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3.0mm plate is too thin for a shock mount, I personally would have 8.0mm in high tensile steel or chromoly. 3.0mm flex is extreme in a upper shock mount, it should have close to zero flex. Things that flex break.

Tube is only strong in compression and tension, not in torsion like you have it. I'd cut out the shock mount plates and tube and start again.

There really needs to be one or two tubes straight from your shock mount straight to where the OEM shock mounted on the backbone.

Your theory of 3.0mm flex here equals 6.0mm flex there is basically engineering nonsense.

My advice here is all about load strength and safety.

You should not weld next to the carbs, it might cook the diaphragms. You really need to get some K&N filters before you weld everything up and find out you don't have any room for filters, and it won't ever run right with no filters or tiny junk Emgo ones.

I know you are trying, doing and learning but this does not make any engineering sense at all:

" Yes I agree, however I believe the load here on the top shock mount can be thought about as a twisting load on my new frame crossmember that supports it, as the shock is mounted offset (ie. not directly beneath it). Thick walled tube of this length is tough to twist.. And then the main load is exerted upward (downward load is only weight of the unsprung parts) and therefore a tensile or 'pull' or 'stretch' load on the section of rearward angling frame tubes from swingarm area to the cross tube (again less than 3")."

Don't take criticism the wrong way. If guys wanted to abuse you they would have and if they thought you where a total fool no one would have bothered to reply to your build thread.
 

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There really needs to be one or two tubes straight from your shock mount straight to where the OEM shock mounted on the backbone.
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I like that idea, with a little triangulation I can see that holding.
You would be effectively restoring some of the original frame geometry, which was dependant upon directing the forces towards the steering head.

You don't want flex, flex equals cracks in the welds if not in the tube. Frame flex also equates to an ill handling motorcycle. You need a stiff well shaped frame, yes you can use the engine to assist with making things stiffer and stronger, but at the same time the frame should serve to strengthen the fragile engine castings, not test its strength.
 

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I like that idea, with a little triangulation I can see that holding.
You would be effectively restoring some of the original frame geometry, which was dependant upon directing the forces towards the steering head.

You don't want flex, flex equals cracks in the welds if not in the tube. Frame flex also equates to an ill handling motorcycle. You need a stiff well shaped frame, yes you can use the engine to assist with making things stiffer and stronger, but at the same time the frame should serve to strengthen the fragile engine castings, not test its strength.
Exactly.

That motor does not have fragile engine/head cases, it was designed from the start for extreme stressed member service.

FreE wIne : hic.
 

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Discussion Starter · #44 · (Edited)
3.0mm plate is too thin for a shock mount, I personally would have 8.0mm in high tensile steel or chromoly. 3.0mm flex is extreme in a upper shock mount, it should have close to zero flex. Things that flex break.

Tube is only strong in compression and tension, not in torsion like you have it. I'd cut out the shock mount plates and tube and start again.

There really needs to be one or two tubes straight from your shock mount straight to where the OEM shock mounted on the backbone.

Your theory of 3.0mm flex here equals 6.0mm flex there is basically engineering nonsense.

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I think I need some clarification. I believe your pricinipals are sound, however I think you would build a frame much heavier than I, if you feel that 8mm plate in the manner I am using plate (on either side off the shock bolt and less than an inch from the tube it's mounted to) is the minimum you would use. I think that's overkill. The factory upper shock mount on this frame is less than 3mm plate and is part of a much larger piece.

I do agree with you that tubes are strongest in tension or compression, however as we don't ride powered unicycles all frames have bending loads on tubes. I believe choosing the appropriate wall thickness and material size is key.

Also your comment about my hypothetical flex being nonsense - are you sure? To repeat I was talking about shock vs wheel travel ratio at around 2:1, hence.3mm of flex at the shock mount would equal 6mm of wheel travel (not flex).

I'm wondering why you're so focused on flex at the shock mount. Do any of your bikes have rubber bushes in the shocks?

I do note and latke your point on eliminating breakage and safety, and I am also very aware of eliminating flex, so I think we're on the same page, however I think you're making a lot of assumptions without considering actual material strength. That doesn't mean you're wrong, just that you might be..

My plan is bracing rods that run from the shock mount to just above the swingarm pivot. This will form a triangulated reinforcement mostly in tension due to shock loads. If I tried to run tubes up to the original shock mount they'd be long and due to the angle would be operating in bending moment and therefore not a great solution. They would also block air filters, where currently I have no problem fitting k&n's, or velocity stacks with a shield that I will likely run. The nice thing about the modern wishbone linkage is all the pivots are kept very close together.

Earlysport
XS400 DOHC project, future cb750 project, Ducati 996R
 

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3mm is more or less thick and stiff enough for those mounts. 8mm makes no sense. In fact it there's enough force to twist and distort those mounts, then the force would basically tear them off the cross tube.

