What do the letter designations on OS Max two stroke engines indicate? anything? FS FX FP SX FSR etc

FS= Four Stroke - it also means Far Superior

FSR - Ditto, but the "R" means "Ringed"

The suffixes: LA, FX, RX, AX, VZ, SX, etc. are just model designations (I think). Though "LA" is frequently referred to as "Lame" in the circles I fly in. ;-)

Some other designations

BB - Ball Bearing
ABC - Aluminum case, Brass sleeve that is Chrome plated. ABN would be nickel plated sleeve.
CL or C/L - Control Line (no throttle).
Ringed - piston has a ring (easier to break in)
II - Mk II - second model in a specific version

But I have an old (1984 model I think) OS Max 40 FSR that is a "2 stroke"

You may have to allow for Japanese translations too. Who knows and it doesn't truely matter in the greater Zen of things. Except for the LA (Lame Arse) engines they have all been pretty good. Even the LA's had their place, I guess.

AFAIK the model designation doesn't mean anything except possibly to the Japanese engineeers. The only one that may mean something though could be the original SR which was a pure racing engine. This was also their first Schneurle ported engine so it could stand for Schneurle Racing. Later engines were front induction but used the same crankcase in which case F might be Front induction but seeing they still have just SR cast under the exhaust port they were called FSR. It's the only way I can make sense out of it .

Front Shaft?

Go have a look at the [link=http://www.osengines.com/history/ostimeline01.html]OS engines timeline[/link].
Even though OS may have tried maintaining a system to the naming of engines there are many deviations.

It seems the only ones that are obvious is the FS designation for four strokes. For them, the F may be for Four Stokes followed by an S for Single and T for Twin.

Moving on to two strokes, I have some observations. The FSR line had Front intake and Schnuerle Scavinging, so maybe it's a combination of Front and the SR as suggested by downunder. Note that while it's possible that the R could have originally been Ringed, they made several ABC FSR engines. Further evidence suggesting that the F stands for Front is that the rear intake engines, such as the VR series, start with a different letter. However, that theory goes out the window when you consider there were several front intake, rear exhaust engines with a VF designation.

After spending 15-20 minutes looking through the 2 engine charts I have from the 80s, I found there were too many exceptions to come to any definite lettering pattern. The following is the closest I could find to a pattern.

F in the first position usually means front intake. However, there are also V designated engines with front intake, so you can't say that if it's not an F that it can't be front intake.

V in the first position appears to indicate something other than a "traditional" front intake, side exhaust configuration. On the V designated engines, the second letter usually identifies Front or Rear exhaust, but I found both front and rear exhaust R designated engines.

R in the first position appears to mean Rear intake.

G'day Min
FS does mean Four Stroke.
But FSR does not mean Four Stroke with ring,
I have a 61FSR ABC, it is a 2 stroke, I believe it means "F" front induction, "S" Schnerle ported, "R" is Racing, as opposed to the RSR which is rear induction.
Check out the time line here, http://osengines.com/history/ostimeline01.html

Then there used to be the MAX-S engines that could be R?C or control line depending on the carb?

The SX versions were usually a little more racy than the FX line.

Now there is the AX line that is cheaper to make but also run pretty good.

I thought the LA40 to be rather lame myself. I had two Magician Control line planes for more than 30 years. I sold them to a guy about 3 years ago and he flew them both one day. On one he had one of my old OS-max-S 35 engines and the other had a LA40 control line engine. Wow, what a difference. The LA40 would run circles around the old 35.

I never saw a LA45 that I thought was lame. The 45 always ran pretty good.