I'm a newb at troubleshooting engine problems looking for tips and advice.
I've owned 2 engines and until now they have both run fine. The one I'm having issues with is an O.S. .46ax. I run an APC 11x5 or 11x6,O.S. A3 plug,Omega 15%. I'm guessing it may have 4 gallons through it. I use a home-made exhaust deflector,basically a piece of tubing that runs down and exits at the landing gear.
Just recently,mid flight,I noticed a loss of power and the engine didn't seem to be revving as high at full throttle. It was running ok aside from that. I landed and checked with a tach. It read around 11,000. I leaned the needle til it sounded like it wouldn't go any higher,and then backed off a bit and tached it around 13,300. That put the pep back in it,but I don't know why it dropped in the first place. After the adjustment, I started getting a single surge or stutter when I'd open up the throttle all the way(not during transition,but right after it spools up). I could not replicate this on the ground later.
After getting it home,I pulled the glow plug to check it and noticed it is very black on the bottom(the coil looks normal,but the bottom of the glow plug housing is black). Hooked up to the ignitor,it glows red and appears to be working properly.
Any suggestions on things to check for?
thanks,
Jeff

Try richening it up another click or two and see if the surge goes away.

As the outside air temperature warms up, you are going to have to lean it some more. If you have a cold spell, you will have to richen the needle some.

When in doubt, try fresh fuel and a new OS #8. If you don't want to buy a new gallon, bum a tank from a bud. The OS A3 may be an OK plug for the engine but since you are having trouble I'd put an 8 in it. There may be other issues but I use these two items as a baseline for trouble shooting. If you rule out old/bad plug and old/wet fuel, you are left with trouble shooting fuel delivery (trash/tank/filter/lines problems), air leaks (needle/carb/head/backplate), etc..

Bill

Hi!
That long tubing is no good!
Adds a lot of heat to the engine if you tweak the needle too much!

Thanks for the tips. I am the only one here who flies glow,so i'm outta luck on the fuel. But the fuel I have isn't that old and I'll have to pick up a new gallon soon anyhow. I flew just a week ago with the same fuel and no problems.
I have spare A3's. I don't have any #8's. This engine has always wanted to fire backwards. I wonder if the hot plug has anything to do with that? I run the A3 in it because that's what the manual recommends.

Yeah I wondered if maybe it's running too hot after I saw the black char on the glow plug.
On the other hand,my TTPro .46 seems to love the exhaust tube. I got higher rpms and it has been running great for a few years. I took it's plug out to compare and it is nice and clean. If I continue having problems I will try it without the tube and see if that is the culprit.

I would lose the pipe. They make 'tuned pipes' for engines which are supposed to increase performance at a given throttle setting, and they are adjusted specifically for each individual engine. When you first put on one you are far from max performance, even running below optimal rpm range.

Point is that a long tube like you've got can really affect how the engine runs, and can definitely cause it to run worse than it was before.

I would lose the pipe, at least until you get your problems fixed. If then you decide to put it back on, you can figure out if it was a factor or not. I think it will probably do more harm than good.

Yes the OS AX Series engines are the best available in terms of reliability / lasting, its all to do with your current tune. as mentioned get rid of the extension pipe and also make sure your fuel is top notch stuff to the mix and make sure all fuel lines are set how they should be including the pressure nipple tube to tank. i have used OS engines for many years without any hick ups atall.

Ok thanks for all the tips......I just think it's very odd that I'm in my second season of flying this plane,with this exact setup,and have never had a problem until now. I would think that if this problem was created by the exhaust deflector,then it must have already caused irreversible damage,because it has run great for all this time. It seems to me more likely that perhaps something got gunked up in the works and caused the sudden drop in rpms. I probably aught to take things apart and inspect them closely.
I was actually hoping someone could explain the blackness on the plug. I figured that was a tell tale sign of some tuning mistake or something. But,since I leaned it out quite a bit to get the rpm's back up after the strange drop-off,perhaps I was simply masking another problem and am now running too lean?

G'day

Th A3 plug is at the hot end of the OS plug range. It is OK as a running in plug but I would not normally use one in an AX46 for flying. Hot plugs advance the timing of the engine. So does adding nitro to the fuel. 15% is quite a lot and will also be advancing the timing. The combination of the two is probably too much. A lean mixture also advances the timing. Eventually something has got to give and things will either get hot or the plug will get fried.

Generally speaking, two strokes don't like long exhaust pipes. They need to breathe to be able to get rid of burned fuel products and heat and a long pipe does not help this.

I suspect that you may be having some pre-iginiton problems when the engine is running at part throttle too with all those factors which advance the timing. Does the engine seem to make a crackling sound at part throttle? Some one once described it as the sound of frying bacon. If you do have this, you are not doing the engine any good. Pre-ignition means that the fuel is starting to burn too early and this puts unwanted stresses on the con rod and piston which can lead to premature failure.

