7/22/2019 SL162B Helicoil.pdf
1/2
y oming652 OliverStreetWilliamsportPA 17701
U.S.A.717/323-6181
SERVICELETTERService Letter No. L162B(Supersedes Service Letter
No. L162A)
January 29, 1982TO:SUBJECT:
All Owners, Operators and Service FacilitiesHeli-Coil Service
Repair Kit
Gentlemen:The repair of threaded holes is a problem often
en-countered in aircraft engine maintenance. Corro-
sion, tight fits between dissimilar metals and the ef-fects of
repeated heating and cooling, are the usualcontributing causes for
damaged threads, or loosefits between threaded parts. Conventional
methodsof repair to threaded parts include retapping anduse of
oversize threaded parts; installation ofbushings; and redrilling
and tapping to accom-modate step-threaded parts. Except for the use
ofoversized threaded parts supplied by Avco Lycom-ing, none of
these methods of repair are generally ac-ceptable because of
structural weakness introducedby enlarging the tapped hole.The
Heli-Coil thread insert is an ideal method forrepair of many types
of thread damage. It requiresvery little enlargement of the tapped
hole, and beingmade of stainless steel provides a better thread
thanthe original. Consequently, Heli-Coil inserts are notonly
recommended for repair of thread damage butare used extensively in
new Avco Lycoming aircraftengines at locations where threaded parts
are sub-
ject to frequent removal and where corrosion may bea factor.In
order to promote the use of Heli-Coil thread in-serts as a means of
thread repair in Avco Lycomingengines, as well as to provide
maintenance facilitieswith an efficient, time-saving tool. Avco
Lycominghas designed a kit, containing inserts and tools forrepair
of the most common sizes of threaded holes inAvco Lycoming engine
parts. These tools and in-serts are specially designed for use in
aluminumparts.The kit is made up of eight repair packs, each
packcontaining thread inserts, tap and installing tool for
a particular size thread. Heli-Coil thread inserts areinstalled
in the following manner:CAUTION
Do not install Heli-Coil inserts in anythrough-hole on an
assembled enginebecause of the possibility of metal par-ticles
entering the engine.1. Drill hole to adequate depth using the drill
size as shown in the following chart.
THREAD INSERT DRILL SIZE DRILLED HOLE DIAMETER1/4-20 NC H5/16-18
NC Q3/8-16 NC X1/2-13 NC 33/641/8-27 NPT U10-24 NC 13/6410-32 NF
71/16-27 NPT 9/32
Heli-Coil Products, Div. of Mite Corp., Danbury,
Connecticut.
.2640-.2710.3300-.3370.3950-.4020.5136-.5206.3660-.3730.2011-.2071.1990-.2050.2790-.2860
Page 1 of 2
7/22/2019 SL162B Helicoil.pdf
2/2
Service Letter No. L162B
2. Tap the drilled hole using the Heli-Coil tapsupplied with the
pack. Check thread size onshank to make certain correct size is
used. Do notattempt to use any other tap. On pipe threads, tapthe
depth indicated by the copper wire wrappedaround the tap. For
shallow holes it may benecessary to grind-off and re-chamfer the
end ofthe pipe tap.
3. For coarse thread series Heli-Coil thread in-serts, screw the
thread insert on the mandrel ofthe installation tool; be sure tang
of the insert isfully engaged in slot of mandrel. For pipe
threadinserts and fine thread series, thread insert shouldbe placed
in well of the prewinder, tang end for-ward. Rotate mandrel through
insert until drivingtang is fully engaged in slot of mandrel.
Continueto rotate until insert is engaged on 1 or 2 threadsin
prewinder body.
4. Screw the insert into the tapped hole until thetop of the
insert is 1/4 to 1/2 turn below the topsurface of the hole.5.
Remove the tang from the insert by breakingit off with a rod having
a diameter that fits intothe assembled insert. Strike the rod
sharply with ahammer, the tang is notched to insure that it
willbreak off easily. Tangs on pipe thread and largediameter
inserts can be removed with long-nosedpliers.
CAUTIONHeli-Coil insert installing tangs canbecome airborne when
broken off with ahammer and rod. Care must be exercised toprevent
injury to anyone in the vicinity.
NOTEAny time that a cylinder hold-down studhole thread is
repaired by installation of aHeli-Coil insert, the limits for stud
drivingtorque must be maintained. See Table ofLimits, SSP1776.
In the event it is ever necessary to remove a Heli-Coil insert,
it can be accomplished as follows:With a small triangular file, cut
a notch in the top
coil of the insert about 1/4 turn from the end of thewire. Be
careful not to damage the threads in thetapped hole. Then place one
edge of a 3-edge scraperin the notch; while maintaining a steady
downwardpressure, turn the scraper counter-clockwise untilthe
entire insert is backed out. Scrap the insert andretap the hole to
insure it is clean, then install a newinsert.Any of the packets, or
individual inserts contain-ed in the kit may be replaced by
reordering throughany Avco Lycoming distributor. Be sure to
statepart number as shown below for each item required.
Part No. ST-184 Heli-Coil Thread Repair Kit Consists of:
Qty. Part No.1 4028-41 4028-51 4028-61 4028-81 4029-21 4028-31
4024-31 4029-1
DescriptionRepair Pkg. (30 pc. 1/4-20 NC)Repair Pkg. (24 pc.
5/16-18 NC)Repair Pkg. (18 pc. 3/8-16 NC)Repair Pkg. (12 pc. 1/2-13
NC)Repair Pkg. (10 pc. 1/8-27 NPT)Repair Pkg. (30 pc. 10-24
NC)Repair Pkg. (30 pc. 10-32 NF)Repair Pkg. (10 pc. 1/16-27
NPT)
Part
No.STD-1173STD-1164STD-1171STD-1642STD-1872STD-1353STD-2183STD-2212
Individual InsertsInsert, 1/4-20 NCInsert, 5/16-18 NCInsert,
3/8-16 NCInsert, 1/2-13 NCInsert, 1/8-27 NPTInsert, 10-24 NCInsert,
10-32 NFInsert, 1/16-27 NPT
MinimumQuantityPackage
151296515155
NOTEAny of the above repair packages may be purchased
separately. In addition to con-taining inserts, each package
contains a special Heli-Coil tap and installing man-drel.
Individual replacement inserts are packaged and sold as listed.
NOTE: Revision B adds repair packages to kit; changes text;
eliminates illustration and changesdrilled hole diameters.21491 -
This number for Avco Lycoming reference only.Page 2 of 2
