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Old Jul 25, 2015, 07:42 AM
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OS 1.20 AX Issues

I quickly searched threads, but didn't see any with recent experience.
I purchased a nib 120 AX that was new, but the older version. Great performance! I'm running a 16x10 APC at ~8400RPM on 10% Omega. Awsome P/W for this engine; it replaced a Webra S120, and dropped 4oz. in the process, and picked up 300rpm's. I have a Mac's wrap to center header, and 20cc quiet tuned pipe. Now, for the issues:

1) Smoking Plugs. I get about 3-4 reliable flights out of a plug, usually an OS-F, but I've tried McCoy, and Fox also. Idle bar, and none. I put an OS 8 in yesterday. All results the same; the coil turns white, and the engine quits mid flight. It'll restart and run, but then will just die at any throttle setting. I'm thinking, in order - 5% Omega? - Short, cold plug? - lower comp. ratio with thicker head gasket.
2) Worn out bearings. With ~3 gallons through this motor, the bearings are shot. I rolled the prop to close the ports yesterday after flying, and noticed the slop in the bearings. I used to change my .61RF bearing without any noticeable play, and this one has ~1/64-1/32 'click' in it! Bearings are on order. Any thoughts here? Seems like a crappy Chinese engine, not an os. I shudder to think what the sleeve looks like, but will check when the bearings arrive.
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Old Jul 26, 2015, 11:50 PM
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How was the plug life on the engine when you used the standard muffler? Because of cylinder timing, some engines are not suited for pipes. Also consider a lower pitch prop like a 16 x 8. The 16 x 10, per OS, is the maximum load for the engine. Depending on the configuration of your airframe (low drag or high drag), that 10 may be to much of a load and your cooking the plug.
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Old Jul 27, 2015, 07:31 AM
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You pretty much pointed in the right direction in your original post.

I believe your bearing failure is taking out the plugs. The material you are losing as they fail impinges on the glow element, compromising performance or killing it completely.

NOTE: You mentioned it was NIB, but the older version. Two negatives towards plug life there. First is that this same effect occurs on any new engine or one that has new parts installed. During the first runs microscopic particles wear off as they seat in and with a 2-stroke everything flows through the combustion chamber. Unfortunately with a 4-stroke most remain inside the case and do more damage.

Second can come from improper storage and internal corrosion to any ferrous parts, (crank, liner ring and bearings, which are particularly vulnerable). Those too can all come loose during the first runs.

What I mean by improper storage would be a lack of oil protection and open to the environment. As temps and humidity levels change any engine can "Breathe" if open to atmosphere and will bring in fresh moisture or other contaminants. On my 2-strokes I cap the carb and exhaust on active engines and store others long term in plastic freezer bags. Have pulled more than one from 20+ years in storage and fired them right up.

There are many arguments over the best oil to use for this, but personally I have mixed ATF and Air Tool Oil, (basically turbine oil) 50/50 for 3 decades now. Even straight ATF will work fine and last nearly forever.

The fact it is far enough into the season some engines have enough time on them for this problem to come up in the posts. In fact, there have been at least two in the last week that look like they suffer the same malady.

If you do not find any other damage on the way to replacing the bearings, (and on this engine it is relatively easy and inexpensive) then try and run the first few tankfuls using an old plug.

On a final note, that prop sounds a bit too aggressive. Specs show a peak of 9500 and you are well below that. Mentioning as 2-strokes have a rather narrow peak power band and you may be far enough down to not be making the most efficient use of its power.
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Old Jul 27, 2015, 07:58 AM
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Cougar,
Thanks for the direction; I hadn't considered the interaction between bearings and plugs, but it does make sense. The material is definitely going somewhere, and the propensity to kill all plugs suggest it's not the plug itself.
I've never seen the issue of burning plugs with poor storage conditions, which, I must admit, I'm guilty of on many occasions. I have an OS61FSR Special Eddition from 1983 that get's 're-purposed' every now an then, after having little done but putting it back in the box (no bag, liner, etc.). It has never had a plug issue. Then again, I've never run through a set of bearings in 3 gal. of fuel before either!
I read a comment on one thread, which called OS bearings "Crap". I wonder if there's a history, particularly with this engine?
The 16x10 turns around 8400, but doesn't seem bogged. I have a 16x8, but I'm worried about the extra rpm's and noise (pattern flying...). I thought about a 17x8, but couldn't find one at the hobby shop. NTL., the 16x10 is listed, and the bearings should hold up better....so we'll see with the next set.

