Unleaded Petrol and the 820
Basic design faults have caused the earlier 820's to burn out exhaust valves. The heads were designed to run on unleaded being fitted with toughened valve seats etc, but the valves were just not up to the job, this caused them to burn out in as little as 50,000 miles, the shot below shows a valve fitted to my 820 which burnt out after only 20,000 miles.
The above pictures (click for larger image) are both of a valve that had just covered 20,000 miles, I had been running the engine on unleaded fuel and this is what happened. Rover sensibly stated in owners manuals after 1988 that it is not good to run the engine on unleaded. One good thing is that you can run an M16 on either fuel without adjustment, the Ignition control ECU on both SPFi and MPFi models will automatically retard or advance the ignition if pinking is detected.
Above, two seemingly identical manuals but take a look at the backs, the top being from my 1989 820Si and the bottom being from a car boot sale but dates around 1987.
As you can see from the above shot from the 1988 onwards manual it clearly states that the engine should be run on leaded fuel only, this is why I choose to run on LRP, unleaded at a push, and only when I don't have much cash. Also the car runs far better with some leaded (potassium) flowing through it.
Above, a shot of the 1986 to 1988 manual, observe how it states how unleaded fuel can also be used. It would be too easy to blame Rover for bad design, many people at the time did and this tarnished the 800's reputation. I say the blame lies with the car industry as a whole. Here you had a new fuel, tried and tested in America but not over here. When the 800 series was coming out unleaded was beginning to catch on, with all the environmental awareness the average car owner thought 'oohh I'll do my bit and shove unleaded into the motor'. It has been said to me by several mechanics that since the advent of 'green' petrol more and more cars have had their head off for valve work than ever in the past. Unleaded by its nature runs at a higher temperature and puts added strain on the head and engine. My valve blew to pieces after a quick ranting in second under full load, I got to fifth and the car made a banging noise, a belch of black smoke coupled with some gritty looking bits shot out the exhaust, goodbye exhaust valves I thought!!!.