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Post by madmax on Nov 19, 2014 15:40:52 GMT -5
I've just found this guys website, don't know much about him (Howard) but hopefully he's picking up where the late Tony Hall of Halco left off. Anyhow - this make for interesting reading www.smedspeed.co.uk/tech.html The theory behind rephasing is fascinating but of more immediate interest to me is the paragraph on valve clearances, it makes sense so is there a but? Cheers all. Max
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Post by weekendrider on Nov 27, 2014 11:05:58 GMT -5
Hey Max, Thanks for posting the link. And I have the same thoughts on the part about valve clearance. Not only for the XS, but another brand I have. Common advice is to open the clearance up for it also.
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Post by richard on Nov 30, 2014 18:22:20 GMT -5
That is interesting. I especially like articles with numbers like that because it gives me some hard evidence and numbers I can experiment with on paper. I have a 71 XS1B and two later XS650s. I do see the advantage of tight valve clearances, but it is always a trade off in a configurations like the XS650, because the other end of the rockers/tappets ride on the cam lobe which theoretically is coated with 3 to 4 thousandths of oil. From my way of thinking if you close the clearance between the rocker and the cam lobe you lessen the space for that film of oil. Now mind you, I by no means consider this the last word, however it is something to think about. There is a saying that is probably older than me that "It is better to hear your tappets than not here them at all". What I've found, and I have experimented a lot, is that tight valves show up as an occasional miss at idle, which on an XS650 usually kills the engine. On an XS1 that means a restart from neutral at a stop light. I hate that, so as a habit I set them to spec, but a little heavy feel on the feeler gauge.
I'm still undecided on rephrasing for all the same reason he listed in the math of his article. I'm not 100 percent sure on this, but it seems like dispersing the mass of the two piston, the weight of the rods and pins by 277 or 83 would decrease the low end torque off idle. It sure would make a world of difference in vibration and mid range though. In California there is a lot of stop and go and idling through traffic. The vibration on my xs650s really doesn't bother me on the short 100-200 mile trips I make 60 mph.
I kind of wonder if in rephrasing since your splitting the vertical mass inertia of the pistons, rods, pins and crank would it really work out to splitting the vibration by half? I've read some opinions from guys that say it makes the bike feel buzzy. I don't know, it's not like there are a lot of rephases around to test ride.
I have no opinions on synthetic oil in a motorcycle, however I know oil does make a difference on how my clutch acts under load.
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