In traditional soldering applications, the solder was meant to provide a seal around an already good electrical connection, therefore stopping deterioration. From this perspective, a crimped connection which is then soldered would appear to be superior.

Having said that, as pointed out by the author, there are risks of capillary action solder up the strands, hardening of the insulation, or worse - weakening of the insulation crimp leading to reduced strain relief. For these reasons, I prefer to never solder a crimp. Instead I fit a Hellermann sleeve.

There is no way for “dirt” to enter the lube oil with current filter designs. Any debris particles in the lube oil pressure circuit would have to come from the engine components themselves.

Regardless of how much coolant flows through the jacket, if the liner wall is too thick, or has a low material CTE, or is thermally isolated from the coolant flow, the bore surface will not be adequately cooled.

Besides the measures described in the article for increasing local coolant heat transfer rates, there are other less extreme approaches. First, since heat transfer between the liner wall and coolant flow only takes place within a thin boundary layer, designing the jacket shape such that it forces as much coolant flow against the liner as possible would help. Ideally it would be a thin, high velocity flow. Second, a bit of surface texture on the liner would help, since it would trip up the coolant boundary layer flow and increase the local heat transfer rate.

While inert surface coatings like oxides or phosphates can prevent galling, they only remain effective as long as they are present. Oil additives work because they constantly renew this layer on the metal surfaces. The only real benefit of phosphate coatings is to provide some limited corrosion resistance.

Racing valves which must be extremely lightweight can be made hollow from separate diffusion bonded titanium parts.

As the author notes, production engine valves are inertia welded from different materials to reduce cost. Inertia welding is also commonly used to join turbocharger turbine wheels to their shafts.

But the most recent use of friction welding is that used to produce lightweight, hollow steel diesel pistons. These hollow, welded steel pistons are lighter and have better fatigue life than aluminum pistons.

Therefore the package for high demanded engines shall be nitrided rings plus PVD. In some cost sensitive cases side chromium might be offered