Frame bracing, boxing vs tubing.

[kochic]

I made this with scrap metal for the boxing.
Marc
CIMG5560.jpg

[kochic]

from a flat plate to this.
Marc
CIMG5555.jpg

[GregT]

Cool thread!
Just like to know if any of these bikes were built for racing?
Because reducing weight is important for race bikes.
Thanks.

If you're using a modified stock frame it's still a trade-off. Modern tyres have made frame stiffness even more important. From my experience and watching others, the period style bracing is nowhere near complete enough for modern slicks. The lower frame rails are not touched in the old model bracing. I've gussetted the area where the front crosstube joins the downtubes - and the area where the rear crosstube behind the motor joins the lower cradle tubes.
Just folded 2mm sheet in an "L" section. This is enough to stop the front downtubes "scissoring" under lateral loads. The steering head area is better than Z1's - but that's not saying much.

Talking to the guys involved with running the Team Classic Suzuki Katana in the IOM 2 years ago, the disadvantages of running what is actually a replica of a stock frame vs the purpose built XR69 replicas became apparent very early on. 119MPH laps represent shall we say, very large gonads.....Better suspension and geometry show up very quickly on the IOM.

[kochic]

[QUOTE=GregT;2582034] I've gussetted the area where the front crosstube joins the downtubes - and the area where the rear crosstube behind the motor joins the lower cradle tubes.
Just folded 2mm sheet in an "L" section. This is enough to stop the front downtubes "scissoring" under lateral loads.

Do you have a couples of pictures?
Any help is welcome and thanks to the OP for the thread.
I will relocate the headstock and brace the frame between the lower front crostube too.My first plan was to use 2 tubes in a V between the crosstube and the OEM bracing under the headstock.
Marc

[GregT]

No, sorry lost the pics I had. Bike's at the owner's place now.
The gussets were simple triangle folded sheet, about 50mm on a side.

I wouldn't have thought there'd be room for an X brace under the steering head with the pipes there.

[kochic]

It will be something like this, If I have trouble with the header flange I will go with a spigot set-up.
Marc
skizzokat-details-3.jpg

[GregT]

It will be something like this, If I have trouble with the header flange I will go with a spigot set-up.
Marc

I'd still sooner go for triangular gussets under the crossmember. On the back or engine side of the downtubes.
Lighter and simpler.

[kochic]

I'd still sooner go for triangular gussets under the crossmember. On the back or engine side of the downtubes.
Lighter and simpler.

When you do this, do you need to switch to outside engine mounting plate?
Marc

[GregT]

When you do this, do you need to switch to outside engine mounting plate?
Marc

Looked at the pic again. Left side behind the downtube, right side in front. Won't make any difference strength wise but you won't have to change the mounts.

I've actually got a late 750 race motor apart here at present. Built back in the day in Australia. Big bored and hot cams. AFAIK it's done very little work - possibly just one meeting. Shows signs of being very hot indeed - and the usual lower end bearing stress signs.

The less interference with cooling air to the engine on those ones, the better.

[Spiff]

Good point about the lower frame bracing. Altough it'll mean more work to be done :-P

Started some cardboard templates today, will be making my plate brake tomorrow.
Also with these gussets it is my understanding that one does NOT weld the two short sides across the tube, just weld along the tube right?

[kochic]

[QUOTE
Also with these gussets it is my understanding that one does NOT weld the two short sides across the tube, just weld along the tube right?[/QUOTE]

Yes for the short side and try to fit the gas tank with the cardboard gusset to check the clearance.
I was not able to fit a one piece gusset there without rubbing under the tank.I made them in 3 pieces that follow the frame line once welded.
Marc
CIMG5566.jpg

[GregT]

If the tubing was light gauge high tensile, yes, avoid welding across the long axis.
With OE frames, you're dealing with thickwall, mild steel in soft condition.
A short run along one side of a folded "L" section won't hurt.

On light gauge, you often see the tube bend toward the weld. Never seen it happen on a GS frame. I suspect they're made in stress relieved tubing.
Or self stress relieve with age....

[Spiff]

Some reading material; https://motochassis.com/Articles/Frame.mod/KawaMods.htm

It would seem triangulating with tubes is much preferred over gussets providing there is enough space for a tube to run right?

[kochic]

not mine but you can see lower front bracing.
Marc

[kochic]

another frame,
images.jpg