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Learning how to build Lotus Seven replicas...together!
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PostPosted: Sun Jan 08, 2012 3:41 am 
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Some work this week. I'd realized after I did the first design of the cylinder tube that it would be difficult to produce for your average home forge. To be strong, it needs to be a high-temperature material, like iron, but most home forges are used for aluminum, making it difficult to produce in the manner I was envisioning. So, facing that, I turned to other fabrication options, and hit upon a solution. Rather than cast this part, you could lathe it from an existing iron tube. So I then took a list of common piston sizes, and tube sizes, and hit a solution. NPS 3 Schedule 80 tubes have an interior diameter of 73.66mm, and a common piston size is 73mm. The 0.66mm falls within the normal gap around the piston for the rings, which varies from 0.58-0.79mm in most engines. So am re-designing it around this new size.

Incidentally, this piston size is the same size used on the Ferrari 250 GT engine, used on the GTO and Tessa Rosa. A 4-cylinder engine using the same stroke would be 1000cc.

I also realized that a Boxer arrangement would be simpler for the home engine casting process, due to the inherent balance of the design. I'm almost done with the design, and should have something on here next week.


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PostPosted: Sun Jan 08, 2012 1:25 pm 
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I used to turn my big bore liners for my dirt bikes using cast iron drain pipe. Alternately you could use mild steel liners and cast iron rings.

A lot easier than casting your own up unless you're just doing it for the satisfaction of doing it yourself.


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PostPosted: Sun Jan 08, 2012 1:40 pm 
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I think that's what I just said. Still talking about casting the block, mind you.


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PostPosted: Tue Jan 10, 2012 6:01 pm 
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Downix wrote:
NPS 3 Schedule 80 tubes have an interior diameter of 73.66mm, and a common piston size is 73mm. The 0.66mm falls within the normal gap around the piston for the rings, which varies from 0.58-0.79mm in most engines. So am re-designing it around this new size.


Do I follow you correctly, that you're suggesting a liner out of 3" schedule 80 pipe? Material wise, that stuff is junk steel. I'm not sure it'd be suitable for running rings on. And my notes list a nominal id of 2.900" (which is your 73.66mm) but most of the pipe I've seen is neither round enough (usually it's lumpy or eggy, definitely not round) or finished well enough on the inside to run pistons on (you might have a weld seem, definitely won't have a machined finish on the inside), so you'd need to bore it in order to use it, and it might take a significant cut to get it to clean up (might need .030" on the diameter) Regardless, I don't think a 73mm piston would work in that application.

And, .58mm to .79mm seems like a big clearance to me (that's .022" to .031" in numbers I relate to). For reference, Wiseco recommends .004" (.10mm) piston to wall clearance on a 4" (101.6mm) bore small block chevy piston. I'd expect for the nominally 3" parts you're talking about you'd want to be down closer to .003" (.076mm).

Hope that helps keep things on track...

JustDreamin


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PostPosted: Tue Jan 10, 2012 6:34 pm 
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JustDreamin wrote:
Downix wrote:
NPS 3 Schedule 80 tubes have an interior diameter of 73.66mm, and a common piston size is 73mm. The 0.66mm falls within the normal gap around the piston for the rings, which varies from 0.58-0.79mm in most engines. So am re-designing it around this new size.


Do I follow you correctly, that you're suggesting a liner out of 3" schedule 80 pipe? Material wise, that stuff is junk steel. I'm not sure it'd be suitable for running rings on. And my notes list a nominal id of 2.900" (which is your 73.66mm) but most of the pipe I've seen is neither round enough (usually it's lumpy or eggy, definitely not round) or finished well enough on the inside to run pistons on (you might have a weld seem, definitely won't have a machined finish on the inside), so you'd need to bore it in order to use it, and it might take a significant cut to get it to clean up (might need .030" on the diameter) Regardless, I don't think a 73mm piston would work in that application.

And, .58mm to .79mm seems like a big clearance to me (that's .022" to .031" in numbers I relate to). For reference, Wiseco recommends .004" (.10mm) piston to wall clearance on a 4" (101.6mm) bore small block chevy piston. I'd expect for the nominally 3" parts you're talking about you'd want to be down closer to .003" (.076mm).

Hope that helps keep things on track...

JustDreamin

Well, do remember this is the first time I've looked at a piston based motor. (previous work has been on electrics or turbines) As for being junk steel, depends on the pipe source in my experience. As for round enough, you could use 3" schedule 160, which would be an internal diameter of 2.624, and bore it out. And, you can also get solid iron cores to do the same thing if need be as well, such as here:

http://www.grainger.com/Grainger/Rod-Stock-2KUP9

But, that brings to me to, what hardness would be suitable for such work?


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PostPosted: Tue Jan 10, 2012 7:20 pm 
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I really don't have a dog in this fight, but I wonder why you don't start with the sleeves from a commonly available engine. Choosing an existing wet sleeve would allow you to start with available rings and pistons that could be lightened and..... You could make your own block, crank, rods etc. even pistons if you'ld like. But why reinvent something if you don't have to? There must be enough variations of wet sleeves to find one close to what you require. Especially if you don't already know the metalurgy required to fab the part.

