RZ/RD 350 & Misc. 2-Stroke Tech BBS

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PostPosted: Wed Jan 20, 2010 4:34 am 
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The Task: - Install an FZR400 swing-arm on an RZ350 & still have the bike handle well.

The Problem: - The pivot for the dog-bones, on the FZR400 swing-arm, hits the shock.

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If I lengthen the dog-bones so that the pivot clears the shock, then the ride height is 40mm (about 1.75") too low.

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Possible Solution #1: - Shorten the Link, from shock to frame, by 10mm and use 90mm long dog-bones

Then the swing-arm can drop down further and I can get the OEM ride height.

Pro- I can keep the center-stand
Con – The Link will cost about $500 + dog-bones

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Possible Solution #2: - Lower the Top Shock mount by 35mm and use 115mm dog-bones.

The bottom of the shock pivots down & forward about 10mm.
Once again, the swing-arm can drop down further and I can get the OEM ride height.

Pro – Cost will be about $20 + dog-bones
Con – will have to lose the center-stand & I don’t like the angle that the link is on (pointing down).

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Assumptions: - Changing the Link length, Dog-bone length, or dog-bone pivot location on the swing-arm,
will affect the rate at which the Shock compresses when compared to Rear axle travel.
This will affect the handling of the bike.


Drawings: - I measured the OEM rear suspension setup and made sketches of what I thought was relevant.

I then measured & made sketches of the 2 proposed solutions.

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The Next Step: - Transfer the dimensions on the 3 sketches into CAD drawings.

Then move the rear axle through its 100mm of travel and determine the rate at which the shock compresses.
From this I should see how each of the proposed solutions compares to the OEM suspension.

I could then use the modification that more closely resembles the stock set-up.


The Questions: -

Does any of this make sense?
Am I on the right track?
Will one idea work better than the other?
Does anybody see problems with either idea?
Does anybody have a different solution?
If anyone has done either of these mods, how well did it work?


Disclaimer: - I am not an engineer, a designer, a machinist, and I’m certainly not an artist.


I’m just looking for advice, so that this bike doesn't end up handling like a 25 year old 4 stroke. :smt003

Any information would be appreciated.

Thanks.


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PostPosted: Wed Jan 20, 2010 5:09 pm 
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can you make housing for spring grinding material on swingarm ?

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PostPosted: Wed Jan 20, 2010 8:08 pm 
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How about if the dog legs where made with a bend in them so they fit both ends and fit a spacer where they bolt to the swinging arm.


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PostPosted: Thu Jan 21, 2010 1:58 am 
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ax-racing wrote:
can you make housing for spring grinding material on swingarm ?


I don’t think I can.
If I grind 10mm of material from the swing-arm,
I will be into the dog-bone pivot

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slinger wrote:
How about if the dog legs where made with a bend in them so they fit both ends and fit a spacer where they bolt to the swinging arm.


Straight dog-legs will clear the shock and line up with pivot on the swing-arm.
(if I understand you correctly, on which way the bend goes)

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I found the following write-up in my Manual.
Pretty good explanation on how the rear suspension works.
Yamaha refers to the Link as a Relay Arm & the Dog-bone as Arm 1.

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I find this part interesting
“The relay arm amplifies the movement of arm 1, as the wheel strokes more.

So what happens when you lengthen Arm 1. (as you do when you install an FZ600 swing-arm)
I can’t visualize this in my mind. Will have to see it on paper.

Hopefully, I can get the 4 CAD drawing done by the weekend.
(Stock suspension, FZ600 suspension and Mod 1& Mod 2 of the FZR400 Suspension.

I will set L=10mm and then calculate l1, l2, l3…..l10.
I should be able to graph the results and see how the modified set-ups compare to stock.

I’m trying to keep my suspension rates as close to Stock as I can.
After all, Yamaha had a team of really smart engineers design this suspension.


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PostPosted: Thu Jan 21, 2010 2:39 am 
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steve, same problem we discovered today. 86 FZ600 swing dog bone and shock. I am updating my thread, let's see what we can find out. I will post some links from swingarm swaps to help us out. My thread is scratch built rz350, you'll see it.
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PostPosted: Thu Jan 21, 2010 3:04 am 
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Off Road wrote:
Assumptions: - Changing the Link length, Dog-bone length, or dog-bone pivot location on the swing-arm, will affect the rate at which the Shock compresses when compared to Rear axle travel.
This will affect the handling of the bike.


