Rastinejad wrote:
May be not rats, but mice can sometimes carry acorns
into the timing belt covers and I have seen pieces of
acorn shell in there. A piece of acorn shell on the belt
can certainly cause a slip at the crank.
Indeed, now THERE is a novel failure mode that none of us have ever
mentioned before. Diminutive saboteurs! And it really is possible, too.
Imagine starting up one day with a cache of mouse victuals in there, or a
mouse himself. That could easily cause a slip or a belt break.
Kowfy wrote:
as far as the canadian or any other tensioner goes i can't
see why there would be any failure aside from a bearing going
south.
As Brian mentioned, there was a first iteration of the mechanical tensioner
that was reputed to have a stress riser somewhere at the base of the spring.
After some use, they would fail at that point, releasing the tensioner's
complete load on the belt and causing an instant, massive slip.
But even with the updated (if it ever was, indeed, updated) mechanical
tensioner, there is another failure mode--and this can exist even if the
tensioner was installed correctly. If the tensioner is allowed to snap
back, from its tensioned position to its free position, the body of the
tensioner can put a small nick in the spring. That nick will act as a
stress riser and can eventually lead to the spring breaking at that point.
I was informed about this by one of the guys at Centerline, and I think that
is what Steve was alluding to when he stated:
My theory is improper installation and even the
Alfa factory bulletin sets up a mech to do it wrong
by snapping tensioner body over center and overtensioning
outer thermal clutch spring.
And as Steve says, the installation tech bulletin says to over-tension the
belt, turn the engine through two revolutions, and then set the tension by
BACKING OFF the tensioner. And if a ham-fisted mechanic simply lays into
the tensioner during the over-tension segment of the installation, who knows
what lasting affect that might have?
The biggest detriment I've found with the mechanical tensioner is in the
installation process. That is, getting it right. First, it can ONLY be
installed correctly with a mirror. There is no way, on the GTV6 or the
Milano, to get direct, parallax-free viewing of the tension pointer or its
indicator mark. So if you've set your tensioner without a mirror, its
tension will be wrong. Let me repeat that: if you've set the tensioner
without a mirror, its tension is wrong. (By the way, the installation Tech
Bulletin neglects to mention the use of a mirror.) Then, there is the
requirement to over-tension the unit, but not too much, and rotate the
engine through AT LEAST two revolutions to seat the belt. And finally, the
careful backing off of the tension while using a mirror to watch the
indicators. Now how many people, even experienced mechanics, have done it
that way? And if it's not done that way, it's inviting failure.
The last time I installed a belt on my GTV6 I conducted a test. After
installing per the tech bulletin and using a mirror, I tried rotating the
engine backwards. That's right, backwards. At first I did it slowly and
gently. And the belt didn't slip. Eventually, I was laying into the handle
of my 3/4-drive ratchet with all of the assertiveness I could muster.
Revolution after revolution, as hard as I could do it. And the belt didn't
slip. Not even a tooth. I reported this to the digest, probably, four
years ago or so.
My Mitsubishi Mirage has a spring-loaded tensioner much like the Alfa
mechanical tensioner. But after the tension is set, the tensioner is locked
down in that position. On that engine, it can be done hot or cold, and
amazingly, with the tension set, I don't see a perceptible difference in
tension when the engine is hot and when the engine is cold. That engine has
a steel block and a much shorter belt, and that may have something to do
with it. I wish we could do something similar on our V6s, but with the
aluminium heads and block, and with the long belt path, there is just too
much expansion and contraction involved. I sure would feel better if
someone could come up with a truly bullet-proof tensioner that we could
install and not worry about. The technique of using the original tensioner,
minus the hydraulic relief, may be a good one, but without having some
really good analysis, it's superiority over the mechanical tensioner is
still unproven. Frustrating.
Rich Wagner
Montrose, CO, USA
'82 GTV6
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