I have owned 100's of motorcycles in my 16 years riding on the road. I have always had a soft spot for the ZZR1100 and have owned 6 so far and have done a lot of work on these bikes and as a qualified mechanic will let you in on what to look for.  We all know the ZZR is a fast and powerful bike but dont let these things sway you and cloud your judgement.

Gearbox. The main issue. Second gear is well known for wearing out and either popping out or sounding very rough. To repair this the engine must come out removing radiator, exhaust, fairing, chain, the engine must be split in two (crank cases) and the gear shaft removed etc. This will cost the best part of £1000 and take some time. So beware "Slight gearbox problem" read instead "Huge Repair Bill".Second gear can be tested on the road test by accelerating hard in second gear, if it pops out it's worn and will only get worse. Second gear is usually the weak one but be wary of any rough sounding gears or false neutrals.

Camshaft wear. Some of the ZZR had slightly iffy cam lobes and due to the fact that Kawasaki's run very fast on choke some pitted their cam lobes (top end of engine is the last part to get oil when oil is cold). If they are worn the top of the engine will sound rattly when cold. So make sure you hear the engine start from cold, touch pipes to see if bike has been started prior to your arrival maybe hiding issues. Ask when valve clearances were last done and check service history if it has one. To prevent motor from ruining camshafts use good quality synthetic oil and warm bike at 2000 rpm.

Chassis. Being a heavy bike (230kg) and a fast bike (170 mph) means most parts get a hard time. Rear tyres first usually last 3500 miles they can last longer but can start to feel past their best around then and start to go 'square'. Budget £150 for a rear, £100 for a front. Next chain and sprockets the ZZR has a tendency to snap worn chains so be aware of any bike with a tight spot in the chain. With bike on  main stand  turn the rear wheel and keep feeling the slack in chain in the middle of the bottom run of the chain. If there is a part that does not flex as much as the rest of the chain or the wheel becomes harder to turn then budget £150 for a new good chain and sprockets. Remember if the chain snaps it often wraps around front sprocket and destroy crank cases. Cush drive these are rubbers located in rear wheel and help take slack out of the drive line they wear very quickly on zzr and make the bike very jerky at low speed on and off the throttle easy to change and around £50.

Front and rear suspension is very good on zzr but will lose its damping at around 20,000 miles if used for touring and loaded up a new rear shock can be up to £500 new but a suspension expert could rebuild forks £150 rear shock £150 and tailor them  to your needs. They feel great when set up properly.

Brakes. Standard rubber brake hoses should be replaced every 3 years and there are 10 or 12 year old bikes with there original hoses on. These should be replaced ASAP with braided hoses (about £100). Spin the wheels on the stand if they dont spin freely at least 2 rotations they may be seized and need rebuilding. On road test if you press front brake at over 50 mph and there is a vibration the disks may be warped and that can cost up to £300

The issues I have raised may seem like a bike with serious issues but are fairly normal for most bikes that may have been wheelied, crashed, abused and badly maintained . Kawasaki made the ZZR1100 to last and with a caring owner who cleans and maintain's his bike and uses's it as intended it will last. This guide is just to make sure you dont get a bike that needs lots of money spent on it. The ZZR1100 does ride really well even when it needs serious money spent on it but so much better when it does'nt. I hope this guide has been helpful.