DesmoNut;270178 wrote: Hi Finnomick.
The GB400TT is a sleeved-down, Japan market version of the GB500TT which was on sale worldwide, I think. Certainly was in UK. In turn, the GB500TT was a tarted-up version of the XBR500. which was a reasonably popular bike although not as popular as many thought it might be given that it's a BIG SINGLE - yes, that's right, your bike is a single, not a twin although I can see where you were mislead since it has two exhausts.
What I've got to say relates to the 500 but will apply equally to the 400. It is a 4-valve head but unlike most (all??) current 4-valve heads, it has radially-sited valves.
The engine is dry sump with an oil tank behind the right-hand-side cover. The oil capacity is very low - I seem to remember about 1.2 litres - and the tank was prone to running dry because the engines were quite heavy oil consumers, even though they didn't leak oil. Make sure you keep an eye on the oil level and also check that, when the engines running, you can see a flow of oil back into the oil tank when you take off the filler cap. If oil flow falls off even for a short time, the top end is likely to be badly damaged.
Performance was OK but mine was really a day-to-day hack. Very good for long-distance moderately fast trips, though.
It might well have been made to commemorate TT wins but those wins almost certainly weren't by a bike using this engine. A nice machine nonetheless but no road scorcher. But it'll certainly be fun.
Most engine spares will probably be the same as the XBR500 and the XBR workshop manual would be useful too, for maintenance procedures & electrical diagrams..
XBR500 photo attached for comparison.