# Half Scale OPV engine



## b.lindsey (Jul 9, 2009)

I had previously posted what I called an Oscillating Piston Valve engine. Though it runs well I always thought it was a bit large so I have been working on a half scale version, albeit with slow progress. Everything but the piston and linkage is now complete and I hope to have it running over the weekend if all goes well. A picture for size comparison with the original is shown below.


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## b.lindsey (Aug 12, 2009)

Well, after a vacation cruising the Alaskan coast, a bout with the flu, a business trip and 5 remakes of the piston, the half scale version of the OPV engine is finished and running well now. I had assembled the parts before the finish/polish work and it ran fine. Once I disassembled it for the finish work and put it all back together...nada, zero, zilch!!! Figuring it was the piston fit I remade the piston...5 times still with no success. Finally after almost giving up I took a file to the flat on the piston to see if that wouold help and eueka!!!. So yet another piston was made with this seemingly insignificant design change and the results were amazing. Actually it runs better than the full size version now so I may have to tinker with "big brother" now to see if the same change will smooth it out more as well. Pictures of both are attached. Video to follow tomorrow.


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## zeeprogrammer (Aug 12, 2009)

Pretty nice!
Bummed there's no build pics.
But pretty nice!
I look forward to the video.
Thanks for posting.


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## b.lindsey (Aug 12, 2009)

Sorry about the lack of build pics Zee. This one sat on the shelf a while partially done and as noted...over the last week or two I was beginning to wonder if it was worth finishing. I though about a recent post which mentioned the Minikin and if i recall,Marv noted some of the problems of small scale engines, lack of power, etc. In that regard it was definitely a learning experience even though the machining is pretty straightforward. Now that its running, I much prefer it in the smaller version.

The project currently on the drawing board is a half scale version of a circa late 1940's early 1059's Briggs and Stratton 6S IC engine. That one will definitely be a build log.

Bill


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## 90LX_Notch (Aug 12, 2009)

Beautiful engine. I love scaled down stuff.


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## b.lindsey (Aug 12, 2009)

Diymania,
Here is some additional info from an earlier post of the full size model. The principle is the same for both sizes.

http://www.homemodelenginemachinist.com/index.php?topic=3382.msg33486#msg33486


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## zeeprogrammer (Aug 12, 2009)

wlindiii  said:
			
		

> ... I was beginning to wonder if it was worth finishing.



Glad you did.

I'll be watching the build log.

Thanks.


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## rake60 (Aug 12, 2009)

wlindiii  said:
			
		

> The project currently on the drawing board is a half scale version of a circa late 1940's early 1059's Briggs and Stratton 6S IC engine. That one will definitely be a build log.



Bill do you mean a model of this Briggs 6S?




I actually sold that one at auction to finance another project. 
Being an small engine collector, I would be very interested in the 
scale model build of one of them.

Rick


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## arnoldb (Aug 13, 2009)

VERY nice little engines Bill, both of them! :bow: (and I like the smaller one just a bit more as well!(
Kind regards, Arnold


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## b.lindsey (Aug 13, 2009)

Rick...Yes thats the one. I bought a non running 6S at a swap meet a year or so back for about $20 with this project in mind. Currently working on the drawings and plan to start construction of the drawn parts soon. The real bear is going to be duplicating the main body casting without using a casting. As an idea of size the shroud (the part with the B&S label in your pic) will be 5.188" high x 3.75" wide. I think it will be a nice size. Unfortunately my engine was missing the gas tank, carb, and air filter. Any idea where I can find these? They don't have to be in great condition even, just intact enough to measure and draw.

Bill


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## rake60 (Aug 13, 2009)

You might find them in a corner of my basement. 

I found a junk tank and carb but no junk air filters.
I do have a good filter that I can loan if you don't 
mind returning it. The tank and carb can be thrown away.






If that will do PM me a mailing address and I will get them
sent out to you.

If you need any copy on the decals I have all of them on
my personal web site. *Briggs Decals and Dates Used*

Rick


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## b.lindsey (Aug 13, 2009)

Here is the video as promised for those that may be interested. The first 4 segments show various angles, and the last one shows it at a somewhat slower speed.

<embed width="448" height="361" type="application/x-shockwave-flash" wmode="transparent" src="http://i257.photobucket.com/player.....com/albums/hh207/wlindiii/OPVHalfScale.flv">

Regards,

Bill


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## Maryak (Aug 13, 2009)

Bill,

Beautiful work. :bow: :bow:

I must admit I haven't quite got the hang of how it works or what controls the supply of air.

Best Regards
Bob


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## zeeprogrammer (Aug 13, 2009)

Maryak  said:
			
		

> I must admit I haven't quite got the hang of how it works or what controls the supply of air.



Whereas I have no idea.
Oscillating Piston Valve hm?
Any pics or drawings that you can direct me to so I can learn how this works?

Very nice!

Thanks.


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## Maryak (Aug 13, 2009)

zeeprogrammer  said:
			
		

> Whereas I have no idea.



I should have said the same ;D

Best Regards
Bob


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## b.lindsey (Aug 13, 2009)

Bob,
The linkage rotates the piston +/- 30 degrees from the centerline. In doing so a flat on the piston begins to aligns itself with the air supply port at top dead center forcing the piston down. At bottom dead center the flat begins to aligh itself with the exhaust port which allows the air to escape as the piston moves back up. These two ports are drilled also at +/- 30 degrees from centerline so as to match the rotation of the piston. The flat on the piston is not wide enough to bridge the entire arc where the two ports enter the cylinder. I had though this was more critical than it turned out to be. In the end I made the flat slightly deeper (and therefore wider) and turned it slightly toward the exhaust port so that air admission lags behind TDC and the flat is aligned or partially aligned with the exhaust port for a longer time in each complete roatation. This apparently releived some of the back pressure on the upstroke of the piston which was causing it not to run. 

Probably not very well said, but hope it will make some sense.


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## Maryak (Aug 13, 2009)

Bill,

Thanks for that, all is revealed :bow: Very ingenious.

Best Regards
Bob


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