What was the question ?
Seriously , I suffer from the short fuse big bang and done syndrome . I deserve all that I get from this crowd and then some . Ar we still talking about this ?
The following was posted elsewhere and because I'm lazy ....
…Shell and John formed Shell Racing Specialties and started to manufacture all the parts necessary for a complete racing motorcycle. The race equipment was sold to Yamaha in bulk to be packaged under their logo and distributed to their dealer network.
From early on, Shell would butt heads with the Japanese engineers. The newly designed Yamaha twins kept blowing oil out the breather. The specs called for 3000cc to be put in the crankcase. Shell told them right up front it was too much and they needed to put in 2500cc.The engineers would try all sorts of baffles and orifices intended to reduce the oil loss, but to no avail. Shell continued to put in his recommended amount until finally the factory engineers followed suit. You can look at the imprint on top of the cases and see the reduction in oil requirements over the years until it settles on the amount advised by Shell.
Many thanks to the 'cafe once again
http://thexscafedotcom.wordpress.com/ in case you haven't been there .
I’ll tell you exactly why your XS650 is blowing oil, and it is very simply cured. It has absolutely nothing to do with blow-by going past your piston rings. In an upright twin where both pistons descend together, the pistons build up tremendous pressure in the crankcase. There has to be a vent to relieve this pressure, or it would blow out the crankcase seals. The crankcase breather is this vent; that is its only purpose. There is no valve in the breather of an XS650; it’s just an opening with a partial baffle plate. If you fill any XS650 to the high mark on the dipstick, it will quickly blow a half a quart of oil out of the breather pipes. We (dealer shop) had an aggressive campaign to replace or modify the incorrect dipstick so we didn't have to listen to the owners complaints . In some cases we just did it without telling the owner . "But the owners manual says ..." . I had a service bulletin dated two years newer that those guys wouldn't even read if stuffed in their face ! Same with tire pressure . "But the owners manual says ..." . Who knows more about a current Dunlop 404 , the guy that translated the original Japanese 30 years ago or the guy that designed the Dunlop tire two years ago ? That's another story entirely but serves to tell the tale . Never fill an XS650 higher than halfway between the low and high mark with an unmodified dipstick . I'll continue to search for the bulletin that actually gives the dimension from the face of the screw cap to the full mark . I have owned XS650s for over 30 years, and I currently have two. The condition can be even further aggravated by the following modifications, and you can be sure over that in 30 years there have been changes to your bike.
Part substitutions may have been made from other model XS650s, which, while they fit, are wrong. There are over 40 versions of the XS650.
Prior to mid-1975 the dipstick called for too much oil and a bulletin was issued to recalibrate these dipsticks. Your bike may have a dipstick (or an engine) from an earlier bike.
Note that your bike does not call for 20W-50; it calls for 20W-40, which is available at truck stops and auto stores and Wall-Mart . Shell Rotella is a good 20W-40 without the additives found in modern automobile motor oils.
Discussed elsewhere is a modification for the early twin outlet breather to be fitted with vacuum brake booster valves that either end in the stock airbox , over individual foam filters or are plumbed in addition to a valve in the exhaust which again is a topic for another discussion .
anecdotal:
It's equally surprising just how much it will take to kill an XS as well as how little . I received one for diag one day and it's back half was covered with oil . I had the correct dipstick and oil level but the airbox was fouled and so were both sparkplugs . After checking the valves , timing , float bowl fuel level and pilot circuits I moved on to the exhaust . The pipes were full of sunflower husks . Hours later I'm again starting the bike and with timing spot on , carbs sync'd and mixture screws , yeah mixture screws one 2 1/4 out the other closer to 4 . hummm . Cam chain ? No , it was actually within a few degrees of correct . Hop a tooth ? No , degree wheel and a lobe center check was normal . Had another XS (mine ) standing by so I swapped carbs . On mine the mixture screws were 2 1/4 on both , my carbs on the victim were again 2 1/4 and closer to 4 . Cold compression test on the bike showed the cylinder with the fat mixture screw to be near 40psi higher but when cold it near 40psi lower .
Out the engine came . Anyone care to hazard a guess as to what I found ? .........
It seems that the bike had been left with a significant amount of fuel in the offending cylinder as well as a bit of moisture . Anyone that has disassembled a rust bucket has seen this . The rust , fuel and aluminum oxide had gummed up the rings on the left cylinder (the one needing a rich mixture and had goofy hot , cold compression) to the point where nearly a third of all three rings circumference was trapped in the grooves . Nothing more than a hone and ring replacement was required .
Some of these bikes are approaching 40 years old . Hard telling what you might find . If you haven't been there the whole time it occasionally helps to go back to basic diag and a bit of head scratching and commiserating with us senile old farts . I learned a long time ago not to jump to conclusions or fix the symptom and not bother with the cause .
Maybe this helps maybe it doesn't . You could guess why I take the time to share these tales but most would get it wrong .
~kop
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