In the ancient times, when my friends bought several new ST-46 engines, some pieces did not build up their compressions after reasonable running time. From my FOXish times I have had some bags of Lustrox, and properly using them, we could break in the Tigers, getting affordable compression.
(I never knew, what is Lustrox made of, and present days is it obtainable, or not... )
Istvan

Dan,
I think, not only one guys mixed the Lustrox (the soft, white powder), with the FOX lapping powder. (Dirty, purple powder, korund, or in other words: Aluminum-oxide. Chemically same as the Ruby. And same hard. Naturally, never allowed to put into running engine. 
Istvan

Paul,

Is the ST chromed or with steel liner?
The *only* correct way is to first make sure that the liner & piston are in good shape (roundness, straightness) and then to measure the parts and make a ring from bar stock to fit with those very parts. Especially with chromed sleeve you must know the exact diameter and machine the ring according to that. Then you must trust that the parts you measure and produce are really round, it's not that simple. The easiest way to ensure it is to use good quality machine tools.
That is the reason why ringed engines in our use have the reputation that they have. There is nothing wrong with the concept, just lots of bad workmanship.
But to your original question; I wouldn't use any loose abrasives for fitting the parts together. The ring is most often made of cast iron, which is a great carrier for abrasive particles. so the particles will get stuck in the ring and you'll wear out the cylinder instead. A big no-no. L

I think you may be asking the ST 51 to run like a FOX 35. The short answer is Don't. Run it with a low pitch (like a 3.75 - 4) and in a medium 2 cycle, with 10 - 15%N and at least 25% total oil (50/50 is good). Don't overload it with to large a prop (11 1/2 - 12" diameter is good) to keep the heat under control. It will handle any 46 size ship well (like a Sig Magnum size) but not a 60 size.

Best,    DennisT

I am looking for the best possible fit between ring and sleeve. That  is the subject of this thread. I never mentioned that I wanted to make the ST51 run as  a FOX 35. I never had a model with a FOX 35. I have been using the ST 51 since 1993. At the Wch in Sweden 1996 with an APC 11-4. Now I am using an 13-5 Brian Eather (not undercambered). I do some simple (reversable) mods to the engine It has sufficient power to pull a 60 size model (70 ounce) without nitro in normal temperatures at sea level. The engine is stable and I am happy with the vertical performance. It lacks braking power in windy conditions. (no pipe) But that's manageable. I am preparing a new engine and I replace the ring with the aftermarket UK version and I was wondering if there would be an optimal way to make the ring fit the sleeve. In the mean time I am also testing a Brian Gardner ABC Sleeve piston combo. Very promising, also better braking going downhill. Little down on power, but the venturi is 4.5 mm, so I can make it a bit bigger to get the power  up.

10.5x5.25 Eather three blades , as recomended for 40 FP's by Adamisin & Co. , give a deeper Four Stroke run , in a 65 ounce plane , for milder conditions . May give better ' BRAKE ' downhill ?, maybe .
Was surprised Id found another ' happy ' prop for it . BUT BIGGER & i cant see it unload into the two , with the 13 , unless youve bunged the bypass & hemi'd the head ? ( Be intresting to see a Big Jim G-51s insides )

For howling gales & 4 inch pitch , ive yet to try a G51 R.C. . The ' stunt ' sounds like the top end will shortly depart on the 10 x 4 three blade Tornado  . Pre Ignition im told . Rather resonant & acoustic , I say . Anyway .

THE BOOK says 11 x 6 . Cant you read .  ( the INSTUCTION MANUAL ) . a good place to start . Power is at 11.000 , so presumably it should be at 10.000 or so , in the two stroke .

RINGS : the ETA 29 ' book ' says " LAPPED " . Obviously its the RINGS that are lapped . METICULOUS CLEANING after getting grinding / lapping paste , near ANY engine is mandatory .
I start with the garden hose , hard out . ( youll get wet ) , then tip a kettle of boiling water over it . Then Acetone rinse . The Olde adage of if a white cloth marks , rubbing it , its NOT clean .

