1981 gs750 (gs750e) Retro Racer project

[LarsKroghStea]

Hate it when I have to redo stuff, but that's how it is sometimes.. One of the connections to the gear indicator wasn't good enough and broke off:

Had to cut them all off to make sure one of them doesn't hold all the load.

I bought some adaptors for the paddock stand. I've used a steel rod through the hollow front axle, but the shop manual says to first torque down the clamping bolts on the short piece (left side) and then tighten the axle bolt to 100Nm/74 ft-lbs. For that I need to use an internal hex tool:

These adapters let the forks rest on the paddock stand, and makes it possible to torque down the axle:

When the axle is tightened, the stand is removed and the fork should be bounced up and down 4-5 times with the weel on the ground. Then the two left clamp bolts are torqued to spec. This ensures there is no unnessesary tension in the axle and that the calipers are aligned.

 

[LarsKroghStea]

So, I rolled the bike out into the sun for the first time in a couple of years. Started it up, and it idles okay at about 1000-1100rpm. Revs okay without lagging too. I've had the carbs apart so I will have to resync eventually.

What I was most exited about, was measuring the forks. The original spring rate is 0,85kg/mm, and I had to set the preload to max to get the sag in the recommended range. Sag with me on the bike is now 36mm on the fork. Suzuki manual says 30-40mm and Race Tech Suspension Bible says 30-35. When bouncing the bike up/down I could get it to compress another 64mm for a total of 100mm. The total stroke is 120mm. This was with compression setting to 1,5 turn, which is standard, but way too soft.

The oil is probably very old, but with adjusted compression and rebound, I'm not afraid to bottom out at the speeds I drive at now. The Race Tech calculator says I should switch to 1,05kg/mm springs, and I probably will when I'm changing oil and seals during the winter. It's only a couple of months left of the season here in Norway, and I want to drive as much as possible.

 

[LarsKroghStea]

Custom side-covers are necessary to get the correct "bone line". I haven't made the cover for the other side yet:

I planned on making a smaller cover like this:

but I'm leaning towards extending it downwards so it lines up with the bottom of the air filter in stead.

 

[steve murdoch]

I fear that stock swingarm might get overwhelmed by the top quality front and rear suspension.
Any plans for an upgrade?

 

[LarsKroghStea]

I fear that stock swingarm might get overwhelmed by the top quality front and rear suspension.
Any plans for an upgrade?

With the risk of something getting lost in translation (I'm from Norway and not fluent in english), I will try to answer. I'm not afraid it will be overwhelmed as in struggling to keep up. I believe that has more to do with how hard the bike is pushed. The main reason for upgrading the suspension was to get a better ride and feel, especially on sharp bumps. The valving on the original forks was way too restrictive and harsh. I also wanted the posibility to adjust compression and rebound to suit me. And the better brakes are of course important. I had a Kawasaki Ninja earlier, and the confidence and feel of safety these front ends bring is night and day compared to a bike from the early eighties.

If you're talking about the (ride)quality of the swingarm lagging behind the rest of the setup, I absolutely agree. Last time I had the bike on the road, I did notice "tracking" or unstability when driving over cracks in the road (going in the same direction as me) or crossing roadmarkings.
In the beginning of the build I dicided against the square swingarm as I didn't think it suitet this look, but now that everything else is beefed up I'm starting to think that it might even look better. I don't want to go full gixxer in the rear, but maybe the 1982 GS110E box-section aluminum swingarm. According to reviews from back then, that swingarm was a definitive upgrade; "the aluminum box-section swing arm resists flex extremely well".
I have no idea if it's a direct swap, but I'll do some research. Thanks for your input

Looks pretty similar:

​

 

[LarsKroghStea]

Did some research on the swingarm. The 750 pivot bolt is thinner than the 1100. This means that either the frame will be drilled to accept a thicker bolt, or the old bolt is used with fabricated "top hat" spacers. Because of strict Norwegian regulations regulating modifications to the frame, I don't want to drill the holes bigger. I can probably make some top hats myself, and the swing arm seems like a good upgrade. There's only one of them on ebay, and 13 people has it in their watchlist. Maybe it's stupid to let that one go?

 

[LarsKroghStea]

I found an image online of a GS with similar exhaust as I have, box swing arm and the same YSS shocks. I'm leaning towards this being a worthwile upgrade, some time in the future.

