RE: Piston Damage (Full Version)

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speedster 1919 -> RE: Piston Damage (4/11/2008 11:54:33 AM)

400 grit with oil like 3N1 or ATF. On a flat counter top lay sandpaper down and swirl top of piston flat against sandpaper. Use the 400 grit and oil to lightly crosshatch cylinder to break glaze and reseat old ring. The head can be sanded with your finger tip on sandpaper. Bevel the edge of piston top at a 45 degree angle to knock off nicks caused by cage going in the intake and out exhaust port and piston shearing it off. A good flush of parts will get rid of grit. Gas , alcohol, whatever...........



Bad Tooth -> RE: Piston Damage (4/11/2008 10:55:05 PM)

Well CRAP! I bought new bearings, and an (overpriced) piston. While I was attempting to remove and salvage the old ring it broke.[>:] I was really hoping to see if I could revive the engine this weekend but......[8|]

Anyway, anyone know where I can find a cheap .50SX piston ring?

And while we are on the subject, what is the purpose of the ring? And (not that I'm going to do it) what would happen to a ringed engine if it were to be run without the ring?



summerwind -> RE: Piston Damage (4/11/2008 11:15:57 PM)

quote:

ORIGINAL: Bad Tooth

Well CRAP! I bought new bearings, and an (overpriced) piston. While I was attempting to remove and salvage the old ring it broke.[>:] I was really hoping to see if I could revive the engine this weekend but......[8|]

Anyway, anyone know where I can find a cheap .50SX piston ring?

And while we are on the subject, what is the purpose of the ring? And (not that I'm going to do it) what would happen to a ringed engine if it were to be run without the ring?

the ring expands and makes the seal needed to buildup the compression.........and NO, it will not run without it.................well maybe it would if you globbed a bunch of castor in there for a bit and threw in some 60% nitro fuel, but it wouldn't be for long[:D]

i know your feeling right now though, nothing worse than nurturing a limping motor back into health and having the ring snap..................can't even use CA to fix this one[:D]



cahusker -> RE: Piston Damage (4/11/2008 11:52:28 PM)


quote:

ORIGINAL: Bad Tooth

Well CRAP! I bought new bearings, and an (overpriced) piston. While I was attempting to remove and salvage the old ring it broke.[>:] I was really hoping to see if I could revive the engine this weekend but......[8|]

Anyway, anyone know where I can find a cheap .50SX piston ring?

And while we are on the subject, what is the purpose of the ring? And (not that I'm going to do it) what would happen to a ringed engine if it were to be run without the ring?

Here is where to buy a good ring reasonable, Frank Bowman in New Mexico 505-327-0696. He makes rings and in my opinion they are better than OEM rings. For an OS50SX it wil be $9 plus $3 shipping. You need the ring to have any reasonable amount of compression in the engine. Just be careful in spreading the ring onto the piston. Chances are with the damage you had the ring was already ruined anyway and needed to be replaced.



Super Splatter -> RE: Piston Damage (4/12/2008 4:36:02 AM)

Big Thought , mail the piston to him, have a pro put it on and than your ready to go. unless you've seen it done, you might wreck it.

Is it worth mailing the piston to him first? I remember K&B 40's , made me switch to ABC.



Bad Tooth -> RE: Piston Damage (4/13/2008 2:36:14 AM)

Alright! Well turns out I didn't have to wait that long for a ring after all. We made a 3 hr trip today for some other things and came across a hobby shop and they had one last piston ring. Got it home, installed and back on the plane. The engine seems to run fine. I did what was suggested and knocked down the high spots on the head with dremel/sandpaper.

What does detonation sound like? I couldn't tell for sure if I was hearing my covering shake or if the engine was making a faint sound, but I may have heard something unusual?

Other than that it ran like a champ! Idle, transition, full, etc. Couldn't tell the difference. So please tell me more about detonation so I can look out for it.



somegeek -> RE: Piston Damage (4/13/2008 5:02:01 AM)

quote:

ORIGINAL: Bad Tooth
Other than that it ran like a champ! Idle, transition, full, etc. Couldn't tell the difference. So please tell me more about detonation so I can look out for it.


Nice work!

somegeek



XJet -> RE: Piston Damage (4/13/2008 5:46:01 AM)

I'm currently working on a series of articles (for RCModelReviews.com) that include video/audio that covers engine-tuning -- and includes a recording of an engine that is suffering from detonation.

The sound is often likened to frying bacon but it's much easier to identify if you've actually heard it (live or in a recording) so I figured this kind of thing would be useful.

