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07-28-2019 12:06 PM
hk4fvj
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Finally got one member of my club to look after. The guy reviewed the exhaust oil colour, he said it was OK as I am using castor/synthetic fuel at 15%.

Added a new OS 8 plug, the guy just barely rotated the idle needle, bingo. Now it is like new. I guess it is a matter of educating the hearing to understand exactly when the engine is fine or under stress.
07-05-2019 03:33 PM
hk4fvj
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Quote:
Originally Posted by Glow-man View Post
I bought two sleeve at Towerhobbies. At that time I could get just the sleeve for 75$US. For some reason they sell the sleeve and piston for the 75AX. If you still want that engine, just get it. I own 2 55AX, 2 95AX and one 120AX. I do not know exactly why the 95s started to give me problems, but I did all the tricks talked about above and it would dead stick on me, but seemed to run great on the ground and have compression. Actually now that I think about it. I would use OS 7 glow plugs. I still do on one of them. What it does is smooth the engine at low rpm. The AX family have a tendency to vibrate at low to middle rpm. Anyway what I noticed, is when I installed a new glow plug, I would get about 3 flights before starting to flame out. When it did flame out I could see the prop windmill. It would loose all compression. I was an expert at dead sticks. That summer I landed about 10 dead stick with my T 28 with bent fix gear at its worst. What I have notice is my engine would destroy my glow plug element. It was visible to the eye. That is when I really realized it had nothing to do with adjusting my carb, shimming the head or what ever trick I was told. It is possible I may have over heated my engine at one point before all this started because I did not properly air cool them. That was when I was trying to keep the cowl scale. However they did not show signs of failing till later. I know it sucks to put more money on what should last longer. In my case I love those engines. They run like a clock. When I go fly at the field I do not have time to fool around with stuff. It has to be start and go. I am a busy family man. Except for that event I just talked about. The OS AX family engines have gave reliable fun.
Oooyaaa! Next thing is after I changed the piston sleeves I always used the stock exhaust. Simply because perhaps using other types of after market brands might have cause my problems. I cannot say for sure. Below is an old video of my Spitfire with a new OS 95AX at the time with custom exhaust. Enjoy the story.
https://youtu.be/AdtwBGbmceQ
And this is how all this started. Dead sticks. The engine works OK on the workbench but dies airbone. Different plugs even OS#7 and the problem remains. Tried different fuels, nada. I have never seen the flame out but the problem is still annoying.
Nice video. Sorry for your plane.
07-05-2019 06:22 AM
Glow-man I bought two sleeve at Towerhobbies. At that time I could get just the sleeve for 75$US. For some reason they sell the sleeve and piston for the 75AX. If you still want that engine, just get it. I own 2 55AX, 2 95AX and one 120AX. I do not know exactly why the 95s started to give me problems, but I did all the tricks talked about above and it would dead stick on me, but seemed to run great on the ground and have compression. Actually now that I think about it. I would use OS 7 glow plugs. I still do on one of them. What it does is smooth the engine at low rpm. The AX family have a tendency to vibrate at low to middle rpm. Anyway what I noticed, is when I installed a new glow plug, I would get about 3 flights before starting to flame out. When it did flame out I could see the prop windmill. It would loose all compression. I was an expert at dead sticks. That summer I landed about 10 dead stick with my T 28 with bent fix gear at its worst. What I have notice is my engine would destroy my glow plug element. It was visible to the eye. That is when I really realized it had nothing to do with adjusting my carb, shimming the head or what ever trick I was told. It is possible I may have over heated my engine at one point before all this started because I did not properly air cool them. That was when I was trying to keep the cowl scale. However they did not show signs of failing till later. I know it sucks to put more money on what should last longer. In my case I love those engines. They run like a clock. When I go fly at the field I do not have time to fool around with stuff. It has to be start and go. I am a busy family man. Except for that event I just talked about. The OS AX family engines have gave reliable fun.
Oooyaaa! Next thing is after I changed the piston sleeves I always used the stock exhaust. Simply because perhaps using other types of after market brands might have cause my problems. I cannot say for sure. Below is an old video of my Spitfire with a new OS 95AX at the time with custom exhaust. Enjoy the story.
https://youtu.be/AdtwBGbmceQ
07-05-2019 05:08 AM
hk4fvj
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Quote:
Originally Posted by Glow-man View Post
I did not read all your thread and did not read how your problem started. I own 2 OS 95AX since 2009. Both run every summer. To keep it short, I had to change the piston sleeve. My engine would flame out once in the air. Trust me I have tried everything first. That occurred in 2012. Since I have replaced the sleeve on both engine they have been great to me. Strange this happen 3 years after I bought them.
Weird things happen. The problem started the last year. The third year but, I did not fly it too much before anyway. How did you get the sleeves? I have been checking and only the full piston set is available.
07-05-2019 02:04 AM
Glow-man I did not read all your thread and did not read how your problem started. I own 2 OS 95AX since 2009. Both run every summer. To keep it short, I had to change the piston sleeve. My engine would flame out once in the air. Trust me I have tried everything first. That occurred in 2012. Since I have replaced the sleeve on both engine they have been great to me. Strange this happen 3 years after I bought them.
07-04-2019 08:04 PM
Propworn
Re: Best Glow Plug OS AX 75: 7, 8, 10?

