Author Topic: Dave's twin  (Read 13507 times)

Offline Dave G

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Dave's twin
« on: July 21, 2012, 01:53:09 AM »
I started this engine build a while back and posted it elsewhere. I have decided to continue here with the posts. For those that have been watching, this will be old news so I will only give a brief description of what I am building.



This engine will be an IC engine with 2 cylinders. The crankshafts are overhung and rotate on taper roller bearings. At the end of the cranks are bevel gears that will act upon a ring gear that is attached to the flywheel shaft. The flywheel will rotate at half speed of the crankshafts. The gear ratio is 2:1 and they are housed in a gear case. The exhaust valves are operated by a cam disk that is inside the gearcase and is attached to the flywheel shaft. The intake valves are atmospheric. The speed will be regulated by the throttle with a single carb.

I am just about finished with all the components and have been working on assembling it. When I installed the seals for the shafts in the gearcase it became difficult to turn over. I have reduced the dias that ride on the seals to the minimum and this has helped a great deal. I'm at the point now where I should be able to motor it over for while before completing the assembly. I don't have much time to work on it right now but I will keep posting the progress. Dave

Offline Dave G

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Re: Dave's twin
« Reply #1 on: July 21, 2012, 02:07:02 AM »
A pic of all the components completed up to now.


Offline Dave G

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Re: Dave's twin
« Reply #2 on: July 21, 2012, 02:09:48 AM »
Another view




Offline Dave G

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Re: Dave's twin
« Reply #3 on: July 21, 2012, 02:13:44 AM »
The internals of the gearcase. The cam disk and the gears.


Offline smfr

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Re: Dave's twin
« Reply #4 on: July 21, 2012, 06:48:00 AM »
Great to see this continued here. This is a fantastic build. Can't wait to see it running, and most of all to hear what it sounds like  :D

Simon

Offline Bearcar1

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Re: Dave's twin
« Reply #5 on: July 21, 2012, 04:41:11 PM »
I agree Simon. I remember when it was four pieces of plate stock being welded together for the crankcase and I was thinking to myself, what the hell is this going to turn into? Now, OMG, what a beautiful and unusual arrangement for an engine. BRAVO!!

BC1
Jim

Offline metalmad

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Re: Dave's twin
« Reply #6 on: July 22, 2012, 12:35:46 AM »
Hi Dave
I can not wait till u get this beauty up and running
Ive sent some Karma to help u get settled in my friend  ;D
Pete
A little bit every day, sometimes the same little bit

Offline Dean W

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Re: Dave's twin
« Reply #7 on: July 22, 2012, 03:56:04 AM »
Wow, you have a lot of really nice work done there, Dave.  Is this an air cooled engine, or are there water
jackets in the cylinders? 
Dean
In beautiful N. Idaho, U.S.A.

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Offline ShedBoy

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Re: Dave's twin
« Reply #8 on: July 22, 2012, 05:23:37 AM »
Nice work Dave, looking forward to seeing this un run.

Brock

Offline Dave G

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Re: Dave's twin
« Reply #9 on: July 22, 2012, 02:20:55 PM »
Thanks guys, I'm looking forward to finishing this thing here too. 2 Karma points already, wow.

This engine will be liquid cooled, I have machined water jackets into the cylinders for cooling. I am going to try to get it running before going to all the work of a cooling system. My plan is to have a circular radiator surround the flywheel shaft bearing housing. I have a 5 bladed fan scavenged from an electric fan that fits into the recess of the flywheel and will direct the airflow through the flywheel. The coolant pump will be run off the flywheel shaft on the other end and will be a simple gear pump. The radiator will have a tank at the bottom which will be under the gearcase for the pump to draw from.

The crankshafts will rotate in opposite directions but as long as no one tells it, it shouldn't know the difference. There is only one cam lobe to operate both cylinders as it will have an even firing order. I'm not too sure how this one will run, it may want to spin in circles as it runs. We will see. I do know one thing though, it is going to be noisy. I haven't filled the gearcase with lube yet, but it seems like the gears are going to be loud when running. This thing came about because I had a set of 2:1 bevel gears laying around with no purpose.

I like to peruse my engine books as all of us do I imagine and found an engine prototype from WW2 that used this configuration with 6 cylinders. I have adapted what I had on hand and came up with this. If it runs well enough, maybe someone would like to try a 6 cylinder version. One of the disadvantages to this design is that only a few teeth on the ring gear will be taking most of the load during the firing stroke and each cylinder acts on the same teeth. As this is just a model and won't be under load there shouldn't be much of a problem.