Lots of newbies also have trouble understanding what 4-stroking is so I've also done a vid showing the difference between 2-stroking and 4-stroking when tuning an engine.

I hope to have it up in a couple of weeks (sorry it's not sooner but I've got a lot of other stuff to do too).



DarZeelon -> RE: Piston Damage (4/13/2008 8:01:40 AM)

quote:

ORIGINAL: Bad Tooth

So please tell me more about detonation so I can look out for it.



Bad Tooth,


Detonation is, in small two-stroke glow engine, what is called a lean-run...

Too lean a mixture causes the premature ignition and faster burning, in-turn causing the maximum combustion pressure to occur too early, as the piston is still rising toward TDC.
...But not so soon as to cause the engine to reverse its rotation...

This causes the engine to overheat; potentially damaging itself. The piston will expand larger and the sleeve will 'bell-mouth'...
Most ABC engines, when run with a significant amount of castor oil in their fuel, could survive a couple of such runs and sustain no permanent damage... But don't push your luck.
...Most ringed engines will probably need a re-ring...

This has nothing to do with an insufficient amount of lubricant, but lubricant break-down at high temperatures; especially of synthetic oils, is definitely not helpful.



panzerd18 -> RE: Piston Damage (4/13/2008 8:34:39 AM)

Wow you got it running again! It looked so bad I thought it would be gone! Is it worth the time to fix when brand new engines are so cheap and the cost of parts to repair is so high?



asmund -> RE: Piston Damage (4/13/2008 9:29:14 AM)

What was the total cost of the repairs??



XJet -> RE: Piston Damage (4/13/2008 9:47:18 AM)

quote:

ORIGINAL: DarZeelon
Detonation is, in small two-stroke glow engine, what is called a lean-run...

Not necessarily -- it's possible to have a lean run without detonation - the two are not necessarily synonymous.

quote:

Too lean a mixture causes the premature ignition and faster burning, in-turn causing the maximum combustion pressure to occur too early, as the piston is still rising toward TDC. ...But not so soon as to cause the engine to reverse its rotation...

Correct.

quote:

This has nothing to do with an insufficient amount of lubricant, but lubricant break-down at high temperatures; especially of synthetic oils, is definitely not helpful.


As you've said, most of the damage from detonation has *nothing* to do with a failure of the oil film -- it is solely due to the high combustion-chamber pressures and the uncontrolled combustion that produces it.

Detonation usually produces damage mainly to the cylinder head and piston-crown which looks like very coarse sand-blasting.

It is often the small particles dislodged by this "blasting" of the head/piston that then get trapped between the piston and bore which leads to galling/scuffing -- even if there is adequate oil (of whatever type) present.



Bad Tooth -> RE: Piston Damage (4/13/2008 8:12:30 PM)


quote:

ORIGINAL: panzerd18

Is it worth the time to fix when brand new engines are so cheap and the cost of parts to repair is so high?


For me it was. I learned a few things I didn't know about these little engines, and had fun doing it. The cost to repair this wasn't all that high either.
- Piston - $29
- Ring - $20
- Bearings - $7

I have been very happy with this engine as I have had it for almost 4 years. To replace it with a similar engine:
.50sx (approx) $150
.46ax - $105
Magnum 46 - $70
Supertigre 51 - $75, etc.
(+ S&H)
Break-in, etc.

I know that some of the engines I've listed here come close to the total cost of my rebuild of $57, but I have engines other than os that I have not been happy with in the past (some included on this list). One that I haven't tried is the Tower .46 that I have heard good things about. Thought about getting this one but it's backordered.

But it really comes down to 3 reasons:

1. I wanted to try and revive it. I was really curious to see if it would run again and how well.
2. I liked this particular engine on my Venus, I didn't really want to try another engine.
3. And it did save me money to repair it. When someone suggested that I didn't need to replace the head; that was the deciding factor.[:D]

Now as for what the future holds for this engine I don't know? Thanks to your suggestions I have learned a lot more about how I should care for my bearings/engines; so hopefully this engine will last many more years with improved maintenance.[sm=wink_smile.gif]




buzzingb -> RE: Piston Damage (4/14/2008 8:43:35 PM)

I wish you the best of luck with this engine but there still could be problems for you down the road if something was overlooked or installed incorectly. People that rebuild automotive engines will tell you that there are many ways to make mistakes rebuilding engines. Most mistakes won''t result in failure right away but will show up down the road. Run about 30-40 gallons through the engine and report back to us on how it is holding up.



djlyon -> RE: Piston Damage (4/14/2008 9:12:45 PM)

Good on you bad tooth and I'll bet you had fun fixing it too. The detonation I was referring is not caused by a lean run but rather by small amounts of gas being trapped between the piston and the squish band. Now that you have some dents in this area you can get small amounts of super compressed gas pre-igniting. The best description of the sound is frying bacon. This condition can also occur on undamaged engines that do not have a tapered squish band (manufactures choice ). Sometimes you need a guy with experience with detonation to listen to it to tell for sure if you got it. Thinking about it I'm not sure the situation I'm describing is properly called detonation.

