Author Topic: A new look at Opposed Twin i.c. Engine  (Read 3328 times)

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #30 on: October 01, 2021, 12:20:04 AM »
Will it start or not? I don't really know. The engine is wearing the newest edition of cylinder heads, with the sparkplug situated more or less in the center of the cylinder. This of course means that it has new valves and valve cages, and I'm never sure if the valves are going to seal properly or not until I actually try to run the engine. With brand new ball bearings on both shafts, the engine is "stiff" to turn by hand. Of course, if it does take off and run on it's own, this stiffness goes away after the first fifteen minutes of running. I will probably be finished with my design work by tomorrow afternoon, then I will try the engine and see what happens.
« Last Edit: October 01, 2021, 12:23:12 AM by Brian Rupnow »

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #31 on: October 03, 2021, 04:26:08 PM »
Yesterday I added 1" extensions to the sparkplugs for this engine to get the plug wires up out of the valley they sat in between the rocker arm towers. I don't know for sure that they were shorting out to the towers, but I think they may have been. I was fortunate enough to buy a couple of extra deep sockets as seen in the foreground that let me install these longer sparkplugs with no difficulty. The socket required a little machine work, but they are perfect for this job. I started a separate thread about the lengthening of the sparkplugs. I set the ignition timing yesterday, and sorted out the wiring required for the snowmobile coil which supplies spark to the plugs. Near as I can tell, the engine is ready to run.---This new camera sees far too much, but this picture shows the extended sparkplugs tightened into place in the cylinder heads.

Offline crueby

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Re: A new look at Opposed Twin i.c. Engine
« Reply #32 on: October 03, 2021, 04:27:32 PM »
 :popcorn: :popcorn: :popcorn:

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #33 on: October 03, 2021, 08:02:06 PM »
I didn't want to start pulling things apart, but I had to check and see if my valves were sealing or not. That required that I make a new "blow yer guts out" tool to screw into my engines sparkplug holes. Of course nothing is easy--The tool I have for this wouldn't fit down between the rocker towers, so I had to make a new longer tool. By watching the rocker arms and turning the engine by hand, you can tell when the cylinder you are testing is up on compression stroke. If both valves are sealing properly, you won't be able to blow at all. If you can blow, then you can determine if the air is coming out the intake or exhaust valves. If you can blow but air isn't coming out the carburetor or the exhaust stack, then your rings are bad.  One cylinder is sealed tight.--No air escaping at all. The other cylinder is leaking a very small amount from the intake valve, but not enough to keep the engine from firing. I tried to start the engine this morning, but it wouldn't fire at all.  My "stretched" sparkplugs aren't shorting out to the rocker towers, but they are working---I checked this out early this morning with the sparkplugs laying out on top of the cylinders----lot's of spark, where it should be.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #34 on: October 04, 2021, 05:28:50 PM »
I pulled the one cylinder head off, and relapped the offending valve so it was air tight when closed. I have a clue as to what is happening. There is a transparent fuel line between the carburetor and the gas tank. On an engine which has proper valve timing, if you crank the engine while holding your finger over the carburetor intake, you can see the fuel in the transparent line go rushing up to the carburetor. This is not happening for me. In fact it is chasing the fuel back from the carburetor back into the tank. The only thing that can do that is incorrect valve timing. Time to get out my degree wheel and do some timing magic.

Offline Craig DeShong

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Re: A new look at Opposed Twin i.c. Engine
« Reply #35 on: October 04, 2021, 11:47:32 PM »
Looks really smart Brian.  :ThumbsUp:
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #36 on: October 06, 2021, 06:26:53 PM »
I finally had to resort to using the old cylinder heads with the sparkplugs located right at the very bottom of the cylinders. There was just no way I could get the engine to run with my reworked cylinder heads which moved the sparkplug up to the center of the cylinders. Finally, today, after a lot of fuss and bother, the engine ran for it's first time on it's own. It isn't running good, but it's running. My next labour will be to get it fine tuned and idling slower. There has been more work to this than I thought there would be.---Brian

