Engine - Head Bolt Hole Thread Repair
REF No. MBNA 01/01, 58/2TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: October, 1982
SUBJECT:
RECONDITIONING TAPPED HOLES FOR CYLINDER HEAD BOLTS
ALUMINUM ALLOY V-8 ENGINE TYPE 116.960/116.961
In order to repair damaged cylinder head bolt hole threads in the subject engines, specific repair procedures and special tools are required. This Service Information details these requirements and supersedes the corresponding instructions outlined in the Introduction Manual - Model Year 1981 (pages 49-52).
To aid in this procedure, a special tool kit (part no. 900 589 00 99 00) has been developed and is now available through the Teaneck, N.J. Parts Depot, in addition to the previously available special tools provided for this repair.
Special Tools
Parts Information
To order additional Heli-Coil threaded inserts, refer to the Parts Information as shown:
NOTE:
Replace damaged threads for cylinderhead bolts with Heli-coil threaded inserts (part no. 000 997 58 15). Threaded inserts (installed) have a length which corresponds to 2.5 times the diameter (14 coils) of the cylinder head bolts.
CAUTION:
Tapped holes 15, 7, 1, 8 and 17 (see Fig. 1) for M 10 x 165 mm cylinder head bolts are drilled slightly diagonally in the cylinder crankcase.
These tapped holes are drilled 1° 52' diagonally from the vertical to the cylinder head mating surface. (see Fig. 2).
To make sure that no pressure marks develop on the cylinder running surfaces (caused by the relatively long Heli-Coil threaded inserts), the respective core holes must be drilled 1° 52' diagonally from the vertical using the drill jig (part no. 117 589 02 23 00).
If damaged tapped holes are not accessible with cylinder head removed (due to limited space), and an angular-type drill is not available, remove the engine.
Reconditioning
1. Clean crankcase deck surface from all carbon deposits and install drill Jig (part no. 117 589 02 23 00) on top of cylinder bank (see Fig. 3).
2. Carefully cover bores in drill jig over cylinders and exposed coolant passages and timing chain housing with wide masking tape.
CAUTION:
Even the smallest light-alloy chips will damage or destroy the cylinder running surface or the piston.
3. Drill damaged holes only with 10 mm tap drill to a depth of 37 to 38 mm. While drilling, lubricate drill with cutting oil or kerosene.
4. Blow out chips and remove drill jig.
WARNING:
Protective goggles should be worn during this and subsequent operations that involve the use of compressed air.
5. Install plastic caps from tool kit into cylinder bores and tape up all coolant passages and timing chain housing opening.
6. Pre-tap Heli-Coil threads as deep as possible, with special tap with pilot tip (part no. 117 589 00 70 00). Lubricate tap with cutting oil or kerosene (see Fig. 6).
7. Carefully blow out all chips.
8. Final-cut the Heli-Coil threads approx. 35 mm deep using an M 10 (12.2mm 0D) Heli-coil tap (included in the thread repair kit, part no. 900 589 00 99 00). Lubricate the tap with cutting oil or kerosene (see Fig.7).
9. Carefully blow out all chips.
10. Screw-in lubricated Heli-Coil threaded insert (1), part no. 000 997 58 15 (Heli-Coil part no. 1084-1OCN 0250) using the M 10 manual installation tool (included in the thread repair kit part no. 900 589 00 99 00) as shown in Fig. 8.
CAUTION:
The top of the insert should be approx. 4 mm below the cylinder crankcase parting surface (see Fig. 9).
11. Check inserted thread by screwing in a clean cylinder head bolt. Screw in depth should be approx. 27 mm.
NOTE:
It is not necessary to remove the driving tang of the Heli-Coil threaded insert.