Author Topic: A new look at Opposed Twin i.c. Engine  (Read 3325 times)

Offline Brian Rupnow

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A new look at Opposed Twin i.c. Engine
« on: September 12, 2021, 04:32:01 PM »
A few years ago, I built my version of an opposed twin i.c. engine. It ran very well, and I was very pleased with it. There was always a problem with the configuration of this engine, because the sparkplugs were at the very bottom of the horizontal cylinders, and if you happened to flood it while starting it, you could crank all day and it wouldn't clear itself. However, it did run, and I made some good videos of it running. The crankshaft was riding on bronze bushings, and the crank wasn't "dead nuts" straight. I was using my standard 1975 Chrysler ignition points, and a cam running on the crankshaft. As time went by, with more and more hours running time accumulated on the engine, the bronze crankshaft bushings began to wear, cause by the crank that wasn't truly perfect. It wasn't a wet sump engine, so that didn't really matter a lot  ---BUT--as it wore, the ignition cam, attached to the crankshaft began to move around with the sloppy crankshaft. Finally, the ignition cam on the less than perfect crankshaft was moving around enough to seriously affect the timing and spark of this engine. This took me the longest time to figure out what was going on, and when I did figure out what was happening the engine went "Up on the shelf". I promised myself at that time that eventually I would redesign this engine, using ball bearings on the crankshaft, a crankshaft that was truly straight, and a configuration which put the sparkplugs at the top of the horizonal cylinders. I would be able to re-use the cylinders, cylinder heads, overhead valve mechanisms and valves and cams, while making a new central crankcase and fan assembly. This is early days yet, and I still have some unanswered questions about the T head engine I have currently been building, but I think this will be the direction I move in next.

Offline steamer

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Re: A new look at Opposed Twin i.c. Engine
« Reply #1 on: September 12, 2021, 04:34:53 PM »
Cool!   

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Roger B

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Re: A new look at Opposed Twin i.c. Engine
« Reply #2 on: September 12, 2021, 05:05:46 PM »
It look's like you could turn the whole crankcase upside down. The exhausts could be moved next to the flywheel with a bend pointing outwards and the inlet ports moved to the side of the head with an additional bend in the inlet manifold.
Best regards

Roger

Offline Jasonb

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Re: A new look at Opposed Twin i.c. Engine
« Reply #3 on: September 12, 2021, 06:54:21 PM »
The biggest problem with reusing the heads to get the plugs at the top is you either have to run an open crankcase or suffer oil leaking out of the tappets when they are below the oil level.

If you want a closed wet sump then the cam at the top is the better option, I would then hand the heads so both inlet valves close to the flywheel, exhausts coming out horizontally and space the rockers further apart so the plug can fit between them, some repositioning of the cam lobes and angling the pushrods outwards may be needed. take a look at the various configurations of the Wall Wizard, some have the plugs at the top of the head, others at the side these were changed from the original lower plug layout.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #4 on: September 12, 2021, 07:24:29 PM »
Thanks Jason. I haven't really thought this thru in any way. I didn't run a closed crankcase on the first horizontal twin--it had a lift off lid on the crankcase which was attached magnetically to allow lifting it off easily and giving a few squirts of oil to the con rods and cams. I did like the flywheel/fan arrangement I originally had, and would try to re-use it. I actually did design and machine a second set of heads, which moved the sparkplug higher in the cylinder, but left it horribly tight to bet a standard sparkplug in there without the high tension lead shorting out to the rocker arms. I wonder if it is possible to get an insulated "extender" which attached to the top of a 1/4"-20 sparkplug and extends out about an inch to move the high tension lead away from the rocker arms. I've never seen such a thing, but then I have never seriously looked for one.

Offline Jasonb

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Re: A new look at Opposed Twin i.c. Engine
« Reply #5 on: September 12, 2021, 08:52:32 PM »
You could probably make something from Corian or similar unless you fancy a go at making your own long body plugs.

Another option may be to go for an atmospheric inlet valve then you only need one rocker and can also save some work on the cams as only two will be needed.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #6 on: September 12, 2021, 10:56:10 PM »
Jason--I plan on reusing the cams that are already on that engine. These are the cams that are machined onto a sleeve and the sleeve Loctited to the camshaft. They worked fine on the original version, they should work okay on the new improved version. I plan on using the original fan/flywheel  and the timing gears as well.

