My First Engine Build

Discussion in 'General Engine Discussion' started by c_mario, Aug 20, 2018.

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  1. Aug 20, 2018 #1

    c_mario

    c_mario

    c_mario

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    Hi,
    I discovered this forum while searching for projects to build with my lathe. I purchase a lathe around 4 months ago. I have never used a lathe before but wanted to make an IC engine. First I just made some simple bushes, Kurled knobs, ornaments and a Gyroscope..
    I found the MP3.2 plans on this site so decided to make it.
    I have attached a photo.

    I was wondering what the starting technique was.
    I have not been able to make it run for more than a few seconds. At first I had very little compression so I grew the cast iron piston by heating then quenching in oil, then tempering. It grew so it no longer fit into the bore. I then lapped it to get a push fit to the top of the bore.
    It seems to have good compression now from what I can remember from my RC flying days when I was in my 20's.

    I get it to fire but it only runs for a few seconds maybe 5 or so at what sounds like an old 4 stroke idling.

    One thing I didn't do was the little ledge on the backplate I circled in the attached 2nd image.
    Mainly because I didn't understand what it was for, it did not seem to be needed for piston clearance.
    Whats it for?
    Anyway I was hoping I could get it to run at least once.
    Thanks for Reading.
     

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  2. Aug 20, 2018 #2

    minh-thanh

    minh-thanh

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  3. Aug 20, 2018 #3

    natalefr

    natalefr

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    Check the carburettor, often you have problems with fuel flow, if the needle has too pronounced taper you can have a too delicate and critical adjustment, which taper has the carburetor needle? Do you have the constructive design of the carburetor?
     
  4. Aug 20, 2018 #4

    c_mario

    c_mario

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    I followed the plans for needle taper as best I could.
    How many turns out should I start with?
     
  5. Aug 20, 2018 #5

    natalefr

    natalefr

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    Normally for airplane engine IMHO try to start and 1 and half if the motor start quickly and stop open more
    For my Hupshur horizontal four stroke (example) the needle taper was 16° and the motor was critical, now the taper is 3° and is better
     

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  6. Sep 6, 2018 #6

    c_mario

    c_mario

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    Still struggleing to get this to run. I remade the cylinder liner as I missread the plan and cut the transfer ports too high. The new liner has the transfer ports at the correct height. I have good glow on the plug, i see fuel is getting to the combustion chamber, I get it to fire on almost every flick of the prop but it just wont continue. I made gaskets to seal the backplate and front crank housing better.
    There seems to be good compression. I tried different needle positions changeing slowly about a 1/4 turn at a time. What can I try next?
     
  7. Sep 6, 2018 #7

    minh-thanh

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    If you put plug into head and flip prop counter clockwise,did you feel resistance by compressed air and hear popping sound?
     
  8. Sep 7, 2018 #8

    c_mario

    c_mario

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    Hello minh,
    Absolutly, there is resistance and popping sound. The engine also fires when igniter is connected.
     
  9. Sep 7, 2018 #9

    minh-thanh

    minh-thanh

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    You should check the carburetor and adjust little by little,
    Lock the carburetor, then open it very little, very little and start the engine, little by little you will have the best position.
    And the carburetor must follow the plan. (I made a mistake when make it did not follow the plan )
     
  10. Sep 7, 2018 #10

    Cogsy

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    Depending on the taper of your needle, 1/4 of a turn might be too much - some are incredibly touchy and go from too lean to too rich that quickly. If you've got an electric starter/drill on it just get it spinning and creep the needle open, listening for changes in the noise to show you if you're getting closer or further away. If you're hand flipping the thing I'd guess your arm is getting sore by this point...
     
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  11. Sep 7, 2018 #11

    c_mario

    c_mario

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    Hi Cogsy,
    I followed the plans and the needle taper is as drawn, and yes I am hand flipping the engine.
    So if I start from a dry engine, should I prime it at all. When I was in my 20's I flew RC planes. Priming was open throttle, needle 1.5 turns out, block carb air intake, flip prop several times to prime. Open carb intake, attached igniter , flip by hand till start. Didnt take long at all.
    So I should try closing needle, no prime? open say 1/16 turn flip a few times, open another 1/16 flip and repeat?
     
  12. Sep 8, 2018 #12

    Cogsy

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    When I flew RC I had pretty much the same starting technique as you describe, but that was with well-known engines. I would say you would still want some prime with yours, but the unknown is how much needle you need and how 'touchy' your needle adjustment is, which can vary between home-made engines even using the same plans. Even with production engines sometimes I'd flood mine and need to close the needle and spin it for a while to clear the issue or it just wouldn't fire.
    If I was you I'd be setting up some sort of electric start driver (probably just an electric drill with a drive hub) so you could prime it, then drive it constantly while slowly adjusting the needle to figure out where it needs to be. It takes a lot of the guess work out of it. I'm sure you'll get to the point where you can had start it when it's tuned properly but it could be tough to get to that point with hand-flipping.
     
