A Primer on
Proper Parting Procedures
Proper Parting Procedures
But then everything changed. The torque
converter became a sealed unit, and even the best mechanics
weren’t equipped with the machining and welding skills
necessary to rebuild these new units. It’s not hard to
see why in-house converter-rebuilding facilities were so slow
to develop.
Most of the early torque-converter
technicians were self-taught and passed that knowledge along
over the years. Being able to cut a converter apart in a manner
that makes reassembly as easy as possible is one of the first
skills new technicians learn. Industry veterans will tell you
they relied on their senses when cutting a converter apart. A
veteran cutter can tell you when the tool bit stops cutting the
harder weld material and starts cutting the softer material of
the cover or impeller by the feel of his hand on the cross
feed. He also can tell you how deep to cut by looking at the
weld. The veteran knows that the discoloration of the metal
next to the weld is about as deep as the penetration of the
weld and that you will see oil when that line disappears (see
Figure 1). Unfortunately, it takes years to develop these
skills, and new technicians need to know what to do now. So
here’s a primer on some basic techniques.
The tools
The fixturing for cutting a converter apart
needs to be as rigid as possible. An industrial- or
military-grade lathe has the mass for a good solid base. A CNC
lathe is also a good choice because of its mass. How rigid your
fixturing is will dictate not only what grade of cutting bit to
use but also the life expectancy of your bits. The experts
agree that a roughing grade of carbide is your best choice, and
most agree that the tool bit should have a 00 relief and that
less radius on the bit will result in less cleanup work. There
is little else that anyone in the industry agrees on.
Since the grade of carbide that works best
depends on how rigid your fixturing is, here’s a good
rule of thumb. Start with as hard a grade of carbide as your
fixturing can handle with as minimal breakage as you can
handle. Work down to as soft a grade of carbide as necessary
for the longevity of your cutting bits. It would be a good idea
to make friends with your tool supplier, since the price of
carbide is a factor! The shops that are cutting their
converters apart on CNC lathes report they are cutting between
400 and 500 converters with a single side of an insert.
How to cut
Where to start your cut? How deep to cut?
Which direction to cut?
These are your next concerns.
With the possible exception of the BM25
converter, the mating parts of all converters are joined by a
single fillet weld, and – with the exception of the ring
gears or mounting rings – the largest diameter of a
converter is usually the overlapping member of the fillet weld.
Figure 2 illustrates a converter with a cover that overlaps,
and Figure 3 illustrates a converter with the impeller as the
overlapping member.
The point where the overlapping member and
the weld meet is where you start your cut, but before you start
you may want to remove any high points that might protrude
above the weld. Carbide does not like interrupted cuts, and any
high points will only widen as the tool bit is plunged into the
weld, causing increased pin-point resistance with each
revolution.
After the high points have been removed,
zero the cross-feed dial and you are ready to start your cut.
The depth of your cut is determined by the thickness of the
overlapping member. Knowing this thickness is the secret to
parting a converter successfully on the first try. Find your
converter on the following chart and plunge in the
corresponding thickness. Please note that where it says flush
on the chart, that means flush with the cover. Touch your tool
bit on the cover, zero the dial, back the tool bit away, and
cut in until the dial returns to zero.
Cut-Open List
General
Motors
TC Cut (in inches)
125 0.170
440 0.130
4L30-E 0.130
4L80-E 0.200
200LU Flush
350CH 0.140
350LU Flush
400 0.190
700LU Flush
BPO 0.165
JSFM 0.150
JTFM 0.150
JXFM 0.150
JZFM 0.150
Powerglide 0.150
Northstar 0.150
Ford
TC Cut (in inches)
5R55W/4/8 0.165
AODE 0.150
A4LD 0.130
ATX 0.125
AXOD 0.200
AXODE 0.180
AXODE25 0.180
AXODESHO 0.165
AXODE25SHO 0.165
C4 11” 0.100
C4 12” 0.140
C5 0.150
C6 Early 0.100
CD4E A 0.145
CD4E C 0.175
CD4E H 0.140
Chrysler
TC Cut (in inches)
470LU 0.170
604 24T 0.170
604 11” 22T 0.170
606 0.150
727 / 727LU 0.170
904 / 904LU 0.170
TC6 / TC6LU 0.170
TC8 / TC8LU 0.170
Cummings NL 0.210
Cummings LU 0.185
W. German Jeep 0.110
Nissan/Datsun
TC Cut (in inches)
DA6 0.125
DA7 0.125
DA8 0.100
DA11 0.150
DA13 0.125
DA16 T.C. 0.210
DA16 T.P. 0.110
DA18 0.150
DA24 0.190
DA25 0.150
DA30 0.155
DA34 0.120
DA37 0.150
DA38 0.110
DA39 0.150
DA44 0.160
DA50 0.195
DA53 0.190
DA55 0.150
Toyota
TC Cut (in inches)
TO18 0.150
TO19 0.110
TO21 0.125
TO28 0.180
TO39 0.150
TO42 0.140
TO51 0.150
TO64 0.150
TO67 0.210
TO74 0.160
Mitsubishi
TC Cut (in inches)
CT10 TP 0.110
CT11 0.110
CT12 0.160
CT12-1 0.150
CT13 0.130
CT15 0.135
CT15-1/CT15-2 0.140
CT20 0.140
CT27 0.170
CT27-9 0.170
CT29 0.140
Honda, BMW,
Jag, Merc, VW
TC Cut (in inches)
HO1 0.115
HO7 0.115
HO12 0.115
HO14 0.210
HO16 0.115
HO17 0.115
HO18 0.115
HO21 0.115
BM11 0.125
BM17 0.125
BM25 0.181
MC6 FLUSH
MC10 FLUSH
MC18 0.160
MC19 0.160
Jag E. 0.131
VW4 0.100
RE8 0.190
RE9
RE10
SU11 0.110
SU12 0.120
SU13 0.120
SU16 0.125
SU18 0.125
SA4 0.075
SA6 0.100
SA7 0.100
If your converter is running true, you then
will move the cutter perpendicular to the plunge cut, moving
away from the weld, until you see oil exiting the converter at
the cutting tip. If your converter is not running true, you
will want to add an additional 0.005-0.010 inch to your plunge
cut before moving the cutter to the side.
Some
additional hints
additional hints
On some Subaru converters (SU15) you will
have to remove the ring gear before cutting the converter
apart.
On the BM25 converter with two welds, cut
at the weld closer to the pump.
On late-model Hondas, do not clean off all
the weld. Leave a 45° angle of weld after the halves
separate. Because of the proximity of the ring gear to the
weld, it is difficult to get a good angle on the welder head
when you are welding the converter back together. The remaining
45° angle will leave a nice area for a bead of weld.
The technical information in this article
also is on the Torque Converter Rebuilders Association Web site
at www.tcraonline.com and will be upgraded as necessary.
Special thanks to Rich Rossiello from
Perfect Shift for his technical assistance in writing this
article.
Next month, the specifics of proper parting
procedures. 
Ed Lee is a Sonnax technical specialist
with a focus on issues of interest to torque converter
builders.
©2005 Transmission Digest