Case Work on Viragos

Have It Done Right

This one makes me a little nervous as it involves the back-and-forth shipping of empty cases: bulky and fragile. Be sure to empty all fittings and just send in the basre aluminum with the cast-in iron parts. Bolt them securely together. Lay multiple layers of bubble wrap around them. Fill with styrofoam "peanuts" or expanding foam. Anything that must be removed or scraped off on our end will incur more costs to you -- if you expect to get them back.

What we'll do:

Chemical dip (unless you ask us to skip it) to strip all grease and dirt. Blasting with several grades of beads, ending with walnut shells. All oil passages will be blocked at this stage. Optionally, we'll powder-coat black or silver inside; your choice outside. Your main bearing bores will be hard chromed down to 90mm ID and the 6308 bearings of your choice will be seated. Bearings that have oiling channels and oil holes could have passages bored into the transmission feed lines in order to make sure that there is no starvation problems as stock these bearings are fed by splash. Case spigots bored to appropriate girth for your application. We'll look into a maximum bore cut with snug-fit aluminum rings for smaller sizes included. All potential obstacles to long stroke cranks will be fly cut off; all iffy protrusions. New dowels for oil passages and a plugged tap hole for those that want to run an oil cooler from near the pressure release, rather than off the filter cover.

That's all that comes to mind at the moment. No prices set. Reckon on $65 each way on shipping. I must get quotes on plating and powder coating and prices on various bearings. All of these procedures take place elsewhere. Before you ask, do NOT ship complete engines for us to build. This location is not zoned for it. And we can't afford to farm it out. Shipping and transportation add up and no matter how good of friends we are with third parties, they won't work for free.

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After many many hours of turnig cranks and watching clear space I realized a few things. In order to gain ground clearance without making the engine unacceptably tall, Yamaha mounted the crank high and ran rather short rods. As the crank moves toward BDC the rods are canted almost parallel to the sleeve bottom. They tug the pistons out of the center of the bore and into contact with the sleeve. Then they approaches BDC and straighten the angle of attack more to the bore center. For a few degrees either side of BDC the piston sits motionless then must accelerate up to where it again sits still at TDC. Stroking the beast would necessitate shorter rods and more severe rod/piston angles; more time motionless at TDC and BDC. The car tuners tell us that a low rod length - stroke ratio is a good thing for acceleration. After considerable thought and measurements, I hazard that the maximum reasonable stroke is 81mm with 3mm shorter rods with the bolts coming in from the top and into blind holes in the caps, 6mm longer sleeves, and considerable skimming of the flyweights. Reckon on $2000 plus for stroked and balanced crank, rod and main bearings, CP-Carrillo rods, a blue-printed oil pump (exchange), and a K&N oil filter.

Bore? The cam drive gears spin on rods lubricated by the oil scraped off the cylinder wall by the rings on the down stroke. Really broad (and longer) sleeves would block this flow. The studs are perilously close to the spigot holes in the case. I hazard that 105mm is the safe limit: it's a popular bore size with vintage racers in OZ. To bore thousand or eleven cylinders (exchange) to accept larger sleeves, commissioning a pair of these sleeves, pressing them into the cylinders, opening up the passages in the cases, acquiring oversize head gaskets, and o-ringing the cylinders would likely exceed $2000.

It would be a good idea to install an oil cooler (exchange on the oil filter cap); about $200. Note that I haven't touched on cams, carbs, pipes, or really anything else. What do you get for your (at least) $4000? 1403cc or 85.6 cubic inches.

To make it powerful, you are looking at cams and springs (exchange), rockers, valves, head-work (exchange), ignition, carbs, and pipes. Reckon on another $5000. What do you get for $8925 plus shipping and the effort or expense of the work involved? I'm considering an engine exchange: an additional $1000 and you pay the freight both ways. First consider more modern running gear: 'upside-down' forks, four live piston calipers all around, wider rear tire, whatever you can think of. Figure on spending maybe $4000 on this. Now you have a bike that can smoke the tire or wheelie in the first three gears. A bike that can run a quarter mile in the elevens. A bike that can't be beat out of the hole. A bike that can pull alongside a four cylinder (or ANY air-cooled twin), roll on the throttle and not get caught. Tons of fun.

For those of you that have discovered Project Silver Back on another of my sites, this configuration is the one likely that I'll use.