Frame bracing, boxing vs tubing.

[kochic]

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

 

[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

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

 

[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,

 

[Spiff]

How does the sump of the engine fit with those braces between the fram rails??

I have now made two gussets, they fit fine but because of the pet cock the left had to be massaged extensively with a hammer and the right one a little bit so the tank could shift a little bit to the left so the petcock can clear when lifting the tank up and down.
I could have chosen not to do this but that would mean I would have had to remove the petcock every time I had to lift or remove the tank and for a show bike sure, but I plan on using this so servicing needs to take priority

 

[Nessism]

I recall from back in the day that using thicker engine mount plates helped beef up the stiffness. No personal experience just sharing...

 

[kochic]

How does the sump of the engine fit with those braces between the fram rails??

I have now made two gussets, they fit fine but because of the pet cock the left had to be massaged extensively with a hammer and the right one a little bit so the tank could shift a little bit to the left so the petcock can clear when lifting the tank up and down.
I could have chosen not to do this but that would mean I would have had to remove the petcock every time I had to lift or remove the tank and for a show bike sure, but I plan on using this so servicing needs to take priority

Good work, I will follow your build.
The last pic I posted is not the lower frame rails, this is the front lower tubes.
Marc

 

[limeex2]

Great thread. thank you for the pics, links and advise.

 

[Spiff]

Making some slow progress, but I have some questions about the headstock bracing! See bottom picture:






A is how the sketch is outlined on the katana fram scheme I posted in my first post, but that interferes with the rubber grommet for the tank so I have to think of something else.
I can do B with steel plates, C would also work with 12mm tubing(that's a hair under 1/2") and I think I might also get D to work without it interfering with the tank. Maybe.
What do you think is the best? I think B and D with C being more of a compromise

 

[salty_monk]

B probably will look better and is more like the bracing they put on modern frames... I also like the fact it is braced counterclockwise as any bumps etc are going to put forces in that plane aren't they?

 

[GregT]

For me - and I've stayed out of this lately because everyone has to make their own mistakes - all that's needed is the lower diagonal in D.
I wouldn't do any more welding on the headstock itself - it is stiff enough already IMO.

What you're trying to do is stiffen the area of the frame where the headstock loads are transmitted downward. The top tubes with your stiffeners will be more than adequate.

Bear in mind my experience is with big fours in tube frames being roadraced on slicks. Including a very quick GS1000 used on bumpy street circuits.
Budget for some really good rear shocks - and don't overspring them.

 

[Spiff]

Hmm... I thought the object of this brace was to prevent the headstock from twisting forces primarily?

As for dampers I have a set of ?hlins dampers from a gsxr1400. Not sure on the springing they might be to stiff I will have to see once the bike is assembled fully. I plan on complimenting them with some new springs in the front fork as well as they seemed soft, might be able to take some of it off with the preload adjustment idk

 

[salty_monk]

Run some straight weight springs around 0.9kg/mm and cartridge emulators if you're using stock forks...

 

[GregT]

Hmm... I thought the object of this brace was to prevent the headstock from twisting forces primarily?

Reply...If you make the headstock very stiff - but feed the loads into a flexible frame, where's the gain ? In roadracing situations, the heaviest loads coming from this area are actually braking loads. When you see -up close - a group of big pre 82 racebikes having a braking duel into a downhill hairpin on a bumpy street circuit, the light dawns.....

As for dampers I have a set of ?hlins dampers from a gsxr1400. Not sure on the springing they might be to stiff I will have to see once the bike is assembled fully. I plan on complimenting them with some new springs in the front fork as well as they seemed soft, might be able to take some of it off with the preload adjustment idk

Little story....We bought Gazi shocks for the 1000. Very good quality and about 1/2 the price of Ohlins. Very popular in Post Classic racing in Australia and well supported too.
AFAIK we're the only Gazi users to buy the softest option spring available. It's perfect on the 1000 with a light/medium rider. We actually have measurable sag.
I'm told that nearly all the posties racing in Aus have no static sag at all.....