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Learning how to build Lotus Seven replicas...together!
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PostPosted: Mon Apr 23, 2012 1:50 am 
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Ok, the V12 crankshaft has come to 698.8mm, with 4 main bearings. There is no definition of counter-balancing elements right now, and the default crank will be quite heavy at first. The idea is, as I said, to get a working unit, and refine it over time.

Block should be ready later today. I've all but settled on a V4 to test.


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PostPosted: Mon Apr 23, 2012 2:29 am 
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Downix wrote:


Block should be ready later today. I've all but settled on a V4 to test.


Which makes sense. Test the unit with the fewest cylinders to keep work loads down and then IF it works as you like you can always build one with more cylinders when you have it as you like it.

How about a twin to begin?

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PostPosted: Mon Apr 23, 2012 12:57 pm 
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carguy123 wrote:
Downix wrote:


Block should be ready later today. I've all but settled on a V4 to test.


Which makes sense. Test the unit with the fewest cylinders to keep work loads down and then IF it works as you like you can always build one with more cylinders when you have it as you like it.

How about a twin to begin?

I was originally thinking a twin, but after careful thought it struck me that the twin would have too many differences from the main design to be as good a test as the V4 would be. The bearings (which, incidentally, I am designing it to use the same bearings you'd find on the 426 Hemi, in order to add plenty of margin for strength) have to support two rod throws each, four pistons. A v-twin would only have two, which means you'd still not know if the crankshaft is strong enough because it would have half of the number of pistons per bearing. The dry sump oil pump is tied to the crankshaft as well, with the number of collectors being tied to the number of rod-throws. But with a v-twin, you'd have to design a different oil pump arrangement, not enough throws. With the V-twin and V4 you'd still need a balance shaft, so no advantage to the twin there. I just cannot find a real advantage to the twin beyond needing 35% less metal to make it.


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PostPosted: Sun Apr 29, 2012 1:15 am 
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Ok, taken some time to study balancing for the V4. Because of how the oil pump is being arranged, I can combine that pump with the balance shaft I think, which should allow some weight savings.

But now am looking at how to connect it to the rest of the world, the transmission. In the open source world there exists already a Honda B-engine transmission mount that would be quick and cheap to adapt, but it would not fit quite right (it is very obviously for an inline-engine). Alternatively, I also have both a Nissan 71C transmission here and have access to a Type 2 VW transaxle. Or I could make a custom mount and push a custom transmission later on (which if I did would be using a chain drive and not gears, fan of the Nash chaingang transmission).


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PostPosted: Sun Apr 29, 2012 11:31 am 
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Downix wrote:
(which if I did would be using a chain drive and not gears, fan of the Nash chaingang transmission).


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PostPosted: Mon Apr 30, 2012 1:15 am 
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Yup, that's it. Although, not talking the whole rear-end drive system like on the Nash, just that the use of chains over gears for most 'gears' save Reverse, which would use a normal gear setup. Chain drive transmissions in my experience are a lot less painful to repair, and cheaper to build. Off the shelf motorcycle drive gears should do, attached to dog engagement gears.


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PostPosted: Wed May 30, 2012 1:04 pm 
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Have not forgotten, instead found a tutorial describing just how to build a V12 engine, which I have been following to make sure I did not fall over any pitfalls.

You can find it here:

http://grabcad.com/questions/tutorial-h ... gine-final


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PostPosted: Tue Sep 25, 2012 8:47 am 
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Location: Germany
I hope I didn't mention this one before. Anyway its worth to share, I can see big advantages in cost power & reliability with this example and it sure has still been a good amount of work to do and makes the owner proud with large parts of it being homemade.

http://translate.google.de/translate?sl ... 2F&act=url

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PostPosted: Thu Jan 24, 2013 3:22 pm 
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I've had one rough year, but have not forgotten about this. I've been working on the aircooled jugs some more, and hit upon a novel solution to the lubrication issue I was running into. With the fork-in-blade design, lubricating the piston was turning into a problem. Difficult to align the lubrication holes in the crankshaft, and the casting for the shaft was more difficult due to the lubrication channels.

