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Old 04-14-2009, 03:48 PM   #1
sikorskys76
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Default how much scratches is too much on piston and cylinder

I have an os 50 and I took it appart and theyre is some scratches on the piston and sleeve.What would you consider too much?Can I polish them?
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Old 04-14-2009, 06:15 PM   #2
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Pictures help and a little info as to why you tore it down
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Old 04-14-2009, 08:37 PM   #3
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I will add pics tomorow.The reason I tore it down was because it quit in flight.and it wouldnt restart.When I looked at the piston the ring was seezed on the exaust side letting all the compression go.

I will ad pics tomorow
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Old 04-14-2009, 09:05 PM   #4
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The piston can get quite a few scratches on it and still be fine. The ring is more critical.
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Old 04-14-2009, 09:32 PM   #5
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What about the sleeve? There's no deep gouges...I bet there .001 if that.
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Old 04-14-2009, 09:40 PM   #6
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How much compression is there when you hand-turn the crank? As long as the compression is good, you're fine.
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Old 04-15-2009, 08:20 AM   #7
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Quote:
Originally Posted by TheBum View Post
The piston can get quite a few scratches on it and still be fine. The ring is more critical.
Have you seen a scratched piston, without a scratched sleeve? (not being smart, real question).
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Old 04-15-2009, 08:43 AM   #8
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My experience is admittedly limited, but my piston currently is scratched and the engine still runs fine. I would assume that you could have scratches on the piston but not on the sleeve because the piston is a softer metal than the sleeve.
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Old 04-15-2009, 11:00 AM   #9
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Here are the pictures.

Can I polish it with some 800 grit and put a new ring?

I can put the ring on the one side,wich is the side it was stuck on when I took it out.I would have to file down the groove were the ring goes in to make the ring go back in.
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Old 04-15-2009, 11:44 AM   #10
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The best approach is to get a piston,ring,sleeve set and a main bearing just because.

The next best approach is to clean it up and put it back together as is.

With regards to the sleeve, before going at it with an abrasive, soak it in muratic acid, rinse, and re-oil. The muratic acid (pool supply) will remove the smeared on aluminum I see in the photo. Odds are, once you get rid of the smeared aluminum, the sleve may be fine.

Before you ask ->
http://www.garagejournal.com/forum/s...ad.php?t=29991

With regards to the piston, the object is NOT to remove the scratches!!! The object is to remove any high spots that extend above the diameter of the piston. Avoid the lower parts of the skirt at all costs.

Finally, make sure the ring gap is cleared of debris, and that the ring moves freely.

Finally, don't run the stinking thing so lean again!
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Old 04-15-2009, 01:15 PM   #11
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Quote:
Originally Posted by JimLerch View Post
The best approach is to get a piston,ring,sleeve set and a main bearing just because.

The next best approach is to clean it up and put it back together as is.

With regards to the sleeve, before going at it with an abrasive, soak it in muratic acid, rinse, and re-oil. The muratic acid (pool supply) will remove the smeared on aluminum I see in the photo. Odds are, once you get rid of the smeared aluminum, the sleve may be fine.

Before you ask ->
http://www.garagejournal.com/forum/s...ad.php?t=29991

With regards to the piston, the object is NOT to remove the scratches!!! The object is to remove any high spots that extend above the diameter of the piston. Avoid the lower parts of the skirt at all costs.

Finally, make sure the ring gap is cleared of debris, and that the ring moves freely.

Finally, don't run the stinking thing so lean again!

Thanks for the info Jim!!

Ive been having problems since I put my new bearings in it.I just got a spare engine last night and flew 10 tanks to break it in.

That way I can order the parts.I have a set of boca ceramic bearings I will put in it and I may as well change the whole works,Piston,sleeve,rod and rings.I paid good money for the ceramic bearing So I may as well put it back togheter properly.

My initial problem was that It was always going to full rich on my carbsmart in all the settings.The thing had alot less power and was really rich.That was after my bearing change.

I havent put in my sensor yet on the new engine.I wanted to break it in properly and then fly a bit with it,and only then put in the sensor to see if it wil do the same full rich all the time thing.

I use a similar solution at work.ITs called W01 and its a diluted solution of phosphoric acid.But I will definitaly get the product you are talking about and try to save my sleeve as a spare.As for the piston and rings I may as well toss em.

Thanks alot again!!
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Old 04-15-2009, 02:11 PM   #12
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The cost of all those parts is getting close to justifying a new engine anyway.
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Old 04-16-2009, 09:40 AM   #13
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You definately stuck it. I'm impressed, that's hard to do with the high oil content we run.

You could maybe save the sleeve if you had access to a precision hone. You'd have to clean the Aluminum off the cylinder walls with mecuric acid first. Frankly, I'd buy a new sleeve. The piston and ring are done and, as mentioned, you probably need to replace the main bearing too.

You're looking at about $100 to fix. A new engine is ~$180.
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Old 04-16-2009, 10:45 AM   #14
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This engine is not that old.It has maybe 10 gallons MAX through it. I may as well get the replacement parts and do it all up again.IT will be spare.

Thanks for all your input guys I really appreciate it
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Old 04-17-2009, 11:19 PM   #15
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Quote:
Originally Posted by TheBum View Post
The cost of all those parts is getting close to justifying a new engine anyway.
Thats what I was thinking...
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