Does anyone have experience with big singles in small alloy frames?

[pete376403]

One of my early speedway bikes used to vibrate like a dog shitting a length of chain. The engine bolts were tight, but the holes in the cases were worn due to having been run with bolts loose before I got it. I fixed a lot of the vibration by reaming the holes to be a close fit to oversize (ie next size up) bolts. Reamimg is more accurate than drilling. I also made a head steady that went from one of the cylinder head bolts to the frame junction under the seat. With the new bolts and the steady, while not smooth as such, I could at least ride it without my foot being vibrated off the footrest.

[roogazza]

Anything you would have done to change the mounts?

Hey bud , I was chatting to you at Manfeild ! My mate is the one with the RGV with the DR650 in it. I know his thing vibrates too, but hasn't suffered from any broken mounts as yet. He lock wires everything and uses Locktite, but still has to go over it after every outing.
Look for him at the winter series his name is Mark, No.176 I think ? Gaz.

[Coyote]

You can check out the RG and see how it's mighty single cylinder engine is mounted

Got me thinking about getting a big engine for the RG project now. A KX500 mill would be fun...

[koba]

One of my early speedway bikes used to vibrate like a dog shitting a length of chain. The engine bolts were tight, but the holes in the cases were worn due to having been run with bolts loose before I got it. I fixed a lot of the vibration by reaming the holes to be a close fit to oversize (ie next size up) bolts. Reamimg is more accurate than drilling. I also made a head steady that went from one of the cylinder head bolts to the frame junction under the seat. With the new bolts and the steady, while not smooth as such, I could at least ride it without my foot being vibrated off the footrest.

Your bloody well right! The top mount was suffering the most, obviously due partly to the bolt being way to small and not a fit and the frame not being braced right.
Fortunatley the softer bit thats been muched is in the mount I've introduced to my hacksaw friend!

[koba]

Hey bud , I was chatting to you at Manfeild ! My mate is the one with the RGV with the DR650 in it. I know his thing vibrates too, but hasn't suffered from any broken mounts as yet. He lock wires everything and uses Locktite, but still has to go over it after every outing.
Look for him at the winter series his name is Mark, No.176 I think ? Gaz.

Hey, hopfully I will see you guys back there in the near future!
Yeah LOTS of locktite! We soon found out which bolts had none on them...!
All this flucking around with mounting and bracing is just to keep the motor in the bloody frame without it shaking its way out!
Maybe his mounts are better built?
I guess Im going to have to get used to coming off the track a few fillings short of a smile
But what smile I do have is going to be very wide!

[Fooman]

teel is a far more flexible material than ally. it absorbs vibration a LOT better than ally.

Ouch, cannae let this one slide...

Steel, as a material is stiffer than alloy, by approximately 3 times. But because alloy is ~ 1/3 the density, you can have 3 times the material for a frame of the same weight, which can increase the overall rigidity.

Essentially rigidity = (some constant) * E (modulus of elasticity) times I (second moment of area of section resisting the bending force)

E for steel is ~ 210 GPa, E for Alloy is ~75 GPa

I is the area moment of inertia, and is a function of the distance perpendicular from from the centroid of the section cubed and/or the distance parallel to the centroid - a rod twice the diameter has 16 times the stiffness.

The problem with alloy frames is not really stiffness, but damping, and susceptibility to fatigue cracking. Alloy doesn't have the same inherent damping characteristics as steel, hence:

Then there are theorys about putting sand in the frame etc etc... but those are just rumors i have heard.

so, an underdamped alloy frame will vibrate at a higher amplitude and for longer than a steel frame (given the same input load). The vibration (repeated displacement) is translated into a repeated (cyclic) stress by the elastic stiffness (E) of the material.

Steels will not fail in fatigue if the cyclic stress is below a certain level. This level is affected by a number of factors - surface finish, stress ratio, material condition, but it is always there. So if the vibrations are low enough, the steel will not fatigue.

Alloy on the other hand, will always suffer from fatigue, regardless of the stress level - the lower the stress, the longer it it last, but it will always fail.

