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How long should a 2 stroke IC last on average?

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Ralph Yeates12/10/2008 11:35:00
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218 forum posts
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I have a os91 hyper that has had about 50 gallons of various makes of fuel through it. The problem is the engine misses a beat some times and also just stops with no warning.
I have adjusted the bottom end the main needle and cleaned the jets thoroughly. The engine runs ok but at random intervals the engine just stops. Being on a heli I can hear when the engine misses a beat and this is at around mid stick position or below which should not matter as the throttle curve keep the revs up on the main needle range. I have removed the engine and inspected it, the compression is ok but not as tight as other engines that I have. The plug has been changed to eliminate this as a cause.
Symptoms:- when the engine stops the engine is hot and cracking can be heard from the exhaust this indicates that the engine is running lean and hot. Increase the fuel flow to cool the engine then the issue is that the engine is running too rich {As per the smoke from the exhaust} and will not rev correctly but even on a rich setting the engine still exhibits the stopping issue in flight as if it is over heating. The cooling on the heli is standard as per the manufacturer spec.
The question is :--> what is the life expectancy of an IC 2 stroke ? advice  so far is 30 gallons is about average is it worth pursuing or just get a new engine ?
feel free to chip in with advice and recommendations
Ultymate12/10/2008 12:47:00
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1693 forum posts
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Ralph is the motor ringed or ABC, if ringed it may be worth trying a ring before condemning it to the scrap heap, however 50 gallons is a lot of fuel even in a 91 sized motor and it may be getting generally tired and at the end of the day you have to work out whether it's financially viable to overhaul or replace it. Has it been in the heli all it's working life, if so it's unlikely to be a prob with the cooling in the heli but if it's been fitted in the heli recently then maybe the heli could be fitted with an upgraded fan, many can be upgraded.
Ralph Yeates12/10/2008 13:07:00
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218 forum posts
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It's ringed. I have 2 identical heli's exactly the same set up only one has the issue and this is the older model. I'll check the price difference on the ring piston and liner but I feel that it will be cheaper to just replace it. Yes it has only been in this heli maybe it's time to send it to engine heaven

Many thanks for your help

Myron Beaumont12/10/2008 13:52:00
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5797 forum posts
51 photos

I'm" feeling free "to "chip in"     I have never had a chopper    BUT certain facts you have mentioned make me think . So I'll throw my penny worth in , Question no 1  Have you the normal power you're used to(disregarding the misfiring bit at half throttle ) ? no2  Doyou normally fly mostly at the setting where the misfiring occurs ? no3  Does it smoke all the time regardless of throttle setting ( which it should if you've enriched every thing to bring about cooling)  on enriching the mixture ,that is to say at any throttle setting & finally -coming to what I'm thinking is it a NEEDLE problem. In other words - Is there wear on the needle/ venturi  bits ? I might be wrong of course 'cos I've never had ( couldn't afford)an OS & dont know the carburettor configuration .Hope I have maybe made a positive suggestion or at least maybe made you think   

 PS  no 4  did the misfiring suddenly start happening & not stopped since it first occurred .Or is it un- predictable so to speak .  All in all I dont think its overall engine wear .BUT thats only my opinion !

I had a few engines back along done more consumption (diesels mind you ) than yours by maybe a factor of 2 or 3 . Mills's ED'S Mercos 'AM's Frogs DC's Elfin's Cox's

.Sorry - should be back on the "nostalgia " thread  where some of  us belong .Trouble is Can't remember where it is !

Ralph Yeates13/10/2008 07:34:00
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218 forum posts
18 photos
http://www.osengines.com/engines/osmg1951-main-2.jpg


Myron hi,
1 not as much as previously flying wise maybe 10% down on the second heli with a younger engine. the climb is faster and stronger when you pump the throttle on the younger model.
2 the misfiring happens generally around the hover about 1/2 stick higher up it's difficult to tell as It is climbing. It happens occasionally but seems to have increased in frequency lately
3 yes constant smoke  what I do see is a gap in the smoke when it misfires which is as indication to the problem.
4 suddenly started happening and not stopped since, once it warms up after 3-4 mins of flight.
the carb on the os has a main needle and a separate off centre screw for the bottom end. In Idle up the revs are higher and should only use the main needle whilst in this mode even though I have tinkered with both settings. What I believe is happening is the engine warms up to a certain temperature and as every thing gets up to working temperature then the clearance between the ring and the liner goes past the recommended limits and the backfire so to speak occurs causing the problem. I could swap the carb from the other heli and see if the results are the same or do a compression test but I wont be able to do that under the same temperatures as flight. I know that heli engines do take a hammering more so than aeroplane engines. I an not an engineer so do not have all the gauges and measuring equipment to do all the tests on the engine I could probably get some of the club members that have this expertise to check all the clearances etc correctly for me. Thanks for your suggestions that's what makes this forum such a great resource

Engine Doctor15/10/2008 16:25:00
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2267 forum posts
25 photos

Hi Ralph . thers not a lot of things to go wrong in a two stroke engine .Is the compression OK? if so suspect the bottom end or crank case compression. Crank case compession is more inportant than cylinder compression on a two stroke engine. after 50 gallons of fuel i would suspect some wear may have occurred on the bearings. Does the engine sond quiet and smooth ? or does it rattle ? When did you last change the glow plug ? These deteriarate after prolonged use . if the top end (piston liner) are ok a set of bearings will set you back about £15 and are not difficult to fit . A bit cheaper than a replacement. Hope you get it sorted .

E.D

David Martin 224/10/2008 18:37:00
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282 forum posts
61 photos

Since getting a ringed OS 32 SXH some 5-6 years ago as a replacement to a cooked ABC cheapie, my heli flying has been a real start and go pleasure affair. I personally would look for other issues before scrapping your OS, is it really a misfire or possible fuel foaming and bubbles in the line caused by a vibration that's recently come about and is hard to spot..? Have you replaced the pipework, especially the end going to the hot muffler nipple..? A brittling here starves the engine of back pressure and shows from half to full throttle as a lack of power and coughing as the tuning goes off...

Hope you can sort it.

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