- Joined
- May 28, 2014
- Messages
- 139
Re: Featherbed frame design went against all engineering pri
I'll still preach to my old point (look back two pages or so)
- Even with dynamically balanced, rigid mounted parallel twin with somewhere around a 3.5" stroke, you're looking at vibration in places you don't want, and an overall embarrassing design for a mainstream production bike in the 70's. Keep in mind that just because we find things acceptable and neat now, doesn't mean they were that way back then. Think ammeter vs. WLA. The mechanical WLA is just excessive, poorly engineered , and not as good as an ammeter (which has the neat feature of "finding the right starting point" used by nearly every big single maker to start a bike easily). The reason for the swap mainly was the negative stigma associated with a gauge that tells you what your charging system is doing, as it indicates there could have been a need for such a thing (implications of unreliability). We know now this is not true...but back in the day different story. Keep in mind the japanese by then were offering bikes with an electric start so reliable, they kept the kickstarter hidden "just in case", only 2 or 3 warning lights, brakes that didn't rust or wear funny and "worked", and had motors that were nearly fully oil-tight. The last thing you wanted was for people to see your current product line as a "old fashioned". Cool when your product is 30 years old, or your customer base is older, but a tough sell for a new product being sold to young people.
- The bigger the reciprocating mass of the engine for a reasonable frame design, the more vibes you will see on a balance factor optimized 360 twin, that's a fact. The key is in reasonable frame design... a featherbed relies a LOT of the engine stiffness (as pointed out before) including the use of the head steady for a large portion of the steering neck stiffness. Put in a vibrational monster in there, and you'll find all kinds of problems quick. Compare that to something like a Seeley, Egli, Foale, etc.. frame and you'll find a very different story usually. The balance factor also plays a big role. Note that most makers at the time were not dynamically balancing cranks and a lot weren't even really balancing them much at all, just due to cost (balance marks were cast in, maybe lightly touched up on many bikes). If you spend the time on an atlas and weight match the pistons, weight match the rods, dynamically balance the crank, and tune the balance factor to the chassis and play around with weights, I'm sure you can get the vibes down a LOT from a factory setup. Doesn't mean that's feasible for a production bike.
- As mentioned before, keeping afloat for the next quarter decade was the main goal for Norton, not creating the next racing machine. In that regards the isolastic made perfect sense...and it actually made more sense than what most British makers were doing at the time. The problem with the commando is just that at the time, it was too much and not enough in a lot of ways, and coupled with poor management that's what ended up killing Norton.
I'll still preach to my old point (look back two pages or so)
- Even with dynamically balanced, rigid mounted parallel twin with somewhere around a 3.5" stroke, you're looking at vibration in places you don't want, and an overall embarrassing design for a mainstream production bike in the 70's. Keep in mind that just because we find things acceptable and neat now, doesn't mean they were that way back then. Think ammeter vs. WLA. The mechanical WLA is just excessive, poorly engineered , and not as good as an ammeter (which has the neat feature of "finding the right starting point" used by nearly every big single maker to start a bike easily). The reason for the swap mainly was the negative stigma associated with a gauge that tells you what your charging system is doing, as it indicates there could have been a need for such a thing (implications of unreliability). We know now this is not true...but back in the day different story. Keep in mind the japanese by then were offering bikes with an electric start so reliable, they kept the kickstarter hidden "just in case", only 2 or 3 warning lights, brakes that didn't rust or wear funny and "worked", and had motors that were nearly fully oil-tight. The last thing you wanted was for people to see your current product line as a "old fashioned". Cool when your product is 30 years old, or your customer base is older, but a tough sell for a new product being sold to young people.
- The bigger the reciprocating mass of the engine for a reasonable frame design, the more vibes you will see on a balance factor optimized 360 twin, that's a fact. The key is in reasonable frame design... a featherbed relies a LOT of the engine stiffness (as pointed out before) including the use of the head steady for a large portion of the steering neck stiffness. Put in a vibrational monster in there, and you'll find all kinds of problems quick. Compare that to something like a Seeley, Egli, Foale, etc.. frame and you'll find a very different story usually. The balance factor also plays a big role. Note that most makers at the time were not dynamically balancing cranks and a lot weren't even really balancing them much at all, just due to cost (balance marks were cast in, maybe lightly touched up on many bikes). If you spend the time on an atlas and weight match the pistons, weight match the rods, dynamically balance the crank, and tune the balance factor to the chassis and play around with weights, I'm sure you can get the vibes down a LOT from a factory setup. Doesn't mean that's feasible for a production bike.
- As mentioned before, keeping afloat for the next quarter decade was the main goal for Norton, not creating the next racing machine. In that regards the isolastic made perfect sense...and it actually made more sense than what most British makers were doing at the time. The problem with the commando is just that at the time, it was too much and not enough in a lot of ways, and coupled with poor management that's what ended up killing Norton.
