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  1. #1

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    RCV 120 ... need help, carb and loud click at TDC

    RCV Support -
    I'm hoping you can give me a little help. To start things off correctly, I am not looking for free or warranty service.

    Background
    I bought an RCV120 on the RCU marketplance from a person who appears to be very experienced in RC and engines. I've been at the hobby for quite a while myself.
    The original owner gave up on the engine in frustration, stating that it vibrated excessively. He never flew it.
    He indicated the following:
    a. A gallon of Omega fuel that met the manual's requirements was run very rich initially, per the breakin procedure.
    b. His attempts to run it in an airplane introduced so much vibration that he gave up.
    c. There is probably less than a gallon and a half in the engine so far.
    d. It has a very good idle.

    When I got the engine I found silicone fuel tubing on the high speed needle, which I guess was there to hold the setting in the presence of vibration. The spare starting hex screw is installed, and the first one is somewhat beat up.
    I also found 0.5 mm of axial play in the carb barrel (part number R120813 in the manual). This seemed excessive, so I pulled the "guide screw" (a name I have given it, PN R120825) that runs in the barrel groove and found the end of the screw deformed, as if the barrel had been hammering it. I made a replacement screw, and now the assembly has less play, but it still moves side to side somewhat, particularly as the throttle opens. I know that there is a spring in the carb body to press the barrel out against the guide screw, and my spring is intact and doing its job. I just wonder if, in the presence of a lot of vibration, this spring is strong enough to hold the mass of the barrel in position.

    I have not started the engine yet.

    Questions
    1. Can I buy a replacement screw for the carb, PN R120825?
    2. How much side to side play is acceptable in the carb barrel, in mm? It would seem to me that this is a very critical tolerance, given that the low speed needle's ability to adjust is driven by this measurement.
    3. The most important question: I have oiled the engine carefully, and when I turn it over by hand, at the point of compression, a very loud metallic click can be heard and a snap felt in the prop. With the plug out, this click is no longer present. If I turn the motor with the starter, this click is very evident. If I rock the prop back and forth over TDC, the click occurs with each passing. The engine is cold when I observe this - I have not started the engine yet. Is this normal? I've never had an engine do this before - I am familiar with the feel of a conventionally set up engine at TDC.
    4. Do you folks think that the engine just needs a bit more break in? In many posts, I see people saying that these engines get more smooth over time, as your manual indicates.

    I'm still working on setting it up in a test stand, and I'm going to go ahead and start it in the next couple of days ... any insight would be much appreciated. I'd like to recover this engine - it is a fine piece of workmanship.

    Regards,
    Rikk
    ... I DO read the instructions ...

  2. #2

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    RE: RCV 120 ... need help, carb and loud click at TDC

    Hi Rikk,



    1. Can I buy a replacement screw for the carb, PN R120825?

    Yes I guess they have it at westonuk.



    2. How much side to side play is acceptable in the carb barrel, in mm?

    Just eyeballing I would say on mine its half a millimeter.



    3. The most important question: I have oiled the engine carefully, and when I turn it over by hand, at the point of compression, a very loud metallic click can be heard and a snap felt in the prop.

    You mentioned a worn starter screw. Thats unusual for an engine that consumed just one gallon so far. Which glowplug is inserted? The only glowplug that should be used is the OS F together with one washer. Its possible that that a wrong glowplug touches the rotating valve.
    A wrong glowplug can also be the reason for vibrations.
    Beside that the reason for vibrations can be a wrong gear clearance.


    Regards
    Andi

  3. #3

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    RE: RCV 120 ... need help, carb and loud click at TDC

    Thanks for the reply ...
    It is an OS F with a single copper gasket, per the manual.

    I guess I can infer from your answer that this loud click is not normal?
    Regards,
    Rikk
    ... I DO read the instructions ...

  4. #4
    thebluemax's Avatar
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    RE: RCV 120 ... need help, carb and loud click at TDC


    ORIGINAL: Lightning Fan

    Thanks for the reply ...
    It is an OS F with a single copper gasket, per the manual.