That's not the issue. The issue is that shock forces need to be fed back into the main frame and doing it via the subframe is not a good way to do it. Try to "move" that cross tube to the main cradle just in front of the shock rather than behind it. If that is not possible, then use additional tubes from back to front and mount the shock between them. check out an RZ350 frame for the way to do that.

But try to get the shock mount tied directly to the main cradle.
 

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It's not flex in the shock mount that is the concern, as you say flex in the shock is just another form of shock travel if it has rubber mounts, which btw mono shocks do not.

Where you don't want flex is in your frame when the loads are transfered through it.
 

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If I built a frame for this motor it would be quite similar to this Egli design. It would be about half the weight of the stock frame.

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Overengineering frames is normal practice to cope with high shock loads.

" Also your comment about my hypothetical flex being nonsense - are you sure? To repeat I was talking about shock vs wheel travel ratio at around 2:1, hence.3mm of flex at the shock mount would equal 6mm of wheel travel (not flex). " . Nonsense?, yes entirely. Frame flex is an entirely different matter than a little sag or give in suspension movement.

You can't eliminate flex in a bike frame, even the best frames flex quite a lot.

Forget fitting "velocity stacks" or cheap pods. You will never tune the bike to start easy or run right ever again.

"The nice thing about the modern wishbone linkage is all the pivots are kept very close together." The bad thing about modern link shock systems it you have a hell of a lot of high stresses all contained in one area. That is the reason they are massively overengineered and heavy.
 

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Forget the big brother aspect, why do you assume it's shade tree engineers commenting here?
I have to assume shade tree engineers because you continue to absolutely refuse to provide any sort of credentials or experience which would lead me to believe you have the slightest clue that you actually know what you are talking about. Every single comment you make, excepting a few cryptic references to potentially mythical experience or conversation, is easily attainable through a simple use of Google.


Still your pal,
 

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I have to assume shade tree engineers because you continue to absolutely refuse to provide any sort of credentials or experience which would lead me to believe you have the slightest clue that you actually know what you are talking about. Every single comment you make, excepting a few cryptic references to potentially mythical experience or conversation, is easily attainable through a simple use of Google.


Still your pal,
I ain't.

Having worked in three professional shops doing race bike chassis modification work, and fixing crashed stock bike frames and front ends over many decades, I guess I have the hands on experience and knowledge to comment here. A-grade qualified welder? Unqualified but experienced machinist? Years of MC crank, cylinder and head work working in a 50 year veteran's professional MC machine shop?

If you are looking for qualifications on the internet, I say you have come to the wrong place.

It's not "mythical experience or conversation" : It's real experience and conversations.
 

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Finally!!!!!
At least some semblance of an answer regarding experience from Witworth. I am just going to assume(yet again) that you are so cryptic about where you have worked because you are uncomfortable name dropping because we will want you to get autographs for us from the famous racing types you have hobnobbed around with. Regardless, in my beneficence, I am going to now treat you as somebody who does have a clue and hold you to that standard. Therefore, as been pointed out, I don't think your assessment of the needs of the upper shock mount, in this case, are accurate or particularly comprehensible. But based on the OP talking about 3 mm of flex and other silliness I can see where the confusion came in. I will agree in principle that the upper shock mount needs to be tied into the main frame tube, but I disagree with the amount of lateral strength that will be needed in the side plates. The lever arm length from the top shock bolt to where the plate is welded to the frame is very short and there are not very strong lateral forces generated in that plane even from very strong cornering forces at the tire contact patch.
 

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You get virtually zero lateral force on a swingarm/bike frame. You get mainly torsional and compressive forces. Lateral forces come into play with sidecars and cars, not bikes. If bikes cornered standing bolt upright with a flat rear tire on the back from a Turbo Porsche 911, they would get strong lateral forces applying to them.

I can't remember ever seeing a linkage type upper shock mount in 3.0mm sheet and it just welded onto a simple tube like that. To my engineering eye, it is too weak, ill supported and the notion of where the stress is concentrated and directed is all incorrect.

I've got no problem with name dropping, not really, but so few "heroes" are anything but barely functioning hyper-focused weirdos that end up dead or mad after a flash of fame and a few trophies. I don't like being reminded of that. So that's why I don't.
 

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Discussion Starter · #52 ·
A good photo of a stock gsxr frame and upper shock mount;

Vehicle Motor vehicle Wheel Auto part Automotive tire


I believe that is a round tube crossmember with a 3mm plate shock mount.

And while I'm sure Roland Sands isn't renowned for raw engineering talent he has done some swingarm conversions in the past too.

