valves and valve clearances in general

I was reading coco's post on checking valves and I started wondering what effects valve clearances actually have on a bike in normal street conditions. I have been riding bikes for quite awhile, but never really get into the technical aspect of bike mechanics except to provide general maintenance. I do most of my own work with the exception of rebuilds which I'd like to tackle someday, but that's another post. So with that in mind can some of the technically savvy mechanics here explain what effects the following scenarios have on bike performance good and bad? I do know some of the answers from personal blundering over the years, but I enjoy learning from people that actually know the technical and mechanical side of maintenance and who deal with mechanics on a regular basis instead of once in a blue moon or whenever something breaks. I am looking for info related to general street riding as well as those who race and why there are differences.

1 What tolerance does one generally have + or - setting clearances from spec? (.006int and .008 exh)
2 What happens when adjustment is too tight/ too loose?
3 Why is the intake setting generally smaller than the exhaust?
4 What would happen if you reverse the int and exh settings?
5 What happens when you have intake set out of tolerance and the exh set at tolerance and vice versa?
6 Why are race cams set at the same clearance int and exh and standard tolerances for street cams set at different clearances?

If there are other bits of info that may be interesting, I'd like to hear those as well. Thanks in advance for being patient and for the information.

Tim

1 What tolerance does one generally have + or - setting clearances from spec? (.006int and .008 exh)

.001 or .002 will still work, but will not run well and can cause issues if you stree the bike at these settings.

2 What happens when adjustment is too tight/ too loose?

Too tight and your valves may not fully close, you'll lose compression, and the engine may not even run. Valve to piston collision is possible.
Too loose and you won't get enought engine breathing, lowering performance. It will also beat up your valvetrain.

3 Why is the intake setting generally smaller than the exhaust?

Exhaust heats parts up and closes the gap more.

4 What would happen if you reverse the int and exh settings?

See above "too loose and too tight" response.

5 What happens when you have intake set out of tolerance and the exh set at tolerance and vice versa?

Partial effects of the answer given in #5.

6 Why are race cams set at the same clearance int and exh and standard tolerances for street cams set at different clearances?

The cam is ground to compensate for clearance.

If there are other bits of info that may be interesting, I'd like to hear those as well. Thanks in advance for being patient and for the information.

I like the little one-size per "lip" feeler tools you can get from Parts Unlimited catalogs, they are angled perfectly for bike's valves. (small steel "sandwich" popsicle-stick like tool with a lip on each end - buy the 3-piece set)

One of the effects of not enough valve lash is improper cam/follower lubrication. The base circle of the cam, where clearance is set, is where the cam picks up lubrication as the nose is pushing on the follower. As the cam comes around to the clearanced part, a wave of oil becomes trapped between the cam and follower and when the clearance is taken up as the nose of the cam contacts the follower and begins to lift the valve, the parts "surf" on a wave of oil that is then forced out of the gap only to be replaced by another as rotation continues. This is also true to a lesser degree to the cups at either end of the pushrods and the tappet/ valve head contact point as well.

Paul, thanks for taking the time to explain and provide that info hopefully others will benefit as well

ludwig said:

spend a few days googling terms like 'camshaft theory , timing , acceleration ,lobe split , quitening ramps... till your head explodes ..

Click to expand...

Exactly why I don't google when I know I can get a direct answer

Danno, thanks as well.

trust my norton brutha, trust