Almost. Only changing the relay link and/or the dog-bone pivot location length will affect the rise rate. Changing the dog-bone length only changes the ride height.

My opinion... change the dog-bone pivot location to that of the original RZ350 swingarm. Then make dog-bones of the correct length to get your ride height where you want it. But... Moving the pivot location might be problematic with that swingarm. :(

Since you have a FZ600 swingarm, you could always just get out some elbow grease and polish it. It's really not that hard. Just getting through the anodizing can be tough. But if you have it blasted with aluminum oxide media beforehand, the ordeal is eased significantly.

Steve

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PostPosted: Thu Jan 21, 2010 4:31 am 
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Hey Alexandros. Yes I saw your thread and you’re correct. Same problem.

My original 83RZ is using the FZ600 swing-arm and dog-bones and the RZ Link.
The ride height is about an inch low.

There’s got to be a hundred of us out here, with the same problem.
We’ll find a fix.

smurph wrote:
Off Road wrote:
Assumptions: - Changing the Link length, Dog-bone length, or dog-bone pivot location on the swing-arm, will affect the rate at which the Shock compresses when compared to Rear axle travel.
This will affect the handling of the bike.


Almost. Only changing the relay link and/or the dog-bone pivot location length will affect the rise rate. Changing the dog-bone length only changes the ride height.


Steve


Thanks for the information. I understand what you are saying about the dog-bones.

Off Topic:
Steve, I read your Homepage and loved it
It’s informative, well written and very funny.
It should be required as mandatory reading for all new forum members.
Good job


I’m still curious to see what kind of information I get back from the CAD drawings.
It may be useful. Then again, it may be garbage.

I have 4, fourth-year engineering students working on the drafting and calculations.
Should be interesting to see what they give me.


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PostPosted: Fri Jan 22, 2010 2:41 am 
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interesting to say the least stevie....

If you look at my ride height it is absurd. End goal is to have the top of the tank angled down front without rider and level with rider. I do have the same problem and Dean stated that we need a longer shock. With enough broken bikes to make your head spin he will undoubtedly have the solution. It is interesting to see that this is a common problem. At 200lbs, an interesting problem to say the least. If I weighed 100lbs 1" lower might be OK because I could lower the front 1" also. No rush here as I know you too are building at a leisurely pace too. Let's see what the engineer students compile.


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PostPosted: Sat Jan 23, 2010 3:31 am 
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alexandros wrote:
No rush here as I know you too are building at a leisurely pace too. Let's see what the engineer students compile.


Calling it a leisurely pace is being too kind. I haven’t picked up a wrench in forever. :smt009

It’s Friday night. Engineering Students are on a pub crawl.

alexandros wrote:
...Dean stated that we need a longer shock.


smurph wrote:
Another way is to shorten the dog-bones and use the RZ relay link. This retains the original RZ rise rate on the linkage.
Steve



Both a longer shock and/or shorter dog-bones will raise the ride height with the FZ 600 swing-arm.
Dog-bones will be harder for me to do.

The stock shock is 290mm,
the R6 shock is 305mm
& my Works Perf. Shock is 295.mm

Like Smuph said, use the RZ350 Link as it will retain the original rise rate.
It’s 5mm shorter than the FZ and this will also help retain ride height.

Image

With the bikes on the center-stand I took ride height measurements and got the following numbers

The measurements were taken from center of the axle, straight up to the top of the frame rail.

Image

Stock 83RZ - Ride Height = 445mm (17.5â€￾)

With FZ600 Swing-arm, FZ dog-bones & RZ Link – Ride Height = 425mm (16.75â€￾)

With FZR400 Swing-arm & RZ Link (when swing-arm hits shock) – Ride Height = 405mm (16â€￾)

Bear in mind, these dimensions were taken late at night, in the dark, using a very precise Tape measure.

The numbers should be close, but you might want to get a second opinion, Alexandros. :smt003


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PostPosted: Sat Jan 23, 2010 10:29 am 
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Just one question. Why are you going with the 400 swingarm rather than the 600 arm :smt017 ? You have a 600 arm that will go in nicely with minimal work. Geometrically speaking, the 400 arm will not work unless the dogbone attachment position on the arm itsef is relocated. That is if you want to retain the proper ride height and rising rate. Good luck with the project!! Looks good.
Pete


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PostPosted: Sat Jan 23, 2010 7:50 pm 
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peterz84 wrote:
Just one question. Why are you going with the 400 swingarm rather than the 600 arm :smt017 ? You have a 600 arm that will go in nicely with minimal work.

