Excellence in engineering.

The courier took a bit longer than I thought*, but I have received the cylinder head back from SRM.

In a word: wow.

Although my assembly was not flawed in terms of "what goes where" (after all, the bike did run!) it's clear that I could have taken care of some engineering jobs before putting valves and such in there.

Think of this as the difference between putting together a Lego set, and properly rebuilding an engine.

Geoff, the engineer who did the work, was very helpful and accommodating in noting the details I shared at the start, my paranoias, and to provide options as to what could and should be done.
This is good customer care (bordering on counselling actually), and the cylinder head got the best possible treatment, tailored to what I want the motorcycle to do.
He reckons that the noise I was hearing was more to do with the head gasket blowing than anything else. He also said that they didn't find anything particularly wrong with what I had done (again, the engine ran) so it was more a question of improving rather than fixing.

I take some pride in that, because it means I didn't completely mess things up, but did a good enough job after all.

Let's go over the details of this refurbishment: "details" being the key word here and they are impressive when you look closely.
Starting with what was less than ideal in the first place, the guides were not really suitable for the valves I fitted because clearances were out of spec.
In addition, the valves were generally not seating and, crucially, sealing properly, which means that although the engine was able to run, it was probably losing quite a bit of power because of that.

Both exhaust rocker spindles and some other parts, such as all thackery washers behind each rocker were replaced, and in the case of the spindles it was more than just a matter of best practice.

Above are the springs, valve guide seals, thackery washers, and exhaust rocker spindles, all replaced with new items. If you zoom in on the spindles you can see they are a bit mangled, not good really.

This is what was done:

To begin with, the head was given a proper clean and it does look fantastic. At first I thought it had been painted (perish the thought!) but it's just a very thorough cleaning.

All four valve guides were replaced with ones machined in-house out of Colsibro. Naturally, the inlet ones are made to accept a spring-loaded oil seal. The guides were then honed against the new valves that would be fitted to ensure optimal clearance and fit. This is how it's done.

The exhaust valve seats were re-cut, and hardened steel inserts were fitted for a proper lead-free fuel conversion.

A new set of valve springs were fitted and the assembled valves were then vacuum-tested for a proper seal, so now we know they all work as they should. This means a more efficient engine, and that no horses are getting lost in the wilderness.

Finally, the head gasket, which I had also sent with the head, was properly re-annealed.

Naturally, assembly of all components is clean and accurate, all I need to worry about is putting the head back on the engine, torquing it down properly and re-torquing periodically as per the workshop manual.

I'm reminded that "any monkey can take these things apart"; putting them back together is fairly easy, but understanding exactly how it should all fit together and how it's all supposed to work takes a bit more brains. Actually doing all that takes excellence in engineering.

_____________________
* the parcel was apparently bounced up and down the UK a couple of times, then nothing seemed to happen over the weekend (surely couriers operate 24/7, right?).