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

  1. #241
    Join Date
    Mar 2008
    Location
    Barrie, Ontario, Canada
    Posts
    9,071

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    Okay Gents--Just so we keep this straight: First try--engine would fire along with drill driving it but only if I held my hand over the carb intake to choke it. This points out lack of fuel, so I tried unscrewing the hi speed jet as much as I could, but that did nothing to fix the problem.****During the course of doing this, the engine had very low compression---it spun too easily . A check and some diagnostics showed that the intake valve was leaking quite badly. I pulled of the cylinder head and relapped the intake valve, and the compression came up considerably. While the head was off and the intake valve was free of it's spring, I clipped one full coil from the intake valve spring.
    **** This did nothing to improve the situation, so after checking my valve and ignition timing to be absolutely sure it was correct, I decided that perhaps the carb venturi vacuum wasn't strong enough to overcome the check ball in my gas line. I removed the check ball and at the same time switched over to a Traxxas aeroplane carburetor which I know works properly (The spare carb I've had laying around for two years was a bit of an unknown). This was the carburetor off the Rockerblock engine, which ran very well. The problem remained the same.
    **** I tried lifting the fuel tank higher, but this made no difference.
    **** The intake spring still seemed a bit stiff to me, so I removed it and cut another full coil from it. This didn't change my original problem of engine starting and running with drill, but then dying away when the drill was removed.
    ****I removed the rocker arm and took another 0.01" off the head of the shcs which contacts the end of the exhaust valve to be absolutely sure that the exhaust valve was not being held open.
    **** I took another half coil off the intake valve spring, but I think that now I've taken too much off it, so will put in a new spring this morning.
    **** I pulled out the sparkplug (which is brand new) and laid it on the water reservoir while turning the flywheels by hand. Lots of spark, coming at what I judge to be the correct time.
    **** I had very little Coleman fuel, so I purchased a new can, hoping that new fuel might make a difference,---It didn't.
    **** One of the things I did notice during all of this, is that the governor is operating just as I had hoped it would, however I don't have it hooked up yet, and won't until I have the engine running properly.
    ****Todays plan is to first try a slightly longer intake valve spring. If that doesn't fix things I will take one flywheel off and try the engine with only one flywheel. This shouldn't make a difference, but I have seen stranger things happen. These flywheels are 1" wide, so if the engine decided it will run with one flywheel, I can thin both flywheels down to get rid of a lot of the weight.
    ****If none of the above things fix the problem, I will make a new piston with a Viton o-ring on it.
    **** Beyond that, if the engine still hasn't decided to run, I will have to seriously consider that perhaps my face cam is the culprit, but I hope not. I'm really proud of that face cam.
    Brian Rupnow

  2. #242
    Join Date
    Mar 2008
    Location
    Barrie, Ontario, Canada
    Posts
    9,071

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    A slightly longer inlet valve spring didn't do it. I thought about this for 30 seconds and then decided to pull the existing iron piston and groove it for an o-ring. Normally I make my o-ring grooves 0.058" deep x 0.093" wide, which works well with a nominal 1/16" cross section o-ring. They aren't really 1/16".--In truth they are 0.070" in cross section. I made the groove for this one 0.060" deep.
    Brian Rupnow

  3. #243
    Join Date
    Jun 2007
    Location
    Anderson SC
    Posts
    1,235

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    After this engine, a good little project might be to make up a compression gauge suitable for engines this size. A few readings from some of your engines and you will know what it takes for a good runner. The gauge would eliminate a lot the trial and error fiddling and remaking parts that may not be necessary. Its what they do on the big engines and these little guys would be no different. They do it on chainsaws.

  4. #244
    Join Date
    Mar 2008
    Location
    Barrie, Ontario, Canada
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    Lack of suckage has been discovered. The elbow which screws into the top of the cylinder (part of the intake manifold from carburetor) was cracked on the back side where I couldn't see it. Of course it has left me with a mess, and broken off flush with the top of the cylinder. So, once again the cylinder head goes up on the mill to remove the broken off shank. Bad as this may sound, it is a relief to know why the engine wasn't pulling up gas from the carburetor.
    Brian Rupnow

  5. #245
    Join Date
    Nov 2011
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    1,245

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    Hopefully this is your last stumbling block before we get another runner.

  6. #246

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    Ah !!! a good discovery.
    I guess now you can put the check ball back into the gas line,,,,
    put the coils back onto the intake spring,,,
    as well as put the groove back into the piston !!!

  7. #247
    Join Date
    Mar 2008
    Location
    Barrie, Ontario, Canada
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    Engine with new fitting to replace cracked one in intake manifold is now picking up fuel from the carburetor on it's own without need for manually choking the carburetor. Getting many short runs, which has me grabbing for the camera, but then it dies out and quits. I thought perhaps the two flywheels were too much weight for a 1" bore engine, so I removed one flywheel, but that didn't change anything. I'm about to give it up for today. The Traxxas carb is a throttled carburetor, and now that I have the engine sucking up fuel on it's own, I may trade back to the hit and miss carb tomorrow.
    Brian Rupnow

  8. #248
    Join Date
    Jun 2007
    Location
    Anderson SC
    Posts
    1,235

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    Quote Originally Posted by brian Rupnow View Post
    Engine with new fitting to replace cracked one in intake manifold is now picking up fuel from the carburetor on it's own without need for manually choking the carburetor. Getting many short runs, which has me grabbing for the camera, but then it dies out and quits. I thought perhaps the two flywheels were too much weight for a 1" bore engine, so I removed one flywheel, but that didn't change anything. I'm about to give it up for today. The Traxxas carb is a throttled carburetor, and now that I have the engine sucking up fuel on it's own, I may trade back to the hit and miss carb tomorrow.
    This may be a dumb question but I have been wondering. Running it without the governor and with a non throttled carb, what stops the engine from reving itself higher and higher until something lets go? Its seems to be the equivalent of a brick on the gas pedal, especially with no load on the engine. (naturally I am talking about once the engine is running well)

  9. #249
    Join Date
    Jul 2017
    Location
    Buffalo NY USA
    Posts
    141

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    I'm just curious how you got the busted fitting out of there. Sideshaft engines are a thing of beauty IMHO.

  10. #250
    Join Date
    Mar 2008
    Location
    Barrie, Ontario, Canada
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    Sparky--Simple--I just shut off the switch on my power box which supplies the 12 volts which feed the coil. When I first started building engines 10 or 12 years ago I had one run away on me. Everything was hard wired with no switch. That engine had never ran before, and I wasn't really expecting it to go. It went---and Oh God, how it went!!! Zero to a billion RPM all in the wink of an eye. I managed to pull the sparkplug wire and get it calmed down, but it almost scared me to death. My very next project was a box which contained a 12 volt coil, an illuminated switch that lit up when it was on, and sufficient wires with alligator clips to run to a 12 volt battery on the floor and to the ignition points on the engine. Haven't had a run-away since. Nickel-fab-city---I set the cylinder head up in the mill vice, moved the table around until the fitting was centered under the quill, and use a 1/4" endmill to cut the broken fitting out, then rethreaded it. This has been done twice now to the same cylinder head. If (God forbid) it happens a third time I will have to either make a new cylinder head or go up one thread size from 5/16"-18 to 3/8"-16.
    Brian Rupnow

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