mini reliability
Discussion
1275 in standardish guise, perhaps a mild cam (266) and a bit of head work, keeping the CR below 10.5:1 about 3.2 FD for 10" wheels. If you ask me, failing that, putting a low boost blower on a low compression engine of similar spec. I have run some wild engines and if they produce a lot of power, you're looking at high wear. I rate the bog standard MG Metro engine, which makes a mini go like stink on 10" wheels with a 3.44 FD. Mine did explode though 
If uprating a later car with the standard gearbox a good mod is to fit the early Cooper 'S' gear set. Apart from giving slightly better ratios, the early gears are stronger as well.
Since a Mini is so awful on long motorway journeys, I always think you might as well go for better acceleration and fit a lower diff. A 3.44:1 with 12" wheels is a very good compromise.
For reliability I would always use either a cross-pin diff or a competition diff pin. It's not the engines which lack reliability, it's the transmission and final drive train where the weakness lies.
Apart from build quality, the issue of reliability largely lies around maintenance. Change the oil & filter often and not less than every 3000 miles. Use a top quality 15/50 or 20/50 oil, not this modern 'weasel-piss'. I always recommend Valvoline Racing 20/50 or Morris Oils 15/50 Multivis. Some like synthetic oil, but that's a personal choice. It still needs to be thicker than a 5W30 or 10W40, IMHO, due to the clearances in what is an old design of engine and box.
As has already been said, any well-built 'A-Series' engine will be reliable if treated properly, serviced regularly and not abused, even fairly powerful ones. The best unit is, clearly, the original Cooper 'S' engine with the forged EN40B crank and 11-stud head, but the later 'A-Plus' blocks and cranks are still very strong. Weakest units are the original 850's and the early 1275GT (Austin/Morris 1300 units with the weak centre main bearing housing).
Since a Mini is so awful on long motorway journeys, I always think you might as well go for better acceleration and fit a lower diff. A 3.44:1 with 12" wheels is a very good compromise.
For reliability I would always use either a cross-pin diff or a competition diff pin. It's not the engines which lack reliability, it's the transmission and final drive train where the weakness lies.
Apart from build quality, the issue of reliability largely lies around maintenance. Change the oil & filter often and not less than every 3000 miles. Use a top quality 15/50 or 20/50 oil, not this modern 'weasel-piss'. I always recommend Valvoline Racing 20/50 or Morris Oils 15/50 Multivis. Some like synthetic oil, but that's a personal choice. It still needs to be thicker than a 5W30 or 10W40, IMHO, due to the clearances in what is an old design of engine and box.
As has already been said, any well-built 'A-Series' engine will be reliable if treated properly, serviced regularly and not abused, even fairly powerful ones. The best unit is, clearly, the original Cooper 'S' engine with the forged EN40B crank and 11-stud head, but the later 'A-Plus' blocks and cranks are still very strong. Weakest units are the original 850's and the early 1275GT (Austin/Morris 1300 units with the weak centre main bearing housing).
Sorry, I got that wrong!
You should never do more than 3000 miles without an oil change. It's because the oil is also the transmission lubricant and the gears break down the structure of the oil itself. Remember also that the oil goes through the pump before it gets to the filter and all the crap that goes around the engine (just take a look at the magnetic sump plug) that goes through the pump before it gets filtered.
On my rally cars I change the oil after every rally.
When you think about it it's not surprising the gearbox gives trouble. After all, the basic box was designed to take 34 bhp in the original 850 and that sort of box should have EP80 or EP90 transmission oil. We are putting in excess of 100 bhp through the box and using very thin oil as well. That's why I won't go any thinner than 15w50.
In respect of engines, undoubtedly the strongest and thus potentially most reliable engines are the original Cooper 'S' series (970, 1071 and 1275). The 'A-Plus', as fitted to later cars including the SPI and MPI cars, is a good unit, although the machining and build quality of the later Rover ones can be a bit suspect and I had a problem with just that quite recently due to machining tolerances on both the cam bearing housings and the main cap machining (centre cam bearing too loose and falling out and centre main too tight causing crank to bind up). Had to 'glue' the cam bearing in and hand linish the back faces of the cente main shells.
You should never do more than 3000 miles without an oil change. It's because the oil is also the transmission lubricant and the gears break down the structure of the oil itself. Remember also that the oil goes through the pump before it gets to the filter and all the crap that goes around the engine (just take a look at the magnetic sump plug) that goes through the pump before it gets filtered.
On my rally cars I change the oil after every rally.
When you think about it it's not surprising the gearbox gives trouble. After all, the basic box was designed to take 34 bhp in the original 850 and that sort of box should have EP80 or EP90 transmission oil. We are putting in excess of 100 bhp through the box and using very thin oil as well. That's why I won't go any thinner than 15w50.
In respect of engines, undoubtedly the strongest and thus potentially most reliable engines are the original Cooper 'S' series (970, 1071 and 1275). The 'A-Plus', as fitted to later cars including the SPI and MPI cars, is a good unit, although the machining and build quality of the later Rover ones can be a bit suspect and I had a problem with just that quite recently due to machining tolerances on both the cam bearing housings and the main cap machining (centre cam bearing too loose and falling out and centre main too tight causing crank to bind up). Had to 'glue' the cam bearing in and hand linish the back faces of the cente main shells.
Gassing Station | Classic Minis | Top of Page | What's New | My Stuff