Author Topic: A new look at Opposed Twin i.c. Engine (Read 5887 times)

Brian Rupnow · « **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.

steamer · « **Reply #1 on:** September 12, 2021, 04:34:53 PM »

Cool!

Dave

Roger B · « **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.

Jasonb · « **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.

Brian Rupnow · « **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.

Jasonb · « **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.

Brian Rupnow · « **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.

Art K · « **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

Brian Rupnow · « **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.

Brian Rupnow · « **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.

Brian Rupnow · « **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.

ddmckee54 · « **Reply #11 on:** September 21, 2021, 05:31:24 PM »

Quote from: Brian Rupnow on September 21, 2021, 01:23:22 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

Brian Rupnow · « **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.

Brian Rupnow · « **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.

Brian Rupnow · « **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.

Brian Rupnow · « **Reply #15 on:** September 23, 2021, 09:56:04 PM »

All four ball bearings have been installed, two on the camshaft and two on the crankshaft. I still have some spacers to make and will put up a picture after they are installed.

mikehinz · « **Reply #16 on:** September 23, 2021, 10:25:07 PM »

Brian, I'm watching this closely as some day, when I get confident enough, I'd like to attempt some version of a twin. I can see clearly that there are various tricky bits!

Thanks for all the great information you give out here on the forum!

I'm watching closely.

Mike.

Brian Rupnow · « **Reply #17 on:** September 24, 2021, 04:20:24 PM »

So, here's a picture of the crankcase with all ball bearings installed. There isn't that much that you really can see. I had to open up a few counterbores and make some bearing spacers, but it's all done without having had to change the overall shape and dimensions of anything. The camshaft bearings set about 0.020" proud of the top surface, but that isn't a problem, as there is a magnetically attached plate over that top surface when everything is put back together. I am so happy that I didn't have to make a new crankshaft o camshaft.

Brian Rupnow · « **Reply #18 on:** September 24, 2021, 05:09:44 PM »

I have never been happy with the base I made for this engine. I am going to build a new, much shorter base because I think the proportions are better.

Brian Rupnow · « **Reply #19 on:** September 25, 2021, 10:39:52 PM »

Today I shortened the plate directly below the crankcase, and machined two new "feet" that are much shorter than the original ones. I stuck that evil looking flywheel/fan on just to make a good picture.

Craig DeShong · « **Reply #20 on:** September 26, 2021, 12:28:07 AM »

Brian

You’re making good progress on this twin. I’ve had a fascination for twins, ever since I nearly traded my Honda for one of those classic BMW motorcycles way back when, that had the twin opposed cylinders. Loved those bikes, but had I stayed with riding motorcycles, today I’d probably just be that cousin in some distant relations photo album.

Brian Rupnow · « **Reply #21 on:** September 26, 2021, 01:56:44 AM »

Hi Craig--- I've got a whole room full of engines setting around, but I've been thinking of redoing the twin for a long time now. I was very lucky that I didn't have to make a new crank or cam. I have two sets of cylinder heads for it. The first set of original heads had the sparkplugs right at the very bottom, and if you flooded it on start up you had to take the plugs out and dry them off and blow out the cylinders. The second set of heads were a redesign that raised the sparkplugs to the center, but I never did get it to run right because of undue wear on the crankshaft bushings and the fact that my short sparkplugs set way down below the rocker arm towers. I think the sparkplugs were shorting out to the rockers, but it was in a very difficult spot to see. I don't have to really make anything more now, just a bunch of rearranging things. Your new project looks very exciting, and I have a look every time you post.---Brian

Brian Rupnow · « **Reply #22 on:** September 26, 2021, 06:24:12 PM »

Today I reworked the flywheel/fan guard to fit the shorter engine base. Also took the opportunity to J.B. Weld shut a bunch of holes I had drilled in the guard to mount a governor. The governor kinda sorta worked, but I could never get the engine to run consistently long enough to get the governor tuned properly. I may still try a governor to control this engine, but if so it will be mounted on a separate base and connected with an o-ring drive belt.

Brian Rupnow · « **Reply #23 on:** September 27, 2021, 10:11:16 PM »

Well, that's a day out of my life, but it's been a good day. There was no way I could rework the coil mounting and switch bracket to make them work with the new engine frame, so I built new ones---and modified the guard for the wicked flywheel/fan to fit the much shorter engine base. Everything looks a bit rough right now, but I haven't done my cosmetic magic yet. Tomorrow I will tidy things up a bit, and see what's involved with mounting the gas tank and cylinders---They should just be direct bolt ons.

Brian Rupnow · « **Reply #24 on:** September 28, 2021, 06:09:07 PM »

Today seen the cylinders cleaned up and reinstalled, along with the pistons and connecting rods. I could have used one of Chris's elves to get down into the crankcase and tighten the rod bolts. I had forgotten just how inaccessible they were when the bottom plate was installed on the crankcase. I had to take everything apart to get at the rod bolts to tighten them. Before I go any farther now, I have to time my valves before my gear cover goes back in place.

crueby · « **Reply #25 on:** September 28, 2021, 06:29:07 PM »

So THAT'S where that little guy went, I was worried he got shut in one of the toolbox drawers.

