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OS 55AX

Old 10-28-2008, 11:03 AM
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ameyam
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Default OS 55AX

Dear All,

recently broke the connrod on my 55 ax. Shards of the rod probably seized the piston. Repairing will cost more than 60% engine price so bought new one. Now that the engine is gone, I want to know of any mistakes we made. I am posting the pictures (two months out of use, so may be a bit "brown" . Can you guys make a diagnosis?

AMEYAM
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Old 10-28-2008, 11:05 AM
  #2  
ameyam
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Default RE: OS 55AX

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Old 10-28-2008, 11:29 AM
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NM2K
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Default RE: OS 55AX

What kind and how much (% by volume) of oil was used in the fuel? How much running time did the engine have? How much nitromethane was used in the fuel? What size prop? We need more information.

Sorry for your loss.


Ed Cregger
Old 10-28-2008, 11:50 AM
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ameyam
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Default RE: OS 55AX

One by one

fuel used: 20% castor little or no nitro
running time: nearly an year, twice a week about 4 flights each time. This engine had the head replaced in February (I damaged the original head by puting in the glow wrong)
prop: initially 12x6. I replaced it with 11x6 in April after which I did more areobatics

After I replaced the head, most people said that it didnt seem to have compression. But it ran fine.

In July (in the off season), I washed the engine with thinner (paint solvent similar to turpentine. Suggested by my instructor). Problems started after that- would cut off in flight usually when inverted. However, in the last two weeks before it broke, it seems to be running ok. It got damaged in air at 40% throttle as I was circuiting to land after doing all my aerobatics in my first flight of the weekend.

Old 10-28-2008, 12:00 PM
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liquid_TR
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Default RE: OS 55AX

This engine is a very mild mannered engine - you couldnt inflict any damage on the conrod if it wasnt crashed alot. I bet its a manufacturing defect.

Ive been using mine for a long time and much more frequently than you have, with a PSPEC pipe at over 15K rpm. (with omega 5%)

Its my favorite, non-problematic engine. It never cut out in the air or the ground. knock on wood
Old 10-28-2008, 05:49 PM
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Default RE: OS 55AX

I suspect bearing/cylinder damage after the thinner cleaning and before the engine got well oiled again. After such an intense cleaning you need to immediately thoroughly oil the engine. I'd suggest filling the case with after-run oil and removing the plug and adding oil above the piston and slowly turning over the engine by hand to fully lube ALL surfaces. Then dump out the excess oil and start with good fuel. I rinse all of my engine parts with clean fuel (oil in fuel) before reassembling a dis-assembled engine. Then oil lightly as above before starting.
Old 10-28-2008, 06:32 PM
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Default RE: OS 55AX

G'day I'm no expert on this but to me there does appear to be evidence of dry running on the inside surface of the big end bearing - darker grey streaks. Also, the crankshaft is showing quite a lot of what could be rust and there is also a stain where the rear bearing would have been seated on the crank. The stain on the crank may indicate that the bearing was actually skidding on the crank? The burned castor on the cooling fins suggests that this engine was running pretty hot too. I have never managed to get engines this caked with burned on castor. I suspect it may simply have been running too lean for too long and the cleaning cleared out its reserve of oil causing the big end to run dry and fail. As Bruce suggested, it is always a good idea to really oil up and engine after it has been cleaned.
Old 10-28-2008, 09:29 PM
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Default RE: OS 55AX

Thats not rust on the crankshaft counter weight - burned castor oil film. with 20% all castor fuel, the engine could look like that very easily if it was spitting fuel back out from the carb venturi, and that sprayed oil getting slowly burned on the cooling fins and crank case. Its actually harder (for me atleast) to set the engine lean with low or no nitro fuel mix. Because the needle is more responsive, one can easily identify the peak and richen back out. In any case, IMO this engine wasnt run with the correct needle settings. There is just too much varnish all around.

But surely we are just speculating here.
Old 10-28-2008, 11:13 PM
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mike109
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Default RE: OS 55AX

I agree - looking at photos, the best we can do is float some possible ( and possibly very wrong ) ideas. I would like to see what the crank would look like after a really good clean. Best totally destroyed engine I ever saw was a Super Tigre 60 control line speed engine which had a shaft run after loosing its little tooth pick prop and sucked the metal mounting bracket off its fuel tank through its very large rear venturi, managed to get it past the transfer ports and then hammered it into the top of the head from the inside. About the only usable bit left was the prop nut.
Old 10-29-2008, 02:11 AM
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NM2K
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Default RE: OS 55AX


Generally, if an engine behaves differently in different positions (upright/inverted), it is a fuel delivery system problem (tank and fuel lines/vent line), NOT an engine problem. In this instance, I am talking about an engine that starts well and runs well until the model's position is changed by roughly 180 degrees. It's early and I'm working on my first cup of coffee, so please forgive the awkwardness in my writing.

