Peter Jenkins Posted September 3 Share Posted September 3 52 minutes ago, Edgeflyer said: Thanks Peter. What about an NGH 17cc petrol? Is that too big and heavy? I'm wondering whether the 15cc or above 2 stroke like os91 will be too noisy. We have a noise testing club site. Problem with most petrols is that they are heavier than the equivalent glow (ignition and extra battery for that) don't have the power output plus they are usually much noisier unless you spend as much as the engine on a decent silencer. The OS91FX is sadly discontinued but examples are still available. Mine was second hand but NIB. It is a bored and stroked OS61FX and has the same crankcase with the same bolt holes. I just took the 61 out and replaced it with the 91 and didn't see any change in CG position. The 91 comes with an extra section for the silencer and evdn with the second smallest prop that is recommemded was pretty quiet. For its size, the Wots Wot is very heavy and not as good as an IC Wot 4 at aerobatics. I have Wot 4 with an Irvine 53 and a throttle pipe and that really is vertically unlimited. It also has better directional stability compared with the bipe. I fly both and they are great fun but I prefer the Wot 4. I wouldn't describe either as aerodynamically pure but by using mixes you can overcome the worst of their habits. Both are knocked into a cocked hat by the Miss Wind referred to in one of the posts above - but then that is a specialist aerobatic aircraft. Quote Link to comment Share on other sites More sharing options...
Edgeflyer Posted September 3 Author Share Posted September 3 Hmm I thought my Saito 82 FS might be best but I quite like the sound of this Os 91fx As it happens there's a cheap one Flea Bay now. Could you please have a look? Maybe condition is good enough? https://www.ebay.co.uk/itm/204958775896?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=uV8ZYtMpQMu&sssrc=4429486&ssuid=Vr_cw50jTgm&var=&widget_ver=artemis&media=EMAIL Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted September 3 Share Posted September 3 Well, it's showing a fair bit of use. As I say, mine was a new in box, unused but don't know how long he'd had it. It certainly looked unused and, like all OS engines it was dead easy to start and set up. Indeed, after the first run of the day, choke, attach plug heater and a back flip gets it going. I suppose for £50 it's worth a gamble. It has some damage to the carb opening. Sorry just seen the bid has closed but you can contact them and make sn offer I expect. He says its got good compressikn so that's encouraging. I'd give it a go. Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted September 3 Share Posted September 3 Looking at the external state of that engine and the use it may have had, it's likely that the liner has had it plating stripped, this is a regular occurrence with OS 2stroke engines of this vintage. A friend recently bought a second hand OS 61FX to discover the liner was in a shocking state and replacements are either very hard to find or far more money than he paid for it. I personally have had this issue with OS engines on a number of occasions. It's worth checking out what spares are available before buying. 1 Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted September 3 Share Posted September 3 Good point. Quote Link to comment Share on other sites More sharing options...
Edgeflyer Posted September 4 Author Share Posted September 4 Well it is offered as used condition so I could remove the head and check the liner and if it is stripped playing then it goes back. Quote Link to comment Share on other sites More sharing options...
GrumpyGnome Posted September 4 Share Posted September 4 If you're contacting the seller, ask them to take the head off and show photographs................. less hassle I'd have thought 1 Quote Link to comment Share on other sites More sharing options...
Edgeflyer Posted September 4 Author Share Posted September 4 I got this thought from Just Engines when asking about spares for a potential OS91FX "I think the 91 FX was a ringed engine, I am pretty sure we can supply a ring. You might be able to save the liner with some very fine wet and dry. The first thing would be to get it apart and assess the damage." So this seems to suggest liner delamination is unlikely? Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted September 4 Share Posted September 4 J.E. are correct, the O.S .91 FX is indeed a ringed engine so might be worth saving. More info here OS FX .91 engine review * Chris * Quote Link to comment Share on other sites More sharing options...
Masher Posted September 5 Share Posted September 5 6 hours ago, Christopher Wolfe said: J.E. are correct, the O.S .91 FX is indeed a ringed engine so might be worth saving. More info here OS FX .91 engine review * Chris * However they are not correct about the wet and dry! You will not recover a piston liner if the plating is stripped. Quote Link to comment Share on other sites More sharing options...
Edgeflyer Posted September 5 Author Share Posted September 5 No clearly played liners once stripped can't feasibly be saved. I was under the impression possibly flawed as usual that the liner with a ringed engine was not plated as the principle was for the ring to expand with heat to form a gas tight seal. Does a anyone know for sure if the ringed 91fx has a plated liner? I found an engineering company that makes unplayed liners apparently of any specific dimensions. Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted September 5 Share Posted September 5 2 hours ago, Masher said: However they are not correct about the wet and dry! You will not recover a piston liner if the plating is stripped. The cylinder is of hardened steel construction. Typically, such cylinders are not plated. The wet and dry paper (I use #400 grit) is used to lightly scuff the liner with a cross-hatch pattern to break any existing glaze and to assist a new (usually cast iron) to bed in. The instructions in the article that i referred to are pretty accurate. Regards * Chris * 1 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted September 5 Share Posted September 5 I'm sure the OS91FX engine I once owned was ABN construction so I don't think they are necessarily all ringed. Quote Link to comment Share on other sites More sharing options...
Christopher Wolfe Posted September 5 Share Posted September 5 3 hours ago, Andy Stephenson said: I'm sure the OS91FX engine I once owned was ABN construction so I don't think they are necessarily all ringed. You may well be correct Andy. I still have some O.S. 40 & 45 FSR engines (they are my favourite O.S. two stroke engines from days of yore) The O.S. 40 FSR engines came in both ringed and ABN variations. The change to ABN (apparently) came at a time when environmental considerations regarding chrome plating became legislated in Japan Also, ABN was cheaper to implement (no electricity required) and so O.S. took the plunge. Other countries whom were not quite so environmentally concerned not only cloned O.S. engines but actually supplied pretty good chromed plate liners copied from O.S. So I happen to own both hardened steel/ringed and ABN versions of this particular engine. In Australia, the Control Line Combat blokes (open combat) will give an arm and a leg for a ringed O.S. 40 FSR as they hot restart so sweetly after a dorking 🙃 * Chris * Quote Link to comment Share on other sites More sharing options...
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