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  1. mayhugh1

    270 Offy

    Thanks, Reducing the compression ratio will reduce the combustion pressures and take some of the stress off the head gasket. This engine has some history with head gasket issues, and since I'm not building one to run on a dynamometer I thought I'd take some easy steps to make life a little...
  2. mayhugh1

    270 Offy

    The two lathe tools shown in one of the photos in my previous post were used to turn the crankshaft journals. Both of them use sharp carbide grooving inserts that were shop modified. The gold colored insert is .120" wide, and in order to reduce chatter its center was notched out. The outer sides...
  3. mayhugh1

    270 Offy

    I came up with 9.7 for the quarter scale Offy's stock compression ratio which agrees favorably with the 9.5 specified in the manual. I couldn't find a head gasket in the drawings and so one wasn't included in my calculation, but Ron has mentioned solving leaks using a gasket and sealant. The...
  4. mayhugh1

    270 Offy

    No, I wasn't aware of those Scott. Thanks! - Terry
  5. mayhugh1

    270 Offy

    After machining a bottom cover plate, the individual tanks were leak-checked. I don't yet have the proper size o-rings for the bottoms of the tanks, and so the o-ring grooves were temporarily filled with Viton cord. A machined slot across the cover's top surface between the two tanks will...
  6. mayhugh1

    Gas tank

    clever idea! ... simple, effective, and free.
  7. mayhugh1

    270 Offy

    . . . 'a little over 20 hours' . . .
  8. mayhugh1

    270 Offy

    Propclock, What you see in the photos is directly off the machine. No manual clean-up. It was, in fact, the reason for the long machining times and the inadequate computing resources in the computer that did the tool path calculations. I usually set the CAM up to leave no more than a .0003"...
  9. mayhugh1

    270 Offy

    The first machining operations on the combo tank were on its complex underside where I was able to reuse some of the CAD/CAM developed for my Knucklehead's fuel pump enclosure. Even though the two inch long 3/8" diameter end mill used for the tanks' deep pocketing operations was pretty noisy...
  10. mayhugh1

    270 Offy

    Our 100+ degree days have been lasting well into the evenings during the past several weeks, and so I've been in our house working on a design for the Offy's fuel and oil tanks. I so much wanted to do something novel with them and ended up wasting a lot of time on a faux bell housing and gear...
  11. mayhugh1

    270 Offy

    https://www.ebay.com/p/1524590838?iid=133421509412 $329
  12. mayhugh1

    270 Offy

    I found this item on Ebay. I've seen them come up before, but they're usually sold before I can post a URL. Evidently, a die cast manufacturer (GMP) started producing and selling these 1/6 replicas of the Offy 270 in 2002. Production continued through 2010 and although I've never seen one, there...
  13. mayhugh1

    270 Offy

    The carburetor was finished up by color anodizing its bowl to match the engine's red magneto. Since my total knowledge of DIY anodizing comes from a couple Youtube videos and Dave's comments above, I was prepared for the possibility that I might end up machining a whole new part. Basically, the...
  14. mayhugh1

    270 Offy

    Thanks for the advice Dave. I actually never bead blasted the bowl that I'm planning to anodize. It was polished, but not buffed to a high luster like the air horns were. Unfortunately, I had already Loctite'd the brass inlet/outlet tubes, and since I don't know how they'll affect the process, I...
  15. mayhugh1

    270 Offy

    The throttle barrels were machined from 5/16" drill rod, and their bores inside the aluminum carb body were lapped with Timesaver for a smooth sliding fit. Grub screws in the carb body ride in grooves machined into the barrels and retain them inside the bores during rotation. The barrels'...
  16. mayhugh1

    270 Offy

    Each needle valve assembly includes a jet with a .022" dia. orifice and a .030" diameter adjustable needle. In addition to metering fuel into the engine, the four assemblies also secure the carb bowl to the carb body. The tops of the jets are sealed to the carb body by a Teflon bowl gasket, and...
  17. mayhugh1

    (CAD) 28 Cyl P&W R-4360

    Have you seen this: https://www.homemodelenginemachinist.com/threads/pratt-r-4360-build.23097/#post-248502 The first post has a link to the builder's website that may be of interest. Terry
  18. mayhugh1

    270 Offy

    Construction of the Offy's induction system began with the machining of its two main components - the quad carb body and the fuel bowl. Just after machining the carb body, I became concerned that the throttle barrels were probably uncovering the air bleed passages a little too early. So, I...
  19. mayhugh1

    270 Offy

    Thanks all for your comments. I'd never heard of color tuning before. It sounds like what Ron did. - Terry
  20. mayhugh1

    270 Offy

    Nice idea. I just added them to the design. As you say, they certainly can't hurt, and they'll make the induction system look more techie. - thanks. - Terry
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