Sportston GT380M Special

[sportston]

I started off with something like this


Woohoo! I finally worked out how to add an image
This is the start of the clutch mods.

[sportston]

After hacking various bits off…

But this has removed so much of the strength of the casing. How do I spread the load, and thereby avoid stress cracking?
I decided to create a brace of braces, as shown below.


Yes, it looks ugly but it will be hidden and it is effective.
Then I needed a dust seal for the other side. A piece of viton was cut and pressed into service.

[sportston]

Once fitted it looked like this.


Then I fitted the master cylinder and bled it.

After playing with bite points and ‘creatively adjusting’ the length of the push rod I eventually ended up with a clutch that bites exactly how I want it; no slipping and no dragging!
So far I have ridden it to, and around, Yorkshire and back to Scotland. Several hundred miles of trouble-free clutch usage has made me rather pleased with myself and the bike. Next year’s trip to Switzerland should be a lot more gentle on my carpal tunnel than it would have been otherwise.

[sportston]

And now the pics of the front brake mods.
It used to look like this

Then I got a used 33mm fork leg with caliper lugs on.

Which, after waving a magic wand, eventually looked like this.

A good used set of GSX750 discs were fitted to the wheel

But… the threaded area on the bolts was a little too short. After using an m8 die, the threads were long enough to allow the bolts to pinch the discs securely.

[sportston]

Rethreading the bolts.

I also got a matching pair of GSX750 calipers, stripped and rebuilt them.

Then fitted them and bled them.

Those of you with sharp eyes may notice that one side has the caliper mounted before the fork leg, while the other is mounted behind the fork leg. It looks a little odd, but works fine. I got the idea after seeing a racing bike in a magazine similarly modified. It saved me having to change yokes and forks for a different sized set from a larger bike.

In the end, I ditched the larger 16mm master cylinder for a 14mm one. The 16mm item leaked! In fact, all 3 of the 16mm items I tried leaked. Adelin must have made a dud batch. The 14mm and the 17.5mm Adelin versions don’t leak.

My next job is to fit a GS550 swing-arm, wheel and brake to the rear of the bike. More pics to follow once I have found the time to do it.

[sportston]

In the meantime here are a few pics of the crash bars I recently fitted in preparation for next year’s European excursion.


They should help keep the panniers from sagging against the exhaust pipes too.


Note the nice new metal indicators. No need to hold them together with insulation tape anymore!
I decided to make a prettier bracket for the rack and crash bars from 6mm thick 316 marine stainless sheet. This will also position the rack a bit lower. I will add more pictures later.

[badgereng]

Top fettling

[Alan H]

A GS550 swing arm fits the GT550 without modification. Hopefully it'll work on the 380 too.
On the 550, I took the shocks out for better access, then just took the swing arm pivot bolt out, remove the GT swinger, and use the same bolt to fit the GS swinger. Chain line was spot on.
Note that the GT & GS rear sprockets are different mounting, but GT750 sprockets fit the GS rear wheel. I have a 40T sprocket on Earwig as it's a bit more powerful than standard.
It would be nice to meet up next year for some comparisons!
Emma the Dunstall GT550 will be having similar treatment, but the swing arm will be the same length as standard instead of a bit longer (can't remember which model GS they came off). I had to fit 1" longer Hagon shocks as the longer Swing arm made the bike sit lower at the back.
I fitted Nonfango panniers to the GT750B and GT550J and just took the bracketry off when not needed.
Great to be different isn't it?!?!

[sportston]

After removing the standard swing arm and comparing with the gs550 one, I can quite confidently say…it don’t fit . The pivot point is 2cm wider on the GS. The rear wheel also needs a longer spindle. I’m not sure if the GS550 that donated its swingarm was an GS550 LT or not. My research suggests that one year only model had a different swingarm and pivot bolt. Perhaps I need a different year model. I have sent out some questions to some breakers offering GS550 swingarms asking the width at the pivot. We shall see if any are 200mm instead of 220mm. The GT380 is 200mm.
If necessary, I may have to modify the GS550 one I have by cutting off 10mm from each side, but I’m not too keen on that idea.

[sportston]

I had to fit 1" longer Hagon shocks as the longer Swing arm made the bike sit lower at the back.
I fitted Nonfango panniers to the GT750B and GT550J and just took the bracketry off when not needed.
Great to be different isn't it?!?!

Thanks for the advice Alan. I measured a 30mm difference in length of the two swingarms. I doubt that will make a significant difference to the ride height. If it does, it may help my stubby little legs reach the ground better. I noticed the difference in fixings for the rear sprocket, so already have a new sprocket and carrier. It appears the only thing I have missing is a 6mm spacer for the rhs. I can fabricate one quite easily from old parts.
The more I think about it, the more I like the idea of cutting the gs550 one down to size at the pivot end. I haven’t got much to lose by trying!
I may have to add an extra link to the chain though.

[Alan H]

I had to fit slightly longer (330mm) shocks to the Earwig due to the longer GS550 swing arm making the back of the bike lower. Unfortunately, it made all the back end lower and nearly had me off in the Isle of Man when spirited cornering caused 'everything' to ground.
Different GS models have different length swing arms just to help the situation.....
Check standard & 'new' ground clearance before spending more money!!
I got a GS550 swing arm (the same length as the standard GT550 part) from DK motorcycle spares a few weeks ago for Emma the Dunstall resto. https://www.suzuki2strokes.com/forum/vi ... 8&start=15 (link to more info.)
I took the standard GT550 swinger with me to compare was was available, and they have a LOT of stashed spares downstairs. You can measure the swinger pivot bushes/bearings at the same time too. Have a look at the bottom shock mounts as there could be differences in length from the pivot too. Jamie & Neil are very helpful there.

[sportston]

They have always been helpful in the past, but reckoned they couldn’t measure anything when I asked this time. They are 240 miles away. It’s a bit of a trek.
I don’t suppose you would be able to measure yours and report back, pretty please? I just want to know if the standard GS550 swingarm is a straight fit at the pivot end.

[sportston]

Today, I decided to cut 20mm off the width off the GS550 swingarm. After a lot of filing and grinding and a new set of bearings fitted, the GT380 now has a GS550 swingarm.
There were some minor clearance issues with the mudguard that were easily solved with a hacksaw. The Higgspeed exhausts also pose a clearance problem but this can be solved by adding a spacer or two.
The bit that presents more of a challenge is getting the offset for the sprocket right. The GT and the GS offsets are 8mm different. My solution will be to reverse the sprocket (it has a 2mm dish on one side) and mill 6mm off the carrier. I will build some strength back into the carrier with a steel brace on the underside, which will unfortunately add some unsprung weight and be a pain to make, but is a necessary precaution for reliability (I don’t want the sprocket carrier to crack while I am touring in Europe). Pics to follow soon.

[Alan H]

They have always been helpful in the past, but reckoned they couldn’t measure anything when I asked this time. They are 240 miles away. It’s a bit of a trek.
I don’t suppose you would be able to measure yours and report back, pretty please? I just want to know if the standard GS550 swingarm is a straight fit at the pivot end.

I'll try & get in the garage later today.

[Alan H]

Both the GS550 swing arms I have are 226mm wide at the frame end - including the dust/grease seals at each side.
Access to the GS550 swinger on the Earwig is dire, but I remember it went in without any issues. I have found out that K, M and A/B GT550 frames are very different, so I think you're in for some filing or grinding!