I have everything I need in a big box to build another engine, and have just got my hands on the older version BGM 177 ally/Nikasil kit (BGM1770B). I bought it cheap just from photos, and I knew it had seized before, but that the barrel was OK, I also knew that the piston and head had been involved in quite a party before it all came to a grinding halt.
I've never played with Nikasil before, but know that you chaps approach with caution, and I've also seen some of your pistons after various degrees of calamity, where you've cleaned-up and carried on with new rings, as I have with my current engine, so I'm hopeful this will all be OK to play with.
So, the first thing to do is to decide whether this kit I've got is going to be worth my time and trouble – that's the question after all the preamble: Is this worth saving, and a decent basis for knocking up a mildly tuned engine?
Below are photos of the barrel after just a scrub, a squirt, and a quick rub with a bit of Scotchbrite; there are very light marks, but no deep damage, anything I can catch with a nail, no signs of any delamination, or damage to Nikasil edges round ports; I can polish the marks out a bit more unless it'll do more harm than good:
Photos below also show the head squish band and the piston crown both have quite a bit of damage . I've given both a good clean and rub-down to get a better idea of depth of damage Note that the raised ring on this head is not the sealing surface, it's the squish band in a recessed head. It seems to me that I could make both of these pristine(ish) again, if it's necessary to go further than I have, and the resulting increase in squish could be recovered by a home-done skimming of top of barrel with wet and dry/plate glass. All measurements/volumes port timings etc. yet to be measured, but removing from the top of barrel doesn't change port timings anyway.
A new set of rings would be on my shopping list (these are 1mm and some flash 'extremely break-proof' material btw), but as an idea of wear to barrel and rings before seize, the ring gap with these rings is 0.3mm. This was one thing I wanted to check before getting too keen because I have no idea about cost/viability of honing Nikasil, but doubt it's easy or cheap, so wouldn't have posted here at all if the Nikasil was already thin and I'd fallen at that hurdle. It seems new rings (and delicate hone?) would get it back within tolerances.
I have a set of head/base gaskets, which are pretty knackered, but I'd make my own anyway, to precisely suit whatever thickness is needed for my port timing, which I would intend to be similar to my current engine (about 123°TD).
I'd be opening the transfers, matching the casings, (also matching to the casings, as best I can, if possible, of the engine I'm running now, so I could swap it if needed), tweaking the inlet pad and crank for inlet timing; maybe looking again at l/s crank if it makes achieving timings easier without Dremelling the Nikasil or skimming the barrel, but not just for the hell of it, or for 10cc.
It seems to me that I could, in the future, get the new BGM 177 piston, this piston is a 'B', so maybe a hone and a 'D' piston? But I would prefer to use this piston for now, and 'B' is not in stock anyway; this used kit cost me less than the new piston.
So, that's the background and plan; question again: is this worth saving, and a decent basis for knocking up a mildly tuned engine? If not, I'll just sit on the job again; I really don't need yet another spare engine, or want to spend loads, I just thought it might be something to fiddle with over winter.