Changing piston do you need to change liner?

[jschief]

I ran my os50 hyper a little lean and the piston broke at the ring land and so did the piston ring. My question is the sleave is just fine but I was told that the liner should be changed also so the new piston will seat properly. Can I get away with just leaving the liner and sanding it a little to make a rough surface to seat the new piston or should I buy a new liner also.

The prices of these parts are just crazy :!:

[WayneBrown]

install the new piston and treat the motor as if it's brand new and break it in again..
It'll be fine.
Don't hone, sand, or screw with the liner, just drop the piston in..

[RC-Bearings]

I would use the finest brake cylinder hone you can find and run the hone ONE TIME through the cylinder. You don't want to remove metal, just rough up the surface so that the new ring will properly seat. The reason I would do this is each time a ring is seated, it imparts its own shape anomalies to the liner. A new ring probably won't match those anomalies quickly and you will have more blowby and a slower breakin. :mrgreen:

[WayneBrown]

okay, makes sense... But how do you do that on a composite cylinder? The modern cylinders are steel, with a layer of brass and then chromed. A hone will destroy the finish, period. Not a good idea..
Install the piston and break it in as new. Blowby is expected to some extent during break-in, but is marginal.
As the piston is a softer material than the liner, the piston wears to the cylinder not the other way around.

[RC-Bearings]

I thought he was talking about a ringed engine?

[WayneBrown]

either ringed or ABC, liners are the same.

[RC-Bearings]

Every ringed engine I have been involved with except for the AAC types have the ring running on a hardened steel liner. No chrome or other exotic processes. I just finished putting together two OS heli engines and both had bare steel liners.

I have also never seen a chromed steel liner in an ABC (or ABN) engine. These were all brass liners with chrome or nickel plating. I would agree that you don't hone those!

[DavidH]

When I install a new ring. I take 600 grit wet/dry sand paper with some light oil. I swirl the paper inside the liner several times lightly. Don't want to remove any material. Just smooth things out some for the new ring to seat into place when the engine is running.
You want the ring to seat to the smoother surface.

David

[SteveL]

Ok I like Wayne was, and still am, under the impresion that all of our engines have a chrome sleeve. However, I thought it was chrome plated brass an I just stuck a maginet to one :shock:
If it is chrome you would not want to sand, hone, or otherwise; however if it is steel a quick hone job would not hurt. So does anybody know for sure what they are made of?

[jschief]

Some one recommended a little scotch bright to the sleave and I did this before I got everyones answer. I do not think this removed any material, I am going to try it when I get the parts this weekend. The sleave looks as smooth as it did before I put scotch bright to it.

[SteveL]

scotch bright could not hurt chrome so you ave done no harm.

[RC-Bearings]

THEY ARE NOT CHROME PLATED! :arggg: They are a martensitic steel. I have a brand new one right in front of me.

[WayneBrown]

what is martensitic steel?

[SteveL]

Here is a link to an explanation. (Basically a high strength stainless.)
While I respect Paul's knowledge on bearings I am not sure I am buying this one. I am not saying he is wrong I just don’t think this is what they are made of after doing some reading.

http://www.outokumpu.com/pages/Page____5552.aspx

[RC-Bearings]

Martensitic refers to the crystalline structure of the steel, not its composition. Yes, there are martensitic stainless steels. There are also martensitic mild steels and martensitic hardened steels.

Here is the technical explaination:

http://en.wikipedia.org/wiki/Martensite

After checking some more, OS may not use martensitic steel as most others do. In any case, it is not chrome plated.

[SteveL]

I was thinking more like chrome moly (Same material as most piston rings)

[RC-Bearings]

Most model engine piston rings are cast iron. That's why they are so fragile.

These cylinders are made from a hardened, fine grain steel.

[WayneBrown]

oh man, that reading made my head hurt..