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Author Topic: Looking for an OS SF-S Crank  (Read 237 times)

Online Peter in Fairfax, VA

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Looking for an OS SF-S Crank
« on: February 21, 2021, 12:06:13 PM »
So I have an OS SF that I'd like to adjust for stunt timing by installing a stunt crank (stamped SF-S).  Anyone have one for sale?  Also open to buying a whole motor.  My Pathfinder requires two ounces of nose weight, which I am thinking might as well translate to longer lines and a heavier motor than its existing OS LA 46. 

thanks,

Peter


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Offline Air Ministry .

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Re: Looking for an OS SF-S Crank
« Reply #1 on: February 21, 2021, 07:10:04 PM »
Got up to page 7 on Randy Smith / Aero Proiducts posts looking for his engine parts ad. . so its P 8 or earlier !!!!!!!!!!

Think it was $ 50 . New.

All those FSR & Clones interchange, tho maybe the T Tiger 46 is overly diametered in the flywheel. Nothing a touch of someting tecnical woulnt fix . Think the timeings the same .

Online Brett Buck

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Re: Looking for an OS SF-S Crank
« Reply #2 on: February 22, 2021, 10:16:00 AM »
So I have an OS SF that I'd like to adjust for stunt timing by installing a stunt crank (stamped SF-S).  Anyone have one for sale?  Also open to buying a whole motor.  My Pathfinder requires two ounces of nose weight, which I am thinking might as well translate to longer lines and a heavier motor than its existing OS LA 46. 

    I can't help you on the crank, but I was also unaware there were two different versions of it. All the good results and anything I ever said about it were with converted RC engines. My limited observation is that "narrow" "Stunt" timing seems to make the 4-2 break more dramatic, and "wide" makes it smoother (and taken to extreme, makes it start backwards a lot, and produce good power that way in extreme cases). All of my RO-Jetts have the "wide" timing which apparently is the same as the Jett Quickie 500 engine.

  Point being, while it's fine to go looking for a crankshaft, don't give up if you can't get it. Just run it like a giant 20FP, maybe a 11.5-4 Bolly or Eather 3-blade to start.

    Brett

Online Peter in Fairfax, VA

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Re: Looking for an OS SF-S Crank
« Reply #3 on: February 22, 2021, 02:59:51 PM »
Brett,

In fact, the engine went back together today with new bearings.  The old ones had baked on crud that looked like a barbecue grill.  Feels pretty good and I'll try it on my Pathfinder ARF, which has a motor mount system that is quite flexible.  As I write, I am hoping that the engine will actually fit the airframe.

thanks for the comments about crank timing,

Peter 

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Re: Looking for an OS SF-S Crank
« Reply #4 on: February 22, 2021, 09:12:16 PM »
Had a look and the chunder tiger crank drops in . it'd give it .8mm more stoke. The piston'd go up .4 mm more. or 8 thou. so a 8 or 10 thou extra gasket'd be needed .

I found the stock SF liked the High Comp. and I couldnt get mine to work till I tried a 12 x 6 . The 330 intake needs 15 % nitro to keep things alight . Drys of on hard turns , like anything else over carbed .
Tho thats for a 80 ounce ship , so the 280/310/320 range depending on the weight .

Id take some 4 /5 & 6 in pitch props to test . Mine runs good deep into the four stroke on the 6 inch pitch . Uses a short Adamisin FP muffler . Seen it said these like to be choked on the exhaust as oposed
to a big open free breathing device , to stop the ' runaway ' .

Tho my FSR 45s seem best on 4 in pitch. yet to see if this stops them overspeeding on outsides in the wind , Tanks 1/8 down on these . SF seems to be aligned with spraybar for equaL RUN .
Think side mounted SF with tank inboard of spraybar ( Extended venturie ( easy with Royal 45 clone ) would self govern in gales .

Online Peter in Fairfax, VA

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Re: Looking for an OS SF-S Crank
« Reply #5 on: February 23, 2021, 08:54:52 AM »
I'll keep an eye on the intake size. 

Here is a photo of the old bearings.


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