Pete


Damn good question, Pete.
I have to admit, it took more than a couple of minutes to come up with an answer.

Yup, I could put on the FZ600 swing-arm and might have to. But..

I really liked the looks of this set-up when I bought it.
Only found out it didn’t fit a couple of weeks back.
Now it’s a bit of a quest.

I’ve been riding for 25 yrs and never really thought about the suspension set-up.
At the moment, I’m just curious.

I can see how changes in dog-bone or link length will affect the suspension.

Now I’m real interested in seeing what happens to the rise rate, if I lower the shock, while keeping the RZ link.
The Link is on a different angle (relative to the ground).
But I just can’t visualize how this will affect the rise rate.

So, to answer your question. Why?

- It will look cool
- It’s an opportunity for me to maybe learn something
- I like to tinker
- I like my toys to be different (my own little touches)

Will it work? Hell, I don’t know.
That’s why I have a Plan B and a backup for it. :smt003


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PostPosted: Sat Jan 23, 2010 10:24 pm 
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The calculated rise rate will be the same no matter what angle position the relay link is. The only problem that comes into play is mechanical binding. Mechanical binding is not just parts touching that prevent movement. It can occur when the leverage is reduced to a point where the rest of the system simply cannot produce the power to move it. So leverage is quite different than ratios. If you have too steep of an angle on the relay link, then it has less leverage on the shock. This is a problem with pivoting linkage that swing in arcs.

Typically, you want the relay link to be in it's arc center when the swingarm is at it's proper ride height. Small deviations from this won't matter too much.

Simply lowering the shock (or longer shock) is only going to increase the ride height, keeping in mind binding, of course. Simply shortening the dog-bones is only going to increase the ride height. The rise rate is determined by the relay link length and the position of where the dog-bones connect to the swingarm. (length from swingarm pivot).

If you polish the FZ600 swingarm, you will be hard pressed to tell the difference between it and the FZR400 arm. The only real difference is that the dog-bone mount point is appropriate on the FZ600 arm. They are both box tube constructed and use the same chain tension mechanism as well as brake attachment.

Anything can be made to work, for sure. And I'll be the last one to tell you that you are crazy for trying them. It's just that more time and effort may be required for some solutions.

Steve

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PostPosted: Wed Jan 27, 2010 3:04 am 
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Thanks for the explanation Steve.
I knew I’d learn something if I posted here.

After reading Steve’s info, and looking at the drawings again,
I realize (finally) that the swing-arm won’t work with the current dog-bone pivot location.

So, what’s the best solution? It’s no longer a question of what looks cool.

The options, as I see them:

1- Use the FZ600 swing-arm, dog-bones and the RZ link. Modify the FZR wheel spacers & brake bracket to fit.

2- Use the FZR400 swing-arm and relocate the dog-bone pivot location to that of the RZ350. (as Smurph suggested)
This would keep the stock suspension geometry, but would require custom dog-bones.

3- Use the FZR400 swing-arm and relocate the dog-bone pivot location to that of the FZ600.
The machining costs are the same, but I can use OEM FZ600 dog-bones.

I took both swing-arms (FZ & FZR) by the machine shop today. The shop specializes in Al. welding.
Asked them if they could machine the cross-brace & put dog-bone pivots on the FZR swing-arm to exactly match the FZ600 swing-arm.
They said no problem. The cost will be about $300. (FYI-The same shop quoted $500 for a custom link)

The costs for each option are about the same. The amount of work (on my part) is about the same.
But, is one solution better than the other?

If this was your collection of parts, what would you guys do?
I’d rather know now, than after I’ve spent my money.

Thanks for all the help. It’s really appreciated.


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PostPosted: Wed Jan 27, 2010 4:01 am 
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Off Road wrote:

If this was your collection of parts, what would you guys do?
I’d rather know now, than after I’ve spent my money.



I would flog the parts on ebay, use the works shock with the stock rear end, and use the profits for freaktastic pipes, engine and/or ignition mods.

:smt002


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PostPosted: Thu Jan 28, 2010 8:10 pm 
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What are you like at welding :smt012 My solution all be it on a different set up was to cut all the old mounts off the frame set up the swing arm where it needed to go then weld new mounts on to suit.

Image

Handles great, knee down baby :smt003


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