Arias forged aluminum 96mm 11:1 pistons bored into a clean pair of 920 cylinders. The pistons are a full 96mm yielding a finished bore size of 96.1mm netting you 1004cc -- . bigger than the Virago thousand or the elusive TR1 (both at 981cc). They protrude into the combustion chamber raising the compression ratio to 11:1 (TR1 -- 8.3:1, Virago thousand -- 7.9:1). A potent combination. With no other changes, you will feel more urge throughout the power band, especially on the low end. With the engine torn down, it would be an excellent opportunity to add sports cams and springs, a free-flowing exhaust, and perhaps some flat-slide carbs.
The pistons are relieved for the most radical cams and over-size valves -- there shall be no collisions at TDC on the exhaust stroke.
What you get: two bored and honed 920 cylinders, the pistons to fit them, a set of rings for each (pre-gapped for the cylinders that they are delivered in), a pair of piston pins, and four clips. A complete gasket set. The case and cylinder locating dowels that get chewed up when you try to take everything apart, too. All the dowel bores have been cleaned and dressed to a nice slip fit, and the threaded holes chased. All the parts have been collected and the machine work done; it should not be necessary to buy anything additional (except the performance goodies I mentioned). Keep in mind that I had to have these made to spec (and have an exclusive) -- the engines are thirty years old. Not even over-sizes are available from Yamaha. The other piston companies dropped the Virago pistons (the few that made any) long ago. Speaking of machine work: the going rate for big bores (anything over .040""/1mm) is ninety per hole. This kit represents .160"/4mm over; a lot of shops would refuse the work. At four hundred for the pistons, a hundred for gaskets, and two hundred for machine work, you are essentially getting the barrels for free.
Everything has been cleaned and dowsed in a light machine oil.. I recommend washing everything with dish detergent and water, drying thoroughly and assembling dry except for a dab of assembly oil on the pins and the leading skirts.. The rings and bores will mate up within a few revolutions and all will be lubricated within a minute of start-up.. Dry assembly does NOT apply to the valve train and cam and followers; dowse everything in that cavity until it runs out the windows. . Also, on Gen I bikes (of which the 920 was one), the oil passage holes in the banjo bolts were sometimes just barely slits, and a lot of early bikes seized their front cams.. Make sure that all holes are full and round.. And on the drive side cam bush -- replace it with a 6205 bearing.. If the bearing is sealed, pop out the seal on the cam sprocket side.. It makes a whirring sound, but it frees up a little power and it'll never seize.
Megacycle (the last mfg with a full line of XV cams) insists that you always use an engine oil that contains zinc on performance bikes.. Motul and Red Line fit the bill. . This leaves you with your original cylinders and pistons.. You can always go back.. Or send me a snap of the top of the cylinders, and maybe I'll make you a offer on them.
This would not be complete without a mention of the Gen I starter setup.. If you need a motor get one with four replaceable brushes; Rick's comes to mind.. Regardless, drill through the case and into the ring gear (be careful how far you go) in at least two places and install set screws.. This will keep the ring/sun gear from just spinning in the housing without turning the engine.. I've had the best luck with the fix-it kit that tightens the spring clips and mounts an o-ring on the shaft.. If idler gear #2 wears out, just turn it over -- there's plenty of room in the case.. Run a heavy gauge dedicated ground lead from the battery to one of the starter motor mounts.. Keep your carbs in tune. . . .
I tried to get a glossy black finish on the barrels with exposed fin edges.. It's a lot of work involving masking, acetone and steel wool, a wire wheel, q-tips, and a hand torch (heat-proof paint doesn't "set" until it's been over about three hundred degrees for a few minutes).. As they are now they'll look fine mounted up; you're free to re-shoot if you think necessary.. And finally: I buy a lot of cylinders.. Ones with bent or broken fins, or marred-up gasket surfaces get thrown away -- too much time and expense to fix.. I never find any evidence of head gasket leaks, but the cam chain tunnel o-ring weeps if you let the torque slip.. Cam tensioner caps leak like crazy: I have to scrub like mad before I can blast, then wire wheel them.. It takes a whole can of paint to do a pair, then exposing the fin tips. . . . Shoot clear over that . . . . A lot of work. . . .
NOTE: the cam tensioner caps in a couple of pictures do NOT come with.. I just bolted some in place to save on masking those surfaces.. Also, the cylinders are not pure black as in the first picture, but high-lighted as in the last. One last thing -- if you have any interest in performance pistons (high compression and/or big bore) for other model XV's msg me and I'll see what I can come up with.