'75 suzuki gt250...Buzzing around the block
- Thread starter joeschuit
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joeschuit
Been Around the Block
Re: '75 suzuki gt250
Update: Rims are at the powdercoaters. I've decided against the polished lip based on some photoshops I've been doing and the amount of work involved masking and actually polishing it. I may do a pinstripe later on. I finished up the caliper brake bracket and the swingarm is now 2" longer. I started off by chopping the old brace off:
I then measured 2" out from the swingarm bushing thing and cut off the legs. In this pic, the steel slugs are a little bigger than they should be. I also bored out the inside, leaving a 0.2" wall thickness to keep up the strength but also take out some of the weight.
I mocked up some cardboard cutouts for the new brace, including where the new wheel and tire is going to sit. The new tire is 1" larger in diameter to I added that in to the dimensions. Overall I'm very happy on how it came out, including the nice tig welds.
Heres the new sprocket and brake plate:
Hopefully next week I can get the rims back and start puting it back together. I'll be able to sandblast and paint the swingarm and pull the front forks and polish them. If I get the time I'll see how and where I need to mount the new rear master cylinder to the frame or peg mount.
Update: Rims are at the powdercoaters. I've decided against the polished lip based on some photoshops I've been doing and the amount of work involved masking and actually polishing it. I may do a pinstripe later on. I finished up the caliper brake bracket and the swingarm is now 2" longer. I started off by chopping the old brace off:
I then measured 2" out from the swingarm bushing thing and cut off the legs. In this pic, the steel slugs are a little bigger than they should be. I also bored out the inside, leaving a 0.2" wall thickness to keep up the strength but also take out some of the weight.
I mocked up some cardboard cutouts for the new brace, including where the new wheel and tire is going to sit. The new tire is 1" larger in diameter to I added that in to the dimensions. Overall I'm very happy on how it came out, including the nice tig welds.
Heres the new sprocket and brake plate:
Hopefully next week I can get the rims back and start puting it back together. I'll be able to sandblast and paint the swingarm and pull the front forks and polish them. If I get the time I'll see how and where I need to mount the new rear master cylinder to the frame or peg mount.
Re: '75 suzuki gt250
Nicely done but if you work that arm hard it will crack at the rear edges of those slugs. Solid or almost solid slugs don't bend the way that the swingarm tubes bend, so any flex starts at the edge of that hard slug and that's where they typically crack up. The slugs need to flex the same way that stock tubes flex and they should end at an angle to spread the load.
And if I understood that section in Tony Foale's book, the brace should be left unwelded at the rear as it wraps around the tubes.
It might be better if you were to make a new arm in say 2"x1" chrome moly tube which would be lighter and stiffer than the first attempt. You can alos get oval shaped chrome moly if you wanted to be really trick, but that would entail even more work and machining.
Nicely done but if you work that arm hard it will crack at the rear edges of those slugs. Solid or almost solid slugs don't bend the way that the swingarm tubes bend, so any flex starts at the edge of that hard slug and that's where they typically crack up. The slugs need to flex the same way that stock tubes flex and they should end at an angle to spread the load.
And if I understood that section in Tony Foale's book, the brace should be left unwelded at the rear as it wraps around the tubes.
It might be better if you were to make a new arm in say 2"x1" chrome moly tube which would be lighter and stiffer than the first attempt. You can alos get oval shaped chrome moly if you wanted to be really trick, but that would entail even more work and machining.
joeschuit
Been Around the Block
Re: '75 suzuki gt250
After reading what you've said, I agree about the new stress points that I've put on the swingarm. I'd rather do it right than wish I did if something bad happens. I looked up the prices of the 4130 chromoly tubing, and its not cheap. I figure it'll cost me $120 in materials alone. However, I do have another option involving a stock yamaha xs400 swingarm. Its already a few inches longer than stock and has plenty of material up front for fitting it to my frame. I'll take a look at it today and see what I can do. Thanks, Joe
After reading what you've said, I agree about the new stress points that I've put on the swingarm. I'd rather do it right than wish I did if something bad happens. I looked up the prices of the 4130 chromoly tubing, and its not cheap. I figure it'll cost me $120 in materials alone. However, I do have another option involving a stock yamaha xs400 swingarm. Its already a few inches longer than stock and has plenty of material up front for fitting it to my frame. I'll take a look at it today and see what I can do. Thanks, Joe
two-smoker
I reject your reality, and substitute my own!
Re: '75 suzuki gt250
Another option, which I used myself, would be to use a Yamaha Radian swingarm. It's also a little longer, and box section to boot. The only problem I ran into was the pivot bolt was slightly larger in diameter, so I had to bore out the holes in the frame to fit it. Other than that, and the appropriate wheel spacing, it went straight in... But of course, my bike was a 380.....
Another option, which I used myself, would be to use a Yamaha Radian swingarm. It's also a little longer, and box section to boot. The only problem I ran into was the pivot bolt was slightly larger in diameter, so I had to bore out the holes in the frame to fit it. Other than that, and the appropriate wheel spacing, it went straight in... But of course, my bike was a 380.....
