td 049 broken rod

getback Sun Mar 23, 2014 9:16 pm

a friend of mine and I were running this TD049 cox engine the other day while still tring to get a engine that will run right for the race to run to run!! any way put the little yellow prop 4.475x4 from cox inter. on first time the thing kept popping would backfire and threw the prop off, well I put the valentine spinner on it , got her fired off running clean at 22,400 on 25% wee were screaming back and fourth at each other , all of a sodden it got quite the prop flew off spinner is in space some were but the stud is still on the crank so I though it just came loose since my buddy had put it on Embarassed

tonite I was oiling it down to pack in a bag for now and realized the piston was not moving DAMMIT!

took it apart and here she lies . Was just reading on another tread this was an older engine with the oil hole too Mad

those pics suck but it was a clean break . I though this engine could handle it ..but did nt know how old it was........ Eric

Jason_WI Mon Mar 24, 2014 12:32 am

I have a couple of pistons that look like that. One from a TD .051 and another one from a GTP Nissan engine that got so hot the connecting rod was blue.

Possible you had it under propped on the ground. If you would have let that unwind in the air it's likely the piston would have come unglued.

Should be able to fit another piston to the #4 cylinder and salvage that.

**RknRusty** Mon Mar 24, 2014 1:36 am

Jason_WI wrote:I have a couple of pistons that look like that. One from a TD .051 and another one from a GTP Nissan engine that got so hot the connecting rod was blue.

Possible you had it under propped on the ground. If you would have let that unwind in the air it's likely the piston would have come unglued.

Should be able to fit another piston to the #4 cylinder and salvage that.

I agree with everything Jason said. I wouldn't recommend a prop less than 5x3. You probably won't get 22k on the ground, but it likely will in the air after it unloads.
Rusty

getback Mon Mar 24, 2014 6:43 pm

Lesson learned well , I let it set and ruunn too long at that RPM> Head Bang

my fault Thanks for fixing me Eric

John Goddard Fri Apr 04, 2014 8:09 am

Don't forget when using a prop that has a pitch greater than .61 of the diameter the tips of the prop 'stall' when model is stationary and lots of the thrust ie wind (cooling) over the cylinder is lost.
The greater the pitch/diameter ratio the more of the prop blade stalls and the less thrust
(cooling wind) passes over the cylinder.
An engine that throws the prop usually does so because it's too lean.

Add the two above and I'd say you've over heated it and that's why the rod has let go.

However
In my experience the Cox Rod isn't the motor's best feature, it's only 'bettered'
in the rubbish part charts by the pistons which again 22/23k? and you're really flirting with
those going POP.
lol!

getback Fri Apr 04, 2014 8:13 pm

you are right John , just glad to be able to have friends like u that tell me where I screwed up , have not put that much thought into the Raito of pitch vs. volume of air produced Sad

I am still learning , and may not always get it right Very Happy

Thanks Getback.

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