TARK-HC Trailing Arm Drill/Tap Guide for installing Helicoil thread inserts.
A frequent source of frustration for Triumph owners is the stripping of the threads holding the rear hub to the Trailing Arms (TA). The TAs are made of cast aluminum which is both soft and porous and the six studs on each side are threaded at 5/16″-24, which Triumph only rated at 14-16 foot pounds of torque. Anything more then that and you can strip the threads in the aluminum. Some people just drill and re-tap at 3/8″, but you’re still threading a steel stud into aluminum. The better solution is to use a threaded steel insert in the TA that the stud can screw in to, but the problem with doing that is drilling and tapping 12 holes that remain on center and perpendicular to the TA. If you have even one misaligned, the brake back plate and the rear hub won’t fit properly or not at all.
One (1) Alignment Jig
One (1) Tap guide Helicoil
One (1) Drill guide Helicoil
TARK – HC – Kit for use with Heli-Coils
The difference between kits 1 & 2 are the insert type you plan on using i.e KeenSerts or Heli-Coils. While the jig back plate is the same for both kits, the drill & tap insert jigs are different so make sure you use the correct inserts with the jig that you are ordering.
These kits DO NOT INCLUDE the drill, bottoming tap or inserts. You will also need a good quality tap lubricant for use in aluminum for both drilling and tapping.
Please note that KeenSerts require an “X” drill size and 7/16-14 bottoming tap. There’s some confusion here because a 7/16-14 tap is supposed to use a “U” drill size, BUT the KeenSerts instructions specify the larger “X” drill size. So don’t make the mistake of using a “U” drill. The KeenSerts directions also call for a countersink but you won’t need one when you use this set-up. If you were “free-handing” the tap, the countersink helps to line you up and get you started. The tap insert used here does all of that for you.
KeenSerts – while these can be sourced at many places, I’ll use www.McMaster.com and their part numbers as these were used for our testing. However……McMaster only ships parts domestically, so anyone outside of the United States may want to order Heli-coils which are more readily available worldwide.
McMaster Part# Description
92070A3377 PIECE KIT with TOOL – BLACK-PHOSPHATE STEEL KEY-LOCK THREAD INSERT, 7-PC THIN WALL REPAIR KT,5/16″-24 INT,7/16″-14 EXT T
PACKAGE OF 7 ADDITIONAL INSERTS – BLACK-PHOSPHATE STEEL KEY-LOCK THREAD INSERT, THIN WALL, 5/16″-24 INT THRD, 7/16″-14 EXT, 7/16″L,
TAP MAGIC CUTTING AND TAPPING FLUID, FOR ALUMINUM, 4-OUNCE CONTAINER
GENERAL PURPOSE HIGH-SPEED STEEL HAND TAP, BOTTOMING, 7/16″-14, H3 PITCH DIAMETER, 4 FLUTE
“X” SIZE DRILL BIT
Heli-Coils are also available from many sources but as a former NAPA store owner I’d just recommend you order NAPA part # BK 770-3082. This kit contains 12 inserts, the insertion tool and the tap. It DOES NOT INCLUDE a 21/64″ drill bit or tap lubricant. Additional inserts can be ordered under NAPA part #BK 770-3132.
Please specify the kit based on the threaded inserts that you will be using.
TR250, TR6, TR4A, Stag
1965, 1966, 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977
Eight (8) cylinder, Six (6) cylinder, Four (4) cylinder
Detailed documents, videos and downloads on installation can be found in Product Support under the Trailing Arm Kit section.
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