Denis



jetpack -> RE: Piston Damage (4/14/2008 9:35:47 PM)

I''ve noticed it is a mix of frying bacon and a steady apparent hiss that you can hear over the exhaust note.



Bad Tooth -> RE: Piston Damage (4/15/2008 12:40:12 AM)


quote:

ORIGINAL: buzzingb

I wish you the best of luck with this engine but there still could be problems for you down the road if something was overlooked or installed incorectly. People that rebuild automotive engines will tell you that there are many ways to make mistakes rebuilding engines. Most mistakes won''''t result in failure right away but will show up down the road. Run about 30-40 gallons through the engine and report back to us on how it is holding up.


That glass is definitely "half-empty" LOL! [sm=what_smile.gif]

The engine since it was new only has probably 7 gallons through it, so if I get that out of it I think I''ll be happy. I don''t know about 30-40 though. It''s ok, I''m happy with the engine. Others may not be, but I''m getting more than I want out of a busted engine: learning and an engine that runs.[:D]

If it breaks down again that''s ok too. I mean it''s not like you''re losing a tooth! Just an engine; right?[sm=wink_smile.gif]



XJet -> RE: Piston Damage (4/15/2008 12:57:37 AM)

I''m with you Bad Tooth!

If it runs then just use it until it stops Even if it only lasts a few months, that''s a few months you''d not have got out of it otherwise.

And as someone who''s had quite a few engines that *should* have failed a long time ago but just keep on going I suspect there''s every chance the engine will give a lot more service before it finally packs-up.



somegeek -> RE: Piston Damage (4/15/2008 1:03:34 AM)

Right there with you, BadTooth. I''d like to be there when the naysayers are dropping their damaged engines in the trash. ;) Run it til it croaks.

somegeek



Bad Tooth -> RE: Piston Damage (4/15/2008 1:24:53 AM)


quote:

ORIGINAL: somegeek

Right there with you, BadTooth. I''''d like to be there when the naysayers are dropping their damaged engines in the trash. ;) Run it til it croaks.

somegeek


By the way SomeGeek, how is your 46 getting along?



somegeek -> RE: Piston Damage (4/15/2008 4:20:39 AM)


quote:

ORIGINAL: Bad Tooth


quote:

ORIGINAL: somegeek

Right there with you, BadTooth. I''''''''d like to be there when the naysayers are dropping their damaged engines in the trash. ;) Run it til it croaks.

somegeek


By the way SomeGeek, how is your 46 getting along?


I''ve not been able to fly since getting it back together. It ran up nicely after I replaced the bearings though. Think I lost ~200rpm from peak. I can''t knock that.

somegeek



rainedave -> RE: Piston Damage (4/15/2008 5:17:52 AM)

I''m with y''all 100% on rebuilding these engines. It is a lot of fun. I''ve learned a heck of a lot from fixing up old engines myself. I''m glad to see that your engines are running again.

David



plugin -> RE: Piston Damage (5/14/2008 5:21:01 AM)

I got a similar failure as somegeek's and Bad Tooth's on a 46AX, NTN bearings also. The front bearing seems to have held up well but I managed to catch the rear one about 2 flights before it shattered. All the balls are dented but they are all still in one piece. The debris still managed to seriously hurt the piston and somewhat the sleeve.



DarZeelon -> RE: Piston Damage (5/14/2008 6:24:33 AM)

It seems OS may have received very large batches of defective NTN bearings... and are intent on installing all of them in their production engines.

I can see no other reason for these bearing to have such short lives in so many of their engines; while engines made by other manufacturers, which use identical size bearings, rarely if ever suffer a failure.



proptop -> RE: Piston Damage (5/14/2008 6:48:57 AM)

JMO but I think they have been using somewhat less than desirable quality bearings for years...

I am also of the opinion that the bearing problems and sleeve plating flaking can be related. (at least in some occasions )



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