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Bracing the headstock on a gs750


gorbys

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Hi! New on this forum, thought I'd join so as to get your opinions since you guys are far more experienced than I am.

I'm working on my 78 GS750 which I'm fitting a an sv1000s fork, a bandit swingarm with twin ohlins shocks on, and I have begun stiffening the frame as per the katana scheme found on this site, now everythings cool except for the headstock area because the way it's outlined on the katana means it interferes with the rubber thingy that the fuel tank mounts to on the older 750. So I have thought of a couple of things:

So A is how the katana picture is done, B is something I could do with a steel plate easily without any tank clearance issue, same with C and I am pretty sure I could get away with D as well If I moved the coils a little bit. What do you think? I think D would be best?

BRACE.png

I have 12 and 15mm tubing to do this, is 12 sufficient? I read that a half inch tubing was adequate for a lot of this stuff and 12 is the closest. (I'm using thicker 24mm tubing for the swingarm area)
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Thanks, the only thing about that is it doesn't have AS a direct path to the top of the headstock as is optimal I think? I have no idea if it has anything to say in practical use though! I'm sure anything is better than nothing??

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..... I removed the stamped steel plate in the headstock area as it is hollow and in some way will flex more than welding the gusset tubes directly to the upper frame tube . I personally prefer tubing over flat plate for any gussets  where frame stiffening is required .... as  tube is more rigid than a flat plate . 

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7 hours ago, no class said:

..... I removed the stamped steel plate in the headstock area as it is hollow and in some way will flex more than welding the gusset tubes directly to the upper frame tube . I personally prefer tubing over flat plate for any gussets  where frame stiffening is required .... as  tube is more rigid than a flat plate . 

Yes that is the optimal way, but like I said in my first post it interferes with the tank mounting on my frame. So I have to look at alternatives to get the same effect 

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I think your D option looks best, if you just can make it working. B would be really compact but I'm not sure how effective it would be. Especially top part of the upper plate looks like it won't have any effect.

Just for reference, here's what I did for my GSX1100 frame years ago.

frame1.jpg

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I doubt very much the benefit of adding tubes to the headstock achieves any measurable difference! Arttu's arrangement using plate gussets adds far more rigidity in engineering terms. The frame with the std. spine plates  removed will be significantly worse for flex compared to stock as the lower bearing area has less restraint ie. with a lot of load via the forks it could fold inwards. Rule of bracing - make triangles, That one has a nice rhomboid behind what it is trying to brace! 

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1 hour ago, vizman said:

The only force that’d fold that via the forks is hitting something stationary at about 50 mph, 

I did say a LOT of load, but doing stoppies would apply lower comparable forces but if done over and over . . . . . fatigue sets in aaaand ! Which comes back to the point of -  if it's likely to take that level of force - why brace at all? I can't say my old Zed framed Kawazuki using GSXR 1100 'L' yokes and forks ever felt 'weak' or 'flappy' and that was entirely stock, framewise. Don't exclude the fact that USD fork and yoke combinations are significantly stronger than OEM equipment and so will transmit forces to frame that would have previously bent the forks or yokes . . . . . .  and i'd put the speed closer to 30 than 50mph! The above frame could be easily 'rectified' as picture attached - triangles !

Added frame brace.jpg

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13 hours ago, gorbys said:

Thanks, the only thing about that is it doesn't have AS a direct path to the top of the headstock as is optimal I think? I have no idea if it has anything to say in practical use though! I'm sure anything is better than nothing??

If you can work out a better way and still manage to get your tank on, then well done, but with the tank mounts where they are i didnt really see any other way.

all the other frames shown are GSX, which dont have the same mountings!!!

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2 hours ago, vizman said:

The only force that’d fold that via the forks is hitting something stationary at about 50 mph, 

So basically riding any B-road or mountain pass here in Norway then? xD

11 minutes ago, 370steve said:

If you can work out a better way and still manage to get your tank on, then well done, but with the tank mounts where they are i didnt really see any other way.

all the other frames shown are GSX, which dont have the same mountings!!!

That's why I posted in the first place to get some feedback since all the guides tend to the gsx. 

Anyways, isn't the point of bracing the headstock like this to prevent lateral or twisting motion? 