So, having an alloy frame for a big vibey single is not ideal - the material characteristics of the frame means that the vibrations will be bigger, and the frame/mounts will eventually crack. This is generally not a problem in production bikes, as engines would be balanced, rubber mounted, and the frames would (should) be designed to last a few billion engine revolutions.

Glenn's suggestion of a sub-frame is a good one - but mount the single with rubber mounts in the sub-frame, and use the sub-frame as a stressed member in the alloy frame, if the engine was originally a stressed member.

Check out John Robinson's Motorcycle Tuning: Chassis book as it has some details on engine mounts.

Cheers,
FM

[avgas]

Ouch, cannae let this one slide...

Steel, as a material is stiffer than alloy, by approximately 3 times. But because alloy is ~ 1/3 the density, you can have 3 times the material for a frame of the same weight, which can increase the overall rigidity.

Essentially rigidity = (some constant) * E (modulus of elasticity) times I (second moment of area of section resisting the bending force)

E for steel is ~ 210 GPa, E for Alloy is ~75 GPa

I is the area moment of inertia, and is a function of the distance perpendicular from from the centroid of the section cubed and/or the distance parallel to the centroid - a rod twice the diameter has 16 times the stiffness.

The problem with alloy frames is not really stiffness, but damping, and susceptibility to fatigue cracking. Alloy doesn't have the same inherent damping characteristics as steel, hence:



so, an underdamped alloy frame will vibrate at a higher amplitude and for longer than a steel frame (given the same input load). The vibration (repeated displacement) is translated into a repeated (cyclic) stress by the elastic stiffness (E) of the material.

Steels will not fail in fatigue if the cyclic stress is below a certain level. This level is affected by a number of factors - surface finish, stress ratio, material condition, but it is always there. So if the vibrations are low enough, the steel will not fatigue.

Alloy on the other hand, will always suffer from fatigue, regardless of the stress level - the lower the stress, the longer it it last, but it will always fail.

So, having an alloy frame for a big vibey single is not ideal - the material characteristics of the frame means that the vibrations will be bigger, and the frame/mounts will eventually crack. This is generally not a problem in production bikes, as engines would be balanced, rubber mounted, and the frames would (should) be designed to last a few billion engine revolutions.

Glenn's suggestion of a sub-frame is a good one - but mount the single with rubber mounts in the sub-frame, and use the sub-frame as a stressed member in the alloy frame, if the engine was originally a stressed member.

Check out John Robinson's Motorcycle Tuning: Chassis book as it has some details on engine mounts.

Cheers,
FM

Fair enough.....except for annodising
but i liked the fact that you mentioned that aluminium cracks. its why i still prefer cro-moly mountainbikes

[Fooman]

Fair enough.....except for annodising
but i liked the fact that you mentioned that aluminium cracks. its why i still prefer cro-moly mountainbikes

Anodising doesn't really affect the physical properties of alloy (stiffness/damping). The layer of aluminium oxide is generally too thin. It will help protect from corrosion, which (sort of) increases fatigue resistance - corrosion pits can act as fatigue crack initiation points. But it won't affect general fatigue crack initiation from things like sub-surface flaws (e.g. oxide stringers or incoherent precipitates) or poor machining.

Cr-Mo-V steel framed pedaly here as well...

Cheers,
FM

[Ivan]

Hey bud , I was chatting to you at Manfeild ! My mate is the one with the RGV with the DR650 in it. I know his thing vibrates too, but hasn't suffered from any broken mounts as yet. He lock wires everything and uses Locktite, but still has to go over it after every outing.
Look for him at the winter series his name is Mark, No.176 I think ? Gaz.

I know the bike it was at tech last year

Black isnt it?

[roogazza]

I know the bike it was at tech last year

Black isnt it?

Thats the one , its finally reliable now but the vibes persist. G.

[The Pastor]

Ouch, cannae let this one slide...

