splane dis 1?

Ok,
The boys took there stooge(that's me) and there new planes flying the other day. I went to start this old McCoy .19 after a few flights and one flip of the prop and I heard a hard knock and the prop turned freely. The first thing I thought of was a busted do-dad inside the engine. A crank, piston rod or something let go. Then I gave a slight pull on the prop and spinner and it came right off in my hand. The nut had somehow come off. Good thing it did not come off on the last flight. Might have been a bad thing. I was sure I got it on tight the last time I changed out the prop. I think it had something to do with the hard knock or pop when I tried to start the engine. What did I do wrong. Also I have noticed that the washer behind the nut does not have the grooves in it like the one on the Fox engine. It is just a flat smooth washer.

Thanks
Paul

It was flooded and backfired!
That's usually what causes props to come loose. I can't begin to tell you how many times that's happened to me. Also, it helps to tighten the prop a little after every few flights.

Paul, a couple of things might have happened. If the engine got a bit too much prime in it, it might have hydraulic locked just enough to loosen the prop when you flipped it. It might have backfired-the pop you heard. Did you have a wood prop on it? The hub of a wood prop can crush and end up being loose enough that it spins free easily.

Makes a good argument for checking the prop nut for tight on a regular basis and slowly turning the prop over a time or two to be sure there isn't too much fuel sloshing around in the cylinder.

Years ago, I had a four stroke that would cough off the prop and spinner in flight once in a while. Got expensive, so it got a double nut arrangement to lock the prop down better. (This was before OS and others made these locking rigs standard.)

Sounds like an accidental flood/backfire.
A wise old modeler once told me to never use a 4 way "model" wrench to tighten my props, always use a "real" wrench. But then you run the risk of bending the connecting rod! Turn the engine over by hand slowly before you begin cranking to make sure it hasn't got a hydraulic lock.
Bill <><

>Sounds like an accidental flood/backfire.
>A wise old modeler once told me to never use a 4 way "model"
>wrench to tighten my props, always use a "real" wrench. But
>then you run the risk of bending the connecting rod! Turn
>the engine over by hand slowly before you begin cranking to
>make sure it hasn't got a hydraulic lock.
>Bill <><
>
>When the character of a man is not clear to you, look at his
>friends.
>Japanese Proverb

Ron B.
F4Fguy

Bill:

Shows how even old modelers can be wrong.A"4-way"wrench is perfectly adequate for tightening props on a .15-.40 sport engine.A"real"wrench(if it's longer than ~6") will,if used indiscriminately,definitely crush a wood prop.There's also a possibility of wringing off the crankshaft threads with too much torque,especially on some of the older engines.

I'm Still looking at my friends and growing more suspicious of me.

Paul:

Check the end of the shaft to be sure it's not broken off where the nut grips.If not,you're probably a victim of creep in the prop.Wood, and most plastics,will relax under load,and will require re-tightening on occasion.Ironically,this happens faster when the prop is OVER-tightened.Use the 4-way and tighten with as much force as you can comfortably apply,gripping as far out on the wrench as you can.Do NOT use an extra "extender",such as a screwdriver to get more leverage.

The drive washer of the McCoy uses a taper seat to drive the prop.if you look closely,you'll see that it has knurling on one face(the prop side)and the other is partially flat with a "cone"on the inner diameter.The cone is the clutch which transfers power from the shaft by friction.

Hope this helps,

Rare occurrence with a McCoy, try a Fox .35. they're notorious for spitting the prop nut. You probably just had it a little flooded, not a big deal.

Thanks guys,
I do have a Brodak wooden 9x4 prop on this engine. Lession learned.
As for a wrench, I have a small 4 in craftsman ratchet and socket kit that I use. I do not own a prop wrench just yet. I try and not use a whole lot of force when I tighten the prop, but I make sure it is tight. I will now check it every 3 or 4 flights.
I will check the washer again and may try and post a picture when I get home tonight, but I think it is flat and smooth on both sides.

Paul

>Thanks guys,
>I do have a Brodak wooden 9x4 prop on this engine. Lession
>learned.
>As for a wrench, I have a small 4 in craftsman ratchet and
>socket kit that I use. I do not own a prop wrench just yet.
>I try and not use a whole lot of force when I tighten the
>prop, but I make sure it is tight. I will now check it every
>3 or 4 flights.
>I will check the washer again and may try and post a picture
>when I get home tonight, but I think it is flat and smooth
>on both sides.
>
>
>Paul
>
>I am a retread, - I did C/L in my youth and did not know
>what I was doing then other then having fun. And not much
>has changed.

