mesaflyer

I'm not sure how old this engine is, less than two years, and I'm sure it has less than 100 flights.
It was running real good, and then started to loose some power. I landed, shut it off, and didn't find anything wrong. After letting it cool, I filled it up and flew around, but still had a power loss. Landed, and had one of the guys at the field look at it, because now it felt like a bearing was grinding? He thought the same thing. I'm sure it was not too lean, as I tend to error on the rich side, with the usual smoke trail. Got home and took it apart. The pictures are what I found. I'm guessing the little pieces of metal (that are stuck to the cylinder head and top of piston) must of came from the side of the piston, because the side of the piston has some nice gouges in it.
I tried to take a pic of the bearings, only because they have a little rust, but turn real smooth. The sleeve does not look damaged at all.
I have not used any cleaning products on anything, just wiped off with a rag.
Almost looks like several small pieces of metal worked their way up between the piston and sleeve, and tore up the piston on the way up.

You guys have any idea?

rcdude7

My Feedback: (264)

I'll bet a piece of the rear bearing cage broke off and got between the piston and cylinder to cause that damage.

Is the engine still under warranty?

w8ye

My Feedback: (16)

Looks like bearing cage damage to me also

Anyway, something went through the engine and got up on top of the piston.

mesaflyer

I'm almost certain it's less than two years old, but not sure if I still have the receipt.

I'll take a closer look at the bearing cage. I never thought about that.
Thanks

Turk1

If it was from particles firstly glow plug should gone.Can it be from high nitro content? (knocking)

Dr1Driver

Yup, looks like the bearing cage let go. I believe OS had a bad batch of bearings for a while and this could be one of them. BTW - there's no such thing as "a little rust" on a bearing. If they're rusted AT ALL - change them out,

MetallicaJunkie

i had the same thing happen to me a while back...i even made a thread about it... and no one gave me any good answers... atleast now i have some closure

rcdude7

My Feedback: (264)

The kick to the groin is that OS replacement parts are way overpriced and costs to repair your engine will be close to the price of a brand new one.

I would put it back together and send that thing to hobby services and let them sort it out, they may replace or repair your engine under warranty, you really have nothing to lose at this point.

airraptor

My Feedback: (66)

I wouldnt say it was the cage but the bearings it self. if it would have been the cage I would think all the bearings would come out and do way more damage then what your seeing.

When you replace the bearing and if the piston is still useable get the Boca bearings in stainless steel. will last a very long time.

fizzwater2

My Feedback: (61)

airraptor - I've seen several bearing cages let go, with engines destroyed, and none of the balls fell out until the bearings were removed from the engines.

For a while, thunder tiger pro .40 bearings would do that when we used 'em in 424 racing. I hear the newer engines have bearings with plastic bearing retainers, not stamped metal cage types. The plastic ones don't come apart nearly as much.

one of my best TTpros ate a bearing last fall - I thought I'd squeeze one more race out of it before I changed the bearing.. live and learn, I guess. At least now I have a spare muffler and carb...

spaceworm

I think K&B developed, or at least used and promoted, non metallic bearing cages back in the day for their ducted fan engines. I am sure others did as well.

rcdude7

My Feedback: (264)

Many of the K&B engines come with the plastic caged rear bearings, not just the high RPM ones, sport engines too.

freakingfast

My Feedback: (3)

Well, you have painfully$$$ learned what a bad bearing feels and sounds like when it's gone too long. But the good news is, 90% of the time, if you pay attention you can catch it before any major harm is done....next time.

Signs of a bearing going out: A gritty feel and sound when the prop is turned while pulling forward, A whining or turbine like sound while in flight, Power loss with correct needle setting, Suddenly glow plugs are going out quickly and its not lean(eminent engine damage).

Cheap fix: stainless & plastic cages.[sm=thumbup.gif]
http://www.rc-bearings.com/catalog/p...roducts_id=715

mesaflyer

Yea, funny part is I was not experienced enough to know what it sounds like. I am now. After a flight last week, one of the guys at the field said he thought the engine sounded like it was coming apart. Guess I'll listen a little closer next time, to the guys at the field.

I looked at the bearing, without removing from the case, and I don't see anything wrong, but I would bet you guys are right.

I was however reminded by my 14 year son the "history" of this engine. It does have a couple hundred flights, and is older than two years from when I bought it. It spent some time in my Pulse, and then I pulled it out and it sat on the shelf for about a year.
I'm only 50, and starting to have "senior moments" with my memory. Crap.

After I pull the bearings (for the experience, and better inspection) I'm just gonna toss it. I'm sure the parts would cost almost as much as a new one.

Oh well, I'll write this one up as a good learning experience for me.

proptop

My Feedback: (8)

Instead of tossing it, maybe someone could use the thing for parts?
There are occasionally guys around here asking for a carb, or head, etc....(just a thought..."recycling" )

bgee

put it on ebay, some very good spares there!

mesaflyer

Thanks for the tips, I'll see if somebody at my club wants it, if not, I'll doing something better than toss it.

By the way, as you can see in the pics the crank is still in it, so what is the next step towards removing the bearings? I don't want to do any more damage to it!

fizzwater2

My Feedback: (61)

remove the prop drive plate from the front with a puller if necessary, don't pry it off with a screwdriver..