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The Egli frame is quite similar to stock. My frame is currently just under 11kg. I think factories all went away from the basic high mounted mono shock as it has a straight or falling rate spring curve, vs the progressive rate of the current wishbone linkage that almost every manufacturer uses.

My reasons for going with this design though are the extreme weight savings of the swingarm and wide tire capability. Making the linkage work is probably the bonus (hopefully!)

Earlysport
 

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The key point of the GSXR top shock mount is that the round tube cross member is tied into the main frame structure, not the subframe like your design. I believe where that GSXR frame tube is welded in it is a cast aluminum structure that ties the swingarm pivot into place also. It is very structural and strong. Until you tie your crossmember into the backbone with some triangulation it will not be as structural as needed.

Of course that is just my opinion and I might be wrong.
 

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"The key point of the GSXR top shock mount is that the round tube cross member is tied into the main frame structure, not the subframe like your design". -exactly.

I think you are confusing the la-la land of the fashion bike internet, with genuine engineering and engineers. It's like the internet is a tunnel of mirrors that magnify and multiply every badly built bike, and then the designs manifest like mushrooms in the garages of the young, like a plague.

There are builders like Sandy Kosman and Indian Larry ( and many more ) , who have built custom and high performance bikes that are proven engineering and deliver the goods.

Then there are Pros who deliver TV hype, BS and bikes that will be wheeled around shopping malls or shown on TV for non riders to gawp at: Like O.C.C. and at least 75% of the "shop built" joke "café racers" on websites for bored young guys to gaze at with dreamy dreams coursing through their brains on the bosses time.

RSD has built some good bikes, your example is not one of them. The mickey mouse bolt-on shock mount re-enforcing struts are a shocker (!) . Also you are incorrect in comparing your shock mount design to his. Yours is a modern link shock system and RSD's is a Suzuki Full Floater design copy: They direct stresses differently and work in a totally different way. RSD would be using high quality chromoly tube and pro TIG welders, not the method you are using. You do realize the RSD XL is a show bike and not a "real" bike, there is a big difference. Plenty of "built" bikes these days are really only suitable to ride two or three miles around Las Vegas and then lock them up again.

Consider TZ350 race bikes would have done 150mph back in the day on 100 or 110 rear tires. Wide tires are for beach buggys and rental Lamborghinis.
 

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And while I'm sure Roland Sands isn't renowned for raw engineering talent he has done some swingarm conversions in the past too.

View attachment 7424

If that little vertical tie rod is what is carrying the rear suspension on this bike, that is a freakin joke of a suspension design. I'm sure it would carry the bike but with no account for contributing to good handling.


Speaking of which, do you see a rear brake on this bike or is it just a mock-up ?:I
 

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Discussion Starter · #57 ·
A break from engineering head space and some more basic grunt work.. :)

Rear loop welded up from an old handlebar which had some nice tight bends. The shape was made for a very neat fit to the shape of the cowl after some re-working.

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The rear cowl after moulding off the tank has had about 3"taken out of the centre and cut down in height. It still maintains the shape of the tank so should integrate nice.

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A wanted a tail light solution both bright and unobtrusive. Some super bright LED's straight out of china I think will do the trick. Integrating them nicely meant for me setting them iinto the loop.

Auto part Automotive exterior Exhaust system Bumper Automotive exhaust


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These lights have dual stages of brightness and an integral heatsink. They are super bright - too much to look straight into at close range on the bright setting (brakes). The cowl was then reworked to integrate them.

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And lastly a shot of testing rider position prior to making the rear hoop to ensure seat height is correct. Overall stance will probably come in for some tweaking after riding via adjustable rear suspension wishbone links and pre-load.

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EarlySport
 

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Discussion Starter · #60 ·
I had some ideas for a clean and functional exhaust system that straight through muffling at a a diameter for minimal restriction. I am also concerned about overall noise level, so decided to custom build a baflled two into one system. Exiting on one side (the far side of the road when riding in Australia) for least impact on the noise police.

I used the stock double walled front pipe sections, and the area for exhaust crossover pipe behind to sump for my two into one.

Left side first..

Auto part Engine Fuel line Vehicle Automotive engine part


Engine Auto part Motor vehicle Vehicle Automotive engine part


I just use some mandrel bends to fabricate exhaust systems welding in piece after piece. I spent a bit more time as I intend to paint the exhaust in high temp flat black, as exhaust wrap is so 2011.. :)

The right side incorporates the baffling.

Pipe


Some perforated tube in the same diameter as the original header pipe that will be wrapped in fibreglass inside a larger diameter outer tube.

Metal Pipe

Auto part Pipe Automotive exterior Bumper Muffler

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And lastly a slash cut to finish it off

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I'm hopeful that there is enough sound deadening and that two into one lowers the sound level enough to meet my noise targets. I expect it to be loud but not Harley loud..

EarlySport
 
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