If you must use 15% (I'd save the money and only use 10) then I would definitely suggest a No 8 plug. Then tune the engine for maximum revs and then back the needle out (richer) to drop the revs by between 300 and 500 rpm or a just noticeable amount (about 1/4 turn). I'd also use a fuel which contains a few percent (up to 5) castor oil. It is good insurance against a lean run.

I also find that unless you run an engine dry at the end of the day, fuel residue in the carby can block things up especially if the engine is left for a considerable time. Before I try to run and engine that has been out of action for a while, I remove the needle and blow some fuel through the carby in both directions to ensure there are no blockages. Fuel residue in the crank case can also attract water which can lead to rusty bearings.

Mike,
Thanks for the tips....that is helpful to know. I would choose 10% or less too,but the hobby shops around here only carry 15 and higher. I don't understand the obsession with high nitro. I am using fuel with castor.
As to your question,no I haven't noticed the sound you are speaking of. I think I may have experienced it before....kind of a metallic popping sound. I can't remember if it was the O.S. or the TTPro that was doing that,but I haven't noticed it from either of them lately. Would the timing issue also cause the engine to want to fire backwards easy? That has been an issue for me with both engines when I try to flip start them. Once the O.S. is warmed up for the day,I can generally start it with a bounce off the compression,but if I flip the prop through the compression,it will fire backwards almost every time.

Hi!
Why your engine now runs hotter than before is due to the accumulated "Castor oil gunk" on the piston shirt, top and combustion chamber (if you run fuel with Castor oil).This black deposits is restricting the heat dissipation from the engine. That's why we pylon racing guys clean our engines from time to time to have the most power from our engines.

Cannot understand why you Americans use so much nitro (15%) when all two stroke engine just run as good on 5-10%!
Use an OS 8 or Enya 3 or 4 glow plug and 5% nitro fuel!

Quote:

ORIGINAL: jeffsend

...I run an APC 11x5 or 11x6, O.S. A3 plug, Omega 15%. .... I use a home-made exhaust deflector, basically a piece of tubing that runs down and exits at the landing gear.
Just recently,mid flight, I noticed a loss of power and the engine didn't seem to be revving as high at full throttle. It was running ok aside from that. I landed and checked with a tach. It read around 11,000. I leaned the needle until it sounded like it wouldn't go any higher, and then backed off a bit and tached it around 13,300.

Jeff,


The A3 is the hottest plug OS makes and is, in general, way too hot for the OS.46AX, unless you are running 0% nitro, or flying at sub-zero temperatures.

This does not mean it will not run with it on 15% with this plug, but you will need to excessively richen the mixture (open the needles), for the engine to run properly...


The running costs of glow engines seem to be taken for granted, by manufacturers, retailers and modelers alike, under the false pretense that 'this is a hobby'...


In glow engines, the needles are the engine's primary 'ignition timing controls', during the run (the plug's heat range is one of the static controls).

A leaner mixture will ignite sooner, the flame would propagate more rapidly and it burns faster too.
So, closing the needles is the same as advancing the spark...

A 'lean-run' is simply detonation; not oil starvation...


So, you need to open the needles further, to compensate for the excessively high heat-range of the glow-plug, just splattering that expensive extra fuel all over the place, with no advantage whatsoever!


Change to a medium heat-range plug!


As to the deflector; it can 'come into tune'; causing either a gain, or much more likely, a real RPM loss.

I have seen a 1,000 RPM loss, in an MVVS .49 engine, as a result of installing a Hobbyco .35-.90 deflector...

Dar,
Thanks for the reply,
The reason I'm running an A3 is because that's what the manual for the engine says to use. The reason I use 15% is because for some silly reason it's the lowest % nitro you can get around here. If a cooler plug will get me better performance,or less wear and tear on the engine,I will give it a shot. But I have been running with no issues for a full flying season and several flights this year......so if I have been running too hot,the damage may be done already.
As for the exhaust tube.....when I first put it on,I checked the rpms. Seems like it had no effect,or very very minor,on the O.S. On my Thunder Tiger Pro .46 the tube is longer,and it increased the power noticeably. Seems like the rpms increased by 1,000 or 2,000. I richened it to keep it from overheating. It has been going strong for a few seasons running the same fuel and plug.
Up until now,I haven't ever had any engine troubles. The way I have always tuned them is to lean it out at full throttle until I get max rpms(judging by ear),then back it off until I hear a slight drop in rpms. Then I generally don't have to change it much after that unless there's a big temperature difference from one flight to the next.
I think what I need to do is take the engine apart and clean it,and check the fuel lines....general maintenance. If I don't find anything,I'll just have to try some of these suggestions.
thanks,
Jeff

Jeff,


OS make some good engines, but people who frequent this forum have seen virtually all of their bugaboos too...

With some of their ABN engines (most notably the first generation .46FX), there were numerous cases of peeling of the nickel off the sleeves...
The bearings seem to need replacement, somewhat more frequently than in other engines...


