Boxerworks.com

Why are the valve clearances set bigger on a new motor?

Nourish wrote:Why are the valve clearances set bigger on a new motor?

Because clearances can decrease dramatically as the head gasket compresses and the valves seat in.

mattcfish wrote:

Nourish wrote:Why are the valve clearances set bigger on a new motor?

Because clearances can decrease dramatically as the head gasket compresses and the valves seat in.

So, should you set them bigger anytime the head gasket is replaced?

Jeff in W.C. wrote:

mattcfish wrote:

Nourish wrote:Why are the valve clearances set bigger on a new motor?

Because clearances can decrease dramatically as the head gasket compresses and the valves seat in.

So, should you set them bigger anytime the head gasket is replaced?

Yes.... or check them alot afterwards.

Surely if the gasket settles the clearances get bigger - shouldn't they be set tighter?

Nourish wrote:Surely if the gasket settles the clearances get bigger - shouldn't they be set tighter?

No, the distance between the cam and the rocker gets shorter as the gasket shrinks, hence the clearance becomes less.

Nourish wrote:Surely if the gasket settles the clearances get bigger - shouldn't they be set tighter?

Like Garnet says.

If the gasket is thinner, it shortens distance between the rocker and the follower. How were you thinking it would make the clearances bigger?

Major Softie wrote:If the gasket is thinner, it shortens distance between the rocker and the follower.

And at the same time, the tip of the valve stem drops closer to the cylinder base by the gasket shrinking, thus moving away from the tip of the rocker...but wait, the rocker block is also moved closer to the cylinder base. And at the same time, the pushrod now pushes up more on the other end of the rocker, thus reducing the clearance. There's also the situation where the head bolt torque gets loose, effectively allowing the cylinder height to grow, reducing the valve clearance. Man, now my head hurts!!

I think it's best to not try and out think this...set the clearances to the standard level and check it at intervals during the first 500-1000 miles. Retorque the heads as needed, recheck the clearances, and ride...

Kurt in S.A.

Nourish wrote:Why are the valve clearances set bigger on a new motor?

Sh!t ... I have never done that.
New or old, I adjust them to spec. although on a new engine (a motor is an electric thing, eh ?)
lash will be re-checked frequently starting at @ 100 miles after the build ...

vanzen@rockerboxer.com wrote: although on a new engine (a motor is an electric thing, eh ?)

That's one definition I've heard. I'm sure we can find varying definitions, but, to my understanding, a "motor" is just the part that makes power. A gasoline "engine" has a motor, an alternator, a water-pump, etc., and they are all part of the engine. Obviously an electric motor has none of the ancillaries that make up a gasoline engine.