My First Engine Build

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

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  1. Sep 14, 2018 #21

    minh-thanh

    minh-thanh

    minh-thanh

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    Hi c_mario !
    When you assemble piston and cylinder, it is dry and clean ? With my little experience of do it is: keep the piston and cylinder dry and clean, and then make it easy to determine whether it is sealed or not .
     
  2. Sep 21, 2018 #22

    c_mario

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    Well, I have checked the piston, remade the front housing for crankshaft , remade venturi, remade cylinder liner to lower the transfer ports, sealed front housing and backplate with gasket sealant, made gasket for cylinder to crankcase yet I still cannot get it to keep running. It will fire almost every time I flick it but just wont keep running. I see the glow plug glowing through the exhaust port so I know its lit, I've checked that the needle closes completely by trying to blow through the fuel tube while slowly opening the needle valve and it definitely cuts off flow. I've primed by choking and flicking over the engine and via a syringe directly into cylinder through glow plug hole. Always get same result, engine fires a couple of times on each flick but will not keep running. I tried a drill to start it but I don't have a spinner on the prop so the nut tends to undo trying to start it. It seems a little excessive to go buy a starter and spinner at this stage just to try to start it, but I may do this out of frustration.
     
  3. Sep 22, 2018 #23

    Cogsy

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    A plastic spinner shouldn't cost much and you can whip up a spinner driver to fit your electric drill I'm sure, just a bit of turned aluminium and maybe some rubber from an old bike/car inner tube should do it. I remember from my RC days that a visibly glowing glow plug isn't a completely foolproof test. If the glow plug battery is a little low, the plug will glow nicely in the air/engine but the cold fuel cools it down very rapidly. A couple of times at the field having starting problems, changing plugs, etc. and then borrow a fresh glow driver and it would fire straight up. Might not be your issue but is something to remember.
     
  4. Sep 26, 2018 #24

    Mechanicboy

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    First of all: Is compression good? When you are turning the crankshaft, it must not be leakage past piston and you feel resistant to turn the crankshaft.

    The engine with good compression will start easy.

    Is the ratio of compression right? The glowplug engine can have a ratio of compression from 1:8 to 1:10. too low ratio of compression make it difficult to run the engine without battery connected to glow plug.

    Is the compression in crankcase good? You will hear "poof" from transferport when you are turning the crankshaft without cylinder head. If no "Poof" there means leakage one place in the crankcase to example leakage via gasket or from crankshaft/bearing if the tolerance is fault.
     
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  5. Sep 26, 2018 #25

    Mechanicboy

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    Minh-Thanh wrote this: When you assemble piston and cylinder, it is dry and clean ? With my little experience of do it is: keep the piston and cylinder dry and clean, and then make it easy to determine whether it is sealed or not .

    I will correct the fault explained by Minh-Thanh:

    With dry piston and cylinder --> the piston feel tight in cylinder -- > OK
    With oiled piston and cylinder--> The piston is loose in bottom of cylinder and feel tight in top of cylinder (tapered cylinder) --> OK

    If the cylinder is not tapered, the engine will lose compression when working temperature is raise due the cylinder is expanding by heat.

    With tapered compression make engine easy to start up and keep cylinder parallel when the engine is running under working temperature without loose compression.
     
    Last edited: Sep 26, 2018
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  6. Sep 26, 2018 #26

    c_mario

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    HI,
    Thanks for your responses. I do understand the principals you explain and I have built the engine according to plans on this site so if the compression ratio is whatever the design produced. I do understand what you mean by 'poof' sound from transfer port opening and I believe I get this however it is hard to check with cylinder head off because the cylinder bolts hold down both the head and the cylinder together as one. I have looked for any leaks in the crankcase and the last thing I can think of before I give up is the fit between the cylinder liner and the cylinder wall. If there is leakage between them I guess that will be a problem. How to seal that? This is the second cylinder liner I have made but it is not a hard fit, i can remove it by hand. If I use a sealant what should it be?
    Thanks.
     
  7. Sep 27, 2018 #27

    Mechanicboy

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    You can listen there is "poof" from cylinder when the glow plug is removed.

    No need to make a new cylinder every time it fails. Relap again until the cylinder is parallel. Make a new piston and lap. Try to fit the piston into cylinder until it stop a half way into the cylinder --> Stop, no more lap the piston.

    Smear the piston with chrome polishing paste (I am using the Autosol Solvol Chrome Polish) and press light into in the cylinder in same time you are rotating the piston into the cylinder until the piston is stuck in the cylinder. Remove piston from cylinder and clean both piston and cylinder carefully free for polishing paste. Take a test fit and check as i wrote in early post. If the piston do not stop up to TDC, repeat again to lap the piston into cylinder and take a test fit after cleaning is done. Also the cylinder must be tapered created by piston under lapping and the piston feel tight near TDC when you are pushing the piston into the cylinder.

    Cylinder of high tensile steel from drive shaft or old wrist pin from piston (must be annealed if to hard to machine the steel, unnecessary to rehardening since alloy steel is hard enough).

    Piston of cast iron as you can find in the old cam shaft made of cast iron (the cam is impossible to machine, between cams is soft and machinable) or thick brake disc (without ventilated disc).
     
  8. Sep 28, 2018 #28

    c_mario

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    Hi Mechanicboy,
    The piston to cylinder liner fit is as you described. I have done the lapping job as described.
    What I was saying was that the cylinder liner fitting into the aluminium cylinder/crankcase is not a very tight fit.
    I think if it leaks between the steel liner and the aluminium that is bad right?
    I can pull it out by hand.
    Should it be a tight permanent fit?
    should I use some sort of sealing material like a gasket cement ?
    Thanks.
     