 

[LarsKroghStea]

I weighed my bike on bathroom scales today in case I decide to order new springs for the fork. It weighs 101kg on the front wheel, and 98kg on the rear. That's without any gas in the tank, and with 10 liters of fuel it will have about the same front rear weight bias as a mid 2000 GSXR. I was aiming for a weight below 200kg, so I'm pretty happy with the result. This will also make the fork handle as intended, wich will contribute to a safe ride
Trail is 114mm and I believe stock is 107mm. I guess that is close enough?

 

[slayer61]

I found an image online of a GS with similar exhaust as I have, box swing arm and the same YSS shocks. I'm leaning towards this being a worthwile upgrade, some time in the future.

The swingarm is a common and popular conversion, so much so, I did it on my wife's Kawasaki GPz!

 

[LarsKroghStea]

The swingarm is a common and popular conversion, so much so, I did it on my wife's Kawasaki GPz!

Nice to know I've now bought it, and will try to do the conversion this winter.

 

[LarsKroghStea]

Ok guys, I've ridden the bike for the first time with the Gixxer fork. So far, it is everything I hoped for It was only 1st and 2nd gear at a large parking lot right by my house, but the brakes and low speed handling and turning couldn't be better.

 

[Rob S.]

Is this a seven/eleven conversion? Side cover says 1100.

 

[LarsKroghStea]

Is this a seven/eleven conversion? Side cover says 1100.

Hi!
If you mean the black/orange bike on the picture, that's not mine. Just a random picture showing the 1100 box-section swing arm.

My bike looks like this (older photo, bike is more complete now)

It has a 16v 750 engine, but with BS34 carburetors from a GS1000 and a Kerker 4-1 exhaust.

 

[LarsKroghStea]

I need a front fender to secure the brake line going from right to left caliper, but I'm not getting things right with the parts I was using. I've decided to go with the full Ducati Monster-setup until I can find something that fits better. On the Monster it looks like this (I don't have a Ducati.. only the fender):

I think the silver brackets make the design a bit noisy, so I did a quick sprayover with black braces and a darker gray on the fender. I think that looks much better.

The the bottom part of the braces are too short to fit over a 19" inch weel, and the holes are also wrong. I will get a piece of straight bar and make two new mounts.

 

[LarsKroghStea]

During the test run I found it hard to change gears, and when I got home I saw something has happened to the left rear set:

When mounting the rearset, I believed I had bent the tab in to position, but I probably just bent the bolt. When I rode the bike, the bolt turned a quarter turn from the weight of my foot and got totally misaligned.

On the other side I modified the aluminum brackets, and that turned out well:

On that side there are two extra bolts, so I just grinded off the tab on the frame.

On the left side, I can not grind off the tab, as I need it to secure the aluminum bracket.

I'll need to split the top of the tab (on the frame) with an angle grinder, and bend it inwards until it's parallell with the riding direction.

Then I'll grind off metal from the back of the bracket until that also sits parallell to the frame. I'll also shorten it. Then the gear-side footpegs will also sit perpendicular to the frame, just like it does on the brake side. At least, that is the plan

 

[LarsKroghStea]

I've changed some of the bolts already, and today the bolts for the lower triple arrived:

From this:

To this:

 

[LarsKroghStea]

The front fender is a more modern look than I wanted, but will have to do for now.

I've bought som flat aluminum rods, and will cut them a little longer than the originals.

 

[slayer61]

I love the attention paid to wiring pinch bolts

 

[LarsKroghStea]

The swing arm has arrived, and I've taken some measurements.

First of all; it's very light:

I haven't weighed the steel one, but I would guess the weight is almost half.



The inner bushing is 16mm (difficult to measure exactly).

And the pivot bolt is 14mm.

I would guess I could just buy a length of steel tubing with ID=14mm and OD=16mm (1mm wall thickness). Easy to get hold of in 304 stainless steel, and as it'll just sit between the bolt and the bushing (not directly on the needle bearing) I'm pretty sure that will be strong enough

 

[LarsKroghStea]

Lots of stuff going on lately, and before I could finish the Ducati fender I came by another front fender that suits my build much better:

It came with som braces and clamps. I didn't like the clamps, and will swap them with rubber lined clamps. I'll use the rear brace, but will have to make a new front brace because it's too short for a 19" wheel. I'll pick up a length of 6mm stainless steel rod tomorrow along with a pack of clamps