running cylinders off rear location of full case?

Discussion in 'Half VW' started by Rob40, May 10, 2017.

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  1. May 10, 2017 #1

    Rob40

    Rob40

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    I know the 1/2 option can be with a full case or cut, but if I ran a full case, and ran the cylinders off the rear portion instead of the traditional front half, I would conceivably have two bearings working in my favor forward of the pistons at work and before the prop flange.

    The application would be within a fully enclosed cowling that would see aero benefits due to the rearward cylinder location as well as the much narrower forward portion of the engine yielding an effective prop extension without a real prop extension.

    Yes, I know of the rear exhaust argument but with proper ducting (not baffling but actual sculpted ducting) the cooling of the exhaust area of the head can be properly managed. So assuming the cooling solved, are there any reasons why one can't run cylinders off the back half of the case instead of the front?

    And now much extra weight does a full case option really cost after engine mount?
     
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  2. May 10, 2017 #2

    Autodidact

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    What sort of crankshaft would you be using? For example, a stock crank would mean having two unused crank throws, and really no more stiffness than the normal configuration for a 1/2 Vdub.
     
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  3. May 10, 2017 #3

    Aerowerx

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    Wouldn't it be the same as a full case half VW, which uses the front two cylinders?

    IIRC a full length crank is used.

    I'm by no means an engine expert, but I don't see why Rob40's idea won't work.
     
  4. May 10, 2017 #4

    cheapracer

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    Can you use the 'front heads' on the rear cylinders?

    Would seem ideal on a full case.

    I'm not that familiar with a half VW, would a 1300 4 cylinder be that much heavier than a full case big twin?
     
  5. May 10, 2017 #5

    Autodidact

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    All full case 1/2 VWs use a cut crankshaft. If you look on the Great Plains website, weight is given as 87 lb with an *, and the *'s note says that the full case engine weighs an additional 5lb. The half crank coupled with the full case is also why all full case engines have a distributor ignition.
     
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  6. May 10, 2017 #6

    revkev6

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    Not without a reverse cut cam. The valves are reversed from front to rear.

    No reason you have to cut the crank but it will result in significantly heavier engine. Do they also cut the cam for further savings?
     
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  7. May 10, 2017 #7

    Pops

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    Not much weight saving from the 116 lb short block VW engine. Just saving the weight of 2 pistons, jugs, rods and lifters. Will have to use the full crank and full cam.

    Dan
     
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  8. May 10, 2017 #8

    Rob40

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    Thank you, Dan. That's what I was wondering as well. An earlier response said everything inside is cut but then I didn't understand how any accessory on the back would work in that scenario. The whole internal kit would have to remain, so if anything, the penalty would be the weight for any of the other benefits I was thinking of. So it could be done, just not reasonably when pit against other needs.

    Thank you all for answering this one.
     
  9. May 10, 2017 #9

    Dan Thomas

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    With the full crank you'd also have to close off the rod oiling holes in the unused crank journals. And not by welding, I'd think: too many stresses introduced in already heavily stressed areas.
     
  10. May 10, 2017 #10

    Dana

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    I'm thinking leaving the full crank in might make for some funny vibrations. But you'd have to keep it, aren't the timing gears in the front?

    Dana
     
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  11. May 10, 2017 #11

    Dan Thomas

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    Yup, along with the oil pump.
     
  12. May 10, 2017 #12

    cheapracer

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    Got ya, thanks for the reply.
     
  13. May 11, 2017 #13

    revkev6

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    Pretty sure you would have to run some sort of bob weight to make balance anyway... so this covers the rod oiling. This how it works when you run funny combinations on a v8 anyway... some giys do this in salt flats racing for class specific engine sizes.
     
  14. May 11, 2017 #14

    cheapracer

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    One of the beautys of horizontally opposed engines is the balance, take the pistons and rods out of both sides and doesn't matter, you still have the balance.

    As for the big end oil galleries, tap the hole, fit an allen screw plug with lots of Loctite.
     
  15. May 11, 2017 #15

    Aerowerx

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    Well, take a look at the Great Plains web sight.

    Capture.JPG
    This is a snip from their web page, of their full-case half VW. Note that the cylinders are at the rear and the prop is at the front! You can also clearly see the plates covering the holes where the front heads would be.

    This could not be done with a cut crank, could it?
     
  16. May 11, 2017 #16

    Pops

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    The pulley end of the engine is considered the front of the aero-VW engine but the rear of an auto-VW engine. That is the normal 1/2 VW engine. I know it's confusing .
     
  17. May 11, 2017 #17

    Aerowerx

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    Whatever. I was going by the prop with spinner being at the front.

    On their full VW engines, Great Plains has the option of mounting the prop on either end, with the flywheel drive being a little lighter. It looks like that is what their full-case 1/2 VW is based on. Still, they could not have cut the crank
     
  18. May 11, 2017 #18

    Aerowerx

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    Whatever. I was going by the prop being at the front.

    On their full VW engines, Great Plains has the option of mounting the prop on either end, with the flywheel drive being a little lighter. It looks like that is what their full-case 1/2 VW is based on. Still, they could not have cut the crank.

    By the way, they have a kit of parts for the full case 1/2 VW.

    Don't recall if it was them, or someone else, but there was a mention of being able to add the missing cylinders back at a later time. That would be more difficult if the crank were cut. And if the crank were cut, how would it be supported in the middle?
     
  19. May 11, 2017 #19

    Autodidact

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    That orange thing is not a propeller, that's the engine stand.
     
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  20. May 11, 2017 #20

    cheapracer

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    Pops, whats the lightest practical VW 4 cylinder you come across, not some special big money item, just one that's had attention paid to it.

    And/Or would you know the weight of a complete long engine (stock 1600, or 1850), no accessories please?
     

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