Atkinson frustrations

Discussion in 'General Engine Discussion' started by Gordon, Jul 9, 2018.

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  1. Jul 9, 2018 #1

    Gordon

    Gordon

    Gordon

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    This post is to vent my frustration but if someone has some insight it is certainly welcome. I am building the Atkinson Differential engine from the Gingery plans and I am not having any luck in getting to run. Gingery said that he had to turn the engine over with an electric motor and a belt to the flywheel for up to 40 hours to seat the rings before it would start dependably. I have been doing that for quite a few hours (25-30) but I am not seeing any improvement. I am sure that the problem is compression but a solution escapes me. Due to the unique design you can only feel the compression on the last portion of the compression stroke because the spark plug hole is covered until the last part of the stroke. There seems to be good suction at the spark plug hole on what would be the exhaust stroke.


    At this point it kind of fires about 1/3 of the time and even that is intermittent. If fires for a while and then quits firing until something like carburetor adjustment or cool off occurs. I have tried different spark timing and different carburetors and carburetor adjustments but nothing seems to change. I am using the S&S ignition and there seems to be a good spark.


    At this point I am reluctant to remove the pistons/rings for inspection because if they are actually seating the rings are going to be in a different rotation when it is reassembled which I assume would at least partially disturb the seating in process.


    There seems to be a surprising lack of information and build logs on an engine which has been built by quite a few others. There are quite a few Youtube videos. There are several errors or at lest omissions on the drawings but I have not seen any reference to this by any others. I have been over by engine and checked it to the drawings many times and as far as I can tell it is made correctly.
     
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  2. Jul 9, 2018 #2

    ThomasSK

    ThomasSK

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    Does it move the intake valve? that is just moved by the suction from the cylinder, and the spring is important. Too stiff a spring here would make it not get enough gas. Make sure there isn't too much friction on the intake valve.

    Does it run assisted? given that it has gas available, does it run when connected to a electric motor?
    Have you tried running it on a dab of starting fluid?

    As long as you can feel the push of the compression, that should be fine. Is your timing of the spark correct? The way that the timing is explained in the book its faily easy to set it up 180 degree wrong, there is a youtube video around that explains it, but I was not able to dig it up.

    The Atkinson differential is perhaps one of the worst engines to get running reliably, but it's a fun engine!
     
  3. Jul 9, 2018 #3

    Gordon

    Gordon

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    Intake valve seems to move well. Visible movement and I have tried stronger and weaker springs.

    It kind of runs with the electric motor. I can hear it fire about 25% to 50% of the time. I cannot get it to fire when turned over by hand. I have also tried weaker and stronger exhaust valve springs. I does not really try to run on starting fluid. Just one pop. It only seems to fire with the carburetor adjustment just barely open. I have tried making a smaller orifice but that has not made much difference. I have also tried choke plates on the intake throat.

    I am sure that the ignition timing is correct or at least not 180° off. I have tried running it both up to 15° BTDC and ATDC.
     
  4. Jul 9, 2018 #4

    ThomasSK

    ThomasSK

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    Just to cover all the basics, power stroke should be the long stroke, and compression stroke the short stroke.

    What kind of fuel do you use?
    It may be that it needs more time to run in, but I would expect it to fire and run for a short time after 30hr.
     
  5. Jul 9, 2018 #5

    Gordon

    Gordon

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    I am using Coleman fuel. I also thought that after running with an electric motor for that long it should show more of a tenancy to fire. I guess I will just try running with the electric motor for a while more.

    Am I correct in my assumption that removing and reinstalling the rings would affect the seating or are the rings rotating in the grooves as it is running?
     
  6. Jul 9, 2018 #6

    ThomasSK

    ThomasSK

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    The rings should be rotating.
     
