I was helping out with an event at our field this weekend when this happened. A plane was in the air when it made what to me was an out of the ordinary sputtering noise and then dead sticked. I know little or nothing about rc gas engines, but when it died, it sounded bad. The pilot landed it without too much problem. The picture below shows what caused the noise.

A veteran in gas engines believed the cause was the way it was mounted. The washers and spacers weren't even causing the crank case to twist a bit. The casing itself seemed to be awful thin in spots, but maybe that is the norm.

I think that is a factory failiure, nothing abaut engine mount, when the piston goes to the ldp the energy of the explosion push it to low and at same time push the cylinder in the other direction with equal force, for my the case was weak and for that reason it was broken.

I agree with the idea of the weak case.
THe engine mounting system could not have caused that failure.

I just read the instruction manual on 3W engines on "aircraft international" web site. If you are going to use standoffs, you must use a thick plywood plate at the end of the standoffs. As to mount to a flat surface. They said in their manual that this mounting tecknique (the one shown in the picture) will cause distorsion and will break the casing. They will not warranty this broken case.

Gunny

Betcha that flyer doesnt buy another 3W...
The engine WAS mounted on a thick plywood piece, the FIREWALL...
the engine was also mounted on 2 1/4 inch aluminum pieces reinforcing that FIREWALL...
The case could not possibly twist, and it didn't, it just came apart..The case is split horizontally, no twist evident..The old 3W heavier case would not have done this, it's way stronger....
In their quest for a lighter engine they have made the cases very thin, only .020 wall in some places, which would be passable with better quality casting, not the sand castings they use......It's possible that something was ingested through the carb and got between the piston and cylinder, forcing the case apart.....No way to tell without examination...
Looks like a no brainer for AI to replace the case, FREE, no matter what the cause....
I am quite familiar with 3W engines, having seen MANY over the last 10 or so years....

I believe the manufacturer (AI) should replace the case at no charge. There is absolutely no way the mounting technique used could have caused this problem. The case was weak and simply broke. I believe that 3W has a 3 year warranty on their engines. I would send it in and have them repair it.

The motor is definitely NOT mounted correctly. The mounting method used is causing tension on the crankcase and very likely caused the failure.

You must mount the motor to a flat surface. If the stanoffs were angled it wouldnt be such an issue but the standoffs are not angled causing the undesirable tension.

I bet I know what doolico does for a living...

Regardless of how the engine is mounted it will be pulling against the mounting lugs. That's unavoidable whether it's mounted on an angle or directly in line with the airframe. The mounting base of the case is a solid structure, not tabbed as with some other engines so the addition of a flat mounting plate between the mounting lugs and the standoffs would add little, if any, additional torsional support. The only thing that I see wrong with the mounting is a lack of flat washers under the mounting bolts, placing two dissimilar metals against each other and permitting a harder metal to vibrate on a softer metal over a small area.

I would send the engine to an independant specialist, one that knows 3W engines, to inspect the engine for another cause. I have a pretty strong feeling that an internal cause will become evident on tear down by one that knows what to look for.

Cases breaking is not something new for 3W, in fact it's was something that happened fairly often a few years ago. As with anything else, if you write enough restrictions and warnings in a manual eventually you won't have to warranty any product because the conditions of use cannot be fully complied with.

3W cases breaking cases fairly often a few years ago ?????I'm calling BS on this one Silversurfer. Who here has seen a case break? I've run 3W and so have several other people I fly with for years and never seen or heard of this type of failure. If it is a defect it needs to be taken care of immediately but the only way to tell is by sending it in to AI or Cactus.

In my opinion, if the mounting system was at fault and caused the warping of the casting which led to failure, the cracks would have extended to the mounting lug(s). This type of failure is just surrounding the cylinder attachment. I can not see how the mounting system would cause this type of failure. I agree with the comments that a flaw in the castings allowed for a weak area which extended to cause this failure.

Just my 2 cents

Elson

Call as you see 'em I always say, but in this case I'll bet I've worked with more 3W engines than you've ever met. No ofense meant, reall, but there were more than a few instances of cases breaking like this not all that long ago. There's some other parts that break all the time, still, but the RC community does not run their engines for enough time to experience them with any frequency.

I saw two of em break - In one case flying along level flight -- suddenly just slowed to a stop we pulled the top of cowl and case was split front to back - not hot - just split.
Th 3W guys promptly warrantied both engines and that fixed both -no further problems -this was 2 years ago as I recall.
There were problems- but 3W did fix em.
Friends of mine are professional pilots for RPV tests - I hear other comments also but this is a model forum not an industrial application forum

Looks to me like the piston R/H may have seized on it's way up to TDC and literally the barrels torn itself out of the crankcase, should show up on the teardown[]

This is exactly what I was thinking.

Look at the date of he original post, ASpril 2005. I think this one has been handled already.

In deference to ZDZ Hanson, I will no longer relate information obtained from more "industrial" uses that bear directly on RC engines.

However, I will continue to use this same information to increase the lifespan and power levels on my RC planes. I guess there's some that just can't see the relationship between one and the other.

You lost me on that one -
was that a positive statement ?
My comment about industrial was only meant to seperate typical model use from applications whre the engines are run for extended periods at full tilt - in frankly industrial applications .
Those of course create a lot of wear n tear in a much shorter time period and under more sustained loads than the model use
good or bad - it is just not the same .

Absolutely it was positive. I don't believe there's anyone here that knows more about the ZDZ line of engines. Mr. ZDZ is not a bad thing, is it?

OTOH, we most definately differ in what we find useful and applicable, but I will defer to your greater judgement. From here on out, you're the man. BTW, did I mention that some switched to a Walbro carb for better fuel economy and reliability a long time ago? That's an industrial use that's not pertinent to an RC application, though.

I'm out of here

No offense taken but you have no idea the amount of experience I have with these motors.

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ENGINES!!!