cutting frame

[modifiedamerican]

i just have a quick question. i have a 79 kz750 twin. if i was to cut the frame a little bit before where my shocks are will i need any bracing at all? i would like to get a bump seat but the frame deff needs shortened to make it look right. thanks alot!

 

[VonYinzer]

If you cut reinforcement off, you should replace it where possible.

 

[modifiedamerican]

heres an example on how i would cut the frame
http://farm3.static.flickr.com/2698/4448514209_747a0678aa_z.jpg

 

[DoubleL3]

Like Von said it really depends on if there was anything rigid helping tie the back of the bike together. I did something similar to my KZ550 with seemingly no adverse affects, the only thing on the back end was a thin piece of sheet metal to support the rear fender and taillight. I have planned on going back and welding in some extra frame stiffeners but I haven't gotten to that point in the build yet.

 

[DreadRock]

this what i did on my xs500 !

 

[modifiedamerican]

is there any way u can make the picture larger so i can see what u did? lol.

 

[DreadRock]

Dont know why it does that ! cant seem to post larger pics even tried to PM them to you. but what i did was cut the frame as close to the shocks as i thought was safe . then found some bar stock to fit inside of the frame and my hoop to help strenghen the hoop to frame weld . then made plates that fit nicely inside the hoop and frame and welded that in. worked out good and gave me a place to put my elec stuff.

 

[crazypj]

Hundreds if not thousands of people have cut frame at that point.
For majority it isn't a problem, however, it's never a good idea to modify a frame which can allow the left and right sides to move independently.
I would weld something back in to tie both sides together. (if I even cut the section out)
Even if you don't corner particularly hard, the next owner might
If you think it's a bad idea, it is.
The fact your asking means you don't know enough to just go ahead (which is a good thing, at least you have a concern about your own safety 8) )
Before you weld a new piece in, measure shock compressed length and make a strut, couple of people have welded in flat plate and found tyre want's to be in the same place as plate.
BTW, the shape if the original plate makes it act as though it is 3~4 times thicker without the weight of a solid piece

 

[pugeyed]

ok here's where i cut my 82 kz750 frame cut about 3 or 4" out then welded the loop from original back end back in.
could have gone closer to shock mounts but the seat will be small enough as it is.

hth Mark.

 

[crazypj]

That looks pretty neat, 'factory'.
You did check wheel clearance on 'full bounce' ?

 

[pugeyed]

yep and its fine, any shorter and i think you would run into problems

 

[Chito]

You know... I was thinking about your question and I'm not experienced with this at all, but couldn't you weld in a cross support (or two) before you cut? That way it would stay exactly where it should. Then if you wanted to add a piece like Pugeyed's (which you should just because it looks infinitely better) it should be right in place.

 

[DreadRock]

I know the frame on my xs500 has a cross support on it . So left it In place and cut befor it then put in
Y hoop!

 

[xbmxxx]

I cut my 76 KZ750 like this

I plan on making a rear hoop to follow the lines of my new seat, but havent gotten around to it yet. I have not felt any difference when cornering.

 

[crazypj]

I plan on making a rear hoop to follow the lines of my new seat, but haven't gotten around to it yet.
I have not felt any difference when cornering.

Your not trying hard enough