Then a bit of serendipity struck, and I'd found my old Suzuki GT380 manual (long lost the bike). The GT380 was an interesting engine in that instead of feeding lubricant through the crankshaft, it used direct oil injectors inside the engine cylinders themselves. I could accomplish this because the pistons were just a bit longer than the stroke of the engine. So, I looked at the pistons I'd designed, and if I extended them by 2mm, they'd also fit the same bill. Simplifies the casting of the crankshaft, while retaining strength.


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PostPosted: Sat Aug 17, 2013 3:23 am 
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Hi

I would like another shot at the idea.

Im planning a v4 with some stock parts. the only custom parts will be a welded mild steel crankcase, cylinder barrels, cylinder head and crankshaft. its an air cooled 90 degree v4. miller cycle. the rotating assembly will be similiar to the ducati desmo v4. OHV with 2 camshafts positioned in a way so the pushrods are on the bottom and very short.

the valve timing will be early intake valve closing. the intake will have 7:1 compression ratio and the power stroke will have 20:1 expansion ratio. its going to use a vgt. from a diesel its very common and cheap nowadays.

i might be able to prototype a 2 cylinder with vestigial lever mounted bobweights on the other. its cheaper and not much different from the v4. the firing pulses will not be even but i thing a proper torsional vibration absorber can smooth it out.

A low cost torsional vibration testing system needs to be built from nano mechanical sensors available off the shelf nowadays. if the torsionals cant be tamed then an open source engine is not possible at all.


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PostPosted: Fri Aug 23, 2013 10:36 am 
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Location: worcester county, Massachsetts
Downix wrote:
I've been working on the aircooled jugs some more, and hit upon a novel solution to the lubrication issue I was running into. With the fork-in-blade design, lubricating the piston was turning into a problem. Difficult to align the lubrication holes in the crankshaft, and the casting for the shaft was more difficult due to the lubrication channels.

Then a bit of serendipity struck, and I'd found my old Suzuki GT380 manual (long lost the bike). The GT380 was an interesting engine in that instead of feeding lubricant through the crankshaft, it used direct oil injectors inside the engine cylinders themselves. I could accomplish this because the pistons were just a bit longer than the stroke of the engine. So, I looked at the pistons I'd designed, and if I extended them by 2mm, they'd also fit the same bill. Simplifies the casting of the crankshaft, while retaining strength.


yes, it did, just like the GT250, GT550 and GT750, but those bikes were all 2 strokes. the oil injection went into the crancase to lubricate the pressed-together roller crankshafts as well as the piston skirts.

in a 4-stroke, you still have to run oil thru the crankshaft to lubricate the main and rod journals, as long as you're using plain bearings. If you want to look at 4-strokes with roller cranks, study the japanese 4-cylinder 4-strokes from the 1970s.
roller bearing cranks are fine up to a point, but they aren't as torsionally strong as even cast single piece plain bearing cranks, for a given journal diameter.

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PostPosted: Fri Aug 30, 2013 3:43 pm 
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Location: Carlsbad, California, USA
Here's an interesting future possibility. A university in Oz has improved the process of making stainless magnesium (no, that's not a typo) for castings and cast a 2.5L V6 engine block as an example. In the article below there is no mention of what became of this casting. That is, did they make the complete engine, etc.? However, if you imagine that the process become perfected and cost effective, it will make for some interesting future, specialist engines such a race cars and motorcycles, don't you think?

Stainless Magnesium Engine block ==> http://www.gizmag.com/stainless-magnesi ... ash/28856/

This thread seemed like a good place to share this information rather than start a new one. If anyone finds out more regarding specifics (weight, completed engine, etc.) then please do post about it.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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