right place 0.3mm from the magnets last time, while it is not possible to get the sensor closer than 0.3mm this time??? This is a standard throttle jockey mount bracket, the sensor is glued with epoxy to the bracket, the bracket seems to be the stuff they make printed circuit boards of, the engine is metal (alu) and the fan is half plastic. Is the plastic fan deforming or what? BTW I'm using heat to break the loctite in the nut fastening the fan, but I thought I never heated above boiling as I put water on the nut during the heatup.

I again replaced the glow plug..

September 2. Finally weather is good enough for flying. First flight the engine runs OK when I put it 1.5 turn + 4 clicks (4 clicks richer than normal). I notice a foam ball halfway the fuel, which I never had before. But it runs hot when I put it at 1.5 turn. But the next flight the header tank goes empty while flying inverted!! Seems to be a fuel supply issue from main to header tank? Hovering it runs acceptable now, a bit hot. Without governor, the engine sags completely when I go inverted, while this throttle curve has always been working properly??

Concluding, the engine does not run properly. Problems seem to be hinting to a fuel leak somewhere. But I reaplced already the main clunk line and tank. Today I tested all other fuel lines, they are all without leaks. The uniflow pressure clunk line was quite detoriated at the root but I could not get any air out there no matter how hard I blew into the line (tested under water). So all fuel line will be replaced but I do NOT have the impression that that will solve anything.

I could really use some good tips on what may be going on here!!
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09-04-2006 09:17 PM  14 years ago
BarracudaHockey

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Jacksonville FL

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Any chance your fan isn't screwed down all the way? This can lead to up/down play in the crank shaft, the crank pin riding on the back plate leading to heating up and would account for the gov sensor not reaching the magnet.Andy
AMA 77227
http://www.jaxrc.com
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09-05-2006 06:37 AM  14 years ago
w.pasman

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Netherlands

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Good idea! There was and there still is no play in the fan. But to be sure I pulled the engine and it looks like the front bearing of the engine did not go down the last 0.5mm. It looked all right but now I compared with another OS50 which has the bearing flush against the small ridge around it. So front bearing sticks out a tiny bit.
I will correct this problem.

But can this account for the overheating problems and problems with the fuel supply, and why only do problems show when inverted?
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09-05-2006 03:37 PM  14 years ago
BarracudaHockey

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Jacksonville FL

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Interesting, I would have thought the problem would be in the rear bearing not seated all the way.

Have you looked at your backplate? Is is scratched up?
Andy
AMA 77227
http://www.jaxrc.com
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09-05-2006 05:52 PM  14 years ago
w.pasman

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Netherlands

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Interesting, I would have thought the problem would be in the rear bearing not seated all the way.
If the rear bearing would not be seated, the fan would be moved downward if at all because the fan is stopped by the front bearing, isn't it?
Have you looked at your backplate? Is is scratched up?
Just checked it. There are a few scratches but I'm pretty sure they already were there. Is it possible to see how recent sratches are?
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09-05-2006 06:50 PM  14 years ago
BarracudaHockey

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Jacksonville FL

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Ok thats a good point and the front bearing explains why the gov magnet would have a wider gap.

Not sure why that would cause over heating, got to be excess friction somewhere.
Andy
AMA 77227
http://www.jaxrc.com
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09-05-2006 07:43 PM  14 years ago
w.pasman

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Netherlands

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Well maybe this ill positioned front bearing could cause some additional friction in the rear bearing. But even if it does, that would cause also problems when straight up? That does not explain major sagging when inverted while flying OK with straight up...
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