Valve Adjustment Theory Or Hypothisis?

ReycleBill

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For starters: this is a hypothetical.

We all know that adjusting the valves too tight is a death sentence for any engine but what about deliberately setting the valves loose? What are the short term and long term consequences of loose valves on an XS650?

I know there's more noise, loss of power and loss of top end but what else, if anything, will loose valves cause?

Yes, I've probably got too much time on my hands...
 
I guess it sort of depends on how loose "loose" is ;-). On my oilhead Beemer, some people actually recommend running the valves on the loose side of the tolerances for better low end and valve cooling. I don't think I'd stray from the recommended tolerances, but you could edge to one end. Too loose will make it harder for the followers to follow the cam profile at high RPM, as well as the conditions you mentioned. I figure the factory should know of what they speak, and set mine at about the middle.
 
i've never seen tolerances for valve setting.. the '78 is .006" exhaust and .004" intake.. never seen .006-.008" or anything like that..

also loose valves will open late and close early
 
Honda VTR1000 (Superhawk) and certain other models are set loose from the factory. The VTR sounds like it has junk in the trunk at higher rpm, but its meant that way so if you forget an adjustment interval. Older FZR Yamahas, ie: 600, 1000, didnt like tight valves and if the adjustment period was ignored they valves would hammer into the seats and wreck the head.
 
There is a range though, Yamaha moved the clearances up and down a couple of times on what is the same old engine. They may have tightened the clearance towards the end to quiet it down for the EPA or who ever it was that wanted bikes quieter.
 
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too loose beats the cam and rockers too.... I've played the "too loose" and "too tight" game a few times, with lots of parts in the trash to show for it...
 
A mechanical cam (as opposed to hydraulic) has what is called accelleration ramps. These are gentle ramps right before the cam lobe that takes up the clearance of the adjustment gap. Too loose and the ramps don't work as designed. Too tight and the ramp lifts the valve off the seat breaking the seal early.
 
There is a range though, Yamaha moved the clearances up and down a couple of times on what is the same old engine. They may have tightened the clearance towards the end to quiet it down for the EPA or who ever it was that wanted bikes quieter.

That's what I was thinking. My shop manuals show variations between 0.002"-0.003" for intake, depending on the year, and between 0.004"-0.006" for exhaust. Surprisingly, they varied the exhaust setting at least twice, closing it down to 0.004" for the TXA and XS-B, then back up to 0.006" for the C. I don't know about models after the D.
 
the early specs reflect cam profile changes. they pretty much settled the cam after 76. In general, you should follow whatever year your cam is for clearances, since (aside from decompression levers and the like) nothing changed in the head or valve train otherwise.
 
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