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Ritech Systems Limited

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Porsche 928 Flexplate Clamp Price: £170 + £4 p&p + VAT

The problem affecting all auto 928s from approx. 1984 on (when the circlip arrangement on the main driveshaft in the torque tube was dropped) is well known and documented.

There are a number of theories put forward as to why this happens, but it is a fact that the driveshaft 'winds' its way out of the clamp (or rather the clamp moves forward) even when the bolt has been overtorqued. This efect seems to be exaggerated if the torque load on the transmission is higher - ie. max acceleration between traffic lights in town.

This movement is one way so that it gradually bows the flexplate inwards towards the flywheel and puts a constant load on the end of the crankshaft. This load gradually wears the central thrust bearing away eventually eats into the block itself.

It is at this time that the engine just stops when it is warm. Letting it cool will allow it to start, only to seize again when hot. The result is a new engine!  This phenomenon is known as TBF – Thrust Bearing Failure, and is a term which will make any 928 enthusiast take a deep breath.

General arrangement of early circlip design


The left view shows the earlier pre '84 design which included a circlip for location.
The right view shows the circlip removed (the shaft actually protrudes but I had to doctor the copied drawing!
)

The circlip 1 holds the retaiing ring 2 in place and the shims X give the correct position for the clamp 3. Thus the system works as it should with any movement absorbed by the flexplate and then retuns to rest. In the right hand image the shaft can slide inside the clamp if the clamping pressure is not great enough.

There are several flexplate clamps on the market, but they all rely on extra clamping force to stop the splined shaft from migrating out of the clamp.

The best of these is well engineered and uses a taper lock mechanism which by far the most effective method for a pure clamp, but unfortunarely it requires the torque tube to be removed to fit it as the original clamp is completely removed.

The Ritech Systems clamp locates behind the splined section of the driveshaft and around the existing clamp to provide positive location of the clamp on the shaft, so that the shaft simply cannot pull out of the clamp.


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Any distance between the inside of the new clamp and the existing clamp is taken up by locking screws (not shown above). The clamp is in two halves and extremely easy to fit.
And to the actual ........  


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Fitting  
Jack car and remove the cover under the flywheel.
Undo the cap head bolt of the existing clamp and release any tension in the flexplate.
In the following picture it can be seen that the shaft has migrated and the flexplate is already under great tension before releasing.
Ensure all tension is released, Re-torque the bolt and fit half the clamp around the existing clamp, ensuring that the hardened ring fits around the end of the splined shoulder.
The end bolts and locknuts should be released at this time. Fit the othe half of the clamp ensuring all bolt holes line up without forcing and fit the hex bolts and spring washers.
Although it may be inconvenient having the heads of the bolts on opposite sides, it ensures complete balance when the clamp is fitted.
The gap between the two halves should be constant.
Excessive force is NOT required to bolt the halves together, just correct location.
You will have to rotate the engine to gain access to the bolts (use the teeth on the flywheel and ensure the engine is rotating clockwise (from front).
Once the two halves are bolted together the end bolts can be tightened by hand until they contact with the back of the clamp body.
Then the locknuts can be tightened. The clamp will then stay in position and hold the shaft and existing clamp solidly.
   
Copyright. All proposals, ideas, layouts, drawings, and detail contained in or sent with this document are property of Ritech Systems Ltd
Disclaimer
This product is intended to positively clamp the driveshaft to the existing clamp and should aid the prevention of the condition in which the shaft migrates back in the standard clamp and places constant forces on the flexplate and crankshaft thrust bearing. Such forces may have already damaged the engine in a way which would not be apparent unless the engine were to be stripped. It is advised that the flexplate tension be checked every year in any case.
Ritech Systems Ltd or any of it’s personnel shall not in any circumstances whatsoever be liable for any engine damage, personal injury or death caused by or arising out of the use of this flexplate clamp.