This car wasn't very quiet when we got it around two years ago, but now the
valve"tapping" noises are so loud that I can hear my wife coming when shes'
still two blocks away (maybe a slight exaggeration). The exhaust system is
fine, its just the valves. The engine seems to be as peppy as at first with
acceleration, and I had the valves adjusted not long ago.
It sounds like it is just a couple of the valves that are loud, one
especially. Does this require an expensive top-engine overhaul? New rocker
arms, or the valves themselves?
Yea, I know the 85 needs regular valve adjustment. As I said, the valves
were adjusted recently, maybe a half-year ago, probably haven't put over
4000 miles on it since. Why? Are noisy, clattering valves a symptom of
out -of-adjustment valves? It was about as noisy before the last valve
adjustment as afterward, and the mechanic said that the adjustment was
"pretty close as is".
You might consider the possibility that the source of the
noise isn't the valves, but an exhaust leak.
My '82 300CD was rather noisy when I bought it, so the first
thing I did was have the valves adjusted. No change. A
previous vehicle of mine, a Toyota pickup, developed the
same sort of noise, and the cause turned out to be a warped
exhaust manifold. The manifold had pulled away from the
engine block, allowing pulses of exhaust gas to escape. The
noise was more of a mechanical clicking sound than the sort
of gaseous chuffing that one would expect.
"One violation is rude; repeated violations are best dealt
with by knocking the front teeth down the esophagus --
The sound you hear is due to excessive valve gap - the valves are being
slapped open not pushed open. The correct gaps (cold engine) are about
.004 inch intake and .014 inch exhaust. Some of your engine's are
substantially larger possibly because the last adjustment didn't snug a
lock nut against the adjustment nut and the adjustment was lost.
The "danger" is that the tapping will eventually fatigue the parts and
some will eventually fail.
The tapping is due to excess gap - way beyond the .004 and .014" spec.
The tap is really a slap as the rocker hits the valve's adjustment cap nut.
Probably the adjustment wasn't snugged up with the lock nut and came
loose. The shop that did it should take a look for the slapping will
eventually cause the parts to fatigue and break - eventually.
On second thought, the air cleaner's support bracket may have broken
from metal fatigue and making a hell of a rattling sound. This is easily
checked by pulling UP on the air cleaner - it should NOT lift up.
The rearward leg of the support bracket breaks from the engine's
sidewards oscillation; it's a poor design that's never been improved -
so much for M-B's engineering excellence; my car is on its third bracket
in 100K miles! I had the last new one reinforced by a welding shop
before it was installed.
the fix on my 82SD air cleaner was getting a towel, folding it a few
times & slamming the hood on it. it took away most of the noise.
a new exhaust system fixed the rest!
2 towels & 70,000 miles later still working.
now at every fuel fill up use the towel to check the oil.
shake the towel out <keeps it from flatting out & sliding towards the
front of the cleaner.
ya would not want it to get in the belts.
now if i could keep the trans from slipping from second to third & third
DON'T USE IT FOR CHECKING THE TRANS FLUID, TO DIRTY
Yea, I had the loose air cleaner problem fixed not long ago.I
will try the towel trick next time the bracket breaks, that is a good idea.
Will probably try my hand at adjusting the valves. I have done quite a bit
of auto repairing, but definitely am no pro. Have to get the gas-engined
Volvo repaired first, though. I have the 300SD shop manual on CD, and I
think it gives the adjustment procedure and clearances. I think you
mentioned some trick a while back about how to rotate the engine for TDC.
Can't remember what it was now. The high compression of diesels doesn't
prevent you from manually rotating the engine for TDC?
The speed that we can rotate an engine by hand is so slow that
compression isn't a factor - at all!
I turn my engine by putting a ratchet onto the power steering pulley's
nut and turning it that way. A ratchet ensures only turning in the
correct rotation direction.
To adjust the valves one needs two thin 14 mm open end wrenches. The
special offset wrenches are preferable but I've been able to get by
using straight Sears Craftsman wrenches. The TOP or cap nut is the
adjustment the lower nut is the lock nut.
I can send you detailed instructions.
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