  7. Jul 10, 2018 #7

    Cogsy

    Cogsy

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    In my mind, the procedure for "running the rings in" is completely wrong and is likely to be the direct cause of poor compression. Best full size practice (and what I use successfully in model size) is not run the rings in at all and use combustion forces to provide correct ring pressure to create a seal. The absence of these combustion forces means the rings will wear in without creating an effective seal and will most likely never seal fully. In a full size engine, excessive idling/low load of a brand new engine results in the same thing and is known as 'glazing'. I wonder if the specified running in procedure is why this engine is known as difficult to get running?

    If it was my engine, I think I'd be pulling it down, lightly honing the bore (as I'm thinking it will be highly polished from the running in procedure) and trying a fresh set of rings, with zero running-in and see if it runs then.

    In my models (and this is all based on cast iron rings which I assume yours is) I lap the valves in and assemble the engine without spinning it at all. Once fuel and spark is set I try to start and the first few pops and bangs seem to increase the valve sealing and compression increases, as does the frequency of the pops and bangs. A few tweaks of the carb and maybe the timing later and it (hopefully) starts. After a few runs (maybe 10-15 minutes total running) compression is noticeably higher than what it first was, due to the rings bedding in properly. I've included 2 videos of the same engine using this procedure. The first is the very first start of it, and the second is with around 15 minutes of running on it. In the second I attempt the first hand-start of the engine around the 1:45 mark.



     
  8. Jul 10, 2018 #8

    Gordon

    Gordon

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    Cogsy: Actually that is pretty much what I have done. I honed the cylinder and lapped the valves. I have remade the rings twice. I have been running it with the electric motor with both ignition and fuel operating. I have not run it at all just spinning free without fuel and spark. As I stated it fires part of the time but not enough to actually run on it's own. I does seem to be improving. If I try to hand start it it will keep spinning for several revolutions because the firing is at lest helping to keep it turning.
     
  9. Jul 11, 2018 #9

    colby15642

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    Also make sure that the entire ignition system is working properly, as the plug may not be firing under compression pressure. That has fooled me a couple of times in the past.

    If you're spinning the engine with an electric motor, it should fire consistently even if it has no piston rings installed.

    Does it emit black smoke or unburned fuel from the exhaust? If not, try enriching the mixture until it does smoke, so you know where you are in the range of fuel / air mixtures.

    Try propane as a fuel (but not in your enclosed basement) to eliminate poor fuel atomization as a cause of the problem. The same carburetor should work well enough with propane to complete a quick test. Or rig up some kind of temporary "spewforth" fuel system for a quick test. Too much propane will produce a black exhaust to let you that the mixture is too rich.

    Clark. Coolspring Power Museum.
     
  10. Jul 11, 2018 #10

    Cogsy

    Cogsy

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    Sorry, didn't realise that (I thought it was just free spinning). Maybe as a quick and dirty test, dump a charge of liquid fuel in the plug hole and try and start it. On a small engine it will initially be flooded but after spinning it over for a bit it should start and run quite well on that single charge for a second or so. If it runs more strongly than usual it's likely you have a fuel issue, if not then it's something else...
     
  11. Jul 11, 2018 #11

    Gordon

    Gordon

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    I think that I may have found at least part of the problem. Due to the design of the intake and exhaust valves there is a very short part of the stroke between exhaust and intake. Both valves are atmospheric operated, that is no mechanical opening, only exhaust pressure and intake vacuum opens the valve. I just found that prior to the actual intake at the carburetor I am getting a short burst of positive pressure at the carburetor throat prior to the actual intake. This may be exhausting the fuel back through the carburetor prior to actual intake. My theory at this point is that the fuel at the jet is exhausted and by the time the actual intake takes place there is no fuel to atomize. I am getting a good suction at the the carburetor but it may be coming too late.

    Off to test my new theory. This certainly is a unique and interesting design but that is why I am doing it in the first place. After 20+ "ordinary" engines I am just looking for things that are out of the ordinary. Last couple of projects have included Howell "V" Twin and a Snow.
     
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