Reconditioning spark plug threads
Note. Reconditioning of spark plug threads must be carried out with removed cylinder head.
Scheme 387
Use combination tap 998 5823-5 and thread repair inserts for spark plug thread M14x1.25 .
Note. Do not drill out spark plug threads.
Combined tap
A: Tap.
B: Reamer.
C: Steering.
Scheme 388
There are times when the cap nut cannot be used because of space restrictions. On these occasions the guide should be taped into place.
Note. As the thread insert for the spark plug thread is thinner (finer) than usual it is extra important to not pressure on the pin when inserting the thread insert (both in the nozzle and the material).
Twist the thread insert down and check that the upper thread is at least a half thread down into the thread and that none of the insert protrudes into the combustion chamber.
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 spark plug.
Thread table
| Values in mm | ||
|---|---|---|
| Thread dimension | Drill - diameter | Examples of areas of use |
| M6x1 | 6.3 | Oil pump |
| M7x1 | 7.3 | Sump to cylinder block, Intermediate section to cylinder block, Water pump to cylinder block |
| M8x1.25 | 8.4 | Studs at the exhaust ports |
| M10x1.5 | 10.5 | Intermediate section to cylinder block, Gearbox to engine |
| M12x1.5 | 12.5 | |
| M14x1.25 | Spark plugs | |
| M14x1.5 | 14.2 | Oil pressure switch. Oil pressure outlet engine / turbocharger unit. |
| M18x1.5 | 18.5 | Oil drain plug in the sump. |
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.