Changing the valve gap (clearance )..?

[romilos]

If i change the clearance (valve gap) is there any critical change at the engine power band?

Oem is 0.20mm intake and 0.40 exhaust.

Can we predict anything by changing the clearance ?
eg from 20-40 to 18-42 (more gap at the exhaust less at the intake) :?:

thank u for your time

[Guy Croft]

It's not a good idea to change from OEM recommended settings on any cam, because the behaviour of the cam to tappet can be upset.

The cam has little ramps at the start of the lift phase and end of the closure phase, to reduce the accelerations, and if the valve clearance is too tight (or loose) you can get quite rapid wear, and overload damage to valve springs, valve tips and cam nose.

Have a look at:

http://guy-croft.com/viewtopic.php?t=363

You can see the ramps on the green cam line quite readily. The more lift and the higher the acceleration of the cams the shorter and less gentle the ramps tend to be, which is one reason why stronger or damped valve springs are needed. Never buy a competition cam unless the maker sells the right springs for it...

GC

[romilos]

Ι see...
so i s not good to "play" with the gaps...
The problem now is that i have a cam and i don t know what cam it is...
(i got a used engine)
It seems to have oem intake and more "aggressive" exhaust!
I measured the exhaust valve lift and it is 1mm more than oem.
So i guess that the duration is also different.

Untill i find that i don t have an oem cam i used to use the oem gaps.
The cam seems to be symmetric so i changed the gaps from 20-40
to 20-30..(a cam that looks to have same specs has 25-25 , but i was afraid to put lees gap at the exhaust...)

is there any way to find out what are the "good" gaps? :?: