OS Max 25 FSR or OS Max 25 FP

I am looking at pictures of engine for sale on ebay. I can not see any physical difference in the case looking at pictures. 3 engines have crank shaft bearings, same case shape, same carb, same muffler. The other engine has bushings.

OS Max 25 FSR bearing ebay 5909500156

OS Max 25 bearing ebay 5909570067

OS Max 25 bearing ebay 5909648950

OS Max 25 FP bushing ebay 5909582133

What is the difference?

Must be different bore, stroke, porting, ???

Gary, browse through the OS gallery of engines it starts at 1936 and goes to 2003.

http://www.osengines.com/history/ostimeline06.html

Went there. Checked every picture of OS 25 FSR engiens. Its not there. It must be an antique. I have 2 of them both are use but like new condition and they are really excellent running engines.

LAST EDITED ON Jul-19-04 AT 11:26 PM (CDT)
 
I don't quite understand what you're asking. The .25FSR is indeed listed on the OS page:

and here's the FP:

The difference between the .25FSR and the .25FP is that the former has two ball bearings, the latter no ball bearings supporting the shaft. The FP is probably also timed more mildly, though I don't know for certain. Both engines are somewhat of a cross between a side exhaust and a rear exhaust - the exhaust port on the sleeve actually points 45 degrees to the rear on the left, and the other ports are likewise rotated 45 degrees. The external exhaust flange on the case points to the side, the muffler mounts on the side, but if you grind all this away (I used to back when I used these engines for Combat) it's a "halfway" engine. No idea why OS did this - it got copied in many a clone. Though one possible reason I can think of is that the wrist pin ends don't ride over any open ports, so the wrist pin simply has two nylon ends that rub against the cylinder sleeve - no need for circlips or other retainers that prevent it from contacting the sleeve.

Current OS engines aren't made this way.

I guess OS has so may different versions of the same engines its probably not possible to put picture of all of them online. My engine is different. It has bearing on the crank shaft like in the picture above. My crankcase has a wide place on both sides near the carburator. The wide place is for ports inside the engine. The exhaust in the crankcase is on the side but the exhaust in the piston sleve is at a 45 degree angle back left side. I have been wanting to buy another 1 or 2 engines on ebay but I keep getting outbid. The last engine sold for $74.00 on ebay a new engine is 84.00 at the hobby shop. Might just buy a new engine it will probably be more up to date on technology and power anyway.