  13. Sep 9, 2018 #13

    GailInNM

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    A few things you might check. These might sound silly, but they are things that I have seen others or my own engines.

    Check that the spray bar is clean on the inside. I have seen an instance where there was a chip inside that prevented the needle from closing all the way resulting in too rich a mixture even when it felt like the needle was all the way closed. You can also hook a piece of fuel line to the fuel inlet and suck or blow to make sure that the needle is actually closing all the way.

    Look down the air inlet and make sure that you can NOT see the cross hole in the spray bar. It is easy to have the spray bar rotate when it is being tightened. If you can see the hole it will not draw fuel when running, but will draw fuel when you choke the the engine when blocking the air inlet and turning the engine over to prime the engine.

    While looking down the air inlet check that the crankshaft valve hole is just opening just after bottom dead center and closes just before top dead center when turning the engine in the normal run direction. I have seen one engine that had the valve hole was in the right absolute angular position relative to the crank pin, but on the wrong side. The engine would run fine in reverse direction, but would not run in the correct direction..

    If the cylinder sleeve is rotated 180 degrees so the exhaust port and the transfer passages are reversed the engine will not run ofter the prime is used up. Not likely in your case because the ports are very different visually, but still worth a quick look look.

    Not so easy to check is the location of the transfer ports relative to the exhaust ports. As you already know it is easy to get them in the wrong place. With the the 45 degree bevel they are hard to machine and even harder to measure them. Still, with proper lighting you may be able to see the piston close the transfer ports while the exhaust port is still 1mm open.

    Last, make sure the two crankcase gaskets are in good condition. Any air leakage into the crankcase will drastically change the fuel/air induction.

    Gail in NM
     
  14. Sep 9, 2018 #14

    c_mario

    c_mario

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    Thanks for all the info GaillnNM and Cogsy. I have almost given up hope. I can confirm spray bar facing correct direction and blowing down fuel hose with needle closed shows it is truely seated. Ports are facing correct direction and transfer ports close before exhaust port. Will check crankshaft valve hole (open just after BDC and close just before TDC).
    I am going to rebuild another crankshaft housing and try to get closer tolerances as I can see fuel coming from the front of the crankshaft. I made a bronze bushing for it but ruined the alignment so have to start again.
    I do see on the down stroke that there is enough pressure in the crankcase that I can hear a leak, fuel will bubble up between the sleeve and the cylinder before the transfer port opens. With all the in and out and pulling apart and checking , if I make it too tight I wont get it out again. Is it meant to be a push in never get out again fit?
    Regards
    Mario.
     
  15. Sep 9, 2018 #15

    vederstein

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    ... At first I had very little compression so I grew the cast iron piston by heating then quenching in oil, then tempering...

    I didn't know of this technique. I may use it for my PITA stirling I'm working on.

    Can you point me to or write up a short procedure?

    Thanks,

    ...Ved.
     
  16. Sep 10, 2018 #16

    c_mario

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    Hello Ved,
    I found some info on a web site somewhere but cant remember which one. It works with Cast Iron so all you do is heat the piston till its glowing red hot, mine was almost orange then quench it in oil. I just used motor oil. Do it outside and drop completely in the oil otherwise you can cause the oil to catch fire ( yes that happened to me) and the smoke and smell was pretty bad. Outside was no problem, I've actually done it twice. I think it expanded about .07mm. After quench and cooled, heat it again till just a straw colour and then let it cool in air , I am told this takes the brittleness out of it.
     
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  17. Sep 13, 2018 #17

    Aerostar55

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  18. Sep 13, 2018 #18

    Aerostar55

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    That flat on the top of the back plate is for piston clearance. If you didn't need it, I would suspect that
    your piston might be too small, or the wrist pin might be in the wrong place. Either of which would affect porting and thus the ability of the engine to pull fuel. Make sure that the crank case has a good seal. ( front bearing, Back plate cover and bypass) Do you feel a slight pop or pull on the down stroke? This is the air "force' that pushes the fuel up over the piston through the bypass. It's critical in any two stroke. Other than that check the dimensions on your venturi tube, needle valve. The spray bar hole must be accurate and turned in the correct orientation to the intake. Try extending the length of the intake tube with a temporary tube, or partially blocking the intake (choking). That said many glow plugs these days
    are just defective. Try several different or new ones.
     
  19. Sep 13, 2018 #19

    c_mario

    c_mario

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    Thanks for the info. I will check the piston size again but I did follow the drawings. I certainly feel a pull on the downstroke.
    When you say bypass, whats that? Is it the vertical channels in the cylinder wall that transfer fuel from the crankcask to the combustion chamber?.
    I will remake the front bearing housing and try to get a better crankshaft to housing fit and install a bronze bush at the very front of the housing.
    I was seeing fuel coming out the front of the engine.
     
  20. Sep 14, 2018 #20

    Aerostar55

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    Yes
    the bypass is the passage that allows the fuel charge to “bypass“ the piston. If you are seeing fuel coming out of the front bearing it should be going up over the piston. It’s normal to get a little during running as this helps to lubricate the crank shaft.
     

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