Building Your XV Engine

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Now then. Whatever you receive is slathered in one or more lubricants, and with the exception of the interior of heads, must be cleaned. If you got piston kits withoiut cylinders you need to know that the widest point on the pistons is at the bottom across the skirts (front-to-back); boring clearnce for the 96mm (1004cc) is .0030" (0.076mm). For the 99mm (1065cc), you need .0031" (0.079mm). This is a lot of clearance for pistons these sizes. They are forged, not cast. Do not go bigger; the goal is to hit these values as closely as possible. Because cold clearance is so great, these pistons will be noisy; scary noisy; until they reach operating temperature. Then they will be no worse than stock. Cylinders, pistons and rings should be scrubbed with dish detergent and water and carefully rinsed and dried. Apply a fine lubricant like WD40 to the sleeves. Let it run out and wipe out the excess. What remains in the cross-hatching should be adequate to prevent corrosion before it all goes together. If you can't assemble within a day or two, box it all up until you're ready. Touch up any exterior scrapes or scratches with high-temp paint and a q-tip. Curing should not be necessary. I clean the dowel bores and chase the threaded holes, but I'm getting old -- double check. The dowels should slip in and out easily by hand. You might even smear a little anti-seize on them. They are locators; they are not meant to be structural. High-temp paint on a gasket surface (other than the head) is not a concern. Yamaha had a "Midnight Virago" in 750cc and 920cc in '83 and the parts were painted by dipping - the engine was black inside and out. Over the years the outside paint flaked off, and the inside dissolved and got dumped out at oil changes. No harm; no foul.

Check the ring-end gap (discudssed elsewhere): with Yamaha pistons it should be .014" to .015" on the top; .015" to .016" on the second, and at least .015" on the oil rails. A thou or two over is okay. From the factory the top two generally sported at least .020". On our Arias pistons - 96mm: .018", then .16"; 99mm: .019", then .016"; then at least .020" on either. A little over is okay. Many big bores fail early because the ring-end gap was not enough for the warmed-up pistons.

Stagger the gaps on assembly - they are wide enough for oil to shoot right up and quench the spark - this is a very frustrating problem to chase down. I have never needed any clamps or tools to drop the barrels over the pistons. Even with the biggest bore, there is still enough taper to pop the rings in with your thumb nails and I always push down the barrels with my chin.

Assemble the barrels dry except for a drop of oil on the leading skirt and in the piston pin bore in the rod. Before we get to this stage, lay the pistons on their sides and slip in the pins. They should slide through and drop out under their own weight, If they don't, dress the bores in the piston, being very careful to clean out any abrasives when you're done. Upon start-up, the first few strokes should have the cylinders mated to the rings, and within a minute enough oil will have splashed up to lubricate everything nicely.

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As for the heads: the more lubricants present, the better. Molybdinum Disulphide grease in the guides and on the valve stems; it'll smoke for a minute while the excess burns out. Special lube from the cam company for the lobes and rockers. The rocker shafts should be slathered in a heavy gear oil. All this will be purged out shortly. You should have a petroleum-based oil for the main engine lubricant. Something light, like a straight thirty. You'll be changing it in 500 to a thousand mile intervals for a while, when you get five on the clock you can go to a pure synthetic if you wish. The cam companies I deal with all want an oil containing zinc for rocker arm motors.

Before I get too far afield - I have worked on many XV engines. There is never a good reason to go into the lower end. Transmission problems can usually be solved by cleaning and adjusting the shift linkage; maybe replacing the shaft seal. If you put the oil filter in backwards, the cams and valve train will wear out very quickly. If you manage to cope with the noise long enough, the rod bearings will smear and start knocking. The mains are fed by splash and only need replacing if you destroy them by trying to prize them off the crankshaft. If you really need to go into the lower end - stop. Break the engine up for parts. There are many non-runners for sale that only need idler gear #2 in the starter assembly. It will be much cheaper to get one of these up than to resurrect an oil-starved engine.