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Thread: SK Engines


  1. #1

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    SK Engines

    I got the following from my SK .90 engine with the stock muffler after about 40 oz of break in with 5% nitro PowerMaster. I used a new SuperTigre glow plug, since it was a medium heat and long, laying around.

    APC 15x6 9400 rpm (1.75 hp)
    MAS 13x8 10500 rpm (1.89 hp)
    Zinger 13x6 11200 rpm (1.77 hp)

    The horse powers are calculated using ThrustHP, just for reference. Idling was consistant around 2200 - 2300 rpm, and the midrange was quite smooth.

    Is this typical? Will it improve significantly, say after a gallon or two? I'd like to see the result of other ppl who tried this engine.

    I'm also interested in SK's .50 engine. I'd appreciate it if anyone tested it, even if a few years back.

    - Ken

  2. #2
    wildchild45177's Avatar
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    RE: SK Engines

    I have a SK-50 swinging a ProZinger 13X5 at 10600 RPM

    Bob

    Thats on CoolPower 15% at 4800 ft elevation

  3. #3
    Sport_Pilot's Avatar
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    RE: SK Engines

    Is this typical?

    It's in the same ball park as other 90 two strokes.
    Glow Head Brotherhood #15

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    RE: SK Engines

    How long did it take you guys to get your SK engines after you placed the order? I ordered an SK 50 A from Kangke USA on the 11th and it still isn’t here. I’m wondering if they are always this slow or if it’s just my order.

  5. #5
    TigerTail's Avatar
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    RE: SK Engines

    I ordered an SK 50 from www.atsrcplanes.com sunday night and got a tracking number monday afternoon. I should have mine thursday. Most reports say it is a good motor.

  6. #6

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    RE: SK Engines

    Well it appears it was just my order! Some how the billing went through Pay-pal and my order went to China. Sβ€”t happens!! They think they now have it straighten out and I should have the SK-50 by Friday. I never did receive a tracking No.

    After break-in I will post some RPM info. I’m hopping it will turn an APC 11X6 at 13,500 rpm

    oldbob

  7. #7

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    RE: SK Engines

    Well I received my SK 50 yesterday and today it was bolted to the test stand and ran twice. I followed their break-in procedure and during the first run the carburetor was sticking when I tried to close or open it and after the second run the carb. barrel would not turn at all. Need to call Kangke tomorrow.

    Hay bubbup, did you receive your engine? If so, how is it running?

    Will keep you posted.

  8. #8
    TigerTail's Avatar
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    RE: SK Engines

    Oldbob, here is a link to my comments on the engine. I didn't want to post here in the tach reading thread.
    http://www.rcuniverse.com/forum/fb.asp?m=4697016

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    RE: SK Engines

    Oldbob
    Did ya ever tach your 50A? Inquiring minds want to know.

    motohead / other old Bob

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    RE: SK Engines

    Moterhead, thanks for the poke. I have been reluctant to post until I had something positive to report, but here goes anyway. I received the new carb yesterday and it looked and felt good. I put it on the engine and opened the high needle two turns, and it would not start until the high-end needle was four turns out. This is unusual from my experience. Two to two and one half turns open should get the engine running. Once running I opened the carb barrel and the engine went lean, closed the carb and it seamed OK, I opened the high needle another half turn and opened the carb to WOT, same thing, but this time when I tried to close the carb the barrel stuck at about 3/4 open, so I pinched the fuel line and shut it down.

    I completely disassembled the new carb and this is what I found. Using a strong magnifying glass I could see a sharp edges sticking UP from the sides of the metering grove. After filing these edges flush with the barrel surface, cleaning it all with lacquer thinner and applying a coat of clean oil it is now rotating smoothly. But this did now explain the lean problem. I used my squeeze bulb and forced air through the needle orifice and it was very hard to force air through it no matter where I set the needle valve. I took the old carb, the one what will not idle, and repeated the squeeze bulb test and much more air seemed to be flowing. With the barrel out and the needle valve removed I could see straight through the main brass end. I then removed the fuel nipple and could see only a small portion of the cross-hole that allows fuel to flow from the nipple into the needle valve seat. I removed the large nut from the main brass end and was able to rotate the brass piece until the cross-hole was in alignment with the fuel nipple opening. Put it all back together and now good airflow through the needle valve at two turns open.

    What puzzles me is why the carb barrel seems to rotate smoothly at first but sticks after the engine is running??

    Tomorrow I will install the carb and run the engine. I will let you know how it turns out.

    oldbob

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    RE: SK Engines

    Well I ran the SK 50 today and it’s all good. The fuel is Power Master 15% nitro and 18% oil sport blend, prop APC 11X6. The top end is 12,000+ RPM and peak hit 12,300. The nice surprise is a rock solid idle at 2,000 RPM with quick spool-up to peak. I let it idle for three minutes or more several times and punched the throttle and it will run-up instantly without a cough or stutter. A three minute idle is more than I need; my down line is only about two minutes.

