Removing rounded clutch oil filler plugs from the flywheel

The heads on the clutch oil filler plugs on my 35 were badly rounded, hand tools could no longer grip them. I had the engine out for other purposes and took the opportunity to remove the flywheel and get serious about the plugs.

Most other stuck bolts I would use the welder and/or heat on the bolt head but I would be very reluctant to use that method on the flywheel. Fortunately the back end of the bolt is exposed and you can work on that. The method is to put a bolt in the back end of the plug and use that to turn the plug out

Step 1 The plugs are 1/2" x 20 tpi, so drill and tap for either a 3/8" or M10 bolt depending on what part of the world you live in. Conveniently the plugs have a centre hole (mine did anyway) so you know you are drilling bang on centre. Drill right through the bolt BUT only tap half the depth of the hole.

Step 2 Screw your 3/8" or M10 bolt into the hole, it will bottom at the end of the threads and drive the plug out.

Step 3 Make replacement plugs. I started with 1/2" x 20 bolts, shortened them, reduced the head height (I made my heads 1/4" high rather than the original 1/8") cleaned out the threads under the head to make sure the head of the new plug screws against the flywheel.