I know in the chevy cam in block world when you use a solid lifter cam you have to set lash. If you set the lash tighter then the spec, it makes the cam act larger. If you set it looser then spec, it makes the cam act smaller. Does the same thing apply to overhead cam shim/bucket setups?
Yes. When tightening up the clearances, the cam contacts the lifter sooner, lifts it higher and leaves it later. When loosening the clearances, the converse is true. We're not talking huge differences in measurements, but at 10,000 rpm the added lift/duration adds up. The looser spec makes a noticeable seat of the pants difference, having the rider believe it's the cat's ass in tuning. What's really happening is that the engine runs in a detuned state until it “comes (up) on the cam”, then the kick in the pants feels greater...it's not. You've gone from running a shitty less than potential to running a not so shitty but still less than potential. The “kick” masks the loss.
i wonder though... look at the final drive chain on the countershaft sprocket and rear wheel. When you are on the gas, the top of the chain is tight. All the slack is below. Less tension on the chain (moving axle forward) doesn't change the chain length up top on gas 1 little bit. Tight is tight. Adjusting a timing chain more or less tight, won't affect it's length on the gas. there is just less tension on decel, and too much can (allegedly ) lead to it jumping time (why some say ya need to run manual tensioners, but not knowing how to adjust causes more issues than they solve). I guess you could argue there will be a difference in how the engine reacts at throttle opening, when the engine is going from decel to acell.. and cam timing will change as the timing chain wears and needs more adjustment by the cam chain tensioner.. but i am just guessin.
my bad ! carry on.. was discussing cam chains on KTM talk and it was in my head when i saw this thread.
As lash decreases, you gain duration much quicker than lift. You are only affecting the clearance ramps of the cam lobe. The extra duration isn't always helpful depending on the application. Loose clearances can be rough on valvetrain by abruptly hammering the valve open. Results may vary.
Here's a thread where valve gap/lash is discussed regarding compression, duration, cooling, etc. Several very smart/experienced people provided valuable input. And I went with the middle of the spec. About 20 laps after I built this engine it sucked a valve (valve spring issue, not adjustment related), but the engine ran really well during those 20-ish laps. Regardless of my outcome, the discussion linked is pretty relevant to the current discussion. http://forums.13x.com/index.php?threads/valve-clearance-on-new-valves.247180/
My F4i has always been faster then it should be once I learned how to ride and could actually gauge it compared to other bikes. Turns out I was setting lash way tight. Killed the valves around 80,000 miles, they were pizza cutter sharp. I had new valves put in, and started setting lash correctly. Now its for sure slower. My guess was the lash made the cam bigger giving me that little bit extra.
because the valve wore into the seat? I would think refurbing the whole head would have been in order at that point.
Sometimes loser valve lash shows power on a dyno. Not just a seat of the pants as described. Of course there is a limit to that.
