Just as a quick update, went for another spin today and even under mild throttle I had a pop a couple of times when I didn't get off the clutch smoothly enough that, after hearing you guys, could certainly have been the belt slipping a spot. So the belt is either loose or the bevel box is moving more than it should creating that slack under load. I'll try to nurse it until first service and have them check both.
As for the break-in, I'm mostly cruising aroung around the 3k mark but have run it up through the revs a few times. (I was immediately deterred by the banging!). The range of revs and loads is modest but certainly not out of a lack of consideration, in fact it's deliberate as I want a good bedding in of the engine.
To put this in context, my usual way of running in engines is to run them flat out for the first 50 miles, under load and through all revs, preferably with non-synthetic oil, then change to synthetic, and job done. Most break-in procedures are a myth IMHO. I've seen poorly maintained high-compression diesel engines with half a million miles on them and you can still see the boring marks from when they machined the cylinders! The first few miles are the most important, but to create a good seal between cylinder walls and piston rings. If you wait 500+ miles before putting load on the engine the rings will already have hardened and never expand properly. You will have poor compression, blow-by, dirty oil, and oil consumption.
Call me crazy but I do this to all my cars, have never had a wear issue despite them all being tuned to rev higher than stock, going on plenty of track days, they have above factory-spec compression even after 150k miles in one case, and they don't need a single oil top up between 15,000 mile services. They've always dyno'd above manufacturer specs too.
Granted I'm not familiar with S&S but I assume they don't chissel the cylinders out of a block of cheese, or am I mistaken?
(Though I am religious about warming engines up properly and NEVER lugging if that helps)
