Just curious - how long to damage a valve if clearance is too low?

This isn't a problem I am having, but would like to know. If someone
installs new shims and doesn't allow for enough clearance - how long
before damage occurs?

What sparked my interest in this is that because this was my first time
pulling a camshaft, replacing the shims and installing new hushers -
i'm driving down the road waiting for the engine to explode. Simply
becuase it's the first time I've done engine work like this and not a
mechanic. I am exaggerating here, but there is that thought in the back
of my mind -- did I do everything right?

Now, I've driven the car about 25 miles and she seems to run perfectly.
But, I was wondering - had I not rechecked my clearances - would I see
valve damage immediately, in 100 miles, in 1,000 miles?

 

Since in a B21,23,200,230or E motor the valves sink in the head as they
normally wear and in doing an adjustment one would replace the found
shims with thinner ones in order to increase the valve clearance the
opportunity for valve damge due to over tight valve clearances is nil.
Not impossible--possible shim mis-installation in the tappet for
example--but highly unlikely. Tight intakes can and do burn from lack of
cooling during overlap but there is no opportunity for damage from
loosely adjusted valves (clearance in excess of .060 mm) except for a
reduction of power at high engine rpm and possible shim kick out but
other wise you're safe.

Bob

 

I've got the opposite problem -- and a new development. I say problem -
there is no damage, only a miscalculation.

I didn't know what size shims were on the car until I went to do the
job. Before I pulled the camshaft, I pulled a few shims but the numbers
were worn off. Later I discovered that they appeared to be 4.025mm
shims.

Because I was measuring over .50mm clearance, when spec was .30 - .40,
my calculations called for me to order 4.10mm shims.

I replaced the hushers and of course they were all tight originally.
After 2 days and about 20 minutes of highway driving - I re-measured
the clearances.

Hayne's says the clearance for a warm engine should be .35 - .45. I
measure .25 on 2 shims and .30 on a 3rd.

So, I am .5 - 1 mm too tight.

I plan on ordering replacement shims and get the engine back to spec.
When I wrote the above post I had not rechecked my shims for a 3rd time
yet.

I'd understand if the clearance was too much, I have too little.

Thanks.

 

I'm doing some math and I'm perplexed. If I had 4.025mm shims
originally, and .50mm clearance and wanted a spec of .40mm clearance,
then

(C-A) + B (Straight out of Haynes)

A = spec clearance
B = Measured clearance
C= Original shim thickness

So: (4.025 - .40) + .50 = 4.125mm shim required. I ordered 4.10mm
shims, and now I get a clearance of .25 and not .35 or .40. That's the
perplexing part.

Now if I recalculate with the 4.10 shims installed I get:
(4.10 - .40) + .25 = 3.95 shim required.

The plan is to swap the 4.10 shims with 3.95 to bring the .25mm
clearance up to .40


Sound right?

 

I don't know from millimeters but looking at your numbers I don't see
how you get from .35-.45 clearance to being .5-1mm tight.
If you measure .25 and min is .35, you're .1mm tight.

Back when I used to race a (stock) overhead cam four banger, I ran
0.008"/0.010" intake and exhaust. .25mm is about 0.010" so you're not
dangerously tight imo. You're not going to hurt it running it until you
get the right shims.

Also, "warm" is rather subjective. Check it cold.

 

The trick when measuring, especially with new dampeners, is to be able
to feel the rubber compress and not the valve depress when you're
jamming the feeler gauge under the cam lobe.

If you have to add .15 to the clearance then you have to take .15 off
the shim. So if your clearance is .25 and the shim is 4.10 then the
proper shim would be three steps thinner or 3.95. So, you are correct.

Bob

 

Thanks Clay and Bob.
Clay - I didn't post that 2 of my valves measured .5mm more clearance
than the others and the 2 shims were different. Sorry for the confusion
with the .5-1mm. I do believe I am 1mm too tight.

To clarify - I am just trying to double check my math.

Bob - thanks for the double check.