My experience in other vehicles has been the tensioner failing. I would try to beef-up this assembly. I would also try to address the idler’s mounting.

 

Totally ancient necrobump here LOL always neat to see contemporaneous discussion about these cars from in-period,
but here in this case was just me misinterpreting something.

I was reading the November 2003 issue of evo magazine where they tested a bunch of the R53 conversions available at the time - JCW, Janspeed, AMD, Digitec, BBR, Hartge, GGR, and Schnitzer - under the BBR entry I misread the description of "a stronger Cosworth-made belt idler" as being an uprated tensioner design...



...but apparently it was just a beefed-up idler pulley.

Still neat to bounce around looking for info though and be thrown back time warp style.

An episode of Top Gear did a similar group testing in 2003 as well, Series 03 Episode 04, but sadly could not find any way to watch it for free.

"Main review:
Richard Hammond tests several new Mini Coopers, finding trouble telling much difference between most of them: the BMW-official Works Cooper S, and the third-party tuned Hartge Cooper S, Digi-tec Cooper S and wild 275 bhp (205 kW) BBR Cooper S. Despite it being the most expensive and second slowest, Richard chooses the official model, favouring a warranty and more assured engineering over the small improvements in performance afforded by the others."

There was a later BBR variant that The Stig test drove which reportedly had £90,000 spent on it which seems like a ridiculous figure.




auction description:

" The phrase 'pocket rocket' could well have been coined for 'P100 BBR', an astonishing Mini with no less than 350bhp on tap, which featured on BBC Top Gear in 2006. It was converted when new by renowned go-faster specialists Brodie Brittain Racing (BBR), with the intention of making it the fastest Cooper S on the planet and, according to the vendor, it remains so to this day. Small wonder then that the total cost, including the purchase of the standard car, was in excess of £90,000. The completely reworked engine features: a big valve head; BBR cam; solid tappets; turbocharger in place of the original supercharge; high-flow fuel system; remapped ECU; oil cooler plus high-flow water pump and radiator to keep the temperatures under control; and a big bore exhaust system and stainless steel downpipes to ensure the gases exit with optimum efficiency. So potent an ensemble naturally required related uprates to the running gear and chassis, which included: a limited slip differential; anti-torque steer suspension; Polybush kit; bigger, ventilated disc brakes, and braided hoses; F1 Goodyear Eagle tyres.

This monster of a Mini is equipped with a 'Works' bodykit and finished in the strident combination of Crystal Light Blue teamed with a White roof, alloy wheels and mirror casings. The full Recaro interior is trimmed in Dark Blue hide complemented by Mid Blue carpets. The mileage covered to date is understood to be a mere 5,500 or so, and the Cooper S comes complete with the suitably apt registration 'P100 BBR' plus its original service record and owners' handbook, and is considered by the vendor to have 'excellent' bodywork, paintwork, interior trim, engine and six-speed manual transmission. Purchasers of BMW Minis have been encouraged to customise them from day one, but this breathtaking example arguably takes the idea to a whole new level! "

.

Amazingly,
the BBR website is still up today and appears to be Mazda specialists for the most part, but they have a couple of evo excerpts on their blog,
here's one of those:

https://bbrgti.com/blogs/road-tests/bbr-mini-cooper-s

And,
here's their old site with the R53 tuning kit entry as preserved by the Internet Archive:

https://web.archive.org/web/20040604...i.com/mini.php

This has been your daily dose of throwback nostalgia.

Cheers!

 

So many people especially newer owners over last five years don’t recall or not around even back then with the ***** show mud slinging lol