Two Five Hundreds?

The valve geometry of the XV's is very close to that of the SR/TT/XT500s. The rocker ratio is similar -- XV's: 1.347:1; 500's: 1.378:1 intake, 1.373:1 exhaust. The intake valve is the same part number (920 and up), and the exhaust will fit: I've run over-size exhausts meant for the XT on my R. The inner and outervalve springs have the same stock part numbers. The guides, seals, retainers, and keepers are different - accessory valve spring kits come with retainers and keepers; I can see no reason not to sub them out in a pinch. Both series thrive on the same cam timing and lift. Two carbs set up for 500s can be bolted onto an XV and run fine with only a slight richening on the rear. The 500 stroke is longer and the bore narrower: it can't be spun quite as tightly. Both will tolerate 11:1 compression and even 12:1 (maybe 13:1) if you can crank them fast enough against the pressure. Both had problems getting enough high pressure oil into the rocker assemblies. This is interesting on a couple of counts. The XV cam-drive gear/sprocket off the crank was under tremendous pressure, yet made do with a sintered bronze bush fed by splash. I have never seen one showing the slightest wear. Yet the rockers were cast iron pivoting on hardened shafts; with the shafts showing significant wear on any high-mileage bike. Early XV's sometimes seized their front cams; the 500 cams rode on ball bearings.

More to come . . .

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