1972 DS7 The Row Boat

Re: 1972 DS7 The Long Road- monoshock conversion done

xb33bsa said:
bike is looking really good nice work but you are going to need to do something with that top shock mount
it is going to twist right off,put a strut onnit straight up to frame
I am no structural engineer, they sit on the other end of the floor. I also don't know the actual rigidity of the frame itself nor what condition the frame tubes are in on the inside. What I did do was take a gander at the setup that the suspension came off of and tried to replicate it. This is the top shock mount for the 2008 EX250:



Now I do know that this is not the same frame and possibly not even the same grade material but I would assume that if the top shock mount was the weak link in this system or the most abused part of this system that Kawasaki would have put a little more meat on that mount.
I do have a few experiences with steel frame monoshock motocross bikes(with similar shock mounts) where more than one time I came up short on a 60 to 80ft jump hard enough to have the lower linkage dig a big chunck out of the ground and the bike held up. I only use this example because its the most abuse that I've put on a similar type setup.
It would seem that the most stressed members would be the lower linkage mount that gets pulled on as the swingarm articulates and the swingarm pivot mounts on the frame. Oh and I'm not advising anyone to do this at home!
 
Re: 1972 DS7 The Long Road- monoshock conversion done

yeah i had looked at an ex frame before i posted the issue with yours is how far it hangs off the tube
you are putting way more twisting force on a lighter weight/strength tube
it would be so easy to put in a strut/compresion member running up,it doesnt need to be welded, bolted in is fine
we are talking in the 500-1000 lbs of load constantly working on there
 
Re: 1972 DS7 The Long Road- monoshock conversion done

One thing that i did to add on mine was to overlap the top onto the rear engine mount. That way if it does twist any some would be transferred onto that point. Seems like there is a ton of data to compile, to do an acurate analysis of the system?
 
Re: 1972 DS7 The Long Road- monoshock conversion done

but the engine mounts are not designed for the extra loads not at all
neither are the engine cases
you just need to eliminate the flexing that you WILL have with that mount hanging out like that ...
a simple compression member run vertically to the juncture of the seat tubes and backbone will do it
 
Re: 1972 DS7 The Long Road- monoshock conversion done

xb33bsa said:
but the engine mounts are not designed for the extra loads not at all
neither are the engine cases
you just need to eliminate the flexing that you WILL have with that mount hanging out like that ...
a simple compression member run vertically to the juncture of the seat tubes and backbone will do it

I agree. Clem this is good advice!
 
Re: 1972 DS7 The Long Road- monoshock conversion done

I did my rd abput the same way
 
Re: 1972 DS7 The Long Road- monoshock conversion done

Xb,
Thanks for bringing this up as it caused me to dig deeper than I initially did during the fabrication. I hunted down the spring rate for the gsxr600 and found the linkage ratio for the EX250. I did consider replacing the cross member with a larger/newer tube but didn't want to mess with the engine mounts at that time but I may reconsider doing that.
I did get a bracket made for the plastic oil tank, it should hide itself under the seat nicely. I guess after payday I'll find a tail light and get that mounted in the seat pan/tail section and buy that ignition switch.
 
Re: 1972 DS7 The Long Road- monoshock conversion done

I worked on the bike over the weekend but really had no progress worthy of photo's. I cleaned the carbs that came with the bike and through a little research, I discovered that what I have is a set of carbs for a RD350C. While this is not all a bad deal, it does cause a little grief for the immediate future. These are the carbs that I would have to have bought when I eventually went up to the 350 cylinders. The immediate problem is that I now have 4 oil injection ports for this two cylinder engine. Now I could easily just JB weld over the carburetor port but I wouldn't want to have to get a drill bit out later on and have to be precise since this is a press fit application. Two ideas that I have, and they may not be the best, are just buy two sets of the oil injector nozzles and plug one set with something or run a tube to connect the two ports together to effectively seal them off. I don't know if the latter will have any adverse effects on the fuel metering process.
The taillight bracket is tacked to the rear of the frame and the seat is cut out to fit around the taillight. I did goof up a bit on that by cutting the top portion out a bit large so I will have to lay a little more fiberglass for repair.
I did do the calculations to determine the stress transferred to the frame/top shock mount. Using .083 wall thickness for the tube and carbon steel for the material, it looks like the shear strength of the tube is well above the actual psi that will be delivered at 3" of shock travel. I will re calculate once I get the actual wall thickness of the tube. I do have some 1" x .120 DOM tube if the correct calculations show that the tube is insufficient.
The engine side covers got dropped off at the powder coat shop so when those get back I'll put up some pics.
 
