Went through 3 motors within a month (pics)

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Attached a bunch of pics. Sorry for the delay, I couldn't find an extended T27 torx bit required to remove the head until now.

Oddly enough I had a 30cc piston and 4 bolt head laying around and decided for fun to see if I could bolt it onto the 2 bolt 29cc bottom end. It fit perfectly fine and the piston moves smoothly with lots of compression. I used the 2 bolt gasket and it seals just fine. Any reason why this wouldn't work? I wasn't able to find any info on people attempting this.

BTW, as for the condition of the damaged piston and head, I noticed the spring clip on one side of the piston was missing. Do you think maybe it flew off and caused all that damage? It honestly does't look like a lean condition failure. It literally looks like a foreign object got grinded up in there. Anyways, opinions please? I'm not engine expert.

Yea ,that would do it ,I had a rod bearing grenade one time an did that!
I think in some engine displacements ,some of the blocks are actually the same size ,if they are a close to the
displacement ,like a 23cc & a 26cc ,but ,jumping up to past 30cc an higher ,the blocks change ,I had seen some
parts where you can change to a bigger head an piston ,like a bore up kit!
 
Would a lean condition cause the spring clips to fly off or is that just a bad luck scenario? IS this sort of thing common? I always thought those spring clips were pretty flimsy considering the speed and heat the components are subjected to.
 
It does happen from time to time, but it's not a common thing by any stretch. Normally it's a defective clip, or installed wrong. Some guys treat them as once and done, I've reused them on a few rebuilds that were hard to get parts for. The only issue I've had was from a no name Chinese piston company off of Ebay. Bought a $25.00 top end (with piston, top bearing, wrist pin and circlips) for a friends saw, ended up spending another $4.00 for OEM circlips. The included ones bent too easy, couldn't even tension them to get them installed. They just bent in half. But like I said not a normal occurrence.
 
Well like i said in post #34 , pistons will offer clues as to whats going on and that is without a doubt something "mechanical". 99.9% of the time piston circlips fail because the were not 100% installed into the circlip groove in the piston. Ive also seen a circlip "forgotten" and the pin walks sideways and destroys the cylinder wall. Ive never seen nor read of a circlip "failing" when installed correctly. This is also a good lesson why you need to be carefull about reading knee jerk internet engine problem diagnosis from people who have no hard facts. I learned many years ago, when you have an issue just take things one step at a time, work in a systematic set of diagnostic steps, take a lot of detailed pics, and ask questions one at a time. Lots of experienced members here on the forum that are very willing to help you move in the right direction. Sorry for your blown top end, but you learned a lot during the process ?

One last caution is now you need to be concerned about where the circlip is and what it could have done as far as damage to your bottom end. The clip may have blown out the exhaust port, or fallen down into the crankcase. If you plan on rebuilding that engine. I highly advise you dissasemble the bottom end and inspect the crank, con rod, and bearings.
 
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Call me crazy but I rarely tune following manufacturer specs.

On rc planes, I acquire engines left and right from members at the field, and sometimes some of those engines don't even have pdfs online. I play it by ear, its your best tuning, and w a prop tach, in your case a rpm tach.

The key to know if its running lean is how it clears out after a wide open throttle pass.

Your issue I find it very strange. By any chance could the oil be bad batch, although rare.

I have had a few 30cc fuelies and they have seized because the air filter fell off and by the time I notice it has about a pound of dirt inside.

The cyliner damage, IMO, looks like a lean condition, or wrong oil mixture. Lets not forget, this is your 3rd engine.

And some engines like to run leaner than others, just like you see weed eaters w different oil mix ratios.
 
R??an made it. Also, here's a small rant, THESE ARENT CY OR FUELIE! Rovan says they are, but they aren't, they are China poop Rip offs lol

Totes! CY are actually pretty awesome motors! They're Taiwanese, and have been around as long as Zenoah. Anything Rovan or KM is a cheap knock off and completely unworthy of the Fuelie/CY moniker.
 
Totes! CY are actually pretty awesome motors! They're Taiwanese, and have been around as long as Zenoah. Anything Rovan or KM is a cheap knock off and completely unworthy of the Fuelie/CY moniker.
Fully agree. The CY29 that came in my MTXL has been awsome. It pulls that tubby truck around at a respectable speed, and the low end punch is good for such a small CC. So far the reliability has been great too. I've had my MTXL for going on 2 years I think and its still just as strong as day one. Unless I have a anomaly its just as good as the zenoah's i've had. Probably gonna grenade it now on its next run for opening my mouth. ???
 
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