Author Topic: Homebrew small displacement motorcycle engine.  (Read 6583 times)

Offline jamoni

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Homebrew small displacement motorcycle engine.
« on: May 04, 2013, 06:48:14 PM »
Hey, guys.
I have an idea for a small engine. Basically what I want to do is take 4 small identical 2-stroke engines and hook them all together. Think weed-wacker engines, 25cc or so.
This would go in a small motorcycle chassis, with some sort of gearbox.
Now, the two strategies I have are:
1: chain them together in series, with no modifications to the actual engines.
2: build a new block and crankshaft, and mount the cylinders to that, to give me an inline 4.

The first option is obviously the easiest, but less satisfactory. It would be hard to get good cooling, as the engines would have to be mounted on the long axis of the bike.
The second option would be best, but harder. I think it would be within my capabilities, but definitely stretching them.
The second hurdle would be tuning the engine.
Then of course, a gear box. For this to work the way I want, I would need a lot of gears. I'm thinking a 4 or 5 speed gearbox with a two speed transfer case, unless someone out there can show me a ten speed gearbox.
Obviously I am just fleshing this idea out, don't have anything on paper yet, but I thought I'd pick your collective brains before going any further.
So, comments, suggestions?

Offline John Stevenson

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Re: Homebrew small displacement motorcycle engine.
« Reply #1 on: May 04, 2013, 07:09:04 PM »
[2]
If a two stroke the crankcases will have to be separate to maintain crankcase compression.

Why do you think you need 10 speed ?
John Stevenson

Offline jamoni

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Re: Homebrew small displacement motorcycle engine.
« Reply #2 on: May 04, 2013, 07:24:32 PM »
You are, of course, correct about the separate crankcases. That's why I ask questions. :)
So now I'm thinking maybe I can run a geared or chain driven shaft under all four engines, so they can have their separate cases, but avoid chain drive, and that way I can still have them width-wise instead of lengthwise. would have to have some sort of oiling system, constant loss probably.

I would like to tune this thing for max horsepower, which would mean minimum torque band. To get good performance, I'd need very closely spaced gearing, and lots of it. I don't know how tunable these little things are, so maybe that's just a pipe dream. :)

Offline Lykle

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Re: Homebrew small displacement motorcycle engine.
« Reply #3 on: May 12, 2013, 11:22:26 AM »
Hmm, what a nice and wacky idea!

It depends on the type of motor, but could you mount them in a star?
So you have a central shaft with a larger gear, meshing with smaller gears on each crank shaft. There is your first speed reduction step.
The trouble I see is in any scenario you pick, is getting the motors in sync. Not just revs but in power. You want them all to contribute equally and that aint easy!

But I really like the idea!
Lykle

Design, Build and Enjoy life.

Offline 75Plus

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Re: Homebrew small displacement motorcycle engine.
« Reply #4 on: May 12, 2013, 06:14:35 PM »
During the Korean War I was stationed at a USAF ammo dump in So. Korea. The ammo was transferred from the ammo ships to the beach on what we called TK boats. Depending on the size of the boat they had different numbers of cylinders for their engines. Each cylinder was an independent, diesel, engine. The flywheel of one was bolted onto a flange of the next. The boats we used had from 2 to 6 cylinders. I believe this might work for your project. The 4 engines you plan to use can be set up to have a power stroke every 90 degrees which should make for a smooth running unit.

Joe

Offline jamoni

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Re: Homebrew small displacement motorcycle engine.
« Reply #5 on: May 16, 2013, 10:19:07 PM »
Hmm, what a nice and wacky idea!

It depends on the type of motor, but could you mount them in a star?
So you have a central shaft with a larger gear, meshing with smaller gears on each crank shaft. There is your first speed reduction step.
The trouble I see is in any scenario you pick, is getting the motors in sync. Not just revs but in power. You want them all to contribute equally and that aint easy!

But I really like the idea!
I never thought of just running them all on one large gear. That would be awesome except it would have to be a vertical shaft, which won't work.

I would love to hear more about these TK boats.

Offline BiggerHammer

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Re: Homebrew small displacement motorcycle engine.
« Reply #6 on: May 17, 2013, 06:15:01 PM »
Saw a video on youtube. Someone had 48 chainsaw engines mounted for a motorcycle. At least I think it was 48. Will have to see if I can find that again. Will post a link if I do. Might be fewer engines. (medicated at the moment dental work. please forgive)  :lol:



at least I think they started as chainsaws. I could be wrong.

Offline sebwiers

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Re: Homebrew small displacement motorcycle engine.
« Reply #7 on: May 17, 2013, 11:38:25 PM »
Nope, those are two stroke cylinders from a small displacement triple.   Its comparatively easy to build up new 2 stroke engine configs, because you don't have valves to worry about, just the crankshaft; you can literally do thing like chop up the jugs from a tripple and mix them into an inline 8.   That's what he did, then geared 6 of those together.  Not sure if the cranks are custom, or just modified v8 cranks.

Offline cidrontmg

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Re: Homebrew small displacement motorcycle engine.
« Reply #8 on: May 18, 2013, 06:05:24 AM »
There's "only" 24 chainsaw motors (German built).
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Olli
Penafiel
Portugal

Offline tekfab

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Re: Homebrew small displacement motorcycle engine.
« Reply #9 on: May 18, 2013, 09:07:19 AM »
Why must they be inline ? and not transverse or even in a V4 configuration ?  As for a multi speed gearbox your really giving yourself a lot of work. How about a variable speed drive there's bound to be something out there that you can either use or copy/adapt for your use.

Mike Young

Offline dirty tools

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Re: Homebrew small displacement motorcycle engine.
« Reply #10 on: May 18, 2013, 12:36:57 PM »
you can make it a V engine
Detroit Diesel made 2 stroke 16 clyinder V engines. the were ported intake and valved exhaust.
the largest DD engines that I have worked on was 16V 149TIB  about 2200 hp.
they had 2 blowers and 4 turbos boost was 25psi.
Basicly 2 V 8 blocks bolted togeather.

Offline jamoni

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Re: Homebrew small displacement motorcycle engine.
« Reply #11 on: May 22, 2013, 04:39:00 PM »
Thanks, guys, but I've abandoned this idea. To do it right is beyond my skill level right now, and to do it wrong is beyond my credit limit. :)