OS Max 40 SF/S

[Alex Givan]

 Hey Guys-
           In my travels I came across a brand new in the box OS 40 SF/S on the bottom shelf way in the back of an old hobby store. As far as I can tell this is very close to an FP 40 but has roller or ball bearings that the crank rides on and the needle valve looks like a "J" hook instead of a round knob on a spring shaft like on the FP models I have seen. I had an aircraft in mind that I  envisioned using an LA 46 on but chose to get this engine and take my chances with it's run quality's and power output. If anyone has any knowledge of the engine let me know. Should I keep it or Pawn it off for an LA 46?

[Larry Fulwider]

Alex --

Does it have a side exhaust? Someone here should know a little about an OS with identifiable bearing races. The only one I ever heard of was the VF, and I guess this isn't one of those, huh?

Larry Fulwider

[Balsa Butcher]

For our event the LA-46 is a much better engine. 

[Richard Grogan]

I have one, but it hasn't been on a plane yet, just the stand.Runs really strong.It was/is an RC version, put a Delrin venturi and ST NVA on it.It It has the RC crank in it. Bought a CL crank for it, but I need the thrust washer puller to change it. A bit porky with the bearing job, but I feel it will most likely keep up with .46 handily.I offered it to Dee to try out, but he's happy with the LA 46 on his Ringmaster 576.

[Andrew Hathaway]

The 40 and 46SF-S were the OS answer to a serious stunt engine in the early 90's.  They've got the nifty banjo fitting nva with a locking collet, and a stunt timed crank... They sold for roughly two and half times the price of a 40FP-S.  Unfortunately the nifty NVA has too many places where it can develop leaks, resulting in inconsistent runs.  I've got two of the .46SF-S engines, but only one ever made it onto a plane and it's never given me anything but trouble.  It might work better if I changed the NVA, but at this point I'm sick of fighting with it.  I've seen a few that worked really well, but they were reworked.  If you haven't run it yet and want to use it, I'd recommend having it reworked by a reputable engine wizard.  

[Larry Fulwider]

The 40 and 46SF-S were the OS answer to a serious stunt engine in the early 90's.  They've got the nifty banjo fitting nva with a locking collet, and a stunt timed crank... They sold for roughly two and half times the price of a 40FP-S.  Unfortunately the nifty NVA has too many places where it can develop leaks, resulting in inconsistent runs.  . . . 
  

Andrew --

You are describing (from what I've read) VF-like issues. Is this a side exhaust version of the VF? If so, does that means it could / should be set up like the VF?

Larry Fulwider

[Andrew Hathaway]

I've run a 46VF on a pipe and it worked exactly as advertised.  The SF has never run a full tank of fuel, the same from start to finish.  I can't emphasize the problems I had trying to get the SF-S to run well.  It wasn't as much a problem of needing to run high rpm - low pitch, instead of trying to run a 4-2-4, as much as the engine wouldn't run the same in any mode consistently.  Since it was built as a stunt specific engine, I'm not sure that setting up like a VF would work since the stunt version has a different crank then the RC version. 

The VF is more closely related to the FSR series from what I can tell.  The SF has the same mounting dimensions as the VF, but it doesn't have the two piece case.  The SF has a one piece case, side exhaust, twin BB, ABC (ABN?) piston/cylinder, etc...  The OS time line shows the FSR as a 1980 engine, and the VF also a 1980, while the SF is shown as a 1987.  The dates they show don't always match with what I remember...

FSR


VF


SF

[Bill Hummel]

Alex, a local flyer, John Duncan, used a Randy Smith reworked 46 SF for many years with much success!  Outstanding stunt run, with MUCH more usable power than a 46 LA.  If you're headed in that direction, a note to Randy might help with answers.