B. N. G. Spagthorpe:
Viking

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  • The Viking was a trick little unit made way back when(forties? fifties?) when Spag was trying to make a go of it in racing. The first iteration (the Springer) was a boxer twin, very similar to Max Friz’s famous design, but with an overhead “point cam” (see below for more on the valve train). The problem was that the thing had no ground clearance whatsoever. The solution was to curve the cylinder bores, so that the ground clearance was substantially increased:

    ==@== <-Springer motor (front)
    Viking motor (front) -> \=@=/

    This is roughly the idea, except that the bores were gradually curved around a radius, as the pistons were loath to make a sharp-angled turn in the middle of their stroke. The engine also had curved connecting rods to accommodate the stroke.The engine stuck out so far because of its revolutionary (and still unique) overhead cam system. Through the use of clever valve timing and an extraordinarily trick valve linkage, only a single cam lobe was required to drive both overhead valves.

    Just as revolutionary was the hydraulic valve actuation, which used a pressurized stream of oil to power the “waterwheel” which kept the lobe spinning over. One side effect that required some rather brutal engineering fixes was that until the engine’s oil pressure came up to normal, the engine’s valve timing would be more or less random, resulting in some impressive start-up valve damage. The solution was a little hand crank that pressurized the cases before you started the beast, remarkably similar to the system used in new Porsches to pressurize the oil system before the car is started (the cage, however, uses an electric oil pump. Wimps).

    Despite this fix, the engine had a nasty propensity for explosively firing its valves into the pistons when a cylinder would temporarily lose a bit of oil pressure in a corner. The solution was to run even higher oil pressures and change the gaskets and seals regularly. This was feasible because it was a racing engine.

    With just a single overhead lobe, and no pushrod/shaft/chain towers because of the hydraulic system, the head of the engine came to an almost perfect point:

                        /\
                       /()\   <-lobe
                      / XX \  <-complex linkage (not shown due to
     valvestems ->   / \  / \    complexity)
                    |  |   | |
                    |  |===| |
                        =0=  <---piston
                         |
    

    Note that the tip was not truly vertical (it was at about a 70 degree angle to the ground, and this drawing doesn't show the curvature because there was none in the head itself. The bore curve would start about where the cylinder bore disappears.

    The effect of the pointy heads on top of a pair of gently (pundits of the day even said sensuously) curved cylinders was much like a pair of finned Viking horns poking out from beneath the gas tank. Thus, the name.

    The Vik was a moderately successful racer, lightning fast when it worked, but plagued by problems relating to its revolutionary technology. Eventually, it was dumped when Spag finally realized that racing was not where the Spagthorpe name would be made. The machines were raced for another year or two by privateers. Confusing the issue is one old Spag staffer who swears up and down that this machine was tooled for production, and that as many as twenty or thirty machines may have come off the line. However, no modern record of a production Viking has survived, and most motorcycle historians discount this story.

    Ryan Cousinetc.|1982 Yamaha Vision XZ550 -Black Pig of Inverness|Live to Ride
    KotRB          |1958 AJS 500 C/S -King Rat                      |to Work to
    DoD# 0863      |I'd be a squid if I could afford the bike...    |Flame to
    ryan.cousineau@compdyn.questor.org  |   Vancouver, BC, Canada   |Live . . .
    From: Ryan Cousineau (ryan_cousineau@compdyn.questor.org)
    Subject: Spagthorpe Viking
    Newsgroups: rec.motorcycles
    Date: 1993-04-20 16:46:56 PST
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