Get the following stuff handy: Oven mitt or hot pads, block of wood (I use a chunk of handy 2x4), and a pizza pan or something you can "cook" an engine on without causing marital strife..

I used to have my own pizza pan, but still, would get "the look" for using the "food oven" for model engines. So now I have a toaster oven in my shop

Remove all the stray bits and pieces from the crankcase except for the bearings. You might even be able to have the crank out if you get the prop drive plate off. You can use a block of wood to gently "persuade" the crank to come out if need be. If not, leave it in.. but DO make sure all the plastic bits are gone (carb, etc).

Put the engine in the oven at about 325 degrees for 15 mins or so, to get things good and heat soaked. Don't go much hotter, you don't want to ruin the temper on anything.

One the crankcase is hot, grab it (here's where the oven mitts or hot pads are VERY useful.. ) then promply smack the backside of the case on your handy block of 2x4. Probably best not to use the kitchen countertop..

If the stars are aligned and life is good, the rear bearing (and crank, if still in the engine) should drop right out of the back of the case. I've only got one engine that the heat trick hasn't worked on, a Taipan .15 and the rear bearing is unusually tight in the case on that one.

Once the rear bearing / crank are out of the way, put a dowel or hardwood piece (as big as you can that fits in the case where the crank was) and tap on the end of the wood piece, the front bearing should pop right out, too.

Clean everything up after it all cools.

When I put one back together, it's basically a reverse. I slide the bearings onto the crankshaft (rear bearing) and set them aside, and re-heat the crankcase by itself. Once it's hot, you can usually slide the crank into the case and the rear bearing will slide right in. DON'T hammer on the crank or the inner race of the rear bearing to seat it if you have to persuade it a little - make sure you only press on the outer race. You don't want to try to drive the outer race into place by pressure on the inner, that might lead to flat spots or divots in the bearing surfaces.

Once the rear bearing and crank are in place, the front bearing is usually a pretty easy fit. Again, if you have to tap it in a little, use a wood block or dowel, and make sure you're only putting pressure on the outer race to seat it. If it's a shielded bearing, you have to be really careful not to let your wood block or dowel make dents in the shield, or it's hosed.

Let us know how that works out!

blw

My Feedback: (3)

You may have a good connecting rod, crankshaft, crankcase, backplate, and carb. I would keep the cylinder head too. People always need mufflers. Anyway, that is a small pile of money for you if someone needs those parts. It beats tossing the engine out.

jaka

Hi!
Just change ball bearings! That's easy!!
The pitting on the piston top is not from a faulty ball bearing cage , it's from a glow plug element!!!

JohnMcGowan

My Feedback: (15)

If that is the case, that must have been a VERY thick and heavy glow plug element to have caused that kind of denting on top of the piston ?

jaka

Hi!
Nothing special! I have seen it many times in F3D pylon racing decades ago when we run MVVS and Rossi engines.

freakingfast

My Feedback: (3)

A few years ago, I had a bearing go bad on a OS 46VXDF (25,000rpm ducted fan engine). When I tore it down, the top of the piston and the head button was literally hairy with hundreds or metal slivers! This engine has plastic cages on the bearings. It turns out the metal is primarily from the balls and secondarily, the races.

I knocked off the slivers and put new bearings in it just for giggles and you know what? that darn thing still tachs great and it's still going today. I have three DF engines I rotate out of service for bearing change every 3 to 4 gallons.

From what I've seen on other engines with steel cage bearings, the balls pit or chip first than eat the races. The roughness of the balls than start to grind at cages. Now, debris is starting to take it's toll on the engine thou the power loss at this point is primarily bearing friction. If you keep going, the crud will score the sides of the piston but the most power robbing damage may occur at the crankshaft housing in the intake port area. Scoring in this area will drop the primary compression and may have more detrimental effects than a scored piston so check this area before you consider a piston/sleeve replacement. If you still manage to keep it running at this point by feeding it glow plugs, soon the cage will scatter or the balls will do a split pea and bring the engine to a permanent halt.

For some reason bearings with plastic cages seem to out last the steel, and it seems like it's rust or corrosion/pitting on the balls happens sooner on the steel caged bearings. The balls and races are vary close to the same steel alloy, but the steel cages are a much softer alloy. Dissimilar alloys in the presents of acids can produce galvanic corrosion, hence pitting! That's my theory, and I'm sticking to it.

mesaflyer

The top of the piston and cylinder head are not pitted. They are, as freakingfast said, "hairy with metal slivers". The glow plug is fine.
I still have not pulled the bearings, but I'll let you guys know when I get it all apart.

mesaflyer

Well removed the bearings. Thanks fizzwater2 for the 'how to".
The front bearing was fine.
The rear bearing is a different story. The side that faces the rear of the engine has a little rust. The side of the bearing that faces forward is damaged. All of the bearing cage round parts that hold the balls in place have what looks like a melted edge/groove on them. Not sure how to describe it, and the attached pic is the best my camera will do. The bearing feels almost fine. Just a slight roughness to it, but I know thats toast. Just thought it would be worse.

Who knows, I might buy the parts and fix this, just for the experience. Also might teach my son something, since he needs to start keeping track of my memory for me.