Why a Light Weight Aluminium Crankshaft Pulley Must Have a Steel Centre Sleeve for Fitment.

posted in: GTT Blog & News
We have seen a few cases where other brands are selling lightweight aluminium crank pulleys which rely on a press fit + the original centre bolt for securing which end up slipping and destroying the pulley/ losing drive to the other pulleys,( from just spinning freely on the crankshaft).
Remember the crankshaft pulley drives all the other pulleys (supercharger/water pump, alternator, Aircon etc) this requires a very secure fitment!
The original crankshaft pulley is steel with an interference fitment on the crankshaft + a single centre bolt.
Our GTT crankshaft pulley comes complete with a stainless steel centre sleeve that has an interference fitment to the crankshaft, 6 equispaced M5 high tensile socket cap bolts + uses original centre bolt to crankshaft. This replicates the original crank pulleys secure fitment (steel on steel inference) + alloys out pulley to remain lightweight & easy to interchange.
Aluminium is much softer than steel and cannot ‘grip’ and secure to the crankshaft with anywhere near what is required under the high load.
The stock item weighs in at around 7 pounds .The GTT item weighs just one pound! The benefits are similar to those experienced with lighter flywheels: i.e. better throttle response and free revving. However both unit cost and fitting costs/time are considerably less than those associated with lightweight flywheels.
Our design features 6 spokes (to achieve the required strength) a separate steel sleeve to achieve the correct interference fit onto the crankshaft nose, and a bolt on pulley wheel. As we’ve said before, an interference fit between an aluminium pulley and a steel shaft is poor engineering practice. This is due to the different expansion rates and also risk of ‘picking up’, a process where the alloy welds itself to the steel shaft when you remove it .
This causes a lot of damage to the alloy part and makes a mess on the steel shaft too. Our pulley is HARD anodised to eliminate corrosion and minimize pulley wear. No other pulley gives you these important design features. The largest diameter +4% version gives the equivalent ‘gearing change’ to the supercharger of ‘-4%’. This means they are best suited to Standard, JCW or cars running a -15% SC pulley. And of course you get the quick spin up too! The above versions are intended for cars running standard rev limit only. GTT design is proven since 2004, some cars having covered 100,000 miles since fitting. V2 features damping patches for reduced resonance.
If your stock crank pulley is ageing and starting to deform causing it to make that ‘cha cha cha’ sound under load and dropping belts, then upgrading to GTT pulley is the cure, and gives much improved engine response.
Sizes available are: – 0% +1% +2% +3% +4%
Please email for advice on best size for your car.
Note: Designed for use for standard maximum engine rpm (rev limiter) only. i.e. 7000 rpm
GTT Lightweight Alloy Crank Pulley vs Standard vs ATI
Here is a quick comparison of all 3 for you guys explaining advantages and disadvantages of each type. (R53 Cooper S)
STD CRANK PULLEY. These are a very heavy but damped item . Earlier versions weighed 7 pounds ! Later versions 5.5 pounds. They can suffer with age causing a cha cha cha sound under load. Also concentricity can be an issue increasing the risk of dropping a belt .
The later version is better, partly as …is lighter but usually of lower mileage too.
ATI Pulley…..This is an aftermarket item that is actually marginally heavier than standard ( 5.8 pounds), and quite expensive. Apart from that if your standard pulley has had it and you are adamant you want to run above the stock 7000 rev limit via remap it could be a good option.
GTT Crank Pulley V2…….These are a 2 part item with steel centre sleeve on the nose of the crank, with a slide on & bolt on hard anodised 6 spoke alloy wheel . Latest versions also include a ‘belt & braces approach’ by bonding damping patches to the inside of all 6 spokes . Advantages are :-
1) VERY light , at approx. 1 pound weight the Standard and ATI items are nearly 6 times heavier!
2) Perfect balance + perfect concentricity even under heavy load.
3) Best possible engine spool up /throttle response time.
4) Hard anodised so will not corrode or wear in the way mild steel or bare alloy will.
5) Good Value ….at £159+vat half the price of ATI item for example.
6) Proven over 12 year period, having covered very high mileages and used regularly on track to.
7) Steel sleeve allows correct interference fit to the steel crankshaft yet can be removed without damage in the way an interference fit ‘all alloy’ pulley can.
Available in 5 sizes to fine tune boost (0% 1% 2% 3% 4%).
Disadvantages…Only designed for stock rev limit of 7000rpm , as a supercharged car this as high as we recommend anyway irrespective of crank pulley choice for various other reasons. Beware ignorant tuners who ignore instructions, increase rev limit then try and blame the pulley when a 12 year old oil pump fails ! Website clearly explains this to. This is true of all this type of pulley BTW. Other companies don’t even mention the max rev limit with their pulley…..They should do IMO .
So in summary with stock 7000 rev limit GTT Crank Pulley ticks all the boxes. With increased limit use a good (later version) Standard item or if passed its best then maybe the ATI item.
GTT Performance R53 Light weight Crank Pulley – Interesting Facts