GTT R53 Eaton M45 Supercharger Rebuilds 5 years on… Updates and Developments.

What is a supercharger.

For beginners we will explain in short. A superchargers purpose is similar to a Turbocharger,(Note: normally aspirated engines have neither) it’s basically an air compressor to force more air into the engine (forced induction).. More air = more power. A supercharger is belt driven from the crankshaft, a turbo turbocharger is powered by exhaust gases. A common upgrade is to fit a reduction size supercharger drive pulley.. The smaller it is the faster the supercharger will spool resulting in more power. Typically -17% or -15% pulley is used on the R53 for more power. This can also be achieved/improved by fitting a GTT oversized Crank Pulley.


Black VS Grey Rotors

Pre-facelift cars all had the grey rotors inside the superchargers, unless it had a JCW tuning kit installed which the supercharger was replaced with the Black Rotor version (the same as Facelifts but the JCW came with a -11% reduction Pulley for more power) Typically the Black rotor versions (Teflon coated) are more hard wearing and run a tighter clearance tolerance between the rotors which has slightly better power efficiency than the grey rotors.

It has been 5 years since we started offering rebuild services for the Gen 1 Cooper S Supercharger, and has proved ever so popular! we have now rebuilt well over 500 units!

We must bring to attention that we have seen an increasing number of owners ignore what their ‘non rebuilt’ superchargers needs.

If your supercharger is noisy, (grumbling/rattling) stop driving. And get it sent to GTT a for GTT rebuild. There have been a number of occasions where owners have just kept driving until the car over heats and causes severe damage to engine. This can also result in the supercharger being beyond Rebuild!

Most should be aware by now the importance of a fully serviced/rebuilt supercharger is due to the engines water pump being driven by it… If this fails it will cause catastrophic engine damage and at huge cost.

Please see previous Supercharger rebuild articles on “News” Section for full understanding of the Eaton M45 rebuilds. For Full Spec of rebuilds please see GTT GEN 1 Supercharger Rebuild Page.

The fact of the matter is that they will all need rebuilding regardless of mileage. This is mostly due to the age of the supercharger being at least 10-15 years old the standard inferior internal oil seals perish causing all the usual damage etc. Even new units bought from MINI Direct are “New, old Stock” (and cost a whopping £3450!! inc vat) and these will all have the same Achilles’ Heel. We often receive these by customers for inspection/rebuilds as they do not want the risk of problems further down the line.

We must also point out the issues from owners who have tried buying and fitting second-hand units of ‘unknown condition’. Not only have these have become scarce and more expensive, we have had reports of loss of drive to the water-pump causing cracked heads and reports of others seizing from debris in the rotor housing……… why take the chance when GTT rebuild your own supercharger to the highest spec?


9/10 Superchargers sent to GTT only require this option, (£499 ex vat) spec Now includes:

 In addition to installing new GTT Up-rated PTO Gear Set, GTT Spindle, up-rated bearings & seals + oil change (as per previous spec). PTO Plus rebuild now also Includes: Removing Snout & inspecting bearings, GTT up-rated Coupler installed + Flushing & Oil Change, Removing & Inspecting rotor pack condition (checking for excessive end float) + dressing out any high spots on the rotors causing rubbing to casing or each other + cleaning of rotors and internally of rotor housing & Repacking Rotors needle roller bearings with High performance grease.



GTT Snout Rebuilds

We do rebuild other sections of the Supercharger such as the snout/nose.. This seems to mostly be required if in the past the drive pulley has been removed/attempted to be removed without correct method/tooling, we highly advise to leave it to qualified technicians.

GTT Snout rebuild consists of: Full snout strip down, clean/flush, inspection and rebuilding. Includes 2 x ball races, new snout seal. GTT Coupler and oil change.

Fitting GTT Reduction Pulley Service

We now offer a Service to Remove Standard Pulley + Supply And Fit GTT Reduction Pulley, It is the perfect time to have your Standard pulley removed & replaced with a GTT reduction pulley during a rebuild. This is the most cost effective time to replace and the most beneficial mod for the Supercharged Mini with approx. 25-30BHP gain! Free fitting with GTT Snout Rebuild Only. £69+vat extra fitting cost in conjunction with ‘PTO PLUS’ Rebuild

Bolt-on VS Interference Fit Supercharger Pulleys

Often discovered during rebuilds damage has occurred to drive pulleys’ shaft… this is usually caused by aftermarket “bolt-on” type pulleys.

These “bolt on” type pulleys can come loose & slide along the shaft, this makes the supercharger pulley out of line with the other pulleys which causes the belt to wear very quickly or even jump off.

With some brands of reduction pulleys’ we have noticed the supercharger seal retaining clip (tab seal) has had to be removed to fit this pulley in the correct position. This is not ideal, and could result in the seal moving and leaking (one image shows how one of these brands has damaged the seal retainer clip as not enough clearance).

Another image shows where Superchargers Snout outer oil see has been severely damaged due to the seal retainer being spun around with the “bolt on type” pulleys inner sleeve.

Bolt-on’ type pulleys are known to slip, slide and even fall off on rare occasion.

Identifying the problem… A sudden loss of power will be caused by this as the supercharger has lost all drive, or intermittently as the pulley jams then slips repeatedly. This means the water pump will too! Over heating is inevitable as the water-pump is driver by the supercharger, if not fixed, worst case could result in catastrophic engine damage!

On some occasions the free spinning of a loose pulley on the shaft wears it so severely it is no longer serviceable.

GTT Supercharger reduction pulleys use an interference fit system to the shaft (same as OEM pulley) so why risk it?


Why Not To Use — Diy Supercharger Oil Replacement Kits With Syringe

We have seen this a few times where people use these kits to refill/replace the superchargers oil through the drain plugs. This is highly risky as you do not know the condition of the internals and by topping up you unknowingly are mixing new oil with all the old sludge/swarf/dust etc making a sort of grinding paste that destroys your PTOs internals… and in some instances beyond rebuild.

BMW can now only supply recon units from Eaton at a whopping £3450 (inc vat) and above…,second hand units of ‘unknown condition’ becoming both scarce and more expensive, a GTT rebuild on your own charger makes much more sense.


Engine Coolant Inside R53 Superchargers PTO?

This is a very rare case (we currently have seen around 5 cases) where the water-pumps seal fails and coolant forces its way into the Superchargers PTO ….

The water pump and PTOs… mating surfaces corrode together making a seal, so the coolant may not even be coolant dripping on the floor at all.

This is the only incident where we’ve seen the coolant get through the second oil seal in the PTO (under small gear) and into the rotor housing..

The seal behind the fork drive is also replaced during a GTT PTO rebuild. We also strongly recommend a new water pump is fitted at the same time.



You can now pay via GTT website for Rebuilds with variable options + combination discounted deals.

We ship worldwide and have been receiving superchargers for rebuilds from all over the world.