It's a grey import, manufactured in 1988 and I'm the ninth registered owner. Some digging around revealed it had arrived in the UK via grey import specialist BAT Motorcycles in 1994. The NC24 and the preceding NC21 model were intended for the Japanese market only and there's little printed material in English. Fortunately the Japanese workshop manual is well illustrated and good online resources include the 400greybike forum and the "Honda VFR400 NC24 & NC21 Community" Facebook group.
Initial inspection of the exhaust system revealed that the collector box was beyond repair. Its also a discontinued part and worse still its not possible to remove / replace without it without removing the engine from the frame.
The replacement subframe (from eBay - where else?), frame and wheels together with the engine covers were powder coated by Triple S Powder Coating in Bingley. New bearings and bushes were easy to source and replaced where necessary.
At the time a used replacement collector box in anything like decent condition was impossible to find. Eventually I discovered MLB Manufacturers in Taranaki, New Zealand who were manufacturing copies and I bit the bullet and ordered one. The fit wasn't perfect but it was a good starting point and it did the job. (Note: I have since replaced this collector box with an as-new original from the Facebook group, more may be available)
The inlet rubber mounts for the carburettors were rock hard and cracked so new ones were fitted. There’s definitely a knack to fitting the carbs on the rubbers. I've found the best way is to lightly smear red rubber grease on the inside of the rubber mounts. Carbs were cleaned, jets replaced using a Japanese service set and float levels adjusted.
Internally the engine required little work other than replacing the water pump due to corrosion and setting the valve clearances. The appearance of the coolant hoses didn't inspire any confidence so these were replaced by a Samco set.
The electrics were in surprisingly good condition except for the HT leads and plug caps which were definitely past their best. A new set was hard to find and eventually I got some made up with some nice leads and plug caps by Rick Oliver. The entire wiring loom was checked for damage and all connections carefully cleaned as some were showing slight signs of corrosion.
The standard regulator has a poor reputation for reliability and R6 regulators seem to be a popular alternative. Fitting details are well covered in the 400Greybike forum. I was initially looking out for a connector off an old R6 wiring loom but found a new connector plug kit for £3. Its very important to solder the connectors rather than crimping them on. The regulator was a tight fit and I had to file two rounded slots in the fins to make room for the ht leads which are routed below it.
Stripping the forks I found that the polymer bush on the fork anti dive mechanism had worn but was I unable to source a replacement - another discontinued NC24 part. The hardened steel piston collar (also discontinued) which fits inside the bush had cracked causing it to be slightly wider where the snap ring fits. Searching online I found plain bronze bushes (8x11x8mm) at £7 for a pack of 5. It was an easy job to press out the old worn plastic bush and fit the bronze bush.
A metallurgical analysis revealed that the collar had been produced from a free cutting steel with a nominal composition of 0.42% carbon, 0.23% sulphur and 1.0% manganese; the surface hardness was 55HRC. High machining rates are achieved during production by using free cutting steels but this is at the expense of ductility and toughness, undoubtedly compounded by the high hardness. I've since had some replacement piston collars machined from Uddeholm THG 2000, a high strength special steel, prehardened and tempered to 40HRC, which I'd expect to be a significantly more crack resistant than the free cutting steel originals. Please note that this modification is the way I carried out the work and should not be understood as the official or necessarily the correct way.
Fork servicing can be tricky if both legs are dismantled and the parts mixed or if they have been previously reassembled incorrectly. Some internals of each leg are different and unfortunately there isn't (to my knowledge) an English manual as the NC24 is a Japanese import. However they are very easy to work on and only needs a few minutes study of the online parts microfiche or the Japanese parts and workshop manuals. Firstly the stanchions are different lengths and the shortest fits in the antidive leg. The oil dampers are different too but are easy to identify from the microfiche and I've shown them in the photo below. The source of most confusion seems to be the alloy oil lock piece which should fit on the antidive side with its flange down. Again this is clearly shown in all the microfiche and manuals but many seem to assume this is a printing error and install it the other way. The fork springs are installed with the tightly wound section uppermost. The images below show the lower fork leg components
In contrast the popular 90s magazine, Grey Bike generally praised the NC24s handling during its road test of a 1987 model. I guess that's both a reflection of suspension at the time and relaxation of the springs over 30odd years.
Some new and aftermarket parts can still be obtained from cmsnl, Wemoto and David Silver Spares. Additionally Rick Oliver, although a Honda NC30/35 specialist, can also supply some parts. Many NC24s have ended their lives at the breakers and there is a large used spares market. However certain items are becoming increasingly rare in good condition and you can expect to pay a premium! These include:
Petrol taps with filters
Air intake snouts and frame retainers
Genuine fairing panels