What result does a "loose" intake valve have?

[ty998]

What exactly is the result of an intake valve that is slightly out of tolerance (.10-.12) from an engine perspective? Does that mean that the valve then allows excessive fuel and air into the cylinder? I do realize it needs fixed.

Thanks.

[tkent02]

Nothing. A lot of us run them at .10, it's just fine.

.12 won't hurt.

[ty998]

Nothing. A lot of us run them at .10, it's just fine.

.12 won't hurt.

Yay!

[kirkn]

...and just to expand and answer the question - excess clearance doesn't mean that MORE fuel and air is let in, it means LESS fuel and air is let in.

The cam only provides so much lift. If that lift is "wasted" by having to take up excess clearance, then LESS lift remains to open the valve.

In the opposite direction, when you have not ENOUGH clearance, as in ZERO clearance, then the valve never actually seats and thus doesn't fully close. Can't have compression if the fuel & air is just pushed backwards out through the carburetor...

[Agemax]

slacker tolerance is better than too tight. as long as its not wildy to slack so you can get your whole set of feelers in there haha

[BassCliff]

Hi,

With slightly larger clearances at the lobe/shim/bucket interface, the valve will stay in contact with the head slightly longer. This allows the valves to dissipate more heat and greatly reduce the chance of a burned valve.


Thank you for your indulgence,

BassCliff

[derwood]

anyone ever see a burnt intake valve?

[tkent02]

Many a time. Burnt a few myself when I was young and stupid.

[ty998]

...and just to expand and answer the question - excess clearance doesn't mean that MORE fuel and air is let in, it means LESS fuel and air is let in.

The cam only provides so much lift. If that lift is "wasted" by having to take up excess clearance, then LESS lift remains to open the valve.

In the opposite direction, when you have not ENOUGH clearance, as in ZERO clearance, then the valve never actually seats and thus doesn't fully close. Can't have compression if the fuel & air is just pushed backwards out through the carburetor...

Thanks for the clarification. That makes sense.

[tkent02]

With a shim and bucket system, I think too loose won't hurt until a shim spits out and does some damage. With the tappet and screw adjuster, too loose will let the adjuster screw hammer into the valve, mushrooming the end of the screw, making it looser and looser, promoting more hammering.

I have only seen this on a crappy chinese toy bike, 40cc something or other imitation dirt bike for kids, and again on an old Yamaha XT 250, but I think the same could happen to our GSes.

Just slightly looser than the correct settings is harmless.