fly boy3 Posted August 27, 2012 Share Posted August 27, 2012 Hi all, My OS 46 LA, threw its prop in mid air yesterday. Found the engine had siezed and very hot. I am not a needle fiddler, and the carb has had the same settings for the past 6months, as that is the age of the motor. On checking found the needle mount to be loose ar rear of engine. Have not yey removed the engine to check. Any idea what may have caused this sieze up. Cheers Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 27, 2012 Share Posted August 27, 2012 How long are you going to keep us in suspense, fb3?? Pete Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 27, 2012 Author Share Posted August 27, 2012 Hi Pete, not long I hope !. If the backplate had become loose and allowed air to enter, would this lean the engine out ?. Cheers Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 27, 2012 Author Share Posted August 27, 2012 Sorry Pete, bad weather stopped engine removal. As my shed is totally blocked I have to work ouside at the moment. Torrential rain has put a stop to it. Will try not to keep you and myself in suspence for long if poss. Cheers Quote Link to comment Share on other sites More sharing options...
John Tee Posted August 27, 2012 Share Posted August 27, 2012 I was puzzled earlier Pete. Still am as there are apparently three replies but I can only see yours and no OP john Quote Link to comment Share on other sites More sharing options...
Eamonn Fahey Posted August 27, 2012 Share Posted August 27, 2012 I was trying to post a similar reply when my internet went down. Are you using witchcraft? Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 27, 2012 Share Posted August 27, 2012 I think fb3 is having some trouble posting, it would seem, as he has tried on another thread too.......... Pete Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 27, 2012 Author Share Posted August 27, 2012 No trouble this end lads exept the rain LoL. Cheers Quote Link to comment Share on other sites More sharing options...
Prop Nut Posted August 27, 2012 Share Posted August 27, 2012 Seized by what? Laughter? Fright? A large bird of prey? Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 27, 2012 Author Share Posted August 27, 2012 There was an element of fear I suppose as it had to be a cross wind landing. all went well though. Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted August 27, 2012 Share Posted August 27, 2012 FB3...where are you------ i cant remember the last time i saw an engine seize up .... some thing badly wrong to cause it... ken anderson ne..1.. where is FB3 dept Quote Link to comment Share on other sites More sharing options...
Pete B Posted August 27, 2012 Share Posted August 27, 2012 Send out a search party - has fb3 slipped through into cyberspace???........... Pete Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 27, 2012 Author Share Posted August 27, 2012 Hi all, all will be revealed to morrow when i can manage to check it out. With all this interest I am getting worried incase I might have to spend any of my old age pension on it LoL. Hi Pete B, could it be the heat in France that is preventing my signals getting through. Ha Ha, just a joke. Still raining here you lucky lad !. Cheers ps what size nut fits the OS 46LA motor ? Edited By fly boy3 on 27/08/2012 22:38:48 Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 28, 2012 Author Share Posted August 28, 2012 Seems I owe a apology. My posts are not appearing on the thread but are on the list., but they are appearing on my PC. Perhaps a mod can look at it please. Cheers all. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 28, 2012 Author Share Posted August 28, 2012 Ok I'm back on the air thanks to the Mods. Cheers. Still not found time to remove engine. Here is an update. Motor is free but very tight on TDC. removed plug, turning competely free. Put plug and prop back on very tight on TDC as before. This motor has had about 4 full tanks of fuel run though it in the air and 1 on the ground. Is it possible it needs more time to run in at a rich setting. ? Seizing up and throwing a prop still baffles me. ,all comments are welcome. I am using the same fuel as I have used on all my models for years. Cheers Quote Link to comment Share on other sites More sharing options...