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    RE: SK Engines

    Thanks, OldBob
    I ordered an SK 50A last week. Maybe it will get here soon. 11x6 at 12000-12300 sounds good to me for 60 bucks.

    motohead / Bob

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    RE: SK Engines

    SK 50 got here today. Broke it in this afternoon and gonna put it in the sky tomorrow. I'll post some initial tach readings when I get it dialed a bit.
    motohead

  14. #14
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    RE: SK Engines

    Interesting.I have 2 SK 50 (3rd will be delivered tomorrow) and no problem at all. Mount and run.Great engines.My first one has about 5-6 hours run.I will try to tach it if I can find a friend with tachometer.
    GlowHead Brotherhood #31

  15. #15
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    RE: SK Engines

    Test Pilot
    Don't run props under a 15-6 on this engine. They are ported for big props and if they are underproped will lean out in the air. Keep them under 10,000 on the ground. 15-6 to 15-8 props are perfect for this engine. Will be trying APC 16-4 wide balde this weekend as i am using this plane on a funtana x50 3d.

  16. #16
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    RE: SK Engines

    ORIGINAL: Cambo

    Test Pilot
    Don't run props under a 15-6 on this engine. They are ported for big props and if they are underproped will lean out in the air. Keep them under 10,000 on the ground. 15-6 to 15-8 props are perfect for this engine. Will be trying APC 16-4 wide balde this weekend as i am using this plane on a funtana x50 3d.
    With Kangke s tech staff s words; (For SK 50) Keep max RPM about 11000-11500 on ground.(Means choose prop accordingly).Otherwise overporting will occur and some unwanted results.
    GlowHead Brotherhood #31

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    RE: SK Engines

    I am running a tiger shark 120 with a 16x6x10 Zinger prop. I mixed my own fuel with no nitro & was turning over 11,500. Am about to order a 90 fro sk to see how it runs.

  18. #18

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    RE: SK Engines

    Jadec, Go back and recheck your tachometer reading. That prop turning at 11,500 RPM is producing 5.7 hp and 24.5 lbs of thrust. This is not possible with a 120 glow engine.
    Does your tiger shark have the Dykes ring or the standard ring?

    Oldbob

  19. #19

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    RE: SK Engines

    i THINK YOU MIGHT BE RIGHT. a ALL I KNOW IS THESE ENGINES FOR THE PRICE ARE KILLERS. i SEE THAT THEY NOW HAVE A 110. i MIGHT JUST ORDER ONE.

  20. #20
    Cambo's Avatar
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    RE: SK Engines

    Hey guys
    After doing some searches i am finding that my sk 90 has basically the power of the 120 size 4 strokes
    With 5% fuel and a tower muffler i am getting
    9300 15-6
    8500 15-8
    9200 16-4
    All of this is running rich (nice smoke trail out the muffler) and only 3/4 of a gallon through it. I have heard that they gain power over 2-3 gallons of gas.

    All of these props have instant spool up.

    I can't wait to try the APC 16-6 i ordered
    Plus, at 5% nitro i am getting great fuel economy and it is cheap too.

  21. #21

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    RE: SK Engines

    I have been running mine with a 16x6x10 Zinger prop. I was making my own fuel without any nitro & was it a screamer. My next engine will probably be the new 90.

  22. #22
    Cambo's Avatar
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    RE: SK Engines

    Update, i tried apc 16-6 today

    8600 richened down to 8200. No bad concidering she is still not completely run in and running 5%

    Idle and transition are still great

  23. #23
    Cambo's Avatar
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    RE: SK Engines

    I have run some more gas through my 90 and have some updated readings

    apc 16-6 8500 8900 peak
    apc 16-4 9000 9400 peak
    zinger pro 15-6 9500 9900 peak

    5% cool power and tower muffler
    300 more rpms can be achieved from 15%

    Excellent flight times for an 11oz tank.
    15-6 has fastest spool up for 3d

  24. #24
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    RE: SK Engines

    I have 3 SK engines, 2 of the .91 and 1 of the 50 (actually .525). All run great. One thing you have to remember about SK engines is they are low rpm torque engines. The port size and timing is such that they will not tolerate a small prop and high rpm. My 2 .91s are real horses on a 15-6. Talk about torque. The 50 is good on a 12-5. Both have execllent idles and mid ranges. I recently has troughe with a Tower .75 running rich in the mid range so I dropped the SK 90 carb on it. Ran perfectly and flew great. Hobbico sent me a new carb and it runs fine, too. I think the first carb has a bad low speed needle. Anyway, the SK carb is excellent. Some of them can have burrs on the rotating barrel in the carb. One of mine had this and I touched it up with a fine file.

    Oldbob who is running an 11-6 at 12,300 rpm, I would be surprised if you don't have leaning out problems in the air. No matter how rich you set the SK, the port size is not large enough to pass the fuel so it will normally go lean in the air and die. The 50 will turn a little faster than the 90, but at 12,000, you may be over the limit. Turk is running an 11-6 prop, but he runs no nitro fuel. I am running a 12-5, which is normally the smallest prop recommended. Don't tell me what the instructions say, they are incorrect, per the Kangke engineer. Please report back to us on how it flies. I would go to an 11-7 or a 12-5.

    Ed Moorman, AMA 553, Former R/C Report Fun Aerobatics Columnist. 76 and up to my old tricks!

  25. #25

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    RE: SK Engines

    Ed, I have not experienced lean runs in the air with my SK 50. I set the needle about 400 RPM rich and fly. No dead sticks and the idle is great. This is the only SK engine I have so I don’t know anything about the 90s or 130s.

    Oldbob


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