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Friction shims

Friction shims

Friction shims


I am at a loss of words, is this really the state of art now? I have read that there are some cam shaft sprockets that are just held with one bolt and just depend on friction to hold location, is that true? Oh and there is no use of the shims in the joint either as if that is a huge help anyway.

RE: Friction shims

VW diesel engine camshafts have a single central bolt holding the cam pulley to a taper on the camshaft. The timing is locked in by holding the crankshaft and camshaft with locking tools with the tensioner correctly set and then torquing the central bolt. No keyway. They've been like this for at least 20 years and I've never heard of one slipping.

RE: Friction shims

The rest of the car in the junkyard long before that becomes an issue.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: Friction shims

This approach would not be used by an OEM if they were not 100% sure of its reliability in service. Auto OEMs are well aware of how costly even a recall to fix a minor problem can be.

The shims have a surface coating of very hard particles that embed themselves in the mating surface. This creates a perfectly matched interlocking fit between the shim and flange at installation. It is somewhat similar to the cap/beam interface alignment produced with a fractured connecting rod design.

RE: Friction shims

A taper will hold okay but still. Even a machine tool taper has drive keys. Yeah all a cost cutting measure, and it just has to hold till the warranty ends. I do remember seeing such things on a certain industrial engine and they were always slipping, it was for the fuel injection pump. Maybe you will see such flippant engineering on mass production but never on high performance and competition engines nor in the aircraft engine world.

RE: Friction shims

Memory says that some sprockets were attached to cams with tolerance rings. The engine crank and cam were aligned and then the ring was inserted into an annual space between the sprocket and cam.

RE: Friction shims

The Chinese GY6 scooter engine has the cam sprocket pressed onto the camshaft without any attempt at fixing at all - it is still removable and replaceable.

RE: Friction shims

The Cummins 8.3CTA engine has the camshaft sprocket fitted on a straight shaft with no retainer. Keyways and bolt holes are an inherent weakness in any shaft. Anything to get rid of the key will make the system stronger and lighter. The propellers on my tug boats are fitted on a keyless tapered shafts.

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