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #37 on: October 09, 2021, 09:03:25 PM »
The engine is running good and starting very easily. The only issue is that I can't coax it into a slow idle. Research shows that a bit of advance on the valve timing will lead to a steadier, more stable idle, but top end rpm will suffer. I am not that interested in reaching a higher rpm, but I do like the slow idle very much. The cam design I am using asks that the cam be set to just start opening the exhaust valve at 40 degrees before the piston reaches bottom dead center. I set everything up on spec, but needed to verify that my valve timing was correct. 40 degrees before bottom dead center is 140 degrees after top dead center. So---accurate measurement should show the valve beginning to open at 140 degrees after top dead center. However, when set up with a timing disc and the end of the dial indicator resting on the end of the rocker arm to clearly identify when the exhaust valve begins to open, it is reading movement beginning at 125 degrees after top dead center. That is too much advance. It makes for a very interesting set-up, so I thought I would post a picture.---Brian

Offline crueby

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Re: A new look at Opposed Twin i.c. Engine
« Reply #38 on: October 09, 2021, 09:20:55 PM »
Nice!!!!

Online Jasonb

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Re: A new look at Opposed Twin i.c. Engine
« Reply #39 on: October 10, 2021, 07:15:06 AM »
I wonder if some of the difference between what you want and what you are measuring is due to the dti being on the rocker adjuster. There is likely to be some loss of movement due to clearances in the rocker pivot and any gap between rocker and valve stem and adjusters moving in an arc.

You say the valve should be moving at 40 and stopping at 125 so may be interesting to measure with the dti on the valve to measure its actual movement, probably have to just squeeze it in on the spring retainer. Worth a try before you change anything and possibly upset the running of the engine as it is now.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #40 on: October 10, 2021, 05:14:01 PM »
Jason--I find that most of the time, valve timing is set "By guess or by God". And amazingly, that seems to work about 90 % of the time. These small engines seem quite tolerant of valve timing. However, I know this particular engine is capable of running much slower, because it did 5 or 6 years ago when I first built it, and all of the parts in the engine are the same parts that were used originally. I will probably know for sure by the end of today after I have reset the timing closer to what it was when first built.--Brian

Online Jasonb

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Re: A new look at Opposed Twin i.c. Engine
« Reply #41 on: October 10, 2021, 05:28:49 PM »
yes, maybe god is on my side as I always just set them by eye rather than measuring any angles.

I do find that advance and retard of the ignition timing has the biggest effect on slow running rather than cam timing, if you look back at the last few IC engines that I have done all that slow tickover is being adjusted by moving the ignition contact with little alteration to throttle setting. Running  abit rich tends to slow them down too.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #42 on: October 10, 2021, 08:01:15 PM »
So, this is the final final. I made a nice video, and forgot to mention that I had not only changed the base, but had also put sealed ball bearings on both the crankshaft and camshaft. Strangely enough, I couldn't get it to run the way I wanted with my Traxxas 4033 carb, so at the last moment I used a carburetor that was originally designed by George Britnel, and that seemed to do the trick. A person could tune away forever trying to get a slower idle, and yes, it will idle much slower than seen in the video, but it gets a bit unstable at very low idle and will quit right in the middle of making a video. I'm happy to have it up and running again, and yes, I will sell a complete, up to date set of plans for $25 Canadian funds paid to Paypal to brupnow@rogers.com   This engine uses a single set of Dodge ignition points with a dual output two cylinder snowmobile coil. I can take pictures of the ignition set-up I used but really, if you build this engine chances are you will be using a different coil set-up than I used anyways. Thanks for following the build.---Brian

Offline Admiral_dk

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Re: A new look at Opposed Twin i.c. Engine
« Reply #43 on: October 10, 2021, 09:20:18 PM »
Great to see that you got it running as it should again  :ThumbsUp:

Offline dwulfe

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Re: A new look at Opposed Twin i.c. Engine
« Reply #44 on: October 11, 2021, 09:11:57 PM »
Thanks for sharing