Offline Art K

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Re: A new look at Opposed Twin i.c. Engine
« Reply #7 on: September 13, 2021, 03:21:24 AM »
Brian,
This looks to be a good rebuild project. Version 2.0 you might say.
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: A new look at Opposed Twin i.c. Engine
« Reply #8 on: September 17, 2021, 09:03:31 PM »
Yesterday I was prowling thru the drawings and models of this build, and I discovered something good. I have been thinking all along that I would probably have to build a new crankcase, and probably new cam and crankshaft.---However---Taking a much closer look, I may be able to modify the crankcase to take sealed ball bearings on both the crankshaft and the camshaft. If so, that would be a real bonus.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #9 on: September 21, 2021, 01:23:22 PM »
This is what some research showed me. At the bottom of this model you see the original crankcase "as is" with a round blue insert on one side to hold the crankshaft bushing and a bushing on the opposite side to hold the the other end of the crankshaft. You can also see a strange shaped red insert on the near side that was the camshaft bushing, with a plain bushing on the far side to hold the other end of the camshaft. The round yellow cylinder represents the outer diameter of the crankshaft bearing, and the green cylinder represents the outer diameter of the camshaft ball bearing. At this point, I believe that I can rework the crankcase to accept ball bearings for the crankshaft and for the camshaft. This would let me keep the original crankshaft and camshaft, which would be a tremendous bonus.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #10 on: September 21, 2021, 01:52:45 PM »
So yes, it can be done. I have been holding off on this project, wanting to completely finish the T-Head engine before wading into this. The T-Head is essentially finished, and my new bandsaw is installed and working, so I think I will be making chips with this rework of my opposed twin engine.

Offline ddmckee54

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Re: A new look at Opposed Twin i.c. Engine
« Reply #11 on: September 21, 2021, 05:31:24 PM »
This would let me keep the original crankshaft and camshaft, which would be a tremendous bonus.

Brian:

Didn't you say that the original crankshaft was what caused the rebuild?  Or did you mean that you could keep the original crankcase?

Don

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #12 on: September 21, 2021, 06:24:25 PM »
DDMcCee--The crankshaft wasn't perfectly 100 % straight. The wobble from the crankshaft wore out the bushing, then the crankshaft orbited instead of rotating, which just made a bad situation worse. A ball bearings inner race will let the crankshaft wobble a bit--the inner race isn't fixed as firmly as you would think---However, the inner race confines the crankshaft and won't let it orbit or wander enough to affect the ignition points.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #13 on: September 22, 2021, 08:49:57 PM »
I'm having a quiet day, tearing down the old engine. I gave myself a terrible flash yesterday with my old A.C. welder, and my eyes are howling about it. The new helmet I got when I bought my tig welder has a sensitivity dial on the side of the helmet, and somehow the dial had been turned to '0", so when I started to weld the lens didn't automatically darken. As I begin removing pieces from this engine, I am impressed by how many machined parts there are, and beginning t wonder if I should just buy some angle of the correct size and make a new crankcase.---Not sure yet.

Offline Brian Rupnow

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Re: A new look at Opposed Twin i.c. Engine
« Reply #14 on: September 22, 2021, 10:37:43 PM »
So, here we are, right down to the nitty gritty. I guess the most surprising thing I have seen is how incredibly dirty everything was. Lots of grease and oil and sludge. I don't know how long ago it was that I designed and built this engine, but it's been a few years. I see a few simple things that I would change a bit if I was starting to build this engine from scratch now, but really not much. I can bore straight thru the large top-hat that supports one end of the crankshaft and out thru the other side of the engine in one set-up. The engine is 2.75" out to out, and the stroke on my mill quill is 3.00" The cam bore will be a little more difficult because the tappet guides are loctited in place and there is only 0.632" between the inner ends. The ball bearings for the camshaft are 0.750" o.d.---I can probably put a bit of heat on the tappet bushings to release the loctite and take them out until the camshaft bearing bore is completed and then loctite the bushings back into place. Actually. the bore for the camshaft bushings is only 0.75" so I would probably just run a 3/4" reamer thru there.
« Last Edit: September 22, 2021, 10:44:48 PM by Brian Rupnow »