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Old Mar 09, 2009, 05:41 PM
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whozit engine ?



I wonder if this one comes directly from the OS factory and I should be curious to drop a glance inside...

http://cgi.ebay.co.uk/OS-Max-80-TWIN...742.m153.l1262
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Old Mar 09, 2009, 09:33 PM
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I wonder how the conrods are missing each other???

I guess you could have one rod with the bushing in the middle but not having the pistons move opposite of one another would kind of defeat the purpose of having a twin.
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Old Mar 09, 2009, 10:17 PM
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I doubt that runs. I might be that only one cylinder works.

Here's one of these types of twins that actually runs.

HP 21 VT Twin Testrun (0 min 53 sec)
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Old Mar 09, 2009, 10:36 PM
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That can't work, unless it is a single with a fake cylinder on one side.
Fora two cycle engine, both pistons have to travel to TDC and BDC in unison in order to work. So that engine has both pistons 180 degrees out of phase with each other. Thus it cannot suck air fuel in, nor pump air fuel into the combustion chambers with any efficiency.
The cylinders would need to be offset so that each has its own separate rod journal so the engines can be set to 180 degrees apart.
My first thought was a photoshopped engine pic.
But then one could simply reverse one engine half from the other since both ends bolt on.
But like you mentioned, one really needs to see what they did inside.
They possibly could have machined a new special crank with offset rods too. So that both pistons moved in sync for BDC and TDC.
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Old Mar 09, 2009, 10:45 PM
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The crank intake timing would be sort of problematic it seems to me (although I haven't taken the time to diagram it out). With the front housing being rotated 90 from "normal" no matter what cylinder you are looking at, the timing is probably going to be out of whack for both.
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Old Mar 09, 2009, 11:00 PM
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Same fellow made a twin VT61. I never heard of the VT61 before.

HP 61 VT Flat Twin -Testrun (0 min 50 sec)
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Old Mar 10, 2009, 12:15 AM
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Quote:
Originally Posted by Kmot
Same fellow made a twin VT61. I never heard of the VT61 before.

http://www.youtube.com/watch?v=eR0ky...eature=channel
It sounds as if both of those twins are firing at the same time, unlike, say, an O.S. 160 or 300
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Old Mar 10, 2009, 09:52 AM
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I have VT.61 in my collection. They are rather unusual. I don't think Mecoa ever produced this size. I think I asked Randy once, maybe the tooling was lost or damaged.

I've gotten into model engineering and on my list of twin projects is an inline two stroke using Norvel .061 pistons/liners and an inline twin using OS FS-30 or 40 parts. I have many things to build before I get to that. The Solidworks models aren't even started yet. Probably next winter at the earliest.

Greg
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Old Mar 10, 2009, 10:49 AM
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[IMG]OS 48 block casting[/IMG] This was modelled with Catia. I hear that Solidworks is similar.
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Old Mar 10, 2009, 10:56 AM
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Originally Posted by 706jim
[IMG]OS 48 block casting[/IMG] This was modelled with Catia. I hear that Solidworks is similar.
Looks good what are you doing with it? I'm working on drawing the FS-30 head. I needed to check some internal clearances prior to modification.

Greg
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Old Mar 10, 2009, 11:13 AM
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Looks good what are you doing with it? I'm working on drawing the FS-30 head. I needed to check some internal clearances prior to modification.

Greg
I own an O.S. FS 40 marine engine that I've installed in a Dumas model boat. A friend of mine really liked it and wanted to buy one. However, the are now out of production, so I figured that maybe I could machine the fins off and install some sort of water jacket for him. This was as far as I got! There is very limited space for the jacket due to the pushrods between the crankcase and the head. I have the use of a machining center and will eventually make something that screws together. (Have patience Dan!!)
The whole thing was reverse engineered using a protractor, scale and vernier caliper, so is not "true" to the original O.S. design dimensions.

Fun exercise though.
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Old Mar 10, 2009, 11:48 AM
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The twin VT61 uses a 4 cycle engine. He only needed to adjust the camshafts to get both cylinders to work. The piston on the downstroke sucks in the air fuel mixture when the intake valve opens.

A 2 cycle engine uses the crankcase bottom end to suck air fuel in and push air fuel into the combustion chamber. If you have one piston going out and the other piston coming in at the same time, then you don't have the engine acting as a 2 cycle engine anymore. So he must have something clever for the crankshaft inside in order to get it to work.

But then who knows, the thing might actually run with the two pistons 180 degrees apart on a single common rod journal. I remember lots of engineers saying things won't work, and a modeller builds it and it does. Sort of like the Bumble bee can't fly myth.
But I suspect if it runs OK, then the builder has a fancy dual rod journal crankshaft inside.
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Old Mar 10, 2009, 12:08 PM
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That's how I do my reverse engineering. I had a chance to buy two of the FS-40 marines not too long ago. I shouldn't have passed them up. I'm not a boat guy, but do collect some engines. I have the itch to try a boat. I actually have a couple hydros I need to get rid of. I got them from a guy with a pile of airplane stuff. I think the old FS-40 has more room around the cylinder to fit a water jacket, compared to an FS-40S or FS-48.

My project list is very long. It includes a marine diesel conversion of an FS-120. I was thinking it would make for a mild powerplant in a 48"(?) deep vee I have sitting around.

Here's a Norvel .074.

Greg
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Old Mar 10, 2009, 12:15 PM
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I have both a VT21 and a VT49 in my collection. I had never known of the VT61. Now I must have one!
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Old Mar 10, 2009, 12:31 PM
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Quote:
Originally Posted by gkamysz
I have VT.61 in my collection. They are rather unusual. I don't think Mecoa ever produced this size. I think I asked Randy once, maybe the tooling was lost or damaged.

I've gotten into model engineering and on my list of twin projects is an inline two stroke using Norvel .061 pistons/liners and an inline twin using OS FS-30 or 40 parts. I have many things to build before I get to that. The Solidworks models aren't even started yet. Probably next winter at the earliest.

Greg

I had, ran and flew the VT.49 plain head. Nice engine after one siliconed the shank of the carb to seal it up.

Easy starting, wonderful idle and transition. Power wasn't bad, but it was heavy.

I was ticked when I found out that there was a .61, but that it wasn't sold much here in the US.

Still, the .49 was an interesting and novel engine. It used to gather a crowd at the flying field because of the loud whirr of the gears driving the cylinder head's rotary valve.


Ed Cregger
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