Valve Adjustment Question?

[HaloArchive]

The guide on here says to adjust valves to .008

The same M10 in my 320 has a value of .006 to .008 so I usually do .007

So, school me a bit, Why do we run the valves at a specific value? Why not lower? Why not higher? Why not different on intake/exhaust sides? Technically wouldn't the car run better with a tight intake and larger exhaust gap?

[Napes]

The amazing German engineers who designed the M10 engines made them so fools like me wouldn't get confused - same gap on intakes and exhausts.

My 356 Porsche engines had the same tolerances on intake and exhaust valves - again, so I wouldn't get confused.

There are probably more technicallyl correct reasons out there, and, hopefully someone here will fill you in on the real reasons the gaps are the same.

Bob Napier

[bnam]

My understanding -- the gap is to accommodate thermal linear expansion of the valve stem. Remember, these gaps are being set cold. If you set it closer, there will be insufficient space for expansion and valve stem will distort or excess wear will occur.

If it is set for too large a gap, it valve duration will be affected as the valve will open later and close earlier.

Exhaust valve gaps tend to be larger as they run hotter and expand more.

Byas

[Mike Self]

As was stated, the clearance is to allow for expansion--steel valves and aluminum heads expand at different rates.

Too much clearance--noisy valves plus lost motion--valves don't stay open as long.

Too little clearance--they may not completely close, thus allowing a compression leak--and also allowing the valve's sealing surface to be exposed to combustion heat, thus shortening the valve's life.

So it's better to err on the side of a little too much clearance rather than not enough.

cheers

mike

[c.d.iesel]

..."So, school me a bit, Why does M10 run the valves at a specific value?

Why not (tighter)lower?

Why not (looser)higher?

Why not different on intake/exhaust sides?

Technically wouldn't the car run better

with a tight intake and larger exhaust gap?"...

depends on the design of the valve train, cam/rocker/pushrod/materials/

operating temperatures......

use a Go/No-Go feeler blade 0.006"-0.008" cold

your M10 motor runs consistant temp, little expansion rate,

small/short moving parts(rocker arms) so 0.006 ... 0.008" for intake

exhaust

but have a motor like Mercedes-Benz 617.950 turbo diesel with simular

design, over head cam with rocker arms but with extreme operating

temp change and expansion rates from cold to full

operating temp under turbo boost loads and you have

intake 0.008" and exhaust 0.012" cold settings...

For winter starting Mercedes recommended opening - enlarging

the clearance for the intake valve another .002" so the intake valve gulped

a little less fridgid cold air during the initial Pre-Glowing period and firing.

Not needed for the M10 motor with spark ignition.

Needed for a Compression Igniton diesel. The temp of the

compressed intake air charge is what fires the injected diesel fuel.......