Steel, as a material is stiffer than alloy, by approximately 3 times. But because alloy is ~ 1/3 the density, you can have 3 times the material for a frame of the same weight, which can increase the overall rigidity.

Essentially rigidity = (some constant) * E (modulus of elasticity) times I (second moment of area of section resisting the bending force)

E for steel is ~ 210 GPa, E for Alloy is ~75 GPa

I is the area moment of inertia, and is a function of the distance perpendicular from from the centroid of the section cubed and/or the distance parallel to the centroid - a rod twice the diameter has 16 times the stiffness.

The problem with alloy frames is not really stiffness, but damping, and susceptibility to fatigue cracking. Alloy doesn't have the same inherent damping characteristics as steel, hence:



so, an underdamped alloy frame will vibrate at a higher amplitude and for longer than a steel frame (given the same input load). The vibration (repeated displacement) is translated into a repeated (cyclic) stress by the elastic stiffness (E) of the material.

Steels will not fail in fatigue if the cyclic stress is below a certain level. This level is affected by a number of factors - surface finish, stress ratio, material condition, but it is always there. So if the vibrations are low enough, the steel will not fatigue.

Alloy on the other hand, will always suffer from fatigue, regardless of the stress level - the lower the stress, the longer it it last, but it will always fail.

So, having an alloy frame for a big vibey single is not ideal - the material characteristics of the frame means that the vibrations will be bigger, and the frame/mounts will eventually crack. This is generally not a problem in production bikes, as engines would be balanced, rubber mounted, and the frames would (should) be designed to last a few billion engine revolutions.

Glenn's suggestion of a sub-frame is a good one - but mount the single with rubber mounts in the sub-frame, and use the sub-frame as a stressed member in the alloy frame, if the engine was originally a stressed member.

Check out John Robinson's Motorcycle Tuning: Chassis book as it has some details on engine mounts.

Cheers,
FM

Shit, Im learning about that shit at uni, Motorbikes ftw.

[koba]

Wow fooman!
Thats a lot to digest!
Thanks tho it is very useful info!
I really like the rubber mount subframe idea, however is probably a wee bit beyond my ability/budget at the moment.

Im buzzing with ideas on how to do such a thing but it may be somthing to do medium term with a temporary fix for now.
The bike Isn't going to be doing to many Kms this year so hopefully minimal use will mean minimal damage!

I have made up some braces out of the 7/8 tube (american sounding I know)

Didn't use inch square box (sorry 25mm box) because its just a fraction to tight between the frame and motorand im reluctant to hit the camchain tensioner with a file!

Also tube should also be better where im not 100 percent sure on which direction the major vides are moving? not sure on that but it seems logical.

Looking for the book fooman meantioned!

I've borrowed another book off a mate called "Motorcycle chassis design: the theory and practice" by Tony Foale and Vic Willoughby.

It is an excellent book and highly recomended, its not to technical so Its easy as to read yet still conveys bucketloads of knowledge.

[avgas]

Anodising doesn't really affect the physical properties of alloy (stiffness/damping).

Really? Thats quite interesting to hear as i have never had anything anodized fail on me Yet i seem to always have issues with everyother matierial failing around the anodised aluminum.
But it terms of dampning, anodising is a dog. I was tempted to put it on a few projects in Fonterra - but the vibrations coming off the lines made most earthquakes seem pathetic. Shame too - as it ment that the aluminium/steel guides that were put in didnt last more than 5 years. You keep building shit stronger and the monkeys keep finding ways to break it. Forklifts are a chassis worst enemy round a factory.

[The Pastor]

kinda a stupid thing, but if you fill it with sand, make sure you dry the sand out first..............

[bumsex]

you are lucky that you no longer have the twin balancer shaft assembly. I had a klr600 recently which had shat the balancer shaft drive chain. The rear balancer chain I think also drives the oil pump, so the engine was a mess.

By the way I tried to find an aftermarket counter balancer drive chain to suit but could not find one anywhere. I ended up buying the original part from kawasaki for just over $400. yes, 400 bucks for a length of roller chain.