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y0733 Big Scale-EXTREME, adjustable 3 - shoe clutch

EUR 149,90

piece - + shipping costs
all prices include VAT

1 2 3 4 5  (
piece: piece

Available from stock
Available from stock
Place your order within the next 30.01.23 14:00:00 and we will ship Monday,  30 . January 2023

With the Big Scale-EXTREME an adjustable clutch for very special requirements has been designed:
  • For large-displacement engines
  • For heavy or high traction cars (Losi, HPI)
  • For modified performance engines
  • For the demanding off-road use

Rapid wear of a clutch is a sign of constant slipping, even beyond engagement speed. In this case, the clutch does not transfer the applied torque.

This is where the Big ScaleEXTREME sets a new standard.
The new design of the "Extreme" prevents the centrifugal forces of clutch springs or lever side of the clutch shoes from counteracting the centrifugal force of the friction pad side even after engagement.
As a result this clutch can transfer lots of power with minimal wear.

The new design ensures that the centrifugal forces are transferred in full to the clutch lining. Precise engagement and disengagement even under high loads and inside of closed clutch bell carriers means no problem for this clutch.

The clutch can be easily adjusted to the engagement speed through three set screws without clutch bell removal, so you can match the characteristics of your engine.

The special clutch lining of the Big Scale-EXTREME is particularly wear-resistant and - especially in combination with a high-quality nitrited clutch bell (to the clutch bells), guarantees for an exceptionally long service life! Contrary to the "Cross" or "Race" version there's no need to uninstall the clutch from the engine for maintenance. All parts are easily accessible from the front after removing the front plate.

Please see the specifications tab for further information and handling advices!

The regular price of the Big Scale-EXTREME is EUR 139.90

Handling instructions for y0733 BigScale-EXTREME clutch

The Big Scale clutch will be bolted to the crankshaft using the supplied CSH-screw.
It should be noted that the use of thread locking compound on that screw is neither necessary nor recommended!

Remove the CSH-screw with a 4 mm Allen wrench; then insert a suitable M8 bolt and remove the clutch from the crankcase cone by tightening that bolt.

Hole for adjustment:
For clutch adjustment without removing the clutch bell a 4 – 4.5 mm hole must be drilled into the clutch bell for access to the adjustment screw. Placement of the hole depends on clutch bell dimensions and car; so you have to make your own measurements for the placement of the hole.
It is important that the drilled hole is thoroughly deburred (at least on the inside of the clutch bell) to prevent excessive clutch pad wear.

Many clutch bells already come with an appropriate adjustment hole.

Some models can also still be required to drill an adjustment hole in an appropriate location to allow for clutch adjustment in the assembled state.

If a previous BigScale clutch is replaced by the new "Extreme", no changes are required. The adjustment screws are located in the same plane.

Breaking in:
A new clutch or shoes fitted with new pad should always be broken in. Therefore the clutch engagement speed should not be too high for the first tank of fuel. This gives the lining the possibility to adjust to the clutch bell without glazing.

However, it is not required to wait for the pads to carry full face for a full load. The wear of the clutch is that low, this would actually try your patience.

The springs for the BigScale Extreme clutch are available in the following wire diameters:
  • 1.4 mm, for particularly low engagement speeds. Recommended for exceptionally high torque engines where a high engagement speed makes the vehicle uncontrollable.
  • 1.5 mm (stock spring), well suited for high-torque engines in 4WD and 2WD vehicles
  • 1.6 mm, suitable for heavy or 4WD vehicles with stock engines where you prefer a slightly higher engagement speed
  • 1.7 mm, applications similar to 1.6 mm, but more towards bashing than track
  • 1.8 mm , for particularly high engagement speeds: i.e. for 4WD inroad cars

The setting of the engagement speed is done via a set screw in each clutch shoe using a 2.5 mm Allen key.

Turning the screw in increases engagement speed, backing it out will lower engagement speed. Since the adjustment screws are preloaded by the clutch springs (like the idle adjustment screw on the carburetor) after setting, the use of thread locking compound is not necessary.

Compared to the BigScale clutches "Cross" and "Race", the "Extreme" will only slip in a relatively narrow rpm range. Below this range the clutch is fully disengaged, above that range the torque is transferred with almost no slippage.

Finding the best clutch engagement speed:
The best clutch engagement speed should be found while driving on the track; it depends on engine characteristic, track layout, track surface and driving style.
It is recommended to start with the lowest setting.
That is, the adjustment screw has just about half a turn of preload on the spring plate and you are now slowly, step by step turning the adjustment screws in; 1/8 to ¼ turn at a time while doing test runs after every adjustment.

If you feel that you have exceeded your best engagement speed (clutch will engage at too high rpm), back the screw out for a little bit to avoid excessive wear or glazing of the pads.
When turning out the springs will follow the adjustment screw precisely and without delay.

Of course, one will always try to maintain the bias for all three shoes about the same. However, small deviations have little effect on behavior or clutch wear.

Spare Parts:
No matter how good or reliable, a centrifugal clutch is and will always be a consumable item.
Therefore, all components of the clutch are available as spare parts, of course.
With the clutch shoes you have the choice of either clutch shoes and lining separately for DIY glue-on (with adhesive Clutch-Safe y0743), or as a ready –to -install bonded unit.
Since the connection between lining and shoe is highly loaded, the careful bonding with curing in an oven is of particular importance. We therefore recommend getting the bonded unit, if necessary.

However, due the low wear of the BigScale EXTREME you’ll be probably surprised how long it takes until that moment...<


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