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Scratch Built Radials

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Erik Snyman

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Oct 9, 2019
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Seeing these beautiful radials, reminds me of an engine that was available (or the construction plans, actually) some years ago, known as the HCI or HCL or some-such. I think it was a 7 cylinder design.
I have never seen one or heard of one that was built and operated. Can anyone remember what I am talking about? Are there any out there completed and running?
Erik in Oz.
 

Hot Wings

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f you could make a cam ring and new followers,
Looks like there would only be room (on one plane) for a 3 cyl with mostly stock CG parts. Building a new cam ring would be easy enough (compared to building an engine from parts) but getting it to turn 1/2 crank speed would need a second set of gears - like maybe a planetary set?
 

Hot Wings

Grumpy Cynic
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Seeing these beautiful radials, reminds me of an engine that was available (or the construction plans, actually) some years ago, known as the HCI or HCL or some-such. I think it was a 7 cylinder design.
I have never seen one or heard of one that was built and operated. Can anyone remember what I am talking about? Are there any out there completed and running?
Erik in Oz.
HCI. It was VW barrel/piston and they offered a raw casting kit. Last computer crash (before robust backup system) lost all of my info and I haven't been able to find it on the net in the last decade. There were a few built to running condition but I don't know if any ever flew.


And HBA's own thread

I had considered reproducing the casting kit. That was before the computer crash. Would still consider it if the plans were available.
 

pictsidhe

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the
Looks like there would only be room (on one plane) for a 3 cyl with mostly stock CG parts. Building a new cam ring would be easy enough (compared to building an engine from parts) but getting it to turn 1/2 crank speed would need a second set of gears - like maybe a planetary set?
If the stock cam drive was used, yes, 3 cylinders. But I strongly suspect the crank and rods couldn't be done that tight.
Cam gear is 75mm OD, crank gear 40mm OD. Centres are probably around 52mm apart. Stock cg250 stroke is 65mm. There are tapered small block Briggs vanguard cranks at 66mm. With another 40mm of effective rod length to make that happen, we could squeeze 7 cam gears in. Not sure we have room to get the offset crank gear in then, though. For such problems, I like to cut out paper discs and play with them. If we could arrange it so we used a set of Briggs crank cam gears to run the Honda gears, we'd have all our gears off the shelf.
A cam ring would be far more elegant. KHK has some stock ring gears that may be suitable. Not hardened, so would need careful design and roller followers.
Cam ring speed = 1/ (n-1)
Where n is the number of cylinders. 2/(n-1) (n-1)/2 lobes. That's for a reverse rotation cam ring. It's also possible to do it forward rotation at lower speed. 1/(2(n-1)) with n-1 lobes, I think.

Edit. Oopsie, wrong number of lobes for reverse rotation. Fixed it.
 
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Hot Wings

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Cam ring speed = 1/ (n-1)
Where n is the number of cylinders. 2/(n-1) lobes. That's for a reverse rotation cam ring. It's also possible to do it forward rotation at lower speed. 1/(2(n-1)) with n-1 lobes, I think.
Too many options - IMHO. ;) :rolleyes:

My reason - good or bad - for the simple 1/2 rpm cam drive is to keep everything modular. This might make it possible to use the same parts for any number of cylinders? The reverse rotation cams rings are an elegant solution.
 

pfarber

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Any consideration for electronic valve actuation? Might be a little heavy, but for a low RPM motor could be an option.
 

Sockmonkey

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Apr 24, 2014
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Location
Flint, Mi, USA
Consider that a radial two-stroke that uses a simple crank-mounted blower for scavenging doesn't need to run the fuel through the crankcase, so it can use conventional lubrication. If done with ports for both intake and exhaust, there will be some oil consumption, but it cuts down on the number of parts a lot.
 
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