I bought this engine NOOB (New Out of Box) from a fellow about a year ago, but cannot locate the paperwork. I think it was an "F" or "SF", but cannot remember.

It needs a muffler. I have e-m'ed Tower and Macs but have yet to hear anything.

If someone could help me identify it, life would be much easier.

It is here: http://home.internetcds.com/~barbados/os61%20copy.jpg

It is apx. 33.85mm center-to-center for the muffler mounting holes.

The exhaust opening in the engine is apx. 21.45mm long and 8.8mm high.

The only other marking on the engine is the number " 6707" on the back housing, OS MAX on the left and "61" on the muffler side. It appears to be a ringed engine.

Any help would be greatly appreciated.

well its not a 61sf as mine has sf as a part of the casting, and the size 61 ia also on the casting not stamped onto the casting.

Hummmmm.....

Well, scratch the "SF", I guess.......

Seems like the "OS MAX" on the casting should be some sort of clue, but maybe they all say that.

Thanks, my friend.

P.S..... I just looked and the marking on the carb sez O.S. 7B.

I believe that it's an OS 61 FSR, thet were really nice motors from a time when OS really made quality motors

One vote for FSR!

.....Do I hear a second...!

Thanks, Dennis!

It looks a lot like the .45 FSR that I have.

two piece case and round head.

Well, the FSR seems to be leading the pack...

...It would seem logical they'd make a .45 and a .61 with similar parts, yes?

I think we have another vote for the FSR......

(why can't they just stamp it with the REAL MODEL NUMBER?....perhaps models change in different countries?)

Thanks, Spike!

It'll be an OS Max 61 FSR first made in 1980. Here's a link to a piccie of it
http://www.osengines.com/history/osm...-max-61fsr.jpg

Thanks, Downunder!

I checked the site again and am still somewhat unsure.....although your post gives me confidence.

Here's what they list:

16745 - 61 FSR ABC
16770 - 61 FSR
17700 - 61 SF Ring
17702 - 61 SF
17710 - 61 SF-P Ring
17712 - 61 SF-P
17801 - 61 RF
17802 - 61 RF-P

Now, if the FSR stood for "Front intake/side exhaust/ring", there are more than one to choose from in this list, yes?

I am unable to find a picture of it, just a parts listing.

So we know it's not an ABC, and another gentlemen stated it's not an SF, so the fickle-finger points vaguely to a 61 FSR.

I really feel you are correct, Downunder from Oz.

Any dedicated, died-in-the-wool O.S. men want to corroborate?

(Thanks again Downunder!)

Yes indeed, this is the FSR from the days when OS made real quality. One for the best ever made by OS, my opinion only!

Do not try to read to much into the OS nomenclature, it will give you a clue but not all letters mean something! The FSR was available ringed or abc, and the rear exhaust model was called VF or VR depending on intake location. There were also RSR models available in some sizes.

But to your question, RJL/MECOA has "Replacement muffler for OS FSR .61" for $21.99. You will not find it on the net pages but it is shown in their catalogue.

Thanks, DerFly!

...Thanks for the confirmation and the tip where to pick up a muffler!

After I felt that this was really going to be an FSR, I checked tower mufflers again and, sure enough, there it was....And the port sizes matched, too! However their OEM muffler was US$38 + ship...the US$21.99 sounds much better to me! Feel positive after your post!

The fellow I bought it from said the same thing---it was the best O.S. made....can't wait to fire it up!

Thanks again to all that took the time to help me....Believe me, It is very much appreciated.

Definatly a os 61 FSR A great engine , You will be verry happy with it. A quite powerful and responsive Engine!

Thanks, Ronald for your post!

Yes, I think it is a great engine now that I know what model it is and had time to run it. Why they quit making these is beyond me.

Initially I couldn't get it to run well, so sent it back to Hobby Services.

Two weeks later I got it back saying that the bearings were rough and other problems and they had no parts for it.

So I bench ran it and played with it for a weekend. It runs fine...superb, actually.

Finally I contacted Hobby Services asking why they couldn't have adjusted it for me as-is and they stated that it hadn't even been run!

If there are no parts, they apparently don't even run them!

No charge, but two weeks lost.

Anyway, it's going in my new build and I think it will be a winner!

