Greg, when the ears sheared off of my oil pump last year I started
looking at the pump shafts closer. It was a new "County" pump that
failed. All of the new shafts that I checked were dead soft, but as
you noted the slots were cut with square, leaving a sharp corner,
hence a stress riser. The old pump shafts that I checked all were in
the 50's Rockwell hardness, but I did not cut into them to see if they
were case hardened or thru hardened. I did not have the time to wet
grind one down to test the insides (the heat from dry grinding would
change the hardness).
I made a couple of my own and thru hardened them to a 35 Rockwell and
then case hardened them. I then wet ground the slots into the tops
with a nice radius at the bottom. If I cut the slots first and then
hardened them, the insides of the slots would be case hardened and too
brittle. So far this year it has worked in my race motor, but time
will tell if they last.
Joe(B)
----- Original Message -----
From: "Greg Solow" <gregmogdoc@surfnetusa.com>
To: <fot@autox.team.net>
Sent: Friday, September 05, 2003 9:21 PM
Subject: Re: TR4 Oil Pump Rotors
> Because the manufacturers of the oil pump gears sets, (I believe
they are
> marketed in the US as "county" brand) found the inner gears comming
loose
> from the shaft was a problem, they began to install a pin though the
rotor
> and the shaft about 6 or 8 years ago. We had on of those pins work
loose and
> come out during engine operation and it consequently jammed the
pump, which
> immediately sheared the slotted upper end of the drive shaft. The
pump
> stopped turning completely at this point. The engine kept on running
until
> it ran the bearings.
> Previously, using original Triumph supplied pump rotors, two
times I
> experienced the slot ears shearing off when there was no reason for
them to
> fail except normal stresses of operation. This always stops the
pump from
> turning. These shaft failures, I believe were cause by the shafts
beiing to
> hard and consequently somewhat brittle. They were, and the new repro
parts
> are also, machined with sharp corners to the drive slot in the top
of the
> shaft. These sharp corners are stress risers that will help induce
the
> begining of cracks. We remachine the slots so that there is a full
radius in
> the bottom, then glass peen the inside of the slot to remove the
machine
> tooling marks.
> As for the pin that is designed to keep the rotor from turning
on the
> shaft, We found that the pin on the origiinal gear is VERY hard to
drive
> out, while the pins in the new gears are very easy to drive out. So
we now
> remove all of the pins, tap the hole through the rotor and the
shaft, and
> then loctite in a 3/16 allen set screw as a new "pin". Being
loctited in
> with maximum strength retaining compound and screwed into place, it
is NOT
> going to come out.
> With gears modified in this manner, we have experienced no
failures,
> even in race engines turning over 7,000 rpm and pumping over 90 psi
oil
> pressure.
>
>
Regards,
>
> Greg Solow
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