Pre Crossflow Camshaft Oiling Issues

[73GreenMachine]

Hi,

had a motor fail around a year ago in an unusual fashion, it seemed the timing gear was sheared off the end of the camshaft, which means that somehow there was a seizure in this area of the engine. No spun cam bearings and the hydraulic cam was brand new, got around 300km before the chain came off and pistons hit valves...Remember the engine builder mentioning something about the cam being driven back in the block but not quite sure how this could occur.
Just wondering if anyone has had similar experiences or knows of a weak point in the engine design that could cause this to happen? Am in the process of building another engine and want to try and avoid this happening again if possible!

Thanks!

 

[aussie7mains]

Ive got no direct experience of this failure, but I do know the engines well, heres a few thoughts:-
If the clearance for the camshaft thrust plate was too tight it could sieze up there.
The camshaft cant move unless the sprockect will let it, Im not sure if the taper on the caam lobes pushes or pulls the cam, probably pushes forward.
Could the camshaft bolt have become lose?
The dizzy drive gear could sieze up but its more likely to shear of the drive pin on that shaft, this does happen.

A7M

 

[MustangSix]

There's a spacer that goes on the nose of the cam behind the drive peg. If that's omitted, the cam will seize on the retainer. Usually you catch this right away, but I have seen engines assembled and run this way. Not good!

 

[xctasy]

Hope you've been able to work it all out.

I think your engine build was wonderful