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HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › OS55HZ - Broken piston and con-rod - need help
10-17-2011 05:27 AM  7 years agoPost 1
lajwab

rrApprentice

Chicago, ILL

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Hi,
I have a Sceadu EVO50 SWM, OS powerboost pipe,20% bitro fuel (Optifuel), no governor.
I bought it last year and broken in as it should be. I have been flying it fine and doing some rolls, loops, flips that is all pretty much I can do. My needle settings are like:
High (Long) = 1.75 turn out
Mid (Small) = 1.25 turn out

Yesterday I was flying my third tank and I heard a click and then engine quit and I landed the bird by auto so no damage to bird.

But then I took apart the engine and found the little chip came out from piston and con rod is broken on both ends. The cylinder looks pretty much clean I cannot see any scratches though.
I like to ask you guys what should I do, Shall I go for total rebuilt or I can only replace with new piston and con rod instead. The piston ring looks OK also. I wanna know what you guys would go for.

My head rpm's are seems little on higher side and also the engine was running little leaner but i see lots of smoke.

I have attached some pics for reference.

Thanks

Arshad

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10-17-2011 05:37 AM  7 years agoPost 2
Ravenhyper50

rrKey Veteran

Canada's Capital

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In your case I would try just a new rod, piston, ring and bearings.

If your sleeve is fine and the ring is still black..guess you can save a little reusing your old ring as long as its black and looks good.

Cheers,
Raven

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10-17-2011 07:17 AM  7 years agoPost 3
BladeStrikes

rrElite Veteran

Shelby TWP,Mi

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+1 on what Raven said.
Also,
The rod broke from the high headspeed like you said.When the motor spins faster than it should,it beat's the crap out of the crank,bearing's and rod so make sure you check the bearing's also.Your in the next state over so weather is pretty much the same,kinda cold out for them needle setting's..Where your at now is what I ran on my OS 55 when it was warmer out but a few click's past 1 1/4 on mid.Right about now my needle for high was closer to 2 turn's out and mid was about 1 1/2...It's getting alot cooler out so the motor need's to run a little richer...

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10-17-2011 11:49 AM  7 years agoPost 4
Jeff polisena

rrElite Veteran

westpalmbeachflorida usa

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Look into getting a gov or limiter , this will help with motor over speed with no load . When you keep a load on piston the tolerances stay tight once you unload tolerances start to slop and after a while something goes . It's the overspeed that is hard to correct with throttle curve only .

I stole it ,flew it and gave it back ;)

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10-17-2011 12:02 PM  7 years agoPost 5
airdodger

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Johnston USA

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You are not saving much in that engine, check it may be better to just buy a new engine and start over. You were running the engine on the lean side for sure.

Chris

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10-17-2011 01:46 PM  7 years agoPost 6
rpat

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Weirton, W. Va.

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Almost always when an engine like that blows you get a lot of junk in the bearings. Make sure that you flush out your bearings real good. I grenaded an OS 91 and there was enough junk in the rear bearing to start a junk yard. It took about a half a can of WD40 to clean out the bearing.

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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10-17-2011 03:29 PM  7 years agoPost 7
rcnut

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Rockford, Illinois

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I believe you will need a new piston, ring, and connecting rod.

In the first pic, it looks as if the piston skirt has broken off. Also you are right, you were running on the lean side, and the high head speed didn't help.

Get a gov / rev limiter of some type. Clean out the bearing very well! Otherwise you will be buying a new motor.

Team Miniature Aircraft
"I love the smell of Nitro in the morning!"
...Citizen 654!

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10-17-2011 03:35 PM  7 years agoPost 8
datidun

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N Ireland

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What was the Head speed to begin with

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10-17-2011 05:18 PM  7 years agoPost 9
BladeStrikes

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Shelby TWP,Mi

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Cheap and they work good.. https://rc.runryder.com/t658805p1/

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10-17-2011 06:49 PM  7 years agoPost 10
rpat

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Weirton, W. Va.

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The con. rod broke and took the piece of the piston with it when it let loose.The piston was at the bottom of the stroke when the con. rod broke.

trex 700fbl cal30,minititan,, trx600fbl,trex250,logo 500,Velocity N2

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10-18-2011 02:12 AM  7 years agoPost 11
TruckRacer

rrNovice

Des Moines, Iowa

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What everybody else said plus I'm a bit worried about all the corrosion on the rod. I doubt the corrosion caused the problem but it could have contributed to the failure .... along with the overspeed. Do you do anything between flights to prevent corrosion? Run the engine dry after the last flight of the day, etc. You might see rust on steel parts in a normal engine but I can hardly ever remember seeing that kind of corrosion on a rod ... except maybe on one from an engine that was fished out of a pond or lost out in a field for a period of time. That is nasty!

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10-18-2011 05:09 AM  7 years agoPost 12
lajwab

rrApprentice

Chicago, ILL

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Thanks for your comments.

Well, today I just ordered a Con-Rod and a piston and I will make sure to clean the bearings or replace them. I can see the Ring color is not black or dark. It is like silver.

Shall I take the bearing our and clean or just flush them with WD40 after removing the crankshaft out.

The corrosion on the rod you see is because of the casteroil. I was using 10% nitro with casteriiol mixture but for the last 1 gallon, I switched to 20% nitro OPTIFUEL.

Arshad

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10-25-2011 03:19 AM  7 years agoPost 13
CoronaL

rrKey Veteran

Winnebago IL

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get a new rear bearing too. Don't bother cleaning the old ones. The OS bearings aren't that great to begin with, and the metal cage on them worries me. If you ring is shiney on an OS you need to replace it. YS the rings get shiney when broken in though.

Randy!!! I am the liquor

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10-25-2011 12:35 PM  7 years agoPost 14
lajwab

rrApprentice

Chicago, ILL

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I'm little confused with con-rod direction because I couldn;t see the original's. It was in pieces. So i'm hoping if someone can help me with some pics to see which way the con-rod should go. It look pretty much alike on both sides. I know the end goes to crank pin and the one goes to the piston pin but i gotta know the orientation.

I will appreciate.

Arshad

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10-25-2011 01:54 PM  7 years agoPost 15
CoronaL

rrKey Veteran

Winnebago IL

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on the end that mates to the crankshaft, inspect that end closely. One side will have a slight bevel machined into that end and also the brass bushing. The other side will be perfect flat. The flat end goes OUT towards the back, while the bevel end is the end that mates with the crank first and will face forward, get that orientation correct as it will effect which way you apply the con rod to the piston, as the piston is directional as well.

Randy!!! I am the liquor

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