But, the worst are their manuals... Apparently written by ... their advertising dept. ...

Please read what [link=http://www.os-engines.co.jp/english/line_up/plug/pluindex.htm]OS Japan[/link] say about glow-plugs for air engines...

The manual essentially says you can use the A3 for the OS.91FX, while OS Japan says specifically that the A5 is the only one - a two grades colder glow-plug.
The manual cannot be right!


As far as plugs and break-in go, this manual belongs in the garbage, rather than in your library...[:'(]

Interesting.
I did follow the manual for break-in too.
I will try to get some #8 plugs when I get a chance. It certainly couldn't hurt to try.
However, if the plug is the reason it started acting funny all of the sudden,then it must mean there is damage to the engine right? Because I've never changed a plug in all this time and my engines have run great so far.
The O.S. was still running.....just acting funny. So hopefully the problem is still reversible. The compression still feels normal to me when I turn the prop by hand.

What may be missing here is that just because a plug will glow with the battery connected, doesn't mean it's OK. In addition to a minimum heat, first supplied by a battery and then by the heat of combustion, there is the catalytic reaction between the materials making up the element of the plug and our hydrocarbon fuels. If the plug has been in service for a while and or become coated with... something... this catalytic reaction will not happen properly and the engine will not run (well). If the plug glows brightly but the element is either coated with carbon, silicone or the catalytic elements of the plug have been abraded, the plug is still not going to work (well). Plugs have a finite service life even if they don't physically fail.

As a side note, often "blowing" a plug in flight does not necessarily mean a dead stick landing. If the element is still in place and simply broken, the first sign of trouble we be when you go to start it on the next flight.

I'll stick with my recommendation in post #2.... Try a new OS #8 and fresh fuel and THEN begin troubleshooting. I'll add the followup recommendations of, ditch the extension and castor.

Bill

Thanks.....I will order some #8's and get some more fuel soon as I get a chance to take a trip to the city.

Jeff,


Although the break-in procedure is far from optimal, for ultimate longevity and performance; I doubt it can cause immediate damage to your OS.

These engines are designed to not need a real break-in... Doing a good one would nevertheless, extend the life and the performance of this engine.
Next time do it [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this way[/link].


Your engine is not in my hands, or the issue would have been much easier to diagnose...

But for now, get the right glow-plug, to remove this degree of freedom.

Jeff,

I'll go 'against the grain' here.

If it has been running fine (for about four gallons of fuel) with the existing fuel/plug/exhaust, I see no reason to start making drastic changes.

Try a new A3 plug (since you have one) and see if it cures the issue.

I agree. I have used an A3 in my OS 46AX with no issues, and it runs very well on 15% nitro.

Quote:

ORIGINAL: Ken6PPC

I agree. I have used an A3 in my OS 46AX with no issues, and it runs very well on 15% nitro.

Quote:

ORIGINAL: DarZeelon

This does not mean it will not run with it on 15% with this plug, but you will need to excessively richen the mixture (open the needles), for the engine to run properly...


The running costs of glow engines seem to be taken for granted, by manufacturers, retailers and modelers alike, under the false pretense that 'this is a hobby'...


In glow engines, the needles are the engine's primary 'ignition timing controls', during the run (the plug's heat range is one of the static controls).

A leaner mixture will ignite sooner, the flame would propagate more rapidly and it burns faster too.
So, closing the needles is the same as advancing the spark...

A 'lean-run' is simply detonation; not oil starvation...


So, you need to open the needles further, to compensate for the excessively high heat-range of the glow-plug, just splattering that expensive extra fuel all over the place, with no advantage whatsoever!

Ken,


I definitely did not mention any 'issues' either, except fuel waste...

....But this is a definite issue!


Don't you agree on that?

Update:
It turned out to be a problem with the stock fuel line to the clunk. The stock line is small flimsy hose and I discovered that it could possibly double back on itself and wrap around the air vent line inside the tank. I replaced the line with standard fuel tubing which was stiff enough that it shouldn't do that unless I hit something really hard. Now it seems to be running like a champ again with the same fuel and glow plug I started with.

I live in the US and I don't understand it either, I havelocal shop order me 5% by the case because they never carrry it in stock.I can remember when 10% was the norm,now it seems to be 15%??

I do run my fourstrokes on 10-15%, but everything else is 5%..............

A lot depends on where you live and buy your fuel. A couple of European countries sell nitro as cheaply as in the U.S. Most tax it into near oblivion.<div>If you can get it cheap, why not use it if the engine uses it without problems. Everything I have run so far takes 15% just fine and I never bother with any other percentages. This won't work for everybody, but it is nice for the rest of us.</div><div>
</div><div>Not every r/c item has a great price tag here in the U.S. Marketing kills us on Japanese engine prices compared to other parts of the world. Australia comes to mind. We are paying more than other countries for some Chinese gas engines too.</div>