jjk,
I never ran it with the muffler; the airfram is dedicated to the pipe, however, I never tuned it to this engine, so I'm not certain it's adding any power, other than through lower restriction/volume. As said, I haven't yet tried a smaller prop/load, but one of the reasons for purchasing this engine was it's low peak rpm's. It replaced a Webra Speed 120, who's peak was listed at ~15k Rpm's, or something crazy high like that...I tend not to pay much attention to that spec., unless it's notably different. I ran the webra at 8100 RPM's, and without bearing failures.
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Old Jul 27, 2015, 08:37 AM
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A lot depends on the oil and how clean the engine is at shut down. Synthetic does a better job at long-term lubrication retention and is cleaner, but does not tolerate higher temps like castor, (it retains its lube properties to a higher temp). That's one reason I use a synth/castor mix. Castor tends to dry up and congeal or harden over time.

If any unburnt fuel remains in the case at shut down it mixes with atmospheric moisture to create a corrosive that begins immediately to attack any ferrous items in the engine.

That FSR line is one of the best OS ever produced and at one time I had 5 or 6 ringed 40's. Still keep one in storage as I cannot bring myself to get rid of the last example of what I consider the best 40 class ever made.

As for bearings: no experience with what OS used throughout their history as there are reports they opted for some Pac Rim versions. From my own experience they do not meet the quality I need in both dimensions and metallurgy and quite often failed in one season. I now use NSK or others of equal quality and get good service.

That 16/10 is at the very top of their range for this engine and may work with higher nitro fuels or custom exhaust to get it to peak RPM. Even though quieter that loss of the top 1K could prove substantial in power output, (I see this a lot when trying 3-blade props on 2-strokes, something I never had any success with simply due to drag preventing them getting up into the power band). I also find swinging a larger diameter prop can significantly increase torque effects on the aircraft, especially at low airspeeds such as vertical maneuvers.
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Old Jul 27, 2015, 10:45 AM
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Quote:
Originally Posted by Cougar429 View Post
A lot depends on the oil and how clean the engine is at shut down. Synthetic does a better job at long-term lubrication retention and is cleaner, but does not tolerate higher temps like castor, (it retains its lube properties to a higher temp). That's one reason I use a synth/castor mix. Castor tends to dry up and congeal or harden over time.

If any unburnt fuel remains in the case at shut down it mixes with atmospheric moisture to create a corrosive that begins immediately to attack any ferrous items in the engine.

That FSR line is one of the best OS ever produced and at one time I had 5 or 6 ringed 40's. Still keep one in storage as I cannot bring myself to get rid of the last example of what I consider the best 40 class ever made.

As for bearings: no experience with what OS used throughout their history as there are reports they opted for some Pac Rim versions. From my own experience they do not meet the quality I need in both dimensions and metallurgy and quite often failed in one season. I now use NSK or others of equal quality and get good service.