Ron B.
F4Fguy

Paul:

This afternoon I pulled out all the McCoy .19s I have;five types from early 50s to late 70s.The very earliest has a pressed on drive washer and a cap screw instead of a threaded shaft and nut.All the rest have tapered seat drive washers of varying outward appearance.If yours doesn't have a tapered seat on the inner bore,you've probably got two front washers and NO drive washer.The series 21 engines had a more massive looking drive washer,but the drive configuration is identical to the "Red Head" 19-35-40 Testors/McCoy engines.If,in fact you don't have the proper one,let me know,I'll send you one.Running the engine with the wrong type washer could allow excessive end play,leading to rod and or wrist pin problems and,at the very least,dragging the crankpin on the backplate.

thanks Ron,
I need to pull the prop and check it. I will pull it tomorrow afternoon.

Thanks
Paul

>>Sounds like an accidental flood/backfire.
>>A wise old modeler once told me to never use a 4 way "model"
>>wrench to tighten my props, always use a "real" wrench. But
>>then you run the risk of bending the connecting rod! Turn
>>the engine over by hand slowly before you begin cranking to
>>make sure it hasn't got a hydraulic lock.
>>Bill <><
>>
>>When the character of a man is not clear to you, look at his
>>friends.
>>Japanese Proverb
>Bill:
>
>Shows how even old modelers can be wrong.A"4-way"wrench is
>perfectly adequate for tightening props on a .15-.40 sport
>engine.A"real"wrench(if it's longer than ~6") will,if used
>indiscriminately,definitely crush a wood prop.There's also a
>possibility of wringing off the crankshaft threads with too
>much torque,especially on some of the older engines.

Yeah, That's sorta the reason I mentioned bending necessary parts.

>I'm Still looking at my friends and growing more suspicious
>of me.

Well you are in good company!

>Hope this helps,
>
>Ron B.

I do use a austin craft 4 way, and never have had a problem. Although I have been known to wring the head bolts off a small block Chevy with a 3/8" drive X 10" pull bar.
Bill <><

Apologies to one and all. But I cannot resist...

Back when the family was racing 1/8 RC cars, a good friend had grenaded a motor and just finished getting a replacement installed. As he dropped the chassis on his starting board, pressing crank-mounted flywheel to start motor, the result was that classic knock one can hear when an engine with a loose prop is turned through compression, a bump being the result.

I looked up, "Zale, the flywheel is loose."

He did not believe it, had not a clue as to how I might be able to contribute such important information to the cause. But he did check his work, the 'wheel was indeed loose.

From that moment on, Zale thought me to be some sort of mystic when it came to things mechanical.

He was wrong, of course.

I'm an Austin 4-way user too, but have taken to a 4" Crescent on my carbon fiber props.

See my post on the starter question.
Only harm done is probably to your prop finger.
##### McCoy used to get me all the time. You prime , feel the bump, then POP @#%$**.
Nature of the beast, me thinks.

I've found wood props need tightend every flying day.
Plastic & CF props need wrenched on much less.
I use 5/8"-3/4" dia. #60 sand paper disk with a hole punched in the center help. I put them behind & in front of the prop.

Paul,
As mentioned previously, wood props need to be retightened often because you compress the wood fibers. One way to lessen the impact to the wood is to loosen the prop after a day's flying.
Most of my wood props do not last long enough to bother though.

Paul,
I just remembered an event that ties into what you had happen.
Last year I was at a meet in Huntersville with the Argus/Fox 35.
I had worked out a program of prime and start with the electric starter. New set up and I wasn't comfortable getting a quick start flipping the Fox. We had flown the set up three days in a row before the contest, including the evening before.
I primed, turned the prop back off compression, hooked up the battery, and signaled the judges. All just like I had been doing. The engine would fire after a couple tenths of a second this way, it had done it probably a dozen times before just like this.
Well, the engine fired and threw the prop!
Bad thing was that one of the judges (guy I have known for years) asked, "don't you guys ever do any preventive maintainence?"
Could have flattened his nose!!!! LOL!!!!!
Now I pull the spinner and check the prop on all my wood propped planes when I am getting ready for the official flight.
It happens......
Bill <><