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MikeK · 03-20-2021, 05:00 PM

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You are looking at plastic deformation. The cause is the inherent un-damped shock wave that traverses a crankshaft with no front harmonic balancer.

It is only visible because of the great amount of plastic deformation before grain boundary failure your particular gear has. Is it a 'billet' gear or a cast gear? Billet aluminum exhibits great plastic deformation in exchange for a lower Young's modulus of elasticity. Cast aluminum gears are 'stiffer' and generally fracture (break off teeth) before reaching that must plastic movement. It does NOT mean the gear is inferior, nor the mesh.

If you had a layered fiber gear it would crush away to a point of excessive lash. If you had a short fiber compressed gear it would have broken teeth. If you had a typical 319 or 356 alloy cast gear, usually T5 heat treatment, it would be developing grain boundary faults, prior to emminent failure.

The real question is what is happening with your particular engine, or driving settings that is causing this excessive crank shock. Excessive advance? Too hot a plug causing detonation/ spark knock? The next thing to fail will be the rear crank bearing journal. Snap!!

03-20-2021, 05:00 PM	#6
MikeK Senior Member Join Date: May 2010 Location: Windy City Posts: 2,919	Re: Is this normal wear? Aluminum cam gear Sponsored Links (Register now to hide all advertisements) You are looking at plastic deformation. The cause is the inherent un-damped shock wave that traverses a crankshaft with no front harmonic balancer. It is only visible because of the great amount of plastic deformation before grain boundary failure your particular gear has. Is it a 'billet' gear or a cast gear? Billet aluminum exhibits great plastic deformation in exchange for a lower Young's modulus of elasticity. Cast aluminum gears are 'stiffer' and generally fracture (break off teeth) before reaching that must plastic movement. It does NOT mean the gear is inferior, nor the mesh. If you had a layered fiber gear it would crush away to a point of excessive lash. If you had a short fiber compressed gear it would have broken teeth. If you had a typical 319 or 356 alloy cast gear, usually T5 heat treatment, it would be developing grain boundary faults, prior to emminent failure. The real question is what is happening with your particular engine, or driving settings that is causing this excessive crank shock. Excessive advance? Too hot a plug causing detonation/ spark knock? The next thing to fail will be the rear crank bearing journal. Snap!!