Time to rebuild the cylinder head

Time to rebuild the head. Although the engine was running remarkably well, all things considered, the #3 sparkplug was bothering me. It didn't seat well and I could see the sparkplug threads had been 'repaired', not to mention the crud/deposits under the valve cover. Reason enough to dig-in.

The cylinders look ok. No damage or scoring. Carbon buildup even and not excessive. Head gasket looked ok. Piano top pistons marked 89.47mm (2nd over bore) so I know the bottom end has been done at least once.

(That junk in the cylinder is from the head removal.)

The bottom of the head looks OK as far as the overall sealing surface is considered.

Here is what a properly seated spark plug should look like.

And here is what the #3 spark plug looks like when its FULLY seated. I wonder if this is affecting combustion in this cylinder?

Someone had attempted to repair the threads in the #3 spark plug hole and did not use the proper tool/technique. You can NOT use heli-coil or other standard thread repair tools/techniques to repair spark plug threads. They do not provide a proper seat for the plug nor conduct heat properly. The proper tool is called a TIMESERT. The inserts are not costly but the installation tool isn't cheap. If you need this repair done, and don't do this all the time, find a buddy or a shop who has the TIMESERT tools and inserts.

As long as we're on the subject of special tools, I highly recommend the use of the valve spring compressor/cam removal tool made for the M10 engine. It compresses all of the valves simultaneously allowing the cam to be easily inserted or removed. It can be tricky to remove/install a cam without this tool and you risk damaging an expensive camshaft.

Once the cam is removed, work can proceed on removing the rocker arm shafts. The shafts are driven out of the head with wooden dowels or long BRASS drifts, nothing else. Do not damage the end of the rocker shafts. If you mushroom the end of the shaft you will damage every item you force it through. I highly recommend letting the head soak in a parts washer over night at least. Once everything is clean, use a oil can to apply fresh, clean oil to the rocker arms, shafts, etc. while you drive them out. Take your time. Don't lose your cool and get out the BFH. I used plastic rods to keep all of the components in order as I took them off. Mating, moving parts, develop wear-patterns over time. Make sure parts go back in the positions they came out. (If you're using new parts this doesn't apply.)