<VV> loosening tight bushings, etc

[Bill Meglen]

Don,.  

That's really interesting.

While having my problem I had difficulty accepting that sufficient friction
could exist in a bushing to create the situation I experienced.  I had
concluded that part of my problem was related to not inserting the bushing
deeply enough into the crankshaft. For the first time in doing 4 clutches I
did NOT use the pilot shaft to drive in the bushing.  I used a socket to
drive it only flush.  I had noted later on another engine that the bushing
was recessed about 1/32" below flush.  My bushing was tight enough so that
with some effort when "trial fitting",  I pulled it out it "popped" loudly
suggesting an air tight seal between PS & bushing.  I was not surprised
given its trial fit when I had difficulty snugging the diff and bellhousing
together.  I recall faulting myself for not eliminating a 1/8" gap between
the mating faces before bolting them up. I concluded that if I had drawn it
down with the bolts then the shoulder on the PS may have contributed
additional friction on the unrecessed bushing. My attempts to "wear it in"
did not use your suggested technique allowing cooling. I just shifted up and
down through the gears for a total of about 30 miles. When I gave up and
pulled the power train again, I noted that the bushing which was a tight fit
in the crankshaft looked as if it had been spun. I replaced the bushing with
another bushing which fit much less tightly and I made sure I was able to
spin the PS in it by hand before replacing it. I had difficulty accepting
the too tight bushing conclusion so I did considerable measuring including
checking that the shaft was true, and that linkage was not at fault.  I was
pleasantly surprised that when reassembled it worked.

Your explanation of tight bushing behavior seems to support my experience.

Bill Meglen




On 11/27/07 16:15, "djtcz at comcast.net" <djtcz at comcast.net> wrote:

> Prolonged rubbing even with oil-lite or heavily leaded bronze heats things up.
> The bronze bushing has a relatively high coefficient of thermal expansion, so
> when it gets warm it tries to grow in diameter. As it is a press fit in the
> crank, the expansion forces it to squeeze inward, and tighten, and the vicious
> cycle of cascading thermal runway begins.