Frame reinforcing

I got my frame all stripped down today ! Now, I’m trying to decide if I want to do some frame reinforcing to help reduce chassis flex. I have read on here that the older z1-900 frame are flexy, but the kz900’s aren’t as bad. I have seen the kits available, and by looking at their diagrams, I think I can duplicate the parts pretty easily.

What size wall tubing should I use ? ID and OD ? I want to use mild steel – so I can easily weld it up with my MIG with gas – going to use .030 solid core. For the corners I think I’m going to just use some 10g or 1/8” plate.

2nd question – is this going to be worth it ? Am I going to notice any improvements ? I’m going just ride this bike on the street – no drag racing or tracks(unless for fun one day).

I think I am going to sandblast my frame and paint it black/clear. I like the idea of a clear coat because then it’ll be easy to clean up.

Hey Dan,
I just did the same thing, didn't want to pay $165 for a kit. I just did the top tube reinforcements, like you I am not dragracing or anything.

I used some 1/8" plate steel for the triangualr reinforcement and some mild tube steel for the two short braces. It was probably thicker than the steel the frame is made off, haha.
It was pretty easy to fab up the braces and it came out looking real clean (the only tools I used were a 4"grinder and a dremel). Getting the right contour in the round tubing and getting left and right to match is the hardest part.

Here's a pic



As for the results. Before the bracing was put in I could push apart the top tube and a side tube by hand. Now the backbone is solid. As far as riding goes, yes, I THINK it feels a bit firmer in corners BUT I also reversed the front forks, dropped the front end another half inch and run different shocks so too many changes at once to contribute everything to one change. Bottom line is it won't hurt, it's cheap (especially if you do your own welding) and most importantly NOW is the time since you're down to the bare frame.
Hope this helps...

Post edited by: dutchz, at: 2006/03/26 15:08

the biggest flexing problem on 900-1000 is the stock swingarm .im bracing the frame on my 1327 since it is going to put out a lot of power and id rather use it at the back wheel than twisting the chassis,i made my own gussets out of what i had laying around plain old mild steel the little bit of weight loss wasnt worth $150.00 kosman wants for their kit to me.if your just building a street hotrod save your money and buy a suzuki swingarm and put it on there,ill try and post some pictures of my homemade gussets later this week.goodluck,happy wrenching!

dutchz: Is that all the bracing you did to the frame in that picture ? The Kit out there has 15 peices.. and yes, NOW is the time ! I think I will do some bracing..

wireman: pics would be nice ! I just dont want to waste too much time on this reinforcing if it's not gonna help me. Maybe just a few problematic areas ? I also have an aluminum swingarm planned for this rebuild.

I am thinking of cutting up this old dirtbike frame thats laying around for my tubing, its pretty light - but it should do the trick ?

It's all for now anyways. Most of the flex on these frames is in the steering head and, as wireman posted, the swingarm.
Remember that the kosman kit is designed for dragracing where they run much bigger engines (like wireman's) that put way more stress on the frame. I think wiredgeorge has posted a picture of a (very similar) japanese bracing kit before, it kinda shows you where the pieces would go. I just didn't think it was really necessary with my stock engine. I can always add more later, but really don't think I will at this point. I would get more results out of a swingarm and frontend swap at this point. With the mods so far, I drop a lot easier into corners and the only wobble I feel is on high speed, tight or crowned corners, in the rear. I am running a stock swingarm and shocks, so a GS or GPZ swingarm and some better shocks are an option.

i think the old clymers manuals used to have a section on hotrodding 900-1000s in the back,one of the sections was on frame bracing and top motor mounts i dont remember how detailed it was though.one of my favorite bikes in the Z1 gallery is that yellow Z1 turbo bike it has a good picture of some gussets i think it has the extra braces between downtubes in front of motor it also has top motor mount you can kind of see,ok that is my favorite bike! :whistle: 2nd or 3rd page i think it is.goodluck,happy wrenching

Sorry, don't mean to hijack this, but does anyone have any details or pictures of the top motor mount modification? I would think an upper mount on these bikes would really siffen up the frame for both handling and launching, and also reduce vibration.

It's just a thicker plate and a bigger bolt;)

no hes talking about the extra mount from top of head to frame tubes under tank.if someone ha an old clymers manual can you post a picture of it?thanks;)

I see what you're saying. Never seen that. Hope someone has that old clymer...

Bracing never hurts if done right. The pic from 77KZ650 is a good start. I go with wireman on the swingarm. Definite weak point. Old school round tubing is always an issue especially when they build swingarms out of them. I heard you can double up engine mount plates and go with longer bolts. Nice pic on the reply below you firts post too. I think there is a post/article/archive that deals with prepping a Kawi for roadrace. A steering dampener helps too.