Design and build side-shaft hit and miss engine from bar stock

[nel2lar]

Brian
I feel for you and your frustration, everything says it should but. Good luck and stick with it and maybe it will click and pop away.
Another thing when writing a long post I like to use one of my word programs to write my post. Then copy and paste my post.
Hang in there.
Nelson

 

[Brian Rupnow]

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]

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]

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.

 

[xj35s]

a lot of work. It'll be sweet though.

 

[nel2lar]

Brian
Things are looking up. Good eye to catch the little culprits until you work through then. You will get it, just stick with it and I am positive it will make you happy too.
Nelson

 

[Brian Rupnow]

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]

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.

 

[nel2lar]

Brian
Good thinking and now till the new carb have a good night rest. I know I work more in my sleep when faced with something puzzling me. I think you are on to something. I want to hear I'm happy! You do it so well.
Good luck
Nelson

 

[JohnBDownunder]

Brian,
As is usual with any of your posts I found this to be great reading and an easily followed thread. Hopefully I will recall a lot of the stuff I have leaned from this and your other threads when I need it.
Thank you for posting,
John B

 

[Brian Rupnow]

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.

 

[CFLBob]

It looks like an engine! Not quite done yet but lots of progress in the last 24 hours.

Congrats!!

 

[xj35s]

This is awesome. Sure enjoyed following along. Congratulations!!!!!!!!!!!

 

[Brian Rupnow]

Someone asked if I was going to give any information about the new carb that is currently on the engine. This is the carb, and the download link will get you all the details from a web hosting site.

http://www.mediafire.com/file/wh1gifgyeutf3vt/HIT_AND_MISS_ENGINE_CARBURETOR.zip/file

 

[Brian Rupnow]

This video shows a bit of close up detail on the face cam. I had never built a face-cam before, so I'm rather thrilled.

 

[Johno1958]

Congratulations Brian she is ticking over like clock work.
Cheers
John

 

[nel2lar]

Brian
As usual very nice job. You stuck with it and prevailed.
Wonderful build, Congratulation on the run.
Nelson

 

[minh-thanh]

Congratulations Brian !
Thanks for sharing about how you do it and how you find the cause it not run.
Thanks you !

 

[popnrattle]

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.

Several years ago Cfellows(Chuck) gave me some insight into making the O-rings work. He said you need the groove about .010 wider than the O-ring so it can "roll" a bit at top and bottom DC and the bottom ring groove about .010 bigger than ID of your O-ring. Thats what I do and I got almost no leakage and they only cost about a buck. There easy on the bore too. (Thanks Chuck!) I also put a little 2-cycle oil in the Camp fuel to help lube it. Later, RT.

 

[Brian Rupnow]

I have spent a couple of hours this afternoon "fine tuning" the engine. It has a very fine range on the needle valve, to hit the "sweet spot" where it runs at maximum rpm and runs at that rpm consistently without faltering. I have also been playing with the length and strength of the intake valve spring. It is very close now, almost time to add in the link that lets my governor come into play for the hit and miss action. It is running right on the edge of "scary fast".