  9. Sep 28, 2018 #29

    Mechanicboy

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    It must be light press fit due heat of expansion and keep tight against leakage.
     
  10. Oct 2, 2018 #30

    f2cf1g

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    Hi c_mario and forum, I haven't posted before. Apologies if I have contravened forum etiquette by posting here first. I see you have re-made most of the motor without success and it occurred to me the one thing you haven't tried changing is the compression ratio. I have done a few Nelson head conversions and I find that getting the head volume right is important. If it is too low you can get the symptoms you described, i.e. hard to start then run for a while then stop. It needs to be 10:1 or a bit more, as a previous posted has said, especially using fuel without nitro. Alternatively it could be the head joint leaking, this could have a similar effect. Maybe machine say 0.2mm off the top of the liner and adjust CR with brass shims if this is not how it is already set up, the shims also provide a better seal. This only applies if it's not flooding off due to excessive needle opening or leaning off with not enough fuel. Hope this might helps. Good luck.
     
  11. Oct 7, 2018 #31

    c_mario

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    The plans I went from say the compression ratio is 8.3 :1.
    I have teflon seal at cylinder base and aluminium foil at head. I cannot see leaks.
    After weeks of trying the best I get is a 2 second run. See if the video sound gives anyone a clue what might be wrong.
     
  12. Oct 7, 2018 #32

    Mechanicboy

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    Enough fuel? Turn the fuel needle 1.5-2 turns from closed. Too much fuel out of exhaust port = too much fuel.
     
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  13. Oct 7, 2018 #33

    c_mario

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    I have tried infinite fuel needle positions. The needle was 1/4 turn from closed in this case. It does not seem to make any difference. I can even disconnect the fuel line, close the needle, prime with direct inject into venturi and it will run like that off the prime alone. I made a new needle assembly as well , this time by choosing a sewing needle as suggested in some other text's I've read. f2cf1g spoke of compression ratios , I could make a new head to increase that. I too thought fuel air mix. Now maybe fuel itself, but this is a new bottle of fuel I purchased only 3 weeks ago.
     
  14. Oct 7, 2018 #34

    f2cf1g

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    The motor sounds good and I'm sure is ready to run. However, 8.3:1 is low and may well be the problem whatever the designer says. Don't forget that the teflon and aluminium washers are both reducing the compression ratio. We are talking tenths of a mm here. No need for a new head, just put the one you have back in the chuck, skim 0.2mm off the area which seals against the head and see what difference that makes. But before you do that:
    1. Check that the crankcase is not full of fuel, that could cause the symptoms you are seeing because the liquid fuel douses the plug or causes a hydraulic lock preventing the engine from turning over. Upright engines are very easy to flood and difficult to empty when mounted on a bench (turn upside down and encourage to drain into the cylinder through the transfer ports then turn on one side to empty through the exhaust.
    2. When/if the crankcase is empty, close the needle completely or disconnect the fuel line and prime it though the exhaust port by splashing fuel against the closed piston, open the exhaust port and let the fuel trickle into the cylinder. Then flick and see if it will run on the prime. When it does, reconnect the fuel line, open the needle a turn or so and try again.
    3. Make sure the plug is glowing orange and set the tank so that the fuel is level with the spraybar.
     
  15. Oct 7, 2018 #35

    Mechanicboy

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  16. Oct 7, 2018 #36

    Mechanicboy

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  17. Oct 8, 2018 #37

    c_mario

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    Thank you Mechanicboy and f2cf1g. I read the documents that were pointed out to me , thanks for that. I will try all the suggestions mentioned.
    I am using a hot glow plug.
    I may be experiencing the hydraulic lock mentioned as sometimes after it fires the prop stops/locks on the down stroke.
    This certainly is a learning experience.
    Thanks I will let you know what happens.
     
  18. Oct 13, 2018 #38

    c_mario

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    Hi,
    As suggested by f2cf1g I drained the crankcase, I splashed fuel as suggested, It ran on prime, I reconnected fuel hose opened 1.5 turns continued to fire a few times as before.
    So I did the skimming to increase the compression ratio. Still the same result no matter what I do. Glow plug is glowing orange.
    I know fuel is good, plug is good technique is good because I found my 35 year old OS max 40 that's been sitting in a box for probably 20 years and got it started in less than a minute.
    Thanks for all your info but at this point I think I will give it a rest for now since its just too frustrating and disappointing, i really hate giving up on anything.
    Failure here discourages me from further projects.
     
  19. Oct 13, 2018 #39

    minh-thanh

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    I think it ran but the fuel was leaking when the piston went to the TDC, and leakage of fuel, though very small, would make it hard to run or it does not keep running - check for leaks.
    With compression, it should be really good - check the cylinder and the piston. My first engine, I unfix it and adjusted the cylinder and make new the piston more than 10 times
     
  20. Oct 13, 2018 #40

    f2cf1g

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    I'm sorry to hear that you have no success but it must be fixable, just have to find the cause. For example, I have recently completed an Atom Minor. Initially it wouldn't start without an electric starter, the symptoms were exactly as you describe. I suspected the piston fit which was rather loose (made as recommended for a spark ignition motor by someone on a forum) so I cherry-bombed it to increase its size and re-lapped. It now starts easily by hand. Maybe that's the core of the problem but I know you have remade a lot of parts already..... I recommend trying it on a starter if you can borrow or make one.
     

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