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Thread: Design and build Side-shaft hit and miss from barstock

  1. #231
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    The suction probably WILL pull up fuel, the question is whether it lasts long enough to do so.

    Most of the engines I either have, or have seen, that involve a ball check, have the ball check in a position where it is always under fuel, which partly floats the ball. usually down in the tank or at the bottom of the fuel riser from the float chamber. Not sure if that would make a big difference, bt it might make just enough.

    The relatively short intake pulse may just not get the ball up and fuel flowing without all the help it can get. The intake on a full size engine is longer, and stronger. The comparison of the fuel volume that need to move for the two is not advantageous to the smaller motor. As Sparky suggests, it may just not be enough to get the fuel moving before the pulse is over. A higher tank might improve that, and a lighter ball might also.

    There is also the question as to whether the carburetor vacuum is sufficient. That can be tested by setting up the carb and tank and making air move through the carb. Since you have clear tubing, do you see fuel movement as it is now?
    1601

    Keep eye on ball.
    Hashim Khan

  2. #232
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    Tried that sparky.--Didn't make a difference.---Brian
    Brian Rupnow

  3. #233
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    Quote Originally Posted by brian Rupnow View Post
    Tried that sparky.--Didn't make a difference.---Brian
    Ah Ha ! Should have known you would have tried that.

    What about that stiffness occuring with the side shaft? As described, that may well cause problems. How about your typical "running in" with a external motor.

    Also, as to compression, earlier you posted the compression seemed real good. I'm confused, what changed?

  4. #234
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    Sparky--No compression, some compression, and lots of compression are all relative things. On a brand new stiff engine it is very difficult to decide which you have. With no compression, you flip the flywheels and they spin around like the sparkplug was out. Some compression, you flip the flywheels and the piston kind of slows down as it approaches top dead center. Real good compression is when it bounces back. The difference in compression between a piston lapped into the cylinder with no rings at all, and a piston with a Viton o-ring on it is different for everyone that has ever built an engine. My technique with a brand new engine is to try all the obvious things the first day. The arcane things have to wait for tomorrow.
    Brian Rupnow

  5. #235
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    Mike--I'm pretty sure I've got something else going on here. The easiest thing for me right now is to make a second piston with a Viton ring on it. That takes me a couple of hours, and will immediately tell me if the lack of suction is related to my air-tight piston being not quite as air-tight as I had thought.
    Brian Rupnow

  6. #236
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    Quote Originally Posted by brian Rupnow View Post
    My diamond lapping compound came in yesterday. This morning, bright and early before the Christmas crowd gets here I got up and diamond lapped the piston into the cylinder. I think it went quite successfully. the piston and the inside of the cylinder have taken on a dull grey finish, and the piston will not fall thru the cylinder, but will go with a slight push. If I hold my hand over one end of the cylinder and try to push the piston thru from the other end, it air-locks and won't go.
    This is the post that lead me to believe you felt that it had substantial compression. Naturally it is subjective as you mentioned but your description sounds like the piston/wall seal is excellent. (or was)

  7. #237
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    I was thinking that the total air flowing into the cylinder was not enough to hold the vacuum the fuel and get it moving up. There is a certain mass of fuel to move, and it may not get enough of a kick to move it before the vacuum is gone.

    But if you are saying that the fuel is getting into the air OK, and going boom in the cylinder, but the power produced is not enough, that is a different deal. Compression does affect power......
    1601

    Keep eye on ball.
    Hashim Khan

  8. #238
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    Popping and trying while the drill is spinning it makes one wonder about the overall friction too. I know in a earlier post there was concern about the friction of the sideshaft assy . Only Brian can make that relative judgement with the spark plug removed.

  9. #239

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    Quote Originally Posted by brian Rupnow View Post
    Gambler, I know you are waiting. I have had engines start up and run first time I tried them. I have had engines which made me pull hair out of my already bald head. This engine has a leaky intake valve. How can I tell?--If I spin the flywheels when the piston is going into the compression stroke, it just turns as if there was no cylinder head on it. If I hold my finger over the carburetor inlet and do the same thing, the flywheels bounce back. If I hold my finger over the carburetor throat and turn the engine thru what would normally be the intake stroke, then move my finger off the carb throat, it will pop like a champagne cork. This tells me that the exhaust valve is sealing okay.
    Hi,
    for my 2 cents worth, it seems that if you let off your finger as above and it pops like a champagne cork, then you got good compression, period.
    And, if you hold your finger over the carb and the flywheel bounce back, you got good compression, period.
    Also, you mentioned exhaust valve is timed exactly at TDC & BDC; OK but is it timed to the correct cycle?
    The champagne cork pop tells me to look elsewhere than compression. My gut feeling is timing, timing be it spark or cam timing.
    you got 2 different bevel gears in there, can the cam turn backwards?
    The cork pop with your thumb tells me to look something other than compression.

  10. #240
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    Brian, IIRC you said you had a stronger spring on the intake valve and had to shorten the spring to get it to open. I suggest the spring may be worth consideration as if it is too stiff it will delay the opening of the valve and induce it to close sooner thereby robbing the cylinder of air.

    Full size hit and miss engines I worked with as a young man had very weak springs on the inlet valve.

    John

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