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Discussion Starter #21
I've got tony's book and software, it's how I'm designing the under engine shock and linkage for the swingarm. i think sometimes the issue with looking at old frames is the same as looking at pipeburn 40 years from now, the context is missing so we'll never know how successful the frame actually was. that one for instance looks like it isn't going to handle the loading applied to the frame when dealing with the shock from high speed damping, it looks like when a bump is hit, the frame is going to flex a lot. bump loading like that is actually the most intense stress the frame is going to handle, so it needs to be considered and it seems to be overlooked on a lot of older frame designs.
 

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The old heavy cases should be plenty strong enough to use as a stressed member.
"I'm not an engineer, but I play one on Caferacer.Net"

Unbelievably absurd. The CB cases were never designed to be stressed members. By no means is the alloy used in them anywhere near the same composition as modern alloys used in stressed-member case construction.

How this crap is allowed to remain on what is supposed to be a legitimate board with "knowledgable critics" (however 'harsh' or idiotic in thier criticisms), is beyond me.
 

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I'm not an engineer either, I'm the high school drop out.... As far as the mounts to the valve cover go, no matter which way you slice it, its not a good idea. This engine was never designed with the idea of attaching any mounts above the cases. You have to allow for expansion and contraction of the head and barrel, most likely by elongating the mounting holes and keeping a relatively low torque on the fasteners because the rocker cover can't tolerate much. If the mount is allowed to take up movement from expansion, then its going to allow movement from any frame flex. So why bother? With regards to using the engine as a stress member, again it was never designed with that in mind. You can talk about the type of alloy they used or how thick it is, but it won't have the same type of internal or external webbing that you will find in an engine that is designed to be used as a stress member. Could you use a SOHC 750 that way? It would really depend on what you are asking of it. If the frame was capable of withstanding most or all of the forces put upon it without the engine, then its not an issue.... but then its not really a stressed member situation anymore. You could end up with a good looking functional frame though.
 

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"I'm not an engineer, but I play one on Caferacer.Net"

Unbelievably absurd. The CB cases were never designed to be stressed members. By no means is the alloy used in them anywhere near the same composition as modern alloys used in stressed-member case construction.

How this crap is allowed to remain on what is supposed to be a legitimate board with "knowledgable critics" (however 'harsh' or idiotic in thier criticisms), is beyond me.
"I'm not an engineer, but I play one on Caferacer.Net"

I agree about unreliable engineering crap being posted on this forum GeezyPeezy, mainly concerning what you just wrote.

Egli, Moto Martin, Moko and others have successfully built sohc frames for road and race use that used the cases as a stressed member. Egli would have got his frames type-approved for road use by the German TuV. The TuV knows more about chassis stability, rigidity, durability and strength than you ever will. Fritz Egli too.

Danger, is my business.
 

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BTW, I posted a Moto Martin frame, not a Moto Morini.

No need to use chromoly tubing for a road bike, either. Good quality DOM tubing is just fine. For a race bike as well.

Measuring frame deflection or flex in a jig gives little useful data. It's not really important if frames flex, but how they flex. Manx Norton frames flex a lot, but they flex in a ' friendly ' and controlled way.

Moto Martin frames would have won more races than TF and his frames, ever dreamt of achieving. Moto Martin frames work just fine and cope with the stress of shock bump loads. The last TF race frame that ever won a race would have been when Barry Sheene got his first pair of flared jeans. If ever.

Danger, is my business.
 

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Egli, Moto Martin, Moko and others have successfully built sohc frames for road and race use that used the cases as a stressed member.
Why not show some photos that illustrate a classic CB750 engine being used as a stressed member, where the front end and rear end sandwich the engine as a TRUE stressed member?

I believe what you are talking about are not true stressed member scenarios, but rather suspended engines without lower cradles, a totally different design scheme altogether.
 

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Why not show some photos that illustrate a classic CB750 engine being used as a stressed member, where the front end and rear end sandwich the engine as a TRUE stressed member?

I believe what you are talking about are not true stressed member scenarios, but rather suspended engines without lower cradles, a totally different design scheme altogether.
No, almost all of Egli's frames are stressed member designs. Just like Honda's CBX1000, CX500 and CM400 are as well, most of those would bend the frame without a motor installed just by sitting on it. Stressed member = Q.E.D.

This Egli frame would bend in half without a motor installed as a stressed member.:

Eglidrawings.jpg

Danger, is my business.
 

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Why not show some photos that illustrate a classic CB750 engine being used as a stressed member, where the front end and rear end sandwich the engine as a TRUE stressed member?

I believe what you are talking about are not true stressed member scenarios, but rather suspended engines without lower cradles, a totally different design scheme altogether.
This is getting silly again. Any time the motor is used to contribute to frame stiffness it is a stressed member.

