What we need to know is why did these other frames fail.
Fatigue, poor design, poor welding or poor material choice.
…and age, poor care [left outside etc], internal corrosion, never designed to last forever [they were built to a price], used in a sport where mechanical abuse is part and part of it, vibration, loose engine mounts, poorly repaired. It goes on and on!
I think one area that hasn't been considered is that when a machine/structure is designed the engineer/designer factors in a theoretical life span and the part is built to that specification. In practice the lifespan is usually much longer than intended as the theoretical average user is just that - theoretical - and when you add the required safety factor.
I also think you need to consider that while every factory was trying to produce the best product they could, there are many other factors that stand in the way of your desired 'ultimate' solution.
In real world manufacturing you will never even sight 'ultimate'. When you factor in cost pressures, the need to make a profit, product cycles, deadlines, marketing requirements [the latest fad vs. sound engineering], cultural inertia, design inertia [its always worked before], material availability, tooling and manufacturing processes, etc, etc, it doesn't take a rocket scientist to see that just getting a product to market is a mamoth task.
I agree that we should use our imaginations, shoot for the stars and all that kind of stuff - but we are actually discussing are old dirt bikes designed for a certain price point, bikes designed to wear out [and be replaced], bikes designed to throw at the ground and bikes designed without the benefit of 20/20 hindsight. It is a wonder that so many have survived at all.
And again we see what GMC is saying is true that hand build frames from 4130 last longer than some of the factory CrMo frames.
The anecdotal evidence probably backs up this statement, but it is far from a proven FACT.
You are not comparing apple with apples. Japanese chromemoly from the '70s is an oxymoron if there ever was one - that name means anything with a higher quality than their substandard mild [or high carbon] steel. You also assume that because they were claimed to be constructed from chromemoly that the entire frame was built from the same material - when in actuality this was far from true.
Chromemoly was as much a marketing tool and requirement as it was a superior construction material.
GMCs products fall from a completely different apple tree and their cost reflects the care and attention he lavishes on each one. But I doubt his work practices would really suit the production line reality that manufactures use.
I think it just shows what a difficult task you have taken on in trying to answer your core question. Keep up the good work and good luck.
VMX42