joeschuit
Been Around the Block
Re: '75 suzuki gt250
I ended up picking a suzuki 400 single swingarm. Its a good 3 inches longer and beefier than stock. The spacing on my frame is 7.25" and the 400 is 7.75". Theres enough material to shorten it 0.25" on each side, but the rear is much wider, about 9" on the outside of the arms. I plan on "disassembling" the brace, cut and reweld one of the tubes so the rear width is correct, and reweld in the existing brace, shortened widthwise to fit the narrowed tubes. The tubes won't be changed, and there will only be welds where there was stock, so there shouldn't be any added stress. Another bonus with having the rear width correct is that the shocks won't be bowed out and I can use my existing spacers. I'll be able to get some work done tomorrow. Thanks, Joe
I ended up picking a suzuki 400 single swingarm. Its a good 3 inches longer and beefier than stock. The spacing on my frame is 7.25" and the 400 is 7.75". Theres enough material to shorten it 0.25" on each side, but the rear is much wider, about 9" on the outside of the arms. I plan on "disassembling" the brace, cut and reweld one of the tubes so the rear width is correct, and reweld in the existing brace, shortened widthwise to fit the narrowed tubes. The tubes won't be changed, and there will only be welds where there was stock, so there shouldn't be any added stress. Another bonus with having the rear width correct is that the shocks won't be bowed out and I can use my existing spacers. I'll be able to get some work done tomorrow. Thanks, Joe
joeschuit
Been Around the Block
Re: '75 suzuki gt250
After finally finding a few hours aside from work and school, I came up with this. Overall it came out very nice, just needs a few finishing touches. I need to mill down the the shock mounts at the top by about an 1/8" and put a tab on for the brake stay. However, that cannot happen untill I get the rims back and account for the new spacers that need to be made. Thanks, Joe
Here it is stock:
modified the stock brace, with no welding around the tube, just where it was originally welded on top and bottom:
New shock mount:
Overall look with the old spoke wheel for reference:
One thing I wanted to keep in mind is the rear height. Because of the longer swingarm, it would lower the rear if I were to use the original shock mounts. I did some simple measuring and cad work to figure out the height change between stock and modified. With this I was able to get some solid numbers to keep me in the ball park. Thanks, Joe
After finally finding a few hours aside from work and school, I came up with this. Overall it came out very nice, just needs a few finishing touches. I need to mill down the the shock mounts at the top by about an 1/8" and put a tab on for the brake stay. However, that cannot happen untill I get the rims back and account for the new spacers that need to be made. Thanks, Joe
Here it is stock:
modified the stock brace, with no welding around the tube, just where it was originally welded on top and bottom:
New shock mount:
Overall look with the old spoke wheel for reference:
One thing I wanted to keep in mind is the rear height. Because of the longer swingarm, it would lower the rear if I were to use the original shock mounts. I did some simple measuring and cad work to figure out the height change between stock and modified. With this I was able to get some solid numbers to keep me in the ball park. Thanks, Joe
adriansgt250
Active Member
Re: '75 suzuki gt250
Do you mind me asking how difficult the rear disc conversion was?
I have a spare gt250 front disc and calliper and the rear drum I have is a piece of cr@p
Do you mind me asking how difficult the rear disc conversion was?
I have a spare gt250 front disc and calliper and the rear drum I have is a piece of cr@p
joeschuit
Been Around the Block
Re: '75 suzuki gt250
The hard part is finding the correct rim that is skinny enough to fit the stock swingarm and a sturdy mounting point for the caliper. It was easier for me to do the conversion becuase of the wider swingarm and the complete rearend from a yamaha rz350. Having the correct pieces to start out with will make it easier to modify, rather than starting out with nothing. May I ask what condition the rear drum is in? Usually a good sanding of the drum and new pads will make it work well. I had no problems with my drum brake locking up the tire at any speed. Thanks, Joe
The hard part is finding the correct rim that is skinny enough to fit the stock swingarm and a sturdy mounting point for the caliper. It was easier for me to do the conversion becuase of the wider swingarm and the complete rearend from a yamaha rz350. Having the correct pieces to start out with will make it easier to modify, rather than starting out with nothing. May I ask what condition the rear drum is in? Usually a good sanding of the drum and new pads will make it work well. I had no problems with my drum brake locking up the tire at any speed. Thanks, Joe
adriansgt250
Active Member
Re: '75 suzuki gt250
The drum isn't too bad but I've been struggling to find pads for less than $250
I figured if there was a conversion kit for the GT250 that might be a better option
The drum isn't too bad but I've been struggling to find pads for less than $250
I figured if there was a conversion kit for the GT250 that might be a better option
joeschuit
Been Around the Block
Re: '75 suzuki gt250
I was able to get in a few more hours and fit the front wheel and both tires. I think I'll end up going fenderless. Height is just about right, but I still have much more work ahead of me. I've got some ideas if I get some time that'll involve a better set of pipes that'll go under the bike. I'd like to change the angles up a bit and sacrifice some bottom end for a good punch up top. Thanks, Joe
I was able to get in a few more hours and fit the front wheel and both tires. I think I'll end up going fenderless. Height is just about right, but I still have much more work ahead of me. I've got some ideas if I get some time that'll involve a better set of pipes that'll go under the bike. I'd like to change the angles up a bit and sacrifice some bottom end for a good punch up top. Thanks, Joe
MotorbikeBruno
Over 1,000 Posts
Re: '75 suzuki gt250
Soooo awesome. 8)
Soooo awesome. 8)
famousseajay
Been Around the Block
Re: '75 suzuki gt250
SICK!
SICK!
Boner
Active Member
Re: '75 suzuki gt250
This thread has been an inspiration to me while also building up a GT250 Caff Racer although my baby is nowhere near as exotic as Joes it will still turn my crank. Still having problems with the chambers though cant get my head around the thoery
. I have one race set of chambers that work well on my T250 track bike but power in at high 8's my attempt for a wider range maybe 6 - 9 has been a disaster. But I will soldier on and keep an eye on this thread.
This thread has been an inspiration to me while also building up a GT250 Caff Racer although my baby is nowhere near as exotic as Joes it will still turn my crank. Still having problems with the chambers though cant get my head around the thoery
. I have one race set of chambers that work well on my T250 track bike but power in at high 8's my attempt for a wider range maybe 6 - 9 has been a disaster. But I will soldier on and keep an eye on this thread.