Brian Eather , again - ST .46 Rings  . To Quote ( ish ) TWO DOWELS , a ledge in one to acxcept a ring , floating . fore finger and fumb on dowle ends , hold sleeve in other hand and , and go to it . Check etc .
One can obvioulsly drill & bolt the dowles . the object is a even matte  " mated " finish . Used bores perhaps need ' deglazeing ' usually busted with light scratching with 600 Wt.  dual 30 Deg. cross hatch recomended .
( the period toonin info related holding ring in bore up to a strong light ,to check  for mateing , contricity / roundness etc .  GAP fitted opposite exhaust . i.e. at boost port . But G-51's are PEGGED ? ) .

I believe Supre Tigre 46 Rings were perhaps earlier softer ? for the CHROME BORE , the ' other ' later part number HARDER , for the unchromed sleeve . This is suposition but conventional logic in this respect .
FURTHER V early ( Stamped ' AA ' on lug edge , 46s &  ' V ' 51 / 56 , were pre U S World Engines ' soften em up ' directive ( seen in print ) as ten hours were thought excessive ' run in ' .

That Is , Ten Hours CAREFULL USE , and they were nearing peak performance - which with care & maintanance theyed maintain ! indefinately . From about 1970 S Tigres were ' mass production ' ,
Rather than selectively assembled by a young ROSSI , Himself .
HOWEVEr a Italian G 51 Stunt should improve , with care , so its itself at around four hours use , and will continue idefinately . Though in ten years the nitro may get at the bearings . Unreplaced the debris
might destroy the fit f the rest of it . So Bearing Replacement , could be regarded as regular maintanance , per decade , in regular use . Still - flushing & oiling afyter use & for winter storage helps .
However , if theres any lack of silky smothness rotateing sand plug , Decent Bearings will restablish its magnificance . The .46 rc muffler , tailpipe sawed off & 8 mm hole , will give a W Champs standard. run .

Your Overproped .

AND , Std, intake venturie , opening to .312 odd ( or so ) gently scraping to smooth the machined edges , makes you feel better if nothing else . Improves the run , as does a 1.5 m.m. drill - ( No 53 ? )
through the spraybar end to end and thru the feed hole. CLEAN OUT the sucker afterward . Provides more positve needle Adj. a Olde S T 46 Trick , from  ' the book ' as it was written . If it were ' Stock '
see its deburred , trial assemble , seat . Strip & clean . then fit . I give em the first two hours NO NITRO . They run good on straight 20 / 80 .  a gasket or two extra for 5 or 10 nitro , usually .Thats about IT .

Well, if the real diameter of ring is bore -2-3my at tdc, and all parts are well within roundness tolerance, you cannot go wrong. Ring gap depends on metallurgy, I'd go with 0,025...0,03mm. Axial play 0,02mm, providing the groove in piston is in a good shape.
The problem is that you don't know the diameter of aftermarket ring. If I had to use such, I'd try to buy it oversize and trim to size myself.
Maybe it's better to send the whole piston/cylinder group to the specialist to make the fitting work? Before you could do it with Bowman, maybe also with the guy in UK..? L

My rings came from https://www.benl.ebay.be/str/gcpistonrings
It is quality work, and indeed the gap needs adjusting. Just enter the ring in the liner, set it square with a piston and verify the gap and adjust with sandpaper or small dremel disk. Remove edges.

Thank you all for the feedback. I have learned a lot.
Great!!

    Fox used to advise pouring Lustrox into the intake of a running engine to "loosen it up" and "polish" it. They also sold a garnet powder that you were supposed to use for hand-lapping. Even when I was reading this in some early 70's model magazine, it seemed pretty nuts. This was when I started to realize the legitimacy of most engine advice.

   Sad thing about it was, you needed to do something, because many of the engines were so tight you couldn't possibly turn them over and starting them was out of the question. Factory test run my ass.

     Brett

 Sounds like a perfect business plan.
 Fun fact; I use the very same Meehanite iron for piston rings and lapping tools, to lap the very hard 100Cr6 steel wrist pins and crankshafts before diamond coating, and for finishing after the coating. Diamond paste sticks to it like cancer. L