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Discussion Starter #1
This will show how old and out of date I am. I was looking at another guy's thread here, with a photo of his badly-wiped CR125 piston. Back in the Pleistocene Era we used to get the smeared aluminum out of our cast-iron cylinders with muriatic acid before honing. What's the procedure for cleaning up a Nikasil-plated cylinder? I've never run one.
 

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Discussion Starter #3
Thanks, Dan.

Your "signature" (or internet handle, or whatever it's called) prompts another question. Seems like I'm starting to see quite a few of these things with mixed caps and lower-case letters; is this a security measure I should know about??
 

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You have to be a lot more careful with HCl in a plated cylinder than with an iron liner. The surface of a plated cylinder is a high nickel content silicon carbide matrix but the material backing that is aluminum. Muriatic acid (HCl or hydrochloric acid) can and will eat the aluminum out from behind the coating if there is even the tiniest of nick in the coating. Make SURE you don't leave the liquid in there any longer than absolutely necessary (I recommend wiping it in and out on a terry cloth towel!) to get the job done.
 

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Another case for an Iron liner bore; I believe that the only reason for a plated bore is for the manufacturer to save money. Eventually; they all go at one time or another. A cylinder re-bore is kind of a good thing.

JT
:thumbsup:
 

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Discussion Starter #7 (Edited)
Personally, I like a (high-quality, properly designed, properly installed) iron liner, but while a plated bore may save money, that is far from the only reason for doing it, and the very best developers of the last 2-stroke GP engines are adamantly opposed to any kind of sleeve (these are professional engineers employed full-time for years by motorcycle company racing teams, and have spent their careers doing endless dyno-pulls and going from race to race to see how their developments worked on the track). Heat transfer across the interface between sleeve and cylinder is significantly impeded, no matter the fit, and even if it were an aluminum sleeve in an aluminum cylinder. This is not as critical in boat racing, since we have a whole lake-full of cool water that gets rammed into the motor, absorbs the heat, and gets dumped back into the lake. But it is very important in bikes, karts, sleds, etc., where the water coming out of the radiator is already quite warm, no matter how big the radiator (maximum practical radiator size being restricted by vehicle aerodynamics and packaging considerations).

One of the classic modes of 2-stroke piston failure was the "four-point seizure," caused when a rider throttles up a lot of power before his engine was sufficiently warmed up, and the hot, expanded piston rubbed against the still-cold and unexpanded cylinder. This particular failure mode has become a good deal less common as iron sleeves, with their poor (relative to aluminum) thermal conductivity and the impeded heat transfer across the iron-aluminum interface, have been replaced by Nikasiled aluminum cylinders, which warm up a lot quicker than the old sleeved cylinders.

For any engine that is not having to make state-of-the-roadracing-art power levels, lap after lap, and this applies to nearly all of us, cylinder sleeves are fine, even preferable in many ways as John states. Small aircraft engines made by companies such as Lycoming still are built with steel sleeves. But if you are pulling fifty-plus horsepower out of a 125cc cylinder down a long straight, and trying to stay out of detonation with recirculating coolant that at its coldest point is already hotter than you can touch, you're stuck with Nikasil.
 

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Point well taken Smitty; Why do plated cylinders have the same skirt clearance? Warm up aside.
There have never been steel sleeves, they are cast iron or ductile iron not steel.
 

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Discussion Starter #9
www.lycoming.com

SUBJECT: Inspection and Reconditioning Procedures for Nitride Hardened Steel Cylinders
MODELS AFFECTED: All Avco Lycoming engines with nitride hardened steel cylinder barrels
TIME OF COMPLIANCE: During overhaul of the engine
Many Avco Lycoming engines are presently manufactured
with cylinder assemblies that incorporate
nitride hardened steel cylinder barrels. Because this
cylinder barrel surface is hardened, the repair procedures
are different from those for plain steel or
chrome plated steel cylinders. Worn nitride hardened
cylinder may be returned to Avco Lycoming to be re
 

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Aircraft cylinders are a different story; I haven’t seen one on a cycle lately.
Cycles don’t use steel cylinders. We’re starting to split hairs
 
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