flyerdave

My Feedback: (212)

A friend of mine has both of these engines and has never run either one. They are new in the box just like they came from tower hobbies.Before I buy one,my question is, what is the difference in the two? I had a OS40FSR years ago and it was the best glow engine that I ever owned.
Thanks

piper_chuck

My Feedback: (12)

You can find the specs for the 61SF on this page:http://osengines.com/engines/engine-...continued.html
Unfortunately, the FSR specs aren't there. OS used to include a sheet showing specs for the entire engine line. See if it's in either of the boxes, you can use that to compare.

1320Fastback

Buy them both!

I think the FSR was more of a pattern engine and the SF was more for sport.

Of course there's differences in them but someones else will know more.

iron eagel

I was told that the .40 FSR was a "fast" engine, I have one new in the box but all of the paperwork is pretty limited, just one sheet and quite a bit of that is in Japanese.

rcdude7

My Feedback: (264)

They are similar in power but the FSR is smoother running IMO and maybe a little lighter weight. Buy them both. They were both available in ringed or ABN configuration.

rcdude7

My Feedback: (264)

It may have been a fast engine by 1970's standards, but certainly not today. I have a NIB one also, along with a few used ones in my stash, and a "new" marine version fsr that is about 30-35 yrs old.

jeffie8696

The FSR has a bolt on muffler that usually breaks the crankcase in a crash while the SF uses a bolt through muffler that is more surviveable.
I think the FSR is tuned to the upper rpm range while the SF is slightly lower, at least my 40 sized ones are. Manufacturers have been lowering the tuning rpm range to run larger props at lower rpm to eliminate excessive noise.
In my opinion the FSR with its separate crankcase makes machining the ports easier and therefore breath better. Also makes it easier to change the bearings since you dont have to take out the liner.

landeck

My Feedback: (1)

jeffie8696 is correct. The reason given by OS at the time for going with a one piece crankcase on the SF series is that it provided a more solid front end reducing vibration as compared to the bolt on front housing of the FSR series. I have the .60 FSR ringed, .61 FSR ABN, and three .61 SF ABN engines. They are all great but I like the SF series little better than the FSR series mainly because of the bolt through muffler. The muffler mounting for the SF series is compatible with the later FX and AX series of the same size. One other thing to note is that the carb on the FSR series has a three needle valve set up with one for mid range. The SF series carb has a conventional two needle valve set up.

Bruce

MetallicaJunkie

slap an 11x7 on the 61 FSR and it will be happy is a revver the 61 SF is a longer stroke motor , and produces more torque, they are happier swinging bigger loads maybe 11x10 patter or 12" props.... my dad had a 61 SF on a 8ft Telemaster and he put a 13x6 and it seemed happy swinging it

landeck

My Feedback: (1)

My SF series engines like an 11x8 prop. In fact that is what Great Planes recommends for the .61 SF on the Ultra Sport 60. They also like a 12x7 which I use on a GP Super Skybolt, GP Super Sportster 60 and BH T-28 Trojan 60.

Bruce

Roary m

My Feedback: (67)

I have both engines in ABC and I wouldn't give either one of them up; They both run very well.

turbo.gst

My Feedback: (8)

Check which version the SF is. The early version had many bearing issues which resulted in a new case design that housed a larger rear bearing. After that, the SF proved to be an excellent engine that liked bigger props than the fsr. The fsr is a great engine as well. If you could afford it consider both.....

flyerdave

My Feedback: (212)

How do you tell which version it is?

s. wallace

My Feedback: (24)

If you mean the SF/front bearing question, unfortunately you cannot tell looking at the outside of the engine. The inside of the case was machined to allow the the larger bearing.

I ran a lot of these engines back in the mid-late 80's and I recall OS made the change fairly early on, maybe a year or so after the SF was introduced. The SF and rear exhaust RF versions were 'long strong' designs and especially in pattern (back then there were still designs using side - exhaust engines) they were often piped and running 11x10 - 12x10 props...mine loved the 12x10. Anyway, the load with the bigger props caused the front bearing life to be rather poor so OS made the change.

For sport flying I dont think I would give it a 2nd thought. Like many have said, buy both but if it were me and I could only buy one it would be the SF. I have one on a Hog Bipe and it easily turns a 13x6 APC.

Roary m

My Feedback: (67)

The SF came after the FSR series around 1985-86. The SF was stroked to turn a longer prop at lower rpms since the pattern world was moving to turnaround at that time. The SF delivers more torque at lower rpms, but the FSR is a great fast turning engine, very good quality.

Kweasel

My Feedback: (29)

Everyones experience has mirrored my own on this comparison. The 61FSR works nice with a 11x7, the carb acts too big for less rpm. The SF61 is more versatile and can work with less rpm although the SF will still spin an 11x7 just as well. I put an old OS61 carb on a Supertigre 75 and found more power with the same handling qualities as the OS61s they came from. My NIB 61s now sit in a drawer without carbs.

Roary m

My Feedback: (67)

That would be the 7D carb? Those were very popular and OS mad a long run of them.

MetallicaJunkie

some fsrs came with 7d same carb as the 91fsr and 1.08 and some came with a 7L slightly smaller bore, i also got one with a 7dx(61 FSR gold head special edition)

Roary m

My Feedback: (67)

I wanted one of those goldheads when they came out just to say I had one. I would have ran him into the ground by now. 7DX? Interesting.

turbo.gst

My Feedback: (8)

My OS 61 fsr(ring) came with a 7DV carb.

MetallicaJunkie

sorry DV is correct....thanks Turbo

Roary m

My Feedback: (67)

OH, ok, you threw me. I used to play with those guys and thought it might be a heli design that they tossed over to the air version. The goldhead was a commemorative to the FSR's. I have the 7DV on the VF's I have. don't know the dif.

turbo.gst

My Feedback: (8)

My 61 VF also has a 7DV carb. The 'V' looks to have a venturi insert.

turbo