Re: 1972 DS7 The Long Road- monoshock conversion done

I'm liking this.

I'm putting the same swingarm on my sr500.

What did you figure out about the upper mount?
Your bracket looks about 3x the length of the ex250 bracket, which means that the frame tube and your welds will get 3x the force as the ones on the ex250.
Could you shorten the upper bracket to move the pivot point closer to the frame? What was your reasoning for making it so long? To get the shock as verticle as possible?

Sorry for the 20 questions, just picking your brain before I start welding 8)
 
Re: 1972 DS7 The Long Road- monoshock conversion done

Very impressive, especially like the way you perservered with the seat. It was a mess but you just kept at it and I think it is exceptionally nice now, different than anyone else's, so much better than buying one. The other area that blew me away was your learning about expansion chambers and then just building some beauties. I'll be watching this one!!
 
Re: 1972 DS7 The Long Road- monoshock conversion done

With regard to the upper shock mount, I would use two (one each side L&R) small dia. tubes and triangulate from the center of the shock mount out to the curved frame tubes. Triangles are strong and distribute the load. I'd take a close look at the lower shock mount too? I like the linked mono-shock. I'm currently making a linked mono conversion and just finished my upper mount. Nice bike, and the pipes are going to be killer.
Cheers, 50gary
 
Re: 1972 DS7 The Long Road- monoshock conversion done

SONIC. said:
I'm liking this.

I'm putting the same swingarm on my sr500.

What did you figure out about the upper mount?
Your bracket looks about 3x the length of the ex250 bracket, which means that the frame tube and your welds will get 3x the force as the ones on the ex250.
Could you shorten the upper bracket to move the pivot point closer to the frame? What was your reasoning for making it so long? To get the shock as verticle as possible?

Sorry for the 20 questions, just picking your brain before I start welding 8)
No problem on the questions. The upper mount is actually 3" from shock center to center of tube. I did the calculations on the force(psi) that will be appllied at that point and the tubing will be fine. It is well under the yield and tensile strength of the tubing even at 3" of rear shock compression. I can't say if it will be 3 times as much as the ex250 since I don't know the spring rate on that particular shock.
Having the shock at an angle to the upper mount(lever) and not at 90 degress does lessen the actual force that is applied at the pivot point also. Notice how much of an angle the kawasaki mount is at.
I tried to make the upper mount as close to the frame as possible but it is limited by the open area that the shock passes through. This was the shortest that I could get it without the shock spring rubbing the swingarm.
Rundown, thanks for the compliments. This has been a great learning experience for me. I usually quietly read through threads here and on the net, scratch my head, figure it out then do it. I always tell my children that anyone can achieve anything as long as they are patient, willing to listen and go slowly.

I did get the carbs back together, mounted the throttle up, ordered the headlight brackets and got the engine side covers back from the powder coat guy(before he went on a duck hunting hiatus). I figured out the wiring and actually put together a list of OEM wire colors with there service on the DS7/R5. If I get a chance I may post that up..who knows it may help someone else out.
Oh and I ain't going to work tomorrow!
 
Re: 1972 DS7 The Long Road- monoshock conversion done

rundown said:
Very impressive, especially like the way you perservered with the seat. It was a mess but you just kept at it and I think it is exceptionally nice now, different than anyone else's, so much better than buying one. The other area that blew me away was your learning about expansion chambers and then just building some beauties. I'll be watching this one!!

I agree very good work.
 
Re: 1972 DS7 The Long Road- monoshock conversion done

I feel your pain clem
 

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Re: 1972 DS7 The Long Road- monoshock conversion done

bradj said:
I feel your pain clem
Haha. But your welding goes up alot faster than mine.

This is what I came up with for 2" of shock compression:
Torque apllied @ structural member - 2270.27lb/in
Torsional deflection of shaft(frame cross tube) 1.15deg.
Shear Stress @ structural member - 34,702.48psi
 
Re: 1972 DS7 The Long Road- monoshock conversion done

This thing isn't done yet?

Kidding man. Signed up.
 
Re: 1972 DS7 The Long Road- monoshock conversion done

clem said:
Haha. But your welding goes up alot faster than mine.
sounds like your levels of "give a fuck" are to high
 
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