TR2/3/3A Cam Sprocket Bolts - Shoulder or not

[mgedit]

Picture in the parts book shows that the cam sprocket bolts appear to have a shoulder. Called "Screw, set, chain wheel to camshaft" part number 56370. The bolts in my car have no shoulder and are threaded their entire length. I thought this might be an application with a special bolt, which is why I checked the parts book.

This extract from an engineering website suggest a set screw would have threads its entire length: "The Difference Between A Bolt And A Set Screw: The Bolt: The Bolt is characterised as without a full thread (i.e the thread does not reach the head), this part is known as the Shank. Bolts are generally not available in the shortest lengths as there is no room for the shank, and typically you will receive a Set Screw in place of a Bolt. The Bolt allows for movement. The Set Screw: The Set Screw is characterised as with a full thread (i.e the thread reaches the head). Used to prevent relative motion (no movement)."

So, it seems that a fully threaded bolt ( i.e., set screw) may be correct. Can anyone confirm the style of fastner that should be used.

Cheers, Mike

 

[Merlin63Tr4]

A shoulder bolt is correct.
The cam sprocket bolts are under shear loads while the engine is running.
You should not take up shear loads thru threads .

D.

 

[TR3driver]

Possibly a terminology difference, but the cam bolts are not what I would call a shoulder bolt. A shoulder bolt has an unthreaded section that is larger than the major diameter of the threads; while with the cam bolts, the unthreaded portion is the same 5/16" diameter as the threads. But, the unthreaded portion is important, since it does carry the load (and as noted, shear loads should never be applied to threads). The length is also critical, since it has to not interfere with the threads in the cam, when tightened securely against the sprocket.

Also, the fact that the part number does not start with two letters tells you there is something special about the bolt. If it was a common set screw, it would have a part number like HU0858.

 

[Merlin63Tr4]

You are correct, in common terminology (incorrect) the cam sprocket bolts are "shoulder bolts", but in reality they are "close tolerance machined ground bolts".

D.

 

[TR3driver]

Actually, I don't believe the shank is ground either. The bolts just have a custom grip length to suit the application. That's not to say you couldn't use a close tolerance bolt (if the grip length is right), but I don't believe the originals were.

 

[Merlin63Tr4]

Mine sure look ground, but who knows......

D.

 

[mgedit]

Thanks, I was pretty sure they should not be threaded their whole length. Will add to my next TRF order. Cheers, Mike