Not trying to pick a fight, but I think it would make sense to start with some available building pieces and modify them to your liking. Just asking......Wasn't there a PC program for building your own theoretical engine and e-dyno testing them? (or should I say i-Dyno? Everything seems to be i-something these days.)

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PostPosted: Tue Jan 10, 2012 9:21 pm 
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rx7locost wrote:
I really don't have a dog in this fight, but I wonder why you don't start with the sleeves from a commonly available engine. Choosing an existing wet sleeve would allow you to start with available rings and pistons that could be lightened and..... You could make your own block, crank, rods etc. even pistons if you'ld like. But why reinvent something if you don't have to? There must be enough variations of wet sleeves to find one close to what you require. Especially if you don't already know the metalurgy required to fab the part.

Not trying to pick a fight, but I think it would make sense to start with some available building pieces and modify them to your liking. Just asking......Wasn't there a PC program for building your own theoretical engine and e-dyno testing them? (or should I say i-Dyno? Everything seems to be i-something these days.)



I was thinking the same thing. Honda comes to mind, there's a bunch of different liners in multiple bores.


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PostPosted: Tue Jan 10, 2012 9:45 pm 
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I'm not against that either, and the bore size has plenty of available wet cylinders already which would fit the other parts I've been working on, with piston options from 69-77mm available.


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PostPosted: Wed Jan 11, 2012 9:42 am 
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Downix wrote:
Well, do remember this is the first time I've looked at a piston based motor. (previous work has been on electrics or turbines) As for being junk steel, depends on the pipe source in my experience. As for round enough, you could use 3" schedule 160, which would be an internal diameter of 2.624, and bore it out. And, you can also get solid iron cores to do the same thing if need be as well, such as here:

http://www.grainger.com/Grainger/Rod-Stock-2KUP9

But, that brings to me to, what hardness would be suitable for such work?


After reading your post and re-reading my post, I'm afraid I came off a bit offensive, and for that I apoligize. It was my intent to offer constructive criticism, and I think I did that, but it didn't come off as well as I would have liked.

JustDreamin


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PostPosted: Wed Jan 11, 2012 6:39 pm 
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JustDreamin wrote:
Downix wrote:
Well, do remember this is the first time I've looked at a piston based motor. (previous work has been on electrics or turbines) As for being junk steel, depends on the pipe source in my experience. As for round enough, you could use 3" schedule 160, which would be an internal diameter of 2.624, and bore it out. And, you can also get solid iron cores to do the same thing if need be as well, such as here:

http://www.grainger.com/Grainger/Rod-Stock-2KUP9

But, that brings to me to, what hardness would be suitable for such work?


After reading your post and re-reading my post, I'm afraid I came off a bit offensive, and for that I apoligize. It was my intent to offer constructive criticism, and I think I did that, but it didn't come off as well as I would have liked.

JustDreamin

It takes a lot more than that to offend me. No worries. I know that my inner thought process is not always transparent. My main thought is an open design, that is you *can* make it on your own, with off the shelf parts available as well. Things like the crank case may be hard set as a custom bit, mind you, but can work to keep as much open as possible.


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PostPosted: Wed Jan 11, 2012 7:43 pm 
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Perhaps something like the Crosley COBRA, which was made from stampings and brazed together.

With inexpensive waterjet or laser cutting, you could make a block and head assembly that fit together with tabs and then send the whole thing off to be furnace-brazed.

Some parts would still need to be machined, but if you kept the design simple you could outsource them to a fab shop or hobby machinist.


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PostPosted: Wed Jan 11, 2012 9:48 pm 
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TRX wrote:
Perhaps something like the Crosley COBRA, which was made from stampings and brazed together.

With inexpensive waterjet or laser cutting, you could make a block and head assembly that fit together with tabs and then send the whole thing off to be furnace-brazed.

Some parts would still need to be machined, but if you kept the design simple you could outsource them to a fab shop or hobby machinist.


Never heard of the COBRA before, time to do some research.


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PostPosted: Wed Jan 11, 2012 9:54 pm 
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I remember (very vaguely it was a long time ago and I'm almost as old as Gonzo :shock: ) seeing an engine at the Harrah's auto collection that was constructed with the cylinders bolted to the crankcase and the head tying together the top end so it stayed in alignment. .. rather like an aircooled VW.
Early Cadillac or Lincoln maybe? It was pre WW2 for sure. Not that I saw it before WW2, it was pre WW2!!!
Allison did something similiar in the 40's iirc for the P-51. ..

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PostPosted: Thu Jan 12, 2012 2:10 am 
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Downix wrote:
I think that's what I just said. Still talking about casting the block, mind you.


Indeed you did, that would have involved reading on my part I guess :oops:

I would love to see someone make a fabricated block, Phil Irving's "Tune For Speed" covers that a little bit.


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PostPosted: Thu Jan 12, 2012 3:49 pm 
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Alright, got a lot of details on the CoBra, including finding an actual engine to study in person. I'm modifying the design slightly to allow for either fabrication method to be used. My thinking is, options are good.


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