Thanks, again!

The FSR series was the only 2 piece crankcase where you could pull the front crankcase section and change bearings without having to pull the engine off the plane the VR ducted fan engines were two piece blocks also but the one you have a picture of is an OS Max 61 FSR I still have two of these with hundreds of hrs. on them over the last 20 years. You can't say that about too many other engines !!!!

Crash & Burn, Hobby Services said that the bearings were "rough"? Did you look at them before starting it up? I think I would, just to be sure that I didn't tear up a really great engine. Bearing replacement isn't that hard and even if Hobby Services doesn't have bearings for it, I bet Boca Bearings does. (and at a better price to boot). Bearings can rust in an engine even if it hasn't been run, especially in an older engine. Take a look, just to be sure.
Suptter

I had an FSR-H in one of my heli's. It was a very nice running motor, but rear bearing life was not so good. It has a smaller rear bearing than most current 60's. If you do replace the rear bearing, I would buy the best quality bearing you could find. The Boca economy bearing only lasted me 3 cases. I did not run it lean, and always ran the fuel out and used after run oil. It was not rusty, just notchy. This was on 15% nitro, 20% all synthetic oil. I have since started running some castor (about 4%). According to Clarence Lee, the reason manufacturers have gone to one piece crankcases is because of flex. He says a one piece crank will spin a few hundred rpm faster than a two piece. He also stated that you could pick up rpm's just by epoxying the front crankcase half on. Interestingly enough, a lot of parts between the FSR and the SF are interchangable. (some SF's are long strokes, and will have a smaller piston, and a larger stroke, but the crankcase is the same). I put an FSR piston, liner, crank, and rod in an SF crankcase (the SF has a bigger rear bearing). The hard part was getting the ring to compress while sliding the liner down on top of it. There is no taper there, as with the FSR having a two piece crankcase you can slide the piston into the liner and then put the front crankcase half on. I got around this by putting a small o-ring over the piston ring holding it compressed. The liner pushed it down the piston, and then I just cut it off of the rod. FWIW.

Alan Angus

Suptter...yes, I did disassemble the engine prior to running it and it really looked pristine (to me).

I'm no engine mechanic, but could find no signs of rust or roughness and the bearings felt pretty smooth to me. I had checked it out after I bought it and it looked good then...That's why I couldn't understand why Hobby Services said there was a problem.

Boy, GMPheli, you really know your engines! Thanks for the tip on using good bearings in this engine!

What, exactly are the outward signs of the bearings going bad in service? Loss of RPM? Seizing? I want to keep my eye on this one but don't really know what to look for besides that rough feeling when spinning the prop staticly.

Again, thanks to all for your help and valued input.

I could tell that the bearing(s) where bad just by feel. It still ran fine. A sign that you have a bearing going bad is a flameout with a crushed glow plug element. A piece of the cage has gone thru the motor and killed the plug. This is why phenolic cage bearings are better, but more costly. If you have a bearing really go bad, the crank will run off center, and destroy its tight fit in the crankcase. This tight fit acts a a seal, now your motor will blow fuel from the front bearing. I plan on building an OS 70 (?) from SF, and SFN parts. I will use a longstroke SF crank and rod, with a short stroke SFN ABN piston/liner. The hardest part will be making a thick head gasket shim. The short stroke head extends farther down the liner than the long stroke. I think it will have a bore and stroke of 24 mm x 24 mm, I would have to check the specs. Not really sure of what the displacemant will be, just guessing.

Alan

Ahhh, now I understand! Thanks, Alan!

I've had some old engines that would blow fuel through the front bearing and always eating glow plugs....guess they may have needed new bearings, yes?

Anyway. I'll keep a close watch on this one. Going in a new build this month and we'll see how it does.

Thanks again for the great synopsis of the bearing failure....

....sure wish you lived next door...! LOL

It's a 61 FSR but what is interesting is the carb- the 61FSRs I have seen have 7D carbs (also shown in the OS pic that was linked on an earlier post), yours does not have a 7D. I had two 60 FSRs and they definitely had rear bearing issues, the 61FSR had a much larger rear bearing (which I believe is the same sixe as the 61SF). This should be a sweet-running engine for you, has a reputation as one of OS' best!