Author Topic: Design and build side shaft hit and miss engine from bar stock  (Read 16443 times)

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #240 on: January 11, 2019, 07:06:28 PM »
My butt is kicked for today. I pulled the home made carb off and put a Traxxas 4033 carb on to see what would happen, and removed the one way check valve from the gas line.  Same thing happened. Engine would start if I held my finger over the air intake on the carburetor, but not well enough to stay running on it's own. I advanced the ignition timing a few degrees to see if that would make any difference, but no real notable difference was seen. Even with the leaky intake valve fixed, I'm not getting the compression I would expect to have. So--Weak compression with very poor ability to pull gas into the carburetor--My piston may not be sealing in the cylinder as well as I would have liked. Tomorrow I will make a different piston with an o-ring on it and see what difference that makes.

Online Craig DeShong

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #241 on: January 12, 2019, 01:20:49 AM »
Brian

You're making progress.  I usually have to load the cylinder up work oil on a new engine to get it to run.  After running a few minutes, smoking like crazy, the rings seat and the compression comes up.

You'll get there.  I've had only one engine that ran without "tweaking".
Craig

Offline cfellows

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #242 on: January 12, 2019, 05:53:39 AM »
Hey Brian, I wonder if your intake valve spring might be too stiff?
So many projects, so little time...

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #243 on: January 12, 2019, 02:25:35 PM »
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.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #244 on: January 12, 2019, 03:26:47 PM »
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.

Offline RayW

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #245 on: January 12, 2019, 03:52:17 PM »
Hi Brian,

I had a similar lack of compression problem with my Otto vertical, even after re-making the cast iron rings several times. I changed to Viton O rings and the difference was amazing, with vastly improved compression and much better running.
Just one other thought. Have you checked to see that you are not losing any compression past the exhaust valve? If you are, it might be worth re-lapping the valve and/or replacing the spring with a stronger one.

Ray
Ray

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #246 on: January 12, 2019, 04:04:46 PM »
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.

Online cheepo45

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #247 on: January 12, 2019, 06:11:49 PM »
Thanks, Brian for keeping us up to date on getting your engine running.
 This should really be helpful to a lot of modelers.
There are quite a few of us who have built many air powered models that run fine, but haven't had much luck with I.C. engines.
Your explanations are valuable to all of us.
 Scott

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #248 on: January 12, 2019, 07:59:26 PM »
Scott--I.C. engines aren't all that more difficult than air engines. I'm having some issues with this one, but I've built others that started up and ran immediately. A lot of getting a small i.c. engine to run is being able to do diagnostics. I try and "show it like it really is" when I build and engine and get it running.---Brian

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #249 on: January 12, 2019, 09:13:20 PM »
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.

Offline 10KPete

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #250 on: January 12, 2019, 09:26:58 PM »
 :ThumbsUp: :ThumbsUp:

 :popcorn: :popcorn:

 :cheers:

Pete
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Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #251 on: January 13, 2019, 12:55:51 AM »
I've spent the last three hours going over everything I knew or thought I knew about small i.c. engines and carburetors. I knew I was missing something, but couldn't remember what it was. Okay kiddies, here it is.  The speed of air flowing thru the carburetor is directly proportional to how many times the piston goes from top dead center to bottom dead center in a given period of time. Small high rpm engines can get away with large bore carburetors because at the rpm range they run, the air must flow very fast through the carburetor throat. The venturi effect that creates the vacuum to pull gas up from the tank is created in direct relationship to how fast the air is flowing through the carburetor. On small SLOW rpm engines as I have designed here, the air flowing through a large bore carburetor doesn't have to go nearly as fast, so the venturi effect is much less, and consequently it won't lift the gas from the tank as quickly and efficiently as we would like. To compensate for that, low rpm engines use a smaller bore carburetor, which makes the air flow faster. This in turn makes the venturi effect greater, and allows the engine to lift gas up from the tank as efficiently as we want it to.  There is no doubt in my mind that the cracked fitting in my intake manifold was allowing air to come in thru the crack, so as a consequence the fuel wasn't being lifted up from the tank at all unless I manually choked the carb with my finger. The part I couldn't understand was why, after I had replaced the cracked fitting, didn't the engine run and keep running. The Traxxas carburetor has a 6 mm bore--that is 0.236". My engine would only run with the throttle almost completely closed, and even then would die out within 15 to 20 seconds after the drill was disengaged. My plan for tomorrow is to make a new carburetor with a smaller bore, similar to the carb that was used on the Kerzel and Upshur hit and miss engines, with a 3/16" bore.  :pinkelephant: :pinkelephant:

Offline 10KPete

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #252 on: January 13, 2019, 01:07:36 AM »
 :ThumbsUp:

Makes sense to me!

Pete
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Offline Art K

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #253 on: January 13, 2019, 05:18:46 AM »
Brian,
On my Upshur single I originally tried to match the 3/16" inlet tube. The closest Perry carb was .198". It ran well with that one but if I cracked the throttle to far it would kill it. After I melted that one, I got a .178" one, it'll run 7200 rpm now. I probably don't need to tell you at this point that unlike you, I see how fast it will go instead of how slow. I think it was having the same effect and with to much air was killing it. Looks like you'll have it running soon.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #254 on: January 13, 2019, 05:00:14 PM »
All things cometh to he who waiteth---If he worketh like Hell while he waiteth!! I put the smaller bore non throttled carburetor on this morning, fiddled with the ignition timing a little bit, and away we go. I think my heart may explode!!!  I may fill the reservoir with water, start the engine, and do nothing else today except set and watch the engine run.