Author Topic: Building a twin cylinder inline i.c. engine  (Read 18898 times)

Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #15 on: January 08, 2024, 02:03:13 AM »
Having too much fun today. Have to quit now or good wife is going to kill me---


Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #16 on: January 08, 2024, 04:31:17 PM »
We got gears, we a got a carburetor, and we got an exhaust system. There is a guard for fitting over the gears as well, but I left it off so the gears show.--Almost finished modelling!!


Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #17 on: January 09, 2024, 01:58:44 AM »
The redesign of this engine is mostly finished. It has a 1" bore and ended up with a 0.944" stroke. The three worst parts to machine will be the crankcase, the crankshaft, and the cams. I think I will machine the crankcase first. The crankcase looks huge, but in reality it's a bit less than 3" square and 4 1/8" long. The hard part is going to be the large cavity in the crankcase which is 2 1/8" deep, and is "blind" meaning it doesn't go all the way through. The radius in the corners is 3/16", so first step will be to drill the four corners with a 3/8" drill to full depth and then finish up with an endmill to get a flat bottom. Then mount it on the lathe faceplate and do a couple of overlapping 2.43" diameter blind bores to hog out the rest of the material. This will still leave some material to be removed from the corners that can probably be cleaned out on the milling machine. I think this is the best approach with a home shop/ manual mill and lathe. if anyone thinks of something better, please let me know.


Online Kim

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Re: Building a twin cylinder inline i.c. engine
« Reply #18 on: January 09, 2024, 05:33:36 AM »
You could fabricate it from 1/4" plate rather than hogging out all that material.  That's likely what I'd do.

Kim

Offline Jasonb

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Re: Building a twin cylinder inline i.c. engine
« Reply #19 on: January 09, 2024, 07:08:50 AM »
That is how I did it on my opposed twin. Though I did not drill the corners first just lathe then milling out the rest

Your internal radius could be larger as it is bigger than 3/16 on the original drawing.

You will likely need a long series milling cutter as I did so make sure you hold that in a collet not your usual drill chuck. Should be able to use a 10mm cutter and if you check clearances I think 1/2" cutter will fit and be a lot stiffer.

Cutting from solid should keep everything in line provided you position the holes accurately

Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #20 on: January 09, 2024, 02:17:43 PM »
Four drilled holes on the mill to pick up the corners and two very large bored holes on the lathe while held in the four jaw chuck? Looks a bit scary to me. My largest drill is 1" diameter, likewise my largest endmill.

Offline Jasonb

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Re: Building a twin cylinder inline i.c. engine
« Reply #21 on: January 09, 2024, 02:29:26 PM »
Different engine, bigger bit of Aluminum, similar lathe,  4-jaw no problem. My biggest drill is also 1"


Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #22 on: January 09, 2024, 02:36:57 PM »
I can go to a 0.375" rad in the corners without fouling any moving parts inside the crankcase. This would mean a drilled 3/4" hole in each of the four corners on the mill and two very large bores on the lathe while held in the four jaw chuck.

« Last Edit: January 09, 2024, 02:51:59 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #23 on: January 09, 2024, 02:46:02 PM »
I just talked to my metal supplier, and a piece of aluminum 3" square x 4 1/4" long will cost me $26.00. I think I'm going to buy it and risk machining this from solid.  Nothing ventured, nothing gained.

Offline AlexS

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Re: Building a twin cylinder inline i.c. engine
« Reply #24 on: January 09, 2024, 06:43:27 PM »
"I have three engines designed and built last year" well that is a bit of a machining exercise!

Good to start new year with new engine design.

What about a 270 degree inline twin (90 degree phasing crankshaft)? Like mostly modern motorcycle inline twins nowadays. It should divide vibrations and forces without additions compared to 360 degree twin. But it still be a small displacement engine.

Offline AlexS

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Re: Building a twin cylinder inline i.c. engine
« Reply #25 on: January 09, 2024, 07:02:52 PM »
Make it something special. If you want it.

A 360 inline twin is actually acting like a single on vibration.

What about adding 2 primary balance shafts (rotate the speed of crankshaft)? When design properly weights of crankshaft webs, and countershaft weights, it balance up and down movement of the piston and connecting rod.

It could be added inside the crankcase or bolted on the sides. It would also look interesting to look at because adding 2 or 3 more gears.

I can help with calculating the needed shapes of shafts when the geometry and weight are known (could convert stepfile for a other CAD program).

Normally manufactures add 50-60 % of weight of oscillating movement of piston and connecting rod to weight of crankweb + part (+-1/2 of weight) connecting rod and bigend to crankshaft web.
Internal combustion engine book SAE showed need 100% weight of osc pistion and connecting rod in crank webs. And than 50% of each balance shaft weights of oscillating mass.


It should then run like a inline 4

https://www.youtube.com/watch?app=desktop&v=UyfrqipPmOw

<a href="https://www.youtube.com/watch?v=hwigSbyQ7AI" target="_blank">http://www.youtube.com/watch?v=hwigSbyQ7AI</a>

Online Art K

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Re: Building a twin cylinder inline i.c. engine
« Reply #26 on: January 09, 2024, 09:21:01 PM »
Brian,
You're making good progress on the design. I do recall seeing online some time ago a photo of a 90 degree phased crank for a race Norton 850 Commando, interesting. But seeing you undoubtedly will see how slow it will spin, an unnecessary complication.
Art
« Last Edit: January 10, 2024, 05:52:43 PM by Art K »
"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: Building a twin cylinder inline i.c. engine
« Reply #27 on: January 09, 2024, 10:14:33 PM »
And so, it begins. Today I bought a piece of aluminum 3" x 3" x 4 1/4", brought it home, and machined it to finished size. Tomorrow I will set it up in the four jaw chuck and start to hollow out the cavity in it. In the background you can see the engine I built ten or twelve years ago, which was based on the Jaguar engine by Malcolm Stride. Basically, it is half of the Bobcat which I am building now.


Online Dave Otto

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Re: Building a twin cylinder inline i.c. engine
« Reply #28 on: January 09, 2024, 11:37:16 PM »
If you are going to hollow out the cavity first, how are you planning to deal with the interrupted cut while boring the passage for the camshaft? Might not be much fun.

Dave

Offline Brian Rupnow

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Re: Building a twin cylinder inline i.c. engine
« Reply #29 on: January 10, 2024, 01:11:16 AM »
Dave--I don't anticipate a big problem there. I will put in the bore for the camshaft bearings a couple of thou larger than the ball bearings I will use, then use an alignment rod and the two bearings and a dab of J.B.Weld  on the o.d. of the bearings to line everything up. That scallop you see in the underside of the crankcase won't really be there, just a bore thru the endplates. I will go in tomorrow and fix my solid model.
« Last Edit: January 10, 2024, 01:37:30 AM by Brian Rupnow »

 

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