Ian Rayne Posted August 28, 2012 Share Posted August 28, 2012 Check your Conrod, I had a brand new Magnum 52 motor seize on its 5 th flight and the Conrod had worn through it sleeve. Ian Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted August 28, 2012 Share Posted August 28, 2012 Modern engines are meant to be tighter at TDC which were they want the gas seal, ABC (or similar ringless engines) have a slightly tapered bore to achieve this. But if the engine runs too hot the piston will expand too much and it locks up. Sounds like it might have been a touch lean and that has allowed it to lock up, the overlean could have been the need;le setting or the loose backplate has allowed air in weakening the mixture. Take the exhaust off and check the piston, if it's not scored and engine turns smoothly even though it is tight at TDC it should be OK, all you can do ir run it a couple of clicks richer. BTW you said you hadn't adjusted the needle in 6 months but the engine has only had 5 tanks of fuel through it, if it's only 5 tanks old it might still need to be a little on the rich side. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 28, 2012 Author Share Posted August 28, 2012 Thanks both. Thought for a while every one had gone electric. LoL With the plug removed she turns over sweetly with no hint of tightness. I'll check the piston first, Im hoping there will be no need to strip the engine down, but as Ian has commented on the innards, I might have to do it. I think your post is very logical Frank so I will check and if ok, try to run it at a richer setting with smoke. Cheers Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted August 28, 2012 Share Posted August 28, 2012 If the needle mount was loose (as you say in your OP) then it could well have been passing air - leaning the mixture out. As others have said it should be OK - engines are remarkably hardy little beasts! If the piston isn't badly marked and the cylinder likewise then all should be well. Just sort that needle mount before restarting and maybe make the next few runds a bit on the rish side just to help things bed back in. BEB Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted August 28, 2012 Share Posted August 28, 2012 If the engine turns freely with the plug out then unless the piston is fouling the glowplug, any resistance must be compression. Actually, with the engine cold there really ought to be a tight spot at TDC with the plug out... I can't think of any other sensible suggestion for these observations - unless something very odd has happened to the conrod causing something to lock or bind when compression loads it up...only stripping and examining the components would reveal anything in this direction. P.S. Crankshaft thread is 1/4 UNF (28 TPI if I recall correctly). Edited By Martin Harris on 28/08/2012 23:52:00 Quote Link to comment Share on other sites More sharing options...
Stephen Grigg Posted August 29, 2012 Share Posted August 29, 2012 I did have an OS 46 La get very hot in the air. it changed from blue to black.It would start and run perfectly on the ground but get slower and slower in the air. never found the problem si Im no help am I Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 29, 2012 Author Share Posted August 29, 2012 Hi Stephen, all help gratefully recieved. OK, here we go, engine removed. One bolt out of 2 holding on the carb bracket missing. Engine back plate very tight no signs of any leakage etc. No signs of marks or scratches on the piston. My conclusion, the carb. bracket bolt was a secondary problem. I could have been running engine quite close to lean. Once in the air engine leaned out after a while, piston got hot, expanded and siezed up..this then loosened and threw the prop. What do you think lads. When sorted will run a few more tankfulls on a rich setting. As Mr Haytree is no longer supplying spares for OS, where will I get a set of backplate bolts ? Cheers Edited By fly boy3 on 29/08/2012 21:00:21 Quote Link to comment Share on other sites More sharing options...
Robin Kearney Posted August 29, 2012 Share Posted August 29, 2012 Hi FB, Slough RC had the OS 25 carb screws I was looking for a while back, not on their website but when I rang they had a root through their OS spares box and found them, maybe worth a ring. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted August 30, 2012 Author Share Posted August 30, 2012 Thanks Robin, will give them a bell. Cheers Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted September 20, 2012 Share Posted September 20, 2012 FB3 there is nothing magical about the screws OS use....I would guess the backplate screws are 2.5 or 3mm caphead screws...measure the thread length (10mm??) & then try Modelfixings..... @ Stephen Grigg....what fuel were you using? You can find that castor based fuels will varnish the piston & this will slow it right down when the engine gets hot. Strip it down & polish the piston with Brasso wadding or similar & the performance will be restored.... Quote Link to comment Share on other sites More sharing options...
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