Good running glow engines do not have a preference in positioning once running well. So, the original cause of the engine's problems could be the tank position in the model. Something that would cause a change in engine running from previous flights to the last would be if the previous landing was a bit rougher than usual, which caused the clunk in the fuel tank to slide forward near the neck of the tank. The engine would start and tune normally and would probably fly pretty well for a minute or two and then there would be symptoms displaying of a fuel delivery problem. Rolling to inverted flight would eventually cause the engine to quit, with previous symptoms of running too lean at times up to that point.

It saddens me to see that OS is not using a bushing in the lower connecting rod end. Bushings were there to prevent exactly what happened to your engine. Just having a high silicon aluminum alloy in the the connecting rod is insufficient. A bronze bushing would have, due to its porous nature, most likely made it through these lean runs with ease, because of oil being stored in the bushing's pores. I wish OS would pull their heads from hidden caves and begin using bushings again. That is the mark of a high quality engine.


Ed Cregger
Old 10-29-2008, 03:24 AM
  #11  
Turk1
 
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Default RE: OS 55AX

It seems also after head change,there possibly was a compression leak from head.I dont know if that could be the reason.
Old 10-29-2008, 07:41 AM
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MinnFlyer
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Default RE: OS 55AX


ORIGINAL: Ed Cregger


It saddens me to see that OS is not using a bushing in the lower connecting rod end.
Ed, the connecting rod DOES have a bushing. Here's a pic of it.

My guess is that in the picture, the bushing was removed with the crankshaft and it was removed from the crankshaft before the other picture.
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Old 10-29-2008, 07:56 AM
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ameyam
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Default RE: OS 55AX

There was definately some loss of compression percieved after changing the head, but that was only in the ear since the engine ran well and tuned fine (even inverted).

However, once through the cleaning, the engine did not do well for a long time. Finally after 2 weekends, it tuned well and ran stabilly. In fact on the day it went, it seemed to be working ok.

I have begun to feel that the engine was running too lean especially since the piston top is all black. I borrowed an 0.46 from my instructor standby as I used this oppurtunity to go to a low wing (Tiger40 on .55AX new). When I removed that engine this week, the piston was still bright. The head had externally burnt black varnish, that happens because the carburretor venturi keeps spitting out fine mist of fuel. To remove that, it has to be washed with methanol and he didnt want me to do that.

I am taking no chances with the new engine. Once I get a grip on tuning it (have not got a handle on that yet, earlier my instructor would do it), I am going to run it slightly rich (quarter turn back from the peak). Also exterior cleaning will be done once every three weeks and with methanol.

Ameyam
Old 10-29-2008, 08:08 AM
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MinnFlyer
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Default RE: OS 55AX

Something else worth noting is that you were using an 11x6 prop (After starting with a 12x6)

But the smallest prop recommended is a 12x7

Could be you were turning too many RPM.
Old 10-29-2008, 08:12 AM
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NM2K
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Default RE: OS 55AX


ORIGINAL: MinnFlyer


ORIGINAL: Ed Cregger


It saddens me to see that OS is not using a bushing in the lower connecting rod end.
Ed, the connecting rod DOES have a bushing. Here's a pic of it.

My guess is that in the picture, the bushing was removed with the crankshaft and it was removed from the crankshaft before the other picture.

-


And both ends too! I'm glad I'm wrong. Thanks for the correction. It had me a bit upset, not seeing it in the photo.


Ed Cregger
Old 10-29-2008, 09:16 AM
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Bax
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Default RE: OS 55AX

If the pictures are close, then the connecting rod seized to the crankshaft and then was twisted off. The crankpin shows bluing caused by high heat. The high heat can only be caused by a lack of lubrication in that area. Something happened to the fuel supply of the engine, making it go lean at high RPM. The resulting low lubrication could not keep the connecting rod from rubbing on the crankpin. Eventually, the friction caused enough of a heat buildup that the rod seized. As the crank continued to turn, the rod would try to turn with it, but since it couldn't, the lower end got twisted off. The brass bushing would be shattered into small pieces, and scattered throughout the engine, along with the aluminum of the lower conrod end.

The only repair is to replace the piston/liner assembly, connecting rod, and rear bearing. The crank can be cleaned with 600-grit wet-or-dry sandpaper. Unfortunately, this is very close to the replacement cost of the engine.
Old 10-29-2008, 10:16 AM
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ameyam
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Default RE: OS 55AX

Dear Bax,

that is the most scientific explainarion that anyone could give me so far. And I think it may be correct. On closer examination, I found rubbing marks on the crank pin and there is absolutely no sign of the crankside bush anywher in the case. Also, the remnants of the connrod seem to be out of alognment with the crankpin suggesting twisting.

Just a couple of things I would like to understand: Did cleaning with thinner contribute to the damage? If so what do you recommend for external and internal cleaning. Note that the crockpot/antifreeze method that some are suggesting is not feasible since it is difficult to get antifreeze. Should I simply clean with methanol next time? Last time I also rinsed wither water (after cleaning), dried iff the water with hot compressed air, and then lubricated thoroughly with oil.

