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SK 90-----WOW

Old 12-10-2007, 09:46 PM
  #26  
prgonzalez
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Default RE: SK 90-----WOW

Hi Ernie,

Yes, I checked the opening in the back is about 5 times the inlet. I really do not think the outlet is a problem at this time. I had an OS-61 in this model before and it was working fine. No problems with overheating.

Thanks for the input though.

Due to bad weather, I was not able to test the proposed changes today. The weather forecast says it will be clear skies by Wednesday. I shall see then.

Thanks to everyone providing their knowledge and sharing their experiences.

Pedro
Old 02-07-2008, 08:51 PM
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Default RE: SK 90-----WOW

Finally, I was able to get some time to work on the engine at home. I fully opened the throtle and opened the LS needle until I saw a gap of about 1/64 in the needle. Then, I removed the plug I had on one of the pitts outlets. With the dremell, I made some cuts to the outlets to be able to close them and reduce their area about one half. I also removed some material from the cowl over the engine head. (sorry, I could not upload any pictures, don't know why it would not let me).

Temp @ 68-F, prop TF 15x6, fuel 5% Omega.

I put 5% Omega fuel, primmed the engine, put the igniter, and it started on one flip against compression. Rapidly I opened the throttle to get stable RPMs. Then, I opened full throttle and adjusted HS needle. I was able to go rich from 7K+ to 6K+ in one turn of the HSN. I also had big smoke at the exhaust. I then adjusted the RPMs to about 7000. I throttle up and down for a while. Checked the engine temp after five minutes of WOT and I measured 245-F. Let the 12-Oz tank go empty.

After 20-mins break, I put another tank and went for pick RPMs. I got a max of 8400 RPMs. Then, I back out 1/4 of turn of HSN and got 8100 RPM. I checked temp after five minutes of WOT and got 295-F. Put the plane at 90-degrees vertical and the RPMs increased to 8200 and consistent for about one minute. Then, I checked idle. I open throttle to get around 2400-2500 RPMs. Then, tested at 30-sec, one-minute, and two-minute idle transition to WOT. in 30-sec I got just a bit of load-up. At 2-mins, I got just a small hick-up. This time, the color of the oil at the exhaust gases is clear. No more gray oil like at the beginning.

From WOT throttle to idle, the engine goes to about 3000 RPM and slowly goes down to 2400 RPM. Is this a sign of being a bit rich?

So, I believe I am ready for flying again. I hope I can go to the field tomorrow afternoon.

What do you think about this runs?

Do you think that I still need to open LSN a bit more?

Thanks in advance for your input.

Pedro

edited for uploading pics. Didn't work.[:@]

Old 02-07-2008, 11:44 PM
  #28  
Ed_Moorman
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Default RE: SK 90-----WOW

SK engines, even the ringed ones, have a tapered bore. All other ringed RC engines I know of have straight cylinders. Since the SKs are tapered, the Kangke techs told me to never, never run them rich. There is a break-in schedule in the instructions. As I recall, tank 1 is run at a rich 2-cycle, just after it breaks from 4-cycling. Tank 2 you open and close the needle valve from lean to rich every 10-15 seconds. Tank 3 you set at max rpm and back off 4 clicks, then you cycle the rpm from max to idle every 10-15 secs. Tank 4 is a full power run at max less 4 clicks. On tank 5 you set the idle, then run the rest of the tank out. They will also need a gallon or so of rich 2-cycle running in the air. Expect them to get better for 3 gallons. Sort of like a Saito. (At least mine) I have done 3 SK engines this way and all have run great.

I really like the SK carb. Before I go on, I never mess with the factory low end setting until after I run the break-in. Nearly every engine will run in a rich idle at the factory setting.

As I said, I like the SK 90 carb. I bought a Tower .75 and it had a very rich mid range. I could set the low end to idle for a long time, but the mid was terrible. I dropped on an SK 90 carb and the Tower ran perfectly. Tower did send me a new carb which works fine.

A buddy asked me to check his Evo .61 since the carb wouldn't adjust. I tried it on my bench and it must have an O-ring leak or something because it wouldn't hold a low end setting. Just for grins, I dropped the SK 90 carb on it. The throat diameters are the same. Ran perfectly. I am really impressed with the SK 90 carb.