Scratch building is alot of fun and work but is very rewarding and I highly recommend it to anyone who has their own ideas for an engine. Even if this idea doesn't pan out the journey has made it all worth it.

Edison said he never had a single failure because he learned something from every experiment he did. I wonder how many of his ideas became boat anchors though, Dave

Offline metalmad

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Re: Dave's twin
« Reply #10 on: July 23, 2012, 01:14:41 PM »
Hi Dave
I always enjoy your posts as they show me how good I wish I was  ;D ;D
Pete
A little bit every day, sometimes the same little bit

Offline Dean W

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Re: Dave's twin
« Reply #11 on: July 24, 2012, 04:43:25 AM »
The crankshafts will rotate in opposite directions but as long as no one tells it, it shouldn't know the difference. There is only one cam lobe to operate both cylinders as it will have an even firing order.
I just realized that about the opposite rotation crankshafts, after looking at the gear case for a minute or two.  I was
going to ask about that!  :)
The "even firing order" you mention;  Do you mean the cylinders will fire at the same time, and is that how you get
away with the single cam lobe for the exhaust valves?

Is the carb the one you plan to use, or do you figure you'll need a larger one?
It's a very interesting engine, Dave.  Thanks for your comments and explanations.   :ThumbsUp:
Dean
In beautiful N. Idaho, U.S.A.

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Offline Dave G

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Re: Dave's twin
« Reply #12 on: July 24, 2012, 04:43:12 PM »
The arrangement I will use is called a waist fire system. The single coil has 2 high tension leads which will attach to the 2 sparkplugs. Most 2 and 4 cyl motorcycle engines use this system for simplicity. Both plugs fire at the same time but because only one cylinder is at the point of combustion only that cyl will make power. The other plug will fire but because the cam is in overlap mode and the exhaust  valve is open no power will be made. I plan to use one of Roy Scholl's fine ignition systems, he does make them in waist fire.

The cam runs at one half speed of the crankshafts like a normal 4 stroke engine . It will take 720 degrees of crankshaft rotation to complete all 4 cycles also.  The cylinders are out of phase by 360 degrees of crankshaft rotation giving an even firing order. Only one exhaust cam lobe is needed to operate both cylinders. If you were to grab the flywheel by hand and rotate it until the pistons are at TDC you would see that on one cylinder the exhaust valve is just about closed. At the same time the other cylinder has compressed the mixture and is waiting to be fired. Rotate the flywheel 180 degrees by hand from this point and both cyls are at TDC once again but the cam events have switched cyls. The flywheel is directly coupled to the cam and runs at half speed also.

The carb is the one I plan to use. I normally make my carbs but I had this one on hand and figured I'd give a try. For Hit-Miss style engines I try to make my throttle dias about 10 - 15 % of bore size. For a throttle governed engine such as this one I usually will try to make the throttle dias around 15 - 20% of bore size. This carb was close to what I figured was needed. If I can get this engine to run I want it to be a slow runner and not worry about taking too much throttle. I want it to just chug along as slow as I can get it to. When designing an engine from scratch like this one I will use the dimensions from a full size engine like a V-8 for cam lift and throttle dias and scale them accordingly. This engine has a bore of 1.25" so it is just under 1/3 scale of a 4" bore engine. The valve opening is .125" as a stock V-8 engine lift is around .400". The throttle bore is a little smaller than this scale so I get good velocity through the carb. The smaller the throttle bore the greater the velocity. This helps to draw the fuel from the tank easier. I put a SS check ball in the foot valve at the base of the fuel tank to keep the fuel up to the carb. Very important in Hit-Miss engines.

Hopefully this clarifies things a little. I spent alot of time thinking about this engine before starting to build it and I think it will run. My concerns are the amount of power loss due to friction of all the moving parts( gears and bearings). Engines always seem to run better with a load on them and I hope the load of turning the gears and bearings will help in the tuning. I have tried to foresee any challenges in the design but one never knows how good the soup will be until he takes his first sip. So far I haven't burnt my tongue yet. Who knows, I might have to throw out the whole pot.  :shrug: Dave

chuck foster

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Re: Dave's twin
« Reply #13 on: July 24, 2012, 04:59:04 PM »
holy  :censored: now thats a neat engine  8)

i don't know how i missed this on the other forum  :facepalm:

i will be watching this one  :happyreader:

chuck

Offline cfellows

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Re: Dave's twin
« Reply #14 on: July 29, 2012, 03:42:42 PM »
Very interesting engine, Dave.  The workmanship is also first rate. 

Chuck
So many projects, so little time...