Kawasaki Zephyr 550

So, had to get the impact driver to get the throttle linkage (not sure if that's it's name, but the bar the connects the throttle cable to the carbs) off of the carbs. Once I got it off, I started cleaning all the rust and grime off with a wire brush, and it turned out pretty good. One question about the engine - Would it be wise to get it run and then try and modify it, or modify it as I go through the repair/clean?
 
It's always nice to say get it running before tear down but that's not always possible. Depends on what you can figure out without breaking it open. Oh...and your avatar pic, I've had that on my computer for awhile. So hot.
 
Aha, I've also had it sat on my desktop for a while, not sure where I got it from to be honest. I know it ran before it was left to sit (for 14 years) so I've got to pull it apart and get all the crust and dirt out of it anyway, so I guess I might as well go through and modify it as I go?
 
So here's a question that the answer to might make me cry - I'm hoping for a fairly flat angle over the top of the bike, as in like this beaut

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Not like this,

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(I understand the second is a fairly extreme example, but it was just to make my point clear)

When my bike's on it's wheels the tank is fairly parallel to the ground, where as the seat is angled up - I understand changing this requires frame modification, but just how much, and how, is what I'm asking here

Oh, and here's a pic of the frame....figured it might help :p

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and here's a pic of how the tank sits

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Changing the subframe for a "flatter" look is a pretty large job. You'll need to fabricate a new subframe (including shock mounts) amd weld it in place of the stock set up, while maintaining the correct mounting points for the suspension and proper strength to support the suspension forces and your weight. I know you're leaning towards the "brat" side of things with the final look, but you have a really really cool platform for a little road racer. If it were me I'd fit some low rise superbike bars, a nice clean solo seat and go to town.
 
Ok, I did completely forget that I'd said I was gonna brat this thing. That plan changed a while ago - plan is now a cafe style seat (originally decided on brat so I could ride two up, but decided I'd rather have the bike I really wanted). My issue is, I find that cafe seats at an upwards angle like that just look a bit...wrong. I assume there's is no way to change how the seat sits on the bike, rather than the frame?
 
Right, update to above post. After reading god knows how many build threads, I can't bring myself to compromise on the finished product that I really want (that being something cafe inspired). The way I am planning to get all the mounting points correct and square, is build some sort of jig, using the old suspension (rusty, and shot to bits so need replacing anyway) and will pretty much design the sub-frame from that, rather than try and incorporate mounting point into a sub-frame design, if you get my drift? By all means, if this is a stupid and dangerous plan, go ahead and tell me
 
Be very careful about modifying that tail section/subframe. As it sits you likely have JUST enough clearance for the rear wheel at full shock compression. Drop the ass end any lower and you're running into all kinds of problems.
 
If keeping the tail from looking like a modern sport bike and pointing up in the air is really important, try finding (or making) a solo seat with a low profile cowl on the back. Something not so bulbous and obtrusive. It'll visually keep the lines of the bike "lower" but still allow the needed room out back for wheel clearance. Also, if you're running a solo seat you can probably remove some of the end of the subframe which will physically lower the rear as well.
 
So, here's a REALLY rudimentary paint drawing that I literally did in five minutes a second ago (it's 4am here) Again, I'd like to put emphasis on the fact that no maths or really, any thought beyond 'huh, what about this' went into this. Obviously moving the rear shock mount up would need the front lowering to compensate, and the new lines would cause an issue for mounting a tank - but this is just me brainstorming, apologies for throwing my ideas at you :p

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Oh, and the circle and line up from the shock are showing the new mounting point for the shock, and aren't new metalwork, whereas everything else is
 
Unless you really know what your doing, or pay for someone else to modify the frame as you want, I wouldn't do it. I fear you could end up with a bodged frame which would be dangerous in use.

Instead, to give the flatter seat angle you want, why not just weld in an additional brace on top of the existing seat rails, and also shorten them at the back (assuming your going to fit a single seat unit). Where the thick red line is on the pic below.

Now, you may say, that will look odd with a gap between the old and new seat tubes, and you'd be right, but with a bit of thought a cool looking seat unit could easily hide that gap..
 

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I'm a competent welder, I've just never done a bike frame before, but then again, no ones done a bike frame, until they've done it. Obviously I hear what you're saying, and I understand why you'd say it, as I did come across a bit 'shove that metal there and weld, right? It's that easy yeah?'. I can weld, I just wanted my plan looked at by guys who weld frames, and see if they could point out massive flaws in flattening it like that
 
ok, in that case the one obvious issue with your diagram is the way the upper shock mounts have been raised by about two or three inches (?) that in turn would drop the rear end down and lose ground clearance, and could cause the wheel to hit the seat rails. Unless you fitted longer rear shocks of course, though not sure you could find shocks that are long enough unless you had them build for you by the likes of Maxton. Perhaps you could make the frame changes you want while leaving the upper shock mounts in the same position as they are now?
 
^^^This is exactly what I was thinking about doing, only issue with that is I might end up with a rubbing rear wheel - could I solve this by welding in the new subframe like I drew out, but drop the suspension mounts down an inch or two (on their own little plate type thing) or would the rigidity issues this would cause be too major?

Anyway, I got on with cutting today (don't worry, have another identical bike I can take measurements from to work out where the shock mounts should be). I left in some of the old sub frame too so I'd have a point of reference

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As long as the shock mounts are strong enough, cant see an issue with dropping down from your new frame rails. How strong is strong enough ? I'd replicate the design of the original mounts as far as possible..
 
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