Sheesh! I thought someone would have answered this by now, but I saw no
response on the list, so here goes.
At 11:45 AM 10/17/99 -0800, Gregg Baker wrote:
> I just put a new tensioner on my 1500 MGA and it came with a little red
plastic thing that I "assume" is used by some to install the thing. I see
no need but am always open to being enlightened. Anyone know what it's for?
The answer is "Yes". And now on to expounding on the theory.
Inside the thing there is a tube with a helical slot with stair-step
notches. These notches engage a small pin in the side of the tube. And
there is a spring behind the whole works that pushes the tensioner into
intimate contact with the chain. The idea is that the tube will rotate as
it is pushed forward, and the step notches will engage the pin to prevent
the tensioner from backing off away from the chain. This way it can be
pushed forward with very little force to minimize wear on the rubbing foot,
and still it cannot be pushed backwards at all with the normal slap of the
chain.
If you have about four hands you can usually install one of these things
without any special tools. Otherwise there is (nearly) always some means
to withdraw the tubular plunger for installation. I have sseen replacement
parts where there was no provision for withdrawing the internal parts, so
you had to be a magician of sorts to accomplish the installation.
The original parts had a plug in the back end of the internal tube, and
that plug had a small hex socket in it, and the tail end of the housing had
an access hole with a threaded plug and a lock tab washer. The proceedure
was to remove the threaded plug, insert the appropriate hex key wrench in
through the access hole and into engagement with the hex socket in the
tube, turn the hex key to withdraw the tube back into the barrel of the
housing, install the tensioner on the engine, turn the hex key the other
way to release the tube and advance the tensioner into contact with the
chain, remove the hex key, install the threaded plug and bend the lock tap
up to prevent loosening of the plug.
Some replacement parts may have a small hole in the side of the housing,
and a matching hole in the internal tube. In this case you push the tube
back into the barrel against the internal spring, secure it there with a
pin through the side of the housing, insert the rubbing foot into the
barrel, install the tensioner on the engine, and then remove the pin to
allow the internal parts to push forward and engage the tensioner with the
chain. The advantage of this design is lower cost to produce, as it does
not require the internal hex socket or the threaded plug at the back. One
possible disadvantage is that it leaves open the small hole in the side so
it can leak out a little extra oil, which in theory could reduce the oil
flow through the rest of the engine. In practice this oil flow loss is so
small as to be of no consequence.
I have no doubt that there are other "creative" designs out there intended
to accomplish the same task in various manners. I suspect that most of
them work okay once you figure out how to use them. I also suspect that
some of them arrive with no instructions included. Once you understand how
the tensioner works it's usually easy to figure out how to install it, and
sometimes I wonder why they go to all the bother of including special tools
when all they need is a little bit of paper with instructions for those
non-original designs.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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