The question on Egli and martin frames is how much, if any, stress the crankcases take. Those frames are incredibly rigid compared to stock OEM tubing of that era. Of course that was long before chassis flex was understood by most people, and it's still not common knowledge. How much side flex is needed when a bike is cranked over and the suspension is not able to absorb bumps and other changes in the surface? How stiff does a frame need to be in the fore and aft plane? How stiff does the swingarm pivot point need to be to prevent excessive swingarm twisting? I don't know. I'm not a chassis engineer. All I can tell from my armchair is that over the last decade at least MotoGP engineers are placing more importance on chassis flex and stiffness.

It's not a new subject, but the engineering tools have come a long way, as have chassis designs, tire grip, tire flex measurement etc etc.

My expectation would be that at first look an Egli frame looks like it would be too stiff laterally if fitted with high HP motor and fat sticky tires. With skinny tires and an anemic motor, maybe that's not a problem for any of us mere mortals on the street.
 

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This is getting silly again. Any time the motor is used to contribute to frame stiffness it is a stressed member.

The question on Egli and martin frames is how much, if any, stress the crankcases take. Those frames are incredibly rigid compared to stock OEM tubing of that era. Of course that was long before chassis flex was understood by most people, and it's still not common knowledge. How much side flex is needed when a bike is cranked over and the suspension is not able to absorb bumps and other changes in the surface? How stiff does a frame need to be in the fore and aft plane? How stiff does the swingarm pivot point need to be to prevent excessive swingarm twisting? I don't know. I'm not a chassis engineer. All I can tell from my armchair is that over the last decade at least MotoGP engineers are placing more importance on chassis flex and stiffness.

It's not a new subject, but the engineering tools have come a long way, as have chassis designs, tire grip, tire flex measurement etc etc.

My expectation would be that at first look an Egli frame looks like it would be too stiff laterally if fitted with high HP motor and fat sticky tires. With skinny tires and an anemic motor, maybe that's not a problem for any of us mere mortals on the street.
What he said.

" chassis flex and stiffness. " maybe you meant 'than' not 'and' ?

Danger, is my business.
 

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This is getting silly again. Any time the motor is used to contribute to frame stiffness it is a stressed member.

QUOTE]

I suppose its a matter of how a person defines it. With his design, he is dealing with the difference between a situation where the engine is basically sitting in a cradle frame providing rigidity and a frame where the engine could be a critical load bearing element. He needs to be careful what loads and where he puts them on an engine that wasn't designed with that purpose in mind.
 

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I've got tony's book and software, it's how I'm designing the under engine shock and linkage for the swingarm. i think sometimes the issue with looking at old frames is the same as looking at pipeburn 40 years from now, the context is missing so we'll never know how successful the frame actually was. that one for instance looks like it isn't going to handle the loading applied to the frame when dealing with the shock from high speed damping, it looks like when a bump is hit, the frame is going to flex a lot. bump loading like that is actually the most intense stress the frame is going to handle, so it needs to be considered and it seems to be overlooked on a lot of older frame designs.

You should come to the USCRA races this season...Tony flies over from Spain to race every event.
 

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Yes and No......

Yes there is a difference between bolting the steering head to the top of the motor and swingarm and sub frame to the back compared to using the motor as part of the frame, but in both situations they are stressed ie they carry some of the load and contribute to stiffness.

I'm not too hung up on the semantics of at which point in carrying load should it be classified as a "stressed member". To a chassis engineer, there is probably a definition that matters but to us dudes in a room, it's not so important. IMHO :)
 

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i suppose its a matter of how a person defines it. With his design, he is dealing with the difference between a situation where the engine is basically sitting in a cradle frame providing rigidity and a frame where the engine could be a critical load bearing element. He needs to be careful what loads and where he puts them on an engine that wasn't designed with that purpose in mind.
yahtzee!

Like, for example, the guys taking Honda CX engines and using them as PRIMARY stressed members. Yikes.
 

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yahtzee!

Like, for example, the guys taking Honda CX engines and using them as PRIMARY stressed members. Yikes.
A CX 500 case is about 1000 times more rigid and strong than a front or rear motorcycle wheel's axle. You could tow a semi using a CX 500 case as a stressed member. Almost all of a bikes chassis stress passes through the axles. And they are tiny in comparison to a CX 500's stressed member cases.

Danger, is my business."
 

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Prototype followed by engineering test vehicle and pilot build. Finally a product, that's how it is done.No one will get this right the first time.
Direct from Hawai'i,the big island.
 

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Prototype followed by engineering test vehicle and pilot build. Finally a product, that's how it is done.No one will get this right the first time.
Direct from Hawai'i,the big island.
Exactly.

I guess you are not a stressed member right about now.

Danger, is my business."
 
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