Secondly what care should I take at the end of the day of flying (when not flying for atleast the next week). I usually afterburn (remove all fuel by running till it cuts off) and then put in a few drops of "singer oil" which is a light machine lubricant (It is actually quite good and is used to lubricate everything from lathes to automobiles in light duty and high speed) and give a few flicks. Do you suggest leaving residual fuel in the crank? Anything else? (Actually most people on field take less care than me and few actualy afterburn)

Finally, how to clear burnt or baked varnish off the head externally after flying?. Should I simply clean the same off with some soap water and a small unused toothbrush (Will keep the carb closed at the time)?

Ameyam




Old 10-29-2008, 10:32 AM
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MatheusC20XE
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Default RE: OS 55AX

well.. i got some of my engines running very lean for a error (wrong land adjust) a never had this type of problem.. for me, have more problems there..

but, about cleaning method.. i use pure alcohol after last flight with toothbrush.. if you never allow the castor dry in the engine fins, it´s never will create the difficult to remove "varnish" marks..

BTW, the "Easy of Bang" home clean product is very good to remove a old varnish, but you need leave the engine in this product for a day (24h) to take the varnish more soft and then easy to remove.. it´s works good for me and is very less toxic than antifreezing..


cheers,


Matheus
Old 10-29-2008, 11:48 AM
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ameyam
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Default RE: OS 55AX

External cleaning with alcohol makes a lot of sense. How about internal cleaning and how often should it be done?
Old 10-29-2008, 12:08 PM
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Default RE: OS 55AX


ORIGINAL: ameyam

External cleaning with alcohol makes a lot of sense. How about internal cleaning and how often should it be done?
but need be pure alcohol, no alcohol with high density of water.. water only allow to promote corrosion and doesn´t clean nothing..

here in my country is more easy because we can buy high density alcohol in gas posts, but i think there already have ethanol to buy too.
Alcohol of supermarket is very weak and don´t will clean nothing.

About internal clean, if you didn´t make any wrong thing like crash the airplane in dirt region, its not necessary.. only some carb clean after long time of use, and maybe a head chamber clean if begin a thick castor varnish..

If you fly in off-road land, then, is good to use an air filter to prevent cylinder damage..

Old 10-30-2008, 12:45 PM
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Default RE: OS 55AX

ORIGINAL: MinnFlyer

Something else worth noting is that you were using an 11x6 prop (After starting with a 12x6)

But the smallest prop recommended is a 12x7

Could be you were turning too many RPM.
I doubt that. The .55 AX is quite happy at much higher RPM than one could attain from using a 12x7 prop. A 12x7 prop is on the (too) large size for this one, IMHO.

-Robert
Old 10-30-2008, 01:21 PM
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Default RE: OS 55AX

The bronze bushes (bearings) are porous. They absorb and hold oil. During any cleaning of the internal components with a solvent, you need to make sure any oil leached out is replaced.
Leaving a solvent to soak parts, it is possible to disolve and leach out all the oil. The part then needs to be soaked in oil (preferably at a warm temperature) to replenish the lost oil.
An engine started with a lack of oil in the bearings will cause a lack of lubrication until the bearing soaks up enough oil (from the incoming fuel charge) to become "full".

I've always thought the above was correct but I'm happy to be corrected if it's wrong.
Old 10-30-2008, 06:40 PM
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Default RE: OS 55AX

sorry about your engine but Im glad i run fully synthetic
Old 10-31-2008, 04:00 AM
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Default RE: OS 55AX

Ameyam,


What I can diagnose from your photos.

The crankshaft has some of what appears to be rust, in front of the rear bearing and it seems the crankshaft has spun in the rear bearing's inner race...

But this seems to be a short episode, resulting from a shard of the con-rod lower end having wedged itself between a ball and a race; effectively stopping the bearing, while the crankshaft was spinning.

There is some rust on bearing's races, but it seems there is none on the balls and the (plastic - Touché, OS) cage seems intact.


...I cannot tell why the con-rod failed....

Do you use an electric starter and could you have inadvertently tried to spin the engine over when it was flooded?
Did your engine lose the prop and spun at unspeakable RPM?

If not, I suspect the con-rod had a flaw from manufacturing; a hair-line crack, or something.


If your engine is only one year old, it should still be under the two-year warranty OS gives its customers.


It would be a good idea to contact BAX (Bill Baxter) of Hobby Services; perhaps in the [link=http://www.rcuniverse.com/forum/forumid_133/tt.htm]OS Support Forum[/link].

Perhaps, with the photos you posted, he can just send you the replacement parts that you need, without you needing to send the engine back and forth through Indian customs.


It would cost you nothing to try.

Old 10-31-2008, 05:54 AM
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Default RE: OS 55AX

Paint thinner is definitely not the desirable solvent to clean an engine with. It literally leaches out any oil it is in contact with including the pores of the brass bushing.It also causes damage to any plastic it is in contact and dissolves ,redeposits and hardens gunk in the wrong places.

Your engine was literally starved of oil as castor even though a very good lubricant is rather viscous and would need some time to work in while metal to metal contact was progressively destroying the conrod especially running at high rpms. I suspect the lubricating hole and micro pores may have been inadvertently plugged up by a mixture of varnish and gunk dissolved and hardened by thinner.

Use kerosene to clean the internals of your engine after separating the seals and O rings .Wipe dry, apply light oil and reassemble as recommended by OS.

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