SK 90s are designed for torque and not high rpm. A 14-6 will normally not run well. The transfer ports aren't large enough to pass the needed fuel for high rpm.

Yep, it's got anhedral!
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Old 02-08-2008, 04:11 AM
  #29  
Turk1
 
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Default RE: SK 90-----WOW

Hi Gonzalez,Yes, your LSN seems a little rich.Though I recommend you to decide what kind adjustments you need by flying repeatedly.It seems alittle overpropped to me.I also recommend you to try lesser props but again the best way is testing on air IMO.
Old 02-08-2008, 09:13 AM
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Default RE: SK 90-----WOW

Ed,

The problem I had was the LSN was giving me a lean condition (previous post). When I ran the first tanks, I was not able to make the engine go rich at all even at four and five turns out of the HSN. But, I did followed the break-in procedure even with the weird needle setting. I did not want to touch the LSN and posted my problem. The recommendation was to open the LSN until the HSN was operational. That's what I did. I was able to go rich 2-stroke cycle and the HSN was operational. I never let the engine go into 4-stroking. And, I hope the engine is not damaged by the first lean runs. But, how can I tell?

Also, in the first two flights, I had overheating condition in the first five minutes of flying at 1/2 throttle. So, what I am trying to accomplish are two things: one, make a correct adjustment of the needles; and two, resolve the high temp condition in flight.

Turk1,

Do you think the Top Flight 15x6 is too much prop for it? I believe I am using one of the recommended prop for this engine, am I not? However, Ed indicates a 14x6 will not be a good prop for it. I can't go to an eight because this Giles is not designed for speed as indicated by GP.

Yes, I do have a concern, I think, I am getting low RPMs with this prop at WOT. I was expecting to be between 9K and 10K. But, could it be the fuel I am using is not good? I will be using a new can this afternoon and I will read the max RPMs.

Ed and Turk1, I really appreciate your advice and help you always provide in RCU and I want to thank you both for that on behalf of us being helped. I am happy to continue learning from you.

Pedro

edited for misspelling
Old 02-09-2008, 07:06 AM
  #31  
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Default RE: SK 90-----WOW

Welcome Gonzalez.It is the problem of LSN while testing in Kangke(I dont think they make tests in factory in China) adjusting to good run not for break in so it is not allowing to richen for 4 stroking.I dont use any SK 90 and Ed is doing great job on those engines so I cant say more about props but seemed your revs are low.Recommend you to tighten the head screws and backplate again(with care please).
Old 02-09-2008, 01:44 PM
  #32  
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Default RE: SK 90-----WOW

Turk,

Yesterday, I almost lost my plane. The SK is behaving weird and overheated again. When I realized the overheat, I set for landing but the engine was already very, very unstable and it deadstick at the wrong moment and the plane stalled at about two feet over the runway. Fixing the plane will take me about four hours total.

By the way, I have sent an e-mail to the new service rep for Kangke. After setting HSN for max RPM minus 4-clicks, I set the low speed for good idle and transition, and again at that point, the high speed needle was not operational. I removed the head and inspected the sleeve and piston top. The piston did not have any carbon built up, but the sleeve is not shiny anymore. It has a dark gray mate color in all piston run. The engine still has good compression though.

At this point, I will wait for the answer of Kangke support and I might do one bench run with a TP 14-6 wood prop and whatch for the behavior. At this point I agree with you that the engine might be a little overproped. Maybe is the prop brand design compared to other 15-6 props that have proven to be perfect combination for this engine.

I don't want this engine to become my second nightmare. My first one was one of those XLS-52A which I need to re-tapper the LSN as the cure indicated in another thread. Or, I might try it with the SK-50 carb if it fits.

I will start the break-in of my SK-50. This time, I will use an APC 12-5 prop as everyone else. I am sure I will have good success with this one.

Thanks
Pedro
Old 02-09-2008, 03:14 PM
  #33  
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Default RE: SK 90-----WOW

Once again, it becomes hard to ignore the issues associated with the quality control of low-cost Chinese engines.

My SK90 is a beautiful little engine and runs like a Swiss watch. It was very easy to set up, starts virtually first-flick every time, pulls good revs on large props and is nicely economical on fuel. It's never dead-sticked, never overheated and never given a moment's grief.

Others seem to have not been quite so lucky -- yet they bought the same engine.

