high valve clearances after rebuild ...how unusual?

I know valve lash must be checked/adjusted after top-end rebuilds. My
question is: does anything about these valve lash numbers seem funny to
you experienced rebuilders? (please see numbers below)

Quick background:
My first time doing a top-end rebuild on a 1998 zx7r motor with ~27k
miles.

The rebuild consisted of new ferrea valves with stock valve head
thickness. I had an experienced acquiantance of mine remove the old
valves and oil seals, grind the seats to factory specs, lap the valves,
and install the new valves and oil seals. I did all the rest of the
labor.

Factory valve clearence spec:
Exhaust: 0.22 - 0.31mm
Intake: 0.17 - 0.25mm

Valve clearances BEFORE rebuild:
EXHAUST: ranged from .20-.28mm
INTAKE: ranged from .18-.20mm
The existing shims ranged from 2.85-3.05mm.

Valve clearences AFTER rebuild:
Exhaust: ranged from .457-.559mm!!
Intake: ranged from .610-.635mm!!

where did this increase of ~0.40mm (0.017") come from?

So for whatever reason the valves are either sitting farther away from
their seats or the stem lengths are shorter. First thing I thought was
maybe the new valve heads or stems are actually different from stock
specs. I removed a new intake valve and measured the valve head
thickness and total valve length including stem best i could with dial
calipers and they are the same as the stock valves removed.

Next I thought maybe my friend ground the seats down TOO FAR. Seems
possible to me. But that would have the opposite effect. If the new
valves sink deeper into the engine head, the stem rises higher towards
the cam lobes and the clearence would get tighther. Correct? So it must
be something else...

So i went ahead and got all new shims in range of 3.05-3.4mm. After
reassembly, the new numbers are:
Exhaust: largest clearance .36mm
Intake: largest clearance .43mm!!

Tallest shim I can buy is 3.5mm? That would bring me closer to the high
side of the factory spec range...but I have to check on that...

It took me a long time to figure out how to properly check the valve
clearances but I am certain I am reading the numbers right. Once thing
I realized is how important it is to pre-bend the tips of the Autozone
feeler gauges I am using, so that they are NOT trying to bend as you
insert them between the shim bucket and the cam lobes.

So...does anyone have any insight into any of this? I hope that someone
does...

Thanks!

 

Maybe you accidentally swapped the intake and exhaust cams?

Just eyeballing a pair of cams in a DOHC engine, you would notice that
the cams are not ground symmetrically.

The intake cam is ground to open the intake valve slower and allow it
to close faster, and the exhaust cam is ground to open the exhaust
valve quicker than it allows the exhaust valve to close. The idea of
different opening and closing speeds is to get the acoustic tuning to
work with the exhaust system and the airbox.

Is the diameter of the valve head different? If the valve head is
larger in diameter, the
lapped area on the valve would be further back towards the valve stem,
and that might account for the strange extra valve lash.

Larger diameter valve heads would explain it.

 

FB wrote:

This was my first thought as well. But wouldn't you notice it the first
time you tried timing the engine?

 

As I recall, Kawasakis have punch marks on the ends of the camshafts
for timing purposes.

Suzuki uses scribed lines on the cam sprockets and the scribed lines
have to point stright up, or forward.

 

Most likely, the older shims were thinner to accommodate the wear on
the old valves. The newer valves are not sitting down in the new valve
seats quite as far as the worn valve seats and valves.

Always set the clearance with the engine cold, and at the upper end of
the adjustment spectrum. As the valves wear in, the clearance
tightens.

I hope this helps.
Jim

 

Yeah, but what I meant was I couldn't remember whether they marked them
IN and EX or whatever.

Whenever I'm shimming a bike whose shims are under the cams, I just
zip-tie the cams to the sprockets. Once you've removed the tensioner,
there's enough slack to allow the cams to be moved to one side to
access the valves. You just can't get the timing out, that way.

If I have to remove the cams altogether (like to lift the head) then I
put a blob of paint on a couple of the camchain pins, and corresponding
blobs on the sprocket. And use a different paint for inlet and exhaust.
Again, it makes re-timing a cinch, because you can do it with the crank
in any orientation (as long, obviously) as you don't turn the engine
over half a dozen times while the cams are out. And it means you can't
muddle the cams up....

 

FB, thanks for that suggestion. I will look into it.

mohsin

 

On this kawasaki, the exhaust camshaft and intake camshaft are easy to
differentiate because the exhaust cams have a easy-to-see groove at one
end.

And for timing, there are marks on both camshaft sprockets which you
align with the surface of the head.

mohsin

 

So let me ask this. How would you expect a motor to run with exhaust
valve clearences as large as 0.36mm with a max of 0.31mm specified and
intake valve clearences as large as .43mm with a max of .25mm
specified? Will the motor run decent?

If i can get past the excessive valve train noise, can I ride it until
the valve clearences tighten up without harming the motor in some way?

Thanks guys.

mohsin

 

With those clearances, it'll be an age before it ever does. Better to
find out what's caused it and fix it.

 

Just a thought - did you use the correct torque when tightening the
head down? If you used a new gasket and didn't have the correct torque
that could explain the large clearances.

Leon