What ever engine I am using I first mount it upright in an engine test stand with the fuel tank at the recommended height with the needle valve and get it running perfectly.

Once I am satisfied then I position the engine as it would be in the airframe and reposition the fuel tank as per the installation in the airframe. If it runs any different then I have to address what changes created the problem and make the adjustments to get it to run as I want.

Once that is done I install it in the airframe and it should run as before on the test stand. If not there is something wrong or different about my installation. Cooling or cowl pressure might be the problem but I know its something to do with how I installed it.

In every case so far I have been able to figure out what the problem has been and corrected it. Take your time and you should be able to figure it out.

Dennis
07-04-2019 09:30 AM
hk4fvj
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Quote:
Originally Posted by David Ford View Post
Al,
You might want to take Cougar's offer to look at your engine. I would offer but I am on my way to the US nationals for a few weeks to compete.
Your tests and observations suggest something is going on in the engine. OS says the main needle s/b 2 1/2 turns out, so 3 is still in the ballpark so the engine should run and be some rich, yours seems lean like there is too much load or has a fuel restriction. The black carbon on the piston won't normally be there if it is running rich, that is a sign of lean/high load.
Cougar suggested some reasons for the black, like a bad bearing, all sorts of things like that could cause the black and also make the engine run hot/lean trying to overcome the drag in the engine.
Cougar's suggestion of a second set of eyes is a good one.

Best of luck Al
Thanks David
Unfortunately David is pretty far away, around 3 hours, it does not seem to be easy to meet each other. I will have to find another solution, maybe returning it to the manufacturer, etc. I am planning to go the dealer that sold it to me and ask if they have someone authorized shop/guy to adjust/clean it.

And good luck at the US nationals!
07-04-2019 06:29 AM
David Ford
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Al,
You might want to take Cougar's offer to look at your engine. I would offer but I am on my way to the US nationals for a few weeks to compete.
Your tests and observations suggest something is going on in the engine. OS says the main needle s/b 2 1/2 turns out, so 3 is still in the ballpark so the engine should run and be some rich, yours seems lean like there is too much load or has a fuel restriction. The black carbon on the piston won't normally be there if it is running rich, that is a sign of lean/high load.
Cougar suggested some reasons for the black, like a bad bearing, all sorts of things like that could cause the black and also make the engine run hot/lean trying to overcome the drag in the engine.
Cougar's suggestion of a second set of eyes is a good one.

Best of luck Al
07-03-2019 08:44 PM
hk4fvj
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Guys
I removed the plug and indeed it had carbon built. I open the lid and yes the piston had carbon on top. However, before I carried out this test, I replaced the plug and the previous one was clean, no dirt but wanted to test with a new one just in case. I checked also through the plug hole and the piston was looking clear. I run two full tanks of 15% fuel ( castor + synt.) during my fine tuning so the conclusion is that the carbon built occurred during these two runs. I checked also the needle valve and the point where I "optimized" it was three full turns open. In my modest opinion this is way too rich. But when I tried to close the needle, the engine tried to die. I don't know if the carbon built due to burning fuel too rich. I guess I don't have a fine tuning hearing . Other than the carbon, the engine look in very good shape, again is almost new.
BTW, no traces of metal in the dark dirt.
07-03-2019 08:47 AM
hk4fvj
Re: Best Glow Plug OS AX 75: 7, 8, 10?

Quote:
Originally Posted by Cougar429 View Post
Believe it or not that is not all that dark. There is just a LOT of it.



I have only seen this type of deposit amount on a few make engines; different names, but from reports all coming out the same factory door. Their fit was so poor air leaked in through the rather narrow front bearing and would continue to idle even with the throttle completely closed.

I have also seen this when the needles are so far out of whack the lube comes out the exhaust in visible drops and a smoke cloud you could hide a DDay invasion force behind. It may be worth it to go back and check they are at least close to recommended and or have someone else have a boo. Believe me, over the years I have seen many times where staring at a problem till my focus would blur would not find a resolution, where another set of eyes could see it in seconds. The reverse has also been true.

Generally OS is not known for this and their carbs are excellent. That being said, if there is an air leak you may need to set it this rich to compensate. A few suspects, especially after long-term storage, would be the carb base O-ring that seals it to the case, rear cover seal and even a loose head or plug.

There is the typically difficult to find HS needle O-ring, but that generally leads to lean mixture.

All these are moot if the engine is in poor mechanical condition. The most critical fit is between the crank and case, (where the aforementioned engines would suffer from poor QC). This can be made worse on any engine by running a bad set of bearings, poorly balanced prop and using the engine after a "Goat" with a bent crank.

You're not that far away so could offer to have a look and try and set it up on the test stand, though may be easier to find someone local.
Thanks Cougar. I will PM you.
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