Then we have my SK50 which came with a virtually untapped glow-plug hole, swarf in the combustion chamber, a pinch that really was *too* tight (and I've broken in some *very* tight engines before -- including the Norvel 061 Big MIG) and has decidedly lackluster performance, regardless of prop-size.

Others seem to have been far more lucky however, and more than a few SK50 owners rave about their engines.

Ya pays ya money and takes ya chances I guess.
Old 02-09-2008, 03:26 PM
  #34  
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Default RE: SK 90-----WOW

ORIGINAL: prgonzalez
I don't want this engine to become my second nightmare. My first one was one of those XLS-52A which I need to re-tapper the LSN as the cure indicated in another thread. Or, I might try it with the SK-50 carb if it fits.
Thanks
Pedro

That is a five minute fix, hardly a nightmare Just put the needle in your cordless drill and hold a knife sharpener to the end of the needle while spinning it around until you have a taper that seems ok.

Strange as we have never had to do anything to the carb on several XLS 52`s around here
Old 02-09-2008, 06:38 PM
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Default RE: SK 90-----WOW

Certainly, it sucks to be another count in the statistic of bad units. But, when we have a good unit, we rejoice.
Old 02-09-2008, 07:12 PM
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Default RE: SK 90-----WOW

Have A tiger shark 90 ringed which I believe is the same engine Got from Kange after a couple of tanks of 10% nitro dropped on a diesel head made by A.J. Coholic 15x6 purrs at 9500 good transition
martin
Old 02-10-2008, 07:14 AM
  #37  
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Default RE: SK 90-----WOW

Hi Gonzalez,I want you to check a possible problem which I met once.I have found that whenever I (or servo) play with throttle,LSN was turn slowly by spraybar and after several play LSN would fully block the spray bar.I solved problem by using tghter o rings on LSN.Maybe you have such a problem too.Play throttle manually some time and check the new LSN position which marked before.
Old 02-12-2008, 01:38 PM
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Default RE: SK 90-----WOW

Hi Turk,

I called SK engine support and they told me to send it back for inspection/repair. I will keep you posted on their answer in about 2 weeks.

Pedro
Old 02-12-2008, 07:10 PM
  #39  
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Default RE: SK 90-----WOW

Very Nice plane Ed...it has the colors of our National Flag!! Viva Colombia
Old 02-12-2008, 09:36 PM
  #40  
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Default RE: SK 90-----WOW

I and several others had the same problem. Check this out. Remove the carb and look into the throat at wide open. You should be able to see a gap between the fuel tube and the end of the low speed needle. What was happening was, when the low speed needle was screwed in far enough to control the low speed, it did not back out of the feed tube enough causing a restriction at high speed. the cure is simple, Remove the throttle barrel from the carb. Screw the low speed needle out of the barrel - it has to be screwed right into and thru the throttle body. Grind off approx. 1/16 off the end of the needle. Reassemble,
Start the engine and follow the normal needle adjustment procedures. When all set close to right , again check for clearance between the fuel tube and the LS needle. If a gap is not visible, cut a little more off the LS needle Do this until there is a small gap just visible. You will then find that the HS needle will richen properly. The removal of the end of the LS needle will not degrade the LS adjustment as the tip of the needle is not doing anything when the throttle is closed to idle. It is well into the fuel tube.
Old 02-13-2008, 08:23 AM
  #41  
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Default RE: SK 90-----WOW

Hi Hamaoki,

I believe you are right on the money with the problem I have. As with the LSN set for perfect transition, there is no gap between the needle and the fuel tube. And, if I turn the needle out for even a small 1/32 gap, then the low-end is totally fat. Great tip to remember and keep in my engine notes.

Where did you get that information from by the way?

At this time though, I still will send the engine for repair. I am afraid the engine has overheated so many times that the sleeve and piston life might be reduced already. Also, I never had good RPM with this engine using a 15-6 prop as others.
Old 03-11-2008, 08:37 AM
  #42  
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Default RE: SK 90-----WOW

The engine came back from the repair center. They found no problem with the engine and carb. They tested the engine with stock muffler and my 15x6 prop and it went to 9,400 RPM and with a 14x6 went to 10,000 RPM. After that, they tested the engine with my pitts muffler and RPMs went down to 8,400. So, according to the report the issue is the pitts.