Engine is looking good, getting closer to seeing it run again.

Roger B · « **Reply #26 on:** September 28, 2021, 08:05:26 PM »

A fine rebuild

I'm following along

Brian Rupnow · « **Reply #27 on:** September 29, 2021, 02:23:04 AM »

Hi Roger--Thanks for looking in and leaving a comment.---I just spent an hour reading thru all the posts made on the forum when I originally built this engine, and I discovered something. On the original build, that diamond mesh on the flywheel guard was between the flywheel and the engine. Now it's on the other side. Ah well, I didn't plan on sticking my fingers in there anyways.

Brian Rupnow · « **Reply #28 on:** September 29, 2021, 11:43:42 PM »

So, here we are, all reassembled. Crankshaft and camshaft are both riding in sealed ball bearings. That lever at the very front of the engine has my ignition points mounted on it, so I can adjust the timing by lifting the lever up or down. The plate will rotate to the limits of the curved slot, letting me fine tune the timing while the engine is running. That knurled pulley and key setting in front of the engine go on last, as it has part of my starter which I engage with my variable speed drill. I still have to remove the fan guard and give it a bit of cosmetic work and a new paint job. I might machine a swoopy looking air horn to fit on the intake side of the carburetor. Tomorrow I have some real, paying design work, so I probably won't post anymore progress for a couple of days.

Admiral_dk · « **Reply #29 on:** September 30, 2021, 11:29:36 AM »

So not far from the first pop in the revised version

Brian Rupnow · « **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.

Brian Rupnow · « **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.

crueby · « **Reply #32 on:** October 03, 2021, 04:27:32 PM »

Brian Rupnow · « **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.

Brian Rupnow · « **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.

Craig DeShong · « **Reply #35 on:** October 04, 2021, 11:47:32 PM »

Looks really smart Brian.

Brian Rupnow · « **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

<a href="https://www.youtube.com/watch?v=HXd3b6P5LUU" target="_blank">http://www.youtube.com/watch?v=HXd3b6P5LUU</a>

Brian Rupnow · « **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

crueby · « **Reply #38 on:** October 09, 2021, 09:20:55 PM »

Nice!!!!

Jasonb · « **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.

Brian Rupnow · « **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

Jasonb · « **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.

Brian Rupnow · « **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

<a href="https://www.youtube.com/watch?v=9oOP8SWZiwQ" target="_blank">http://www.youtube.com/watch?v=9oOP8SWZiwQ</a>

Admiral_dk · « **Reply #43 on:** October 10, 2021, 09:20:18 PM »

Great to see that you got it running as it should again

dwulfe · « **Reply #44 on:** October 11, 2021, 09:11:57 PM »

Thanks for sharing

Craig DeShong · « **Reply #45 on:** October 12, 2021, 05:15:56 PM »

Wonderful Brian, it runs well !

mikehinz · « **Reply #46 on:** October 12, 2021, 05:17:40 PM »

Very nice Brian! I think the engine runs wonderfully!

Mike

Brian Rupnow · « **Reply #47 on:** October 13, 2021, 01:08:04 AM »

Graham Vickery---Email me at brupnow@rogers.com I've got your drawings but don't know your email to send them to.---Brian

Brian Rupnow · « **Reply #48 on:** October 13, 2021, 04:11:37 PM »

The first set of 60 .pdf drawings has been sent out to Graham Vickery. This is a fairly complex engine, and I expect Mr. Vickery to have a few questions which I will attempt to answer for him. This engine is a bit more complex than what I usually send out, because it was first designed 5 or 6 years ago, then there were some design changes made about two years ago when I was trying out different cylinder heads, and then the final design changes this year when I made a much shorter base and added ball bearings to the crankshaft and camshaft. Of course the trick for me is to send out only drawings that refer to the current engine as it sets. Good luck Graham, may the force be with you!!!---Brian

Brian Rupnow · « **Reply #49 on:** October 21, 2021, 06:50:15 PM »

Today I was getting pretty bored with my self imposed "Do Nothingness", so I snuck down to my machine shop and made an "Air Intake Horn" for the carburetor. This really adds nothing to the performance of the engine, it just looks neat. Many years ago I actually bought one of these for a Sno-Jet snowmobile I owned, and was sucked in by the salesman who told me about the performance enhansing properties of such an item. It didn't do a damn thing for performance, but if you sat to close to the engine it would suck in your snowmobile suit and stall the engine.---But----It did look neat.

Brian Rupnow · « **Reply #50 on:** January 17, 2022, 08:53:28 PM »

Today we have a blizzard going on outside, and I wanted to add a throttle control to my twin cylinder engine. So, almost a full day later, I have added one of my Casey Jones throttle levers to it. The throttle lever has a couple of Belleville washers (spring washers) down at the pivot point, and they provide enough friction to hold the throttle arm in place. this way the engine doesn't get away on me and rev up to the point where it's screaming and I'm having a heart attack trying to hit the ignition kill switch.

<a href="https://www.youtube.com/watch?v=R4vfq6FjRGs" target="_blank">http://www.youtube.com/watch?v=R4vfq6FjRGs</a>

News:

Author Topic: A new look at Opposed Twin i.c. Engine (Read 5887 times)