That 16/10 is at the very top of their range for this engine and may work with higher nitro fuels or custom exhaust to get it to peak RPM. Even though quieter that loss of the top 1K could prove substantial in power output, (I see this a lot when trying 3-blade props on 2-strokes, something I never had any success with simply due to drag preventing them getting up into the power band). I also find swinging a larger diameter prop can significantly increase torque effects on the aircraft, especially at low airspeeds such as vertical maneuvers.
The bearings will be in Thursday, so I should be ready for the weekend, if I get time. I called RC Bearings (Paul McIntosh) and these are "Dong Hua Pianci" bearings (chinese). He's been around a while - any experience with them? I usually used Boca, but they're an importer too. Also used NSK, but I really haven't had a bad bearing experience before.
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Old Jul 27, 2015, 12:44 PM
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Another first for me with this motor occured yesterday. It was a bit loaded, as an inverted engine will do sometimes, once I got the plane together. I spun the prop a couple of times with my fingers just to clear it out, and got an ignition!! One or two pops only, but enough to get interest from the rest of the pits. Could have been really scary. Never had that one before in 30yrs., but have heard of it.
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Old Jul 28, 2015, 08:56 AM
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Based on advice here, I went ahead and stripped down the motor last night to get a jump on replacing the bearings, and to remove the temptation to fly!
And, yup...more firsts! Did OS actually use a 2.75mm screw head on their cap screws??? Yup. Fortunately, I had one in my archery tackle. Then the 'track' in the crankcase won't let the con-rod slip off the crank pin except when the piston is around tdc. It took a little prying to get off...I hope it didn't damage the pin bushing!
On to findings: particulates all over the top of the piston...very small pieces. The liner shows a little wear above the exhaust port. But the big find was the bearings. Once I got the prop off, I could feel the play easily. The rear bearing was really rusty and worn, and both radial and latteral play were evident. So was the grinding. The kicker?....NSK bearings!! Didn't see that one coming. Either they have a cheap line that OS buys, or they've off-shored to China ("Japan" printed on the front bearing seal). I guess I'll have a conversation with Boca to see what they offer.....
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Old Jul 28, 2015, 09:19 AM
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Then the 'track' in the crankcase won't let the con-rod slip off the crank pin except when the piston is around tdc. It took a little prying to get off...I hope it didn't damage the pin bushing!
In general, this job is a lot easier if you first pull out the liner before you slip the conrod off the crankpin....

Brgds, Bert
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Old Jul 28, 2015, 09:34 AM
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In general, this job is a lot easier if you first pull out the liner before you slip the conrod off the crankpin....

Brgds, Bert
I'd add, "Impossible" if you don't take out the liner first. All I've worked on before slip right off when the liner is out though...this one took a little more umpf than I'm used to. Maybe the liner is thinner, providing less fore/aft movement of the piston assembly?
Everything but the bearings came out easily, and after 5min in the grill, the bearings dropped right out too.
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Old Jul 28, 2015, 09:38 AM
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Maybe the liner is thinner, providing less fore/aft movement of the piston assembly?
That, or there is crud on the wristpin, preventing the rod to slip backwards in the piston....

Then again, some engines are really tight and compact....

Brgds, Bert
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Old Jul 28, 2015, 09:44 AM
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That, or there is crud on the wristpin, preventing the rod to slip backwards in the piston....

Then again, some engines are really tight and compact....

Brgds, Bert
Good to know....again, a first for me across many engine bearing jobs. I just hope I didn't bung it up...it's only aluminum and brass. I guess I'll see. I didn't really pry hard, it's just that I've never had to pry at all before.
(aside: Spent 1/2hr. looking for the woodruff key on the floor!...slippery little booger )
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Old Jul 28, 2015, 11:27 AM
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Isn't that fun. There are rules about how important some part is VS how small and difficult to find.

As stated, bearing failure is usually exponential. It takes only one small bit of damage to inflict more and the parts from those continue the process, etc. Sort of like a nuclear reaction, only it does not normalize or stop.

You probably had material coming off before you noticed, perhaps even during the last flight. Even good quality bearings can fail if mistreated.

That mistreatment can occur during installation if excessive force is applied to the surfaces. Permanent deformation and/or cracks can quickly start the process. Same can and will happen if run without proper lubrication.
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Old Jul 28, 2015, 11:44 AM
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I agree; deterioration is exponential...glad I tore it down, b/c I would have probably gone out again!

One other thought on prop size...OS has their "Special" version of this engine boasting 8% more power on the same bearings that my standard has. It seems that OS thinks these bearings should hold up?
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Old Jul 28, 2015, 02:36 PM
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Rust. That came from improper storage. Pipes are hard on plugs as well
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