Now, I can think on and rationalize the sequence of events ... When I started the engine for the first time, I could not throttle up more than half open. Then, I plugged one outlet of the pitts muffler thinking I had fuel pressure problems. In reality the low speed needle was set lean. (SK documentation says to reset the LSN at 1 and 3/4 turns out). So, plugging one outlet increased fuel pressure and I was able to go WOT. But, with such restriction, back pressure at the muffler was too high affecting the overall performance of the engine, dropping 1000 RPMs. At the end, the engine was running lean all the time except at idle which was rich and loading up. So, the whole scenario was confusing to me. If I would have tried the stock muffler, I would have probably reached to the same conclusion. I never tried the stock muffler.

As soon as I finish the repairs of the fuselage, I will test the engine again. I will remove the restrictions on the pitts and revise the fuel lines to make sure the fuel can flow freely. I will even remove and inline fuel filter I have going to the carb. I hope I can get it to work properly. Ray Nano told me this particular pitts was designed specifically for the SK.

After reflecting about all this, I have learned another valuable leason, break-in engine with stock configuration and use after market addons later. Although my past experience was different when I broke-in my .61-FX broke-in with a pitts muffler from day one and never had any issues with the setup. I have also learned to be careful with vendor documentation. Sometimes, it is not accurate for some particular engine models; i.e. reset the LSN at 1 and 3/4 turns out does not work for my SK-90.

By the way, I broke-in my SK-50 and it performed beautifuly all the way at each step using stock muffler. Now, it's ready for a future plane.

Pedro
Old 03-12-2008, 11:30 PM
  #43  
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Default RE: SK 90-----WOW

I thought Ray Nano had left Kangke last year. Are you sure he was the guy you dealt with?
Old 03-13-2008, 10:50 AM
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Default RE: SK 90-----WOW

72,

Yes, Ray Nano left Kangke. I was referring to some communication I had with Ray before he left the co. When I knew he was leaving, I asked Nano some questions via e-mail.
Old 04-25-2011, 09:03 AM
  #45  
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Default RE: SK 90-WOW

ORIGINAL: Ed_Moorman

Keep the 15-6 on it for a gallon or so. My 2 have run great. I am runing an OS #8, 10% Omega castor blend fuel. I have tried several 15-6 props, Zinger, APC, MA and MAS, but am using the 15-6 Master Airscrew Scimitar. Both of mine have been an old, rebuilt, trash can Ultra Stick 60 that weighs over 8 lbs. Great vertical climb, pulls like a tractor. The engine will keep getting stronger for about 3 gallons of fuel.

My first engine which I took out to air break-in the second, is going in a new Twist 3D 60.

By the way, both engines usually filp start with one back flip. I don't recall ever using a starter on either of them.

I did have a minor problem with both in that the carb started sticking. I took the barrel out and, under magnification and a bright light, I notoced the angled slot that cams the barrel out and in had the edges flared up on the ends. These flared up portions dug into the aluminum carb body, causing it to stick. I would think this is from using a dull cutting tool. I took a small file and touched up the rounded ends of the groove and the carb now works smooth as glass.
I just recieved a new SK 90 and I'm wondering if the OS #8 is correct as this document indicates that "Glow plug, use a medium heat range long reach plug" is needed. See attached doc or link kangkeusa.com/Engines/SK%20Engine%20Manual%20(Instructions).rtf. I'm thinking maybe an OS LC4 might be appropriate.

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Old 04-25-2011, 09:06 PM
  #46  
Turk1
 
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Default RE: SK 90-WOW

Yes,I think OS#8 is suitable.
Old 04-26-2011, 04:18 AM
  #47  
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Default RE: SK 90-WOW

Turk1,


The OS#8 may be suitable as far as its heat-range is concerned.

However, it is not a 'long-reach' glow-plug.
OS made it (and a few more of its standard glow-plugs) 'medium reach', so it is situated recessed in the combustion chamber.


There are many long-reach glow-plugs available, even from OS themselves (the [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXSBW9&P=ML]LC4[/link]), which are as good and even cheaper than the #8.

Old 04-28-2011, 02:41 PM
  #48  
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Default RE: SK 90-WOW

I'll try the OS#8 1st.
ORIGINAL: Turk1

Yes,I think OS#8 is suitable.

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