Threads, Reconditioning
Reconditioning threads, general
Note! As the illustrations in this service information are used for different model years and/or models, some variation may occur. However, the essential information in the illustrations is always correct.
Thread inserts, general
Damaged threads can in most cases be reconditioned using HELICOIL thread inserts.
Thread inserts are available in a variety of sizes, pitches and lengths.
A correctly reconditioned thread will increase the strength of a joint.
Designation of thread insert
Measure the old threads and thread length in the hole.
A Thread
B Thread length
Drilling and tapping new thread in the hole
Drill out the damaged threads with the correct drill, (see tables for reconditioning threads on the cylinder head etc.).
Blow the hole clean.
Tap the new thread with correct tap.
Note! The thread taps are specially made for use with HELI-COIL.
Use denatured alcohol or similar to lubricate the threading operation.
Thread longer threads in stages, back out the tap and blow the tap and hole clean.
Thread the hole to the proper depth (or through if it is to be threaded throughout).
C: drill depth
D: cutting phase
Tools required for installation
This tool, 999 5830, is used for M6-M14. threads.
During some operations the tool must be disassembled by removing the locking ring, for example with countersunk threads.
For threads M16 and larger the specific tool for each thread size must be used The guide and mandrel are included.
Installing the thread insert in the installation tool
Locate the thread insert with the tang facing down in the tool.
Turn the spindle until the tang engages in the recess.
Screw the thread insert into the guide, do not apply pressure, until the thread insert's first turn is flush with the guide opening.
A: Tang
B: Guide
C: Mandrel
Installing the thread insert
Hold the installation tool straight above and centered over the hole.
Screw in the insert without applying pressure on the mandrel handle. Screw in until the end of the insert reaches at least 1/2 a thread revolution into the thread.
The insert must not touch the bottom of the hole or stick out of the other side if it is a through hole.
Break off the tang with the proper tang breaker. For M14 threads and coarser, use a pair of flat-nosed pliers or similar and break downwards.
Removing the thread insert
File a notch in the thread insert, about 1/4 in from the end.
Do not file through the insert.
Take care not to damage the thread in the bore.
Use a triangular scraper or similar to extract the insert by rotating it.
Clean out the threads in the hole with the thread tap and blow clean.
Install a new thread insert.
Reconditioning sparkplug threads
Note! Reconditioning of sparkplug threads must be carried out with the cylinder head removed!
Note! As the illustrations in this service information are used for different model years and/or models, some variation may occur. However, the essential information in the illustrations is always correct.
Hint: Denatured alcohol facilitates operations when working with aluminum.
Tapping thread in sparkplug hole
Use combination tap 998 5823-5 and thread insert P/N 948756-2.
Note! Do not drill out sparkplug threads.
Combined tap
A: Thread section
B: Reamer section
C: Guide (old thread)
Installation of thread insert
Because of limited room the installation tool cap nut cannot be used. Therefore the guide must be taped into place.
Note! For thread inserts that are finer than usual it is extra important not to apply pressure on the tang when threading (both in the guide and the bore).
Screw down the thread insert approximately 10 revolutions and check that the uppermost thread is at least 1/2 revolution in the bore and that no part of the insert is protruding from the bottom end of the bore.
If the insert has been screwed in too far it must be turned until it is all the way through. If it is not deformed it can be inserted again.
Break off the tang with a pair of flat nose pliers.
Check the thread: Install a sparkplug.
Reconditioning countersunk threads
Note! As the illustrations in this service information are used for different model years and/or models, some variation may occur. However, the essential information in the illustrations is always correct.
Drilling
Hint: Denatured alcohol facilitates operations when working with aluminum.
Measure the drill depth so the drill does not go too deep.
Drill out the hole using the specified drill bit size.
Blow the hole clean and try to prevent metal chips or particles entering the engine.
Tapping new threads
Tapping threads in the cylinder head bolt holes requires a longer thread pitch than normal (Tap 951 2584).
On the crankshaft main bearing threads one side has a countersunk hole that is so small that it will also be threaded by the thread tap. This is permitted.
Thread all holes until the tap touches the bottom.
Blow clean and avoid particles entering the engine.
Installation of thread insert
To reach the threads with the thread insert, disassemble the installation tool.
Using only the handle and mandrel turn the insert down until the end of the insert is l/2 revolution into the threaded section. Turn in stages, checking the depth.
Break off the tang with tang breaker.
Blow hole clean and check the tang has been removed.
Test the reconditioned thread with a bolt. It should be possible to screw the bolt to the bottom without using force.
Thread tables
Thread tables, cylinder head/camshaft cover (Part 1 of 2)
Thread tables, cylinder head/camshaft cover (Part 2 of 2)
Thread tables, cylinder head/intermediate section
Threads which must not be reconditioned:
Coolant outlet for the drain nipple, heat exchanger/oil cooler.
Plug hole for crankshaft setting.
Screw holes for cylinder head screws.