I've put in about 15 flights in the past three days. It's been great. Today, however, I tried to get a little fancy with a low, slow inverted pass with my trainer 40. Well, not a good idea, obviously, but I wanted to put her to the limits. Anyway, it didn't work out very well. She couldn't quite hold it. Did a few kartwheels with a bit of repairable damage. No problem. But upon further inspection, I noticed that a fair amount of guck had gotten in and around the carb. I closed the carb and removed the gunk the best I could, hoping that nothing got directly into the engine. Now, I should note that I've been flying with the O.S. 40 LA. I've never deadsticked with this plane ONCE through two gallons of fuel, and it pulls my tower 40 with a suprising amount of authority. In any event, I know that I shouldn't have tried to start it back up again without taking the engine apart, but I did it anyway (I'm still 10 at heart). Well, she started up no problem, but towards full throttle, it seemed as if it wasn't working at it's fullest potential. Okay, well, I'm probably just being neurotic, I thought. Well, about a minute into the flight, it dead sticks. Not just that, but it is very difficult to get going again, and when it does, it again will not max out at full throttle; and about a minute later wants to quit entirely. I tried to start it again several times, but with no sucess. It sputters a bit and dies. So I headed home. I checked all of the fuel lines, and they are all in tact. The tank is still secure as well. I am hesistant to take apart the engine to clean it out, because I did that with my TH .46 and I don't have proper compression (when I turn to prime no fuel is drawn into he carb.any advise on this matter would be much appreciated as well). Thanks for taking the time to read this post. Thank you.

Best,


Yetti

Ewww. First thing after a dirt bath I DO NOT MOVE THE THROTTLE OR PROP SHAFT and squirt loads of WD-40 into the engine held with the carb barrel low. About 15 blasts with a pause in between to allow the dirt to flush out. If you are careful a full dissassembly and cleaning is probably called for. If not you can't go far wrong sending it to the service center and asking for an estimate before work is performed.

When you run an engine with dirt it scratches the cylinder wall and/or piston and you lose compression. The results are much like you describe. No idle, poor transition, low top end, flame-outs. A really hard impact can dent the sleeve with the piston and give similar problems.

If it is in warranty you might be able to send it back for a new sleeve & piston (they did with no charge for my Thunder Tiger .46 even though I held and took full responsibility for the crash).

Man, this sucks. I did flush the carb with fuel before restarting, but I guess I really did it this time. Thanks for the info.

2 strokes are very easy to disassemble and reassemble. I would tear it down, paying close attention to the way the sleeve comes out so you get it lined back up the same, the piston as well. Clean it all with 90% alcohol, inspect it for any obvious signs of damage, EG scratches etc. Then after run oil the whole assembly and reassemble it.

(Keep in mind I'm the new kid on the block, but I have done this many times with the car I used to have, and a couple times with this motor on my plane. If you are careful and pay attention to alignments on disassembly all will be as it should unless there is already damage from the crash and dirt.)

Edit: of course if you find signs of damage, well at least you know for sure.

Edit 2: if you aren't mechanically inclined, or if the engine is under warranty, ignore this whole post and send it in for a check up.

Edit 3: also keep in mind I was the kid who was CONSTANTLY disassembling things to "fix it".

This is an example of dirt an debris running through an overheated engine. You DON'T want this:

Hmm, thanks for the picture. That's what the top of my TH 46 looks like, minus the scarring. I'm going to take apart my 40la right now. Thanks, guys!

The top of the cylinder is slightly browned. I really don't see any debris, but I can't get the cylinder out (correct terminology?). How do I go about doing this. thank you

You should first remove the backplate, then the cylinder head. Keep the gaskets that come off so you wont have to get new ones when you assemble it again. With the help of a heat gun over the crankcase you should be able to slide up the Cylinder Liner, which is the part that surrounds the piston. After you remove this, you can pull the connecting rod (Thats the part which connects the piston head with the crankshaft) out from the crankshaft and the piston will come out the top of the engine. Then remove the crankshaft from the crankcase and clean everything. You might have to check the bearings for integrity. There are plenty of thorough tutorials on how to do this, including videos.

Replacing model engine bearings [link=http://www.youtube.com/watch?v=TuzEco3EDUM&feature=related]Part #1[/link] and [link=http://www.youtube.com/watch?v=OLSoXPLGzOI&feature=related]Part #2[/link]

These videos are very useful as they will teach you how to disassemble the engine and replace the bearings if needed.

