Ignorance of BMC started with Lord Nuffield - trust me, you are not alone.
We elected to skip the damper for the following reasons -
1. The original damper was intended for a 1400 with a longer stroke. It was a rubber molded steel affair, and we had no reasonable expectation that it would last at 8,000 RPM, nor were we convinced it would do any good on this configuration.
2. When we were having the crank made, I checked into the idea of using an aftermarket Chevy liquid damper, and simply having the snout of the crank ground to accept the Chevy piece. It proved unworkable due to the concentric oil pump drive having a smaller diameter than that of a SBC damper.
3. Note the short stroke of the engine - 55.5 mm - the rod journals OD does not extend beyond the OD of the main journals. It's made of EN40, and the combination makes the crank quite stiff and exceptionally over-engineered for a 1 liter engine. The radius grinding is impeccable, as is the rest of the workmanship on the crank.
4. There are plenty of 1275 A-series racing engines running without a damper, and we're talking a much longer stroke with only 3 main bearings! Personally, I wouldn't do it, but the K-series bottom end is a lot more stable than the A-series, plus it utilizes a girdle.
5. I may be wrong on this, and I certainly wouldn't count on it if not for the other factors involved, but I mentioned the oil pump earlier - it's located on the front of the engine and is a concentric drive arrangement that encircles the crankshaft. It's my thought that the pump acting against the oil absorbs some of the harmonics, and I suspect the same holds true for the cam belt. Might be insufficient exertion against the harmonics the crank is likely to see, or I might be completely wrong, but if I am, I’ve still got responses 1-4.
The crank came balanced from the grinder, so I wasn't surprised when Mark posted up that bit of news.
We'll likely just match weight the rod/piston combinations and see if we can keep it to within a gram per assembly. That worked on the Grenade.