COX glow head filament dropping into the cylinder

balogh Sun Jun 16, 2013 2:57 pm

One new COX glow head died in my TEE DEE 051 today by the filament blowing at both ends in the head and dropping into the cylinder. Luckily it did not make too much harm but while bouncing between the piston top and the glow head it cleaned the black soot/ castor warnish off the piston top before being drifted by the exhaust gases through the exhaust port. I wonder what would have happened had the exhaust port been a slit design that would probably have not let the filament leave the cylinder...the filamengt would probably have stuck in the slit exhaust and killed the piston/cylinder fit for good...

Anyone has had similar experience?

Not long ago the cup in the ball joint of the piston in my brand new (vintage) Tee Dee 049 ripped of, and the broken cup fragment could not make it through the (unslit) exhaust port with the engine running. It completely killed the cylinder and the piston, let alone the prop that unscrewed due the sudden stop of the crankshaft and flew away...

fredvon4 Sun Jun 16, 2013 6:19 pm

Come on, admit it you have been playing with 60% Nitro again.....grin

Paulgibeault Mon Jun 17, 2013 10:55 am

Balogh,

I have not seen this mode of failure yet in Cox glow plugs.
Many years ago there was a (huge) batch of Cox plugs with faulty element welding that caused the lower element to come adrift pre-maturely. But in that case the upper weld held on...

It is conjecture to say whether open port cylinders allow the element to escape without doing damage or not, since I haven't seen this type of failure before.

Regarding a piston socket failure. Again this normally ruins ANY type of cylinder. I'm surprised a new old stock piston would fail so early....although it is not uncommon to find the ball-socket joint too loose when new. I have no explanation if you checked it first before running the motor. If you didn't, well then we know why...

pkrankow Mon Jun 17, 2013 12:48 pm

A glow wire is small enough that I would expect if it managed to NOT get stuck partially in the exhaust slit or a bypass, rather little actual damage would befall the engine from the wire rattling around inside the engine. It would probably float about not contacting anything except near/at TDC.

The situation would clearly qualify and "bad" though.

Phil

balogh Tue Jun 18, 2013 9:35 am

Paulgibeault wrote:Balogh,

I have not seen this mode of failure yet in Cox glow plugs.
Many years ago there was a (huge) batch of Cox plugs with faulty element welding that caused the lower element to come adrift pre-maturely. But in that case the upper weld held on...

It is conjecture to say whether open port cylinders allow the element to escape without doing damage or not, since I haven't seen this type of failure before.

Regarding a piston socket failure. Again this normally ruins ANY type of cylinder. I'm surprised a new old stock piston would fail so early....although it is not uncommon to find the ball-socket joint too loose when new. I have no explanation if you checked it first before running the motor. If you didn't, well then we know why...

I agree I may have bad luck with both the filament and the balljoint cap, but at least the filament escaped without any notable damage inflicted on the cylinder and piston.

The other engine was not so lucky with the cap ripped of, it gut stuck between the bottom skirt of the piston (SPI design) and the exhaust port and this "sculpture" was hard to remove from the cylinder. A new piston then helped the re-use of the cylinder and luckily the cranckpin also survived.

I have many COX engines in my possession and still am inclined to believe this is not characteristic to the COX design but is rather a one-in-a million failure

balogh Tue Jun 18, 2013 11:09 am

Paulgibeault wrote:Balogh,

I have not seen this mode of failure yet in Cox glow plugs.
Many years ago there was a (huge) batch of Cox plugs with faulty element welding that caused the lower element to come adrift pre-maturely. But in that case the upper weld held on...

It is conjecture to say whether open port cylinders allow the element to escape without doing damage or not, since I haven't seen this type of failure before.

Regarding a piston socket failure. Again this normally ruins ANY type of cylinder. I'm surprised a new old stock piston would fail so early....although it is not uncommon to find the ball-socket joint too loose when new. I have no explanation if you checked it first before running the motor. If you didn't, well then we know why...

Back to your question if I checked the balljoint fit before thr first run, YES I am always doing that with new engines and set the joint if needed, to have minimum clearence just enough to allow access of castor between the ball and the cup. There must have been some micro-failure in the cup left probably when it was machined or pressed to its shape during manufacturing and a crack may be blamed for the the fracture. Never saw that before and hope will never see that again. My R/C plane was jut in an inverted flight when the engine froze but I could luckily turn it back to normal while sailing and landed safely.

I learned, though, on 2 pistons setting before that without the minimum gap between the ball and cup the ball will sooner or later stick through the piston top due to insufficient lubrication. With this in mind I never overdo clearance setting. Especially on 051-s where new pistons are hard to find on the market.

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COX glow head filament dropping into the cylinder

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