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I have a standard GS750 framed bike with a 1085 engine, and GSXR1100 forks and wheels, braced alloy swing arm, radial tyres.

It's perfectly stable well into 3 figure speeds on bumpy twisties. If you want to go faster than that, probably better off on a different bike!

Whatever you do, unless you've done the testing and maths to prove it adds anything, it's just for looks anyway. I don't think the GS750 frame has an issue, personally, and it's the suspension wheels and tyres that make the difference.

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Your forks will give way before that headstock does, and unless you’re riding at TT/MotoGP/etc standard I doubt you’ll get enough heat into the tyres....so you’re tyres will let go before you put enough flex in the forks to fold that headstock....

 

.....bit of flex is good, triangles are good passing the yield is not good and non of its worth a shit if it’s not stitched together well.

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Forty years ago, professional race teams used this frame, right?  What deficiencies did they find in the factory frame, and how did they reinforce it?  Yes, modern tires and suspension will apply forces a little differently than the old stuff, but a street bike is normally not ridden as hard as a race bike.  There's also the issue of diminishing gains.  Some benefit should be gained by modest reinforcement, but we could over-do it with extra tubes, gussets, etc and end up with an excessively heavy frame.  Even if we eliminate every potential weak spot in the frame, but there will still be other weak spots, namely the rider.  Hit that stationary object at 50 mph, even if the frame could sustain it, the rider should expect to be severely damaged. 

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3 hours ago, Poldark said:

Forty years ago, professional race teams used this frame, right?  What deficiencies did they find in the factory frame, and how did they reinforce it?  Yes, modern tires and suspension will apply forces a little differently than the old stuff, but a street bike is normally not ridden as hard as a race bike.  There's also the issue of diminishing gains.  Some benefit should be gained by modest reinforcement, but we could over-do it with extra tubes, gussets, etc and end up with an excessively heavy frame.  Even if we eliminate every potential weak spot in the frame, but there will still be other weak spots, namely the rider.  Hit that stationary object at 50 mph, even if the frame could sustain it, the rider should expect to be severely damaged. 

Many good points here. I would have loved to see a 750 frame done by pros but all my searching leads me back to this page and the katana brace guide. 

7 hours ago, gs7_11 said:

It's perfectly stable well into 3 figure speeds on bumpy twisties. 

Whatever you do, unless you've done the testing and maths to prove it adds anything, it's just for looks anyway. I don't think the GS750 frame has an issue, personally... 

Well, mine wasn't exactly confidence inspiring doing the ton. Squirmy I would say. And that wasn't bad suspension tyres or bearings as they where all new. 

And if it's just for looks I find it odd that even suzuki added bracing on the later models gsx's and bigger gs bikes. The one between the downtubes and over the swingarm being two examples. 

 

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3 hours ago, vizman said:

good luck with getting your torch in there to do the returns on that red bit

That's the advantage of brazing tubes - dab the rod in at the back/sides and it'll flow through capillary attraction - 'big boys soldering' really!

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12 minutes ago, gorbys said:

Many good points here. I would have loved to see a 750 frame done by pros but all my searching leads me back to this page and the katana brace guide. 

Well, mine wasn't exactly confidence inspiring doing the ton. Squirmy I would say. And that wasn't bad suspension tyres or bearings as they where all new. 

And if it's just for looks I find it odd that even suzuki added bracing on the later models gsx's and bigger gs bikes. The one between the downtubes and over the swingarm being two examples. 

 

If the factory started adding extra pieces to later model frames, it was likely due to feedback from a race team.  I don't think the business managers would have approved increasing the number of steps in manufacturing a frame (increasing costs) for mere cosmetic purpose.  Those later model frame changes are going to be the most bang for your buck.

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13 hours ago, Gixer1460 said:

I doubt very much the benefit of adding tubes to the headstock achieves any measurable difference! Arttu's arrangement using plate gussets adds far more rigidity in engineering terms. The frame with the std. spine plates  removed will be significantly worse for flex compared to stock as the lower bearing area has less restraint ie. with a lot of load via the forks it could fold inwards. Rule of bracing - make triangles, That one has a nice rhomboid behind what it is trying to brace! 

I agree, when you look at the structure it is already pretty sturdy.

 

Just other/modern forks and wheels made quite a difference.

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