Edit: Now that I read your first post I noticed you are talking about a 46LA which is bushing crankshaft and not a bearing supported crankshaft so there will be no bearings to replace. Still these videos are an excellent guideline.

Thank you!

After disassembling the engine, the piston has no damage. The crankcase has a few superficial scratches, but I do not think that they would effect the engine, as they do not go into the crankcase. They are merely superficial . let me know if I am wrong on this one. Thanks for the help!

So, if my piston is not damaged, what can be the cause of my engines poor performace post-crash? Thanks

Given that its a bushing engine I don't know if scratches on the crankcase that compromise the crankshaft's contact area might reduce the engine's power. Are you sure there are no scratches either on the piston or on the liner?

I really don't think there are any scratches on the piston. It looks uniform all the way around. There are one or two scratches on the crankcase, but when I ran my finger over them, I could not feel any depression. Hope this helps.

First of all, if you've already run the engine, any dirt that was there is now gone.

Second, the LA is an Air Bleed Carb, and the air bleed hole is right on the front of the engine. The symptoms you describe coulc be caused by a small particle of dirt in the air bleed hole. This will cause the engine to run rich at the low end, and load up with fuel. When you try to throttle up, the engine hesitates, and may either spool up or dead stick.

Given the location of the air bleed hole, when the plane noses into the dirt, dirt is easily pushed into that hole. Its easy to clean. Just remove the carb (there only one or two screws holding it in) and flush it with clean fuel. Use a small sewing pin to carefully clean out the air bleed hole.

Now the hard part. To ensure the hole is clean, you'll want to remove the air bleed screw. The best way is to turn it all the way in to count the number of turns to open it again. If there is a risk of dirt in the hole, this practice can cause damage to the threads, and will give you an incorrect number of turns.

Instead, visually look at the postion of the end of the airbleed screw in the hole and make a note of it. Now remove the screw and flush the hole with clean fuel. Put the screw back in where it was originally. Before you fly the plane again, you'll have to go through the process of low end tuning, which can be a bit touchy with airbleeds, but is not impossible. Just remember pulling the screw out makes the low end leaner, and turning it in makes the low end richer.

Good Luck,
Brad

Thank you very much, Brad.

Yup, good advice.

If you ever have any left over "old" glow fuel, save it!

It is great for exactly this situation.

After a crash I will brush any dirt from the engine with the carb pointed down.

I take the plane home and remove the engine.

I pull off the carb and glow plug, and w/o turning the piston I repeatedly flush the crankcase with the old glow fuel.

I then remove the backplate and flush with glow fuel again.

I then spray the area with WD-40 and again with glow fuel all over.

Finally I will LIGHTLY turn the crankshaft. If I feel even the hint of grinding or resistance at this point, I stop and disassemble the whole thing.

If not I turn the crankshaft over dropping the piston and again spray and flush to get out any debris.

If after repeated cleanings I feel no resistance ( scoring ), I'll wash the carb in warm water, followed by a WD-40 spray, and then glow fuel...

I dry and clean all of the nipples, etc. with pressurized air.

Thus far I've not had to go as far as pulling the cylinder or bearings and the engines have run reliably.

Thanks again. I took out the air bleed screw and flushed out the area with some fuel. I'll be starting her up later today.Hope all goes well. Thanks for the help. Much appreciated.

Yetti, you've gotten great advice on un-dirting engines. I'm gonna give you some other advice that I think might make your modelling a little less guess-filled!

Invest in a Tachometer. They're inexpensive, and take alot of the guess work out of tuning and maintaining engines. It's not that we shoot for any particular RPM in any particular situation, but it removes the paranoia factor when we screw up. When the engine light in my car comes on, I hear all kinds of worrying noises. Most aren't related to anything but normal function. Same here. The tach can tell us if we're running rich, lean, if we're turning RPMs in the normal range for the engine, etc.

Alot of experienced guys don't use them, but I'm never sure why. I love and understand glow engines quite well, I can tune them by ear, but for me, tuning with a tach is more reliable and repeatable. Probably why I don't deadstick (OK, OK, 2 deadsticks in 3 years, then declared the glowplug dead.).

J

Yeah, I'll need to get one. Thanks for the advice.

On another note, my first re-start went great. High end where it should be etc. Though, it felt like it was running hotter than normal. On subsequent restarts, my original problem returned- poor high end with engine failure shortly thereafter.


EDIT: Just had another restart. Re-tuned High end and running well. Will update with next restart.\



She's back to normal! Starts on a flip or two. Thanks for everyone's help. Learning how disassemble and reassemble a two stroke has been great fun! Thanks
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