    I guess I can infer from your answer that this loud click is not normal?
    Regards,
    Rikk


    Try givingBill Jensen a call at BJ's model engine service. He is the official RCV repair site in the US located in Conn.. He may know exactly what your problem is and may have the parts on hand that you are looking for. He may also be able to answer your warranty questions. The link below is too his web site.

    Good luck



    http://www.bj-model-engines.com/RCV.html

    My biggest worry is that my wife (when I am dead) will sell my R/C stuff for what I said I paid for it.

  5. #5

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    RE: RCV 120 ... need help, carb and loud click at TDC

    OK guys, I got it.
    I broke down and took it apart. Some varnish inside, and coated with black gunk all over.
    The drive gear can freely oscillate 5 to 10 degrees on the drive shaft. Either the key or the keyways are wasted. One hopes for proper material selection and that it is the key. Since the drive gear can rotate a bit on the shaft, the loud sound after TDC comes from the gear train unloading and the backlash as the drive gear slams into whatever is left of the key that prevents further rotation.

    Does anyone know how to pull the crankshaft? It does not come out with hand pressure, so I have to surmise that the bearings are shrunk on like one does in a conventional engine. If so ... what temperature do I take the assembly to get it out?

    Also, the exploded view shows a shim between the drive assembly and the crankcase rear ... I don't have one. Is this OK?
    ... I DO read the instructions ...

  6. #6

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    RE: RCV 120 ... need help, carb and loud click at TDC

    Well guys, here it is.
    For info, Mr. Bill Jensen is a fine person, who spent a lot of time educating me on these engines.
    He knew right away the problem I had, and we spent some time talking about what I need to do.

    I took the crank carrier and crankshaft assy up to about 325 for 10 minutes in a toaster oven, and then a couple of raps on the start screw freed the outer bearing, and it came apart.
    The key has vaporized. Other than a few flecks of metal, there is nothing left of it.
    Bill told me a few important things about this:
    1. The key is only there for timing ... it is not there to carry the load. The gear is supposed to be pressed onto the crankshaft. He was pretty confident that the crank keyway would be elongated, so I ordered a new one to be sure, along with a key. When I got it apart, the keyway seemed to be ok visually. However, the gear rotates on the shaft a bit - no way it is a press fit.
    2. There is a possibility that the drive gear itself is opened out enough that it is no longer a press fit. I'll see when I get the new shaft.
    3. He said that this happens when there is any gear slop at all. The optimum is to have an engine that starts out with the gears so fully engaged that it is hard to turn the engine when cold. I should adjust this by removing shims as necessary to get the gears fully meshed, which would be fine, except that I do not have nay shims installed. In this case, I may have to get a shop to face the carrier a few thou.
    4. He suggested using Loctite (high temp, I do not remember the number) to retain the gear on the shaft.
    5. Finally, he recommended a bearing changeout for a better grade of bearings, since I'm there.

    This has become an obsession now.
    ... I DO read the instructions ...

  7. #7

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    RE: RCV 120 ... need help, carb and loud click at TDC

    Anyone replace their stock carb to another make (O.S.) for better more consistent results?

  8. #8

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    RE: RCV 120 ... need help, carb and loud click at TDC

    I owe a long thread on my journey with this engine. Most of the problems occurred because I got the engine after it sat unused for about four years. There were many things I had to do, but the carb needed all new rubber on the needle. The original o rings were hard and fell apart with only minor prodding.

    After I finally got the engine to what I now know is the "factorycondition", it ran fine on the existing carb. I can tell you this: if the engine vibrates a lot, I know why, and it is not supposed to do it. Also, if it vibrates a lot, it tears up the needle orings, so you have to fix the vibration first. The vibration comes from poor engagement of the gears, which occurs because the crankcase carrier has the crank gear too far out.
    ... I DO read the instructions ...


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