MScott

Well my brother crashed my Superstar 40 for the first time (even with an instructor!).[:@]
The plane landed in a field of giant weeds and luckily the only visible damage was a broken prop. However, when we started the plane again, we heard a weird noise (like something was loose) at any speed above idle.
I now have the engine apart (OS .40 LA) and I decided to try and find out if the crank shaft was bent. I put the threaded (prop) end in my drill motor...and sure enough, the drill shakes a little. I am assuming that, like in a car, this thing should be pretty well balanced and not cause the drill to shake. Is this a correct assumption and have I found the problem?

Geistware

My Feedback: (16)

If you removed the glow plug and did this then I would say something is wrong. If the plug is still installed, the compression could cause it to look like it is out.

DBCherry

My Feedback: (4)

The crankshaft is NOT balanced perfectly. Putting it in your drill and getting some shaking as a result is normal. The part about putting the threads into the drill chuck isn't a good idea though, tightening the chuck enough to hold the shaft may have screwed up the threads.

I won't say the shaft didn't get bent, but your test won't prove anything.

Re-assemble the engine and carefully turn it over with th eglow plug removed. Keep the threaded part of the crank parralel to a flat, straight bit of steel or something, and watch the tip of the crankshaft. If it's bent you should be able to see it move up and down (or side to side) in relation to the steel.

If the shaft was bent, in addition to the "noise" you should have seen a dramatic increase in vibration, and, you should have been able to see the prop 'wobble' if viewing it end on.

Best of luck,
Dennis-

SST

My Feedback: (2)

If you removed the crank to do this test, it won't work, as the prop is rotationally balanced for the weight of the piston/rod assembly as they relate inside the engine, and will be out of balance without them. The way to check the crank would be to mount it between centers and use a dial indicator to measure runout as you turn it. You may be able to eyeball it by rolling the straight of the shaft on a piece of glass, or other flat surface and observing the snout for runout.

What more likely happened is that some of the covering has been popped loose from the structure beneath it and is now rattling against it, causing a drumskin effect. I've seen it before, and it can make a tremendous racket. If you can find the spot, a little ironing will fix it.

Flypaper 2

If you turn it over slowly with a variable speed drill and the glowplug out and the crankcase wobbles, its likely bent. Drill chucks run quite true.

AirBearMA

My Feedback: (1)

I would probably send it back to the manufacturer for a check out as you really can't tell if you have a bent crank for sure without using special equipment.

MScott

Thanks, I had the crank shaft out when I was doing the test (I did make sure not to get the chuch tight enough to damage the threads). I put the engine back together and tried the methods everyone suggested, and I could not see the shaft tip moving. I will try the drill test with the engine assembled and glow plug out...I'm running out of ideas.
I've got one left, have the "pilot" who crashed it by me a new engine! Any suggestions on a replacement??

MScott

I forgot to mention that there is a pretty good vibration down the plane beside the noise that it is making.
When the glow plug is out, should the engine turn over smoothly the whole rotation? It still feels like it is coming on and off of compression, and that is causing the drill to shake.
Is there really anything else that could have bent or gone wrong from the crash...should I just spend the $25 for a new crank shaft since that is most likely the problem?

JimTrainor

Only the prop broke? Doesn't sound like a very hard impact.

Have you balanced the new propeller?

If is running... and you saw no obvious problems when you took it apart... and if I had to guess... I'd guess there is nothing wrong. It is a pretty simple machine, after all.

DBCherry

My Feedback: (4)

From your most recent description it does sound like the shaft is bent.
Dennis-

Grampaw

I can't pass up this opportunity to get in a plug for my favorite engine, Fox. My Fox Eagle 60 III seemed to have suffered some damage in a crash so I sent it to Fox for a check-up and repairs. They found a bent crankshaft and replaced it for the sole cost of the part and I had my engine back in a week. I love their engines and their service.

DBCherry

My Feedback: (4)

Grampaw,
You're a fan club of about one. I've heard many bad comments about Fox engines from club members, BUT! they were ALL based on year's old experiences, so Fox could have improved dramatically.
Dennis-

SST

My Feedback: (2)

Well, MikeSell has, I think, a Contender with a Fox .40, and it cooks...I have a couple myself, and I bolted one into my FliteCraft Cub. Should be exciting.

ajvpb

My Feedback: (3)

It feels like it's coming in and out of compression because the cylinder is tapered, meaning it is narrower at the top than the bottom. The test where you have it over a known straight object is actually very good. With the crankshaft in the engine (don't connect the connecting rod, and the backing plate off), hold the engine over a level, piece of steel, etc. Have someone else put their finger in the back of the engine and slowly turn over the crankshaft. It should be obvious if there is any bend in it. Like the other's said, if you only broke a prop, you almost certainly didn't bend the crankshaft. I've crashed hard enough to break the remote needle off the backing plate, and the crankshaft was still straight. They are very strong. I'd say re-assemble it, using lots of after run oil to lube everything up before you put it together, and try again. Run it real rich at first, like your breaking it in, to remove any dirt that may have got into it. Run it up again, and it may smooth out. The only thing I can think of is mabye you put the piston in 180 degrees around. Even that shouldn't be a big deal.

To sum up:
It is very very unlikely that you bent the crankshaft, unless it hit a rock or something like that when it crashed. If the spinner was still on it and not broken when you found the engine, I'd say you are assured your crankshaft isn't bent. Give it another shot and report back. Hope this helps,

Alex

RC Havoc

My Feedback: (-1)

Actualy, the LA Motors have bushings intead of ball bearings. Put the crank back in the motor and pull it back and forth. If there is slop in the crank shaft, then the noise you hear is probably the crankshaft rubbing aginst the backplate. All you need to do is replace the bushings, or better yet, install ball bearings...