1981 gs750 (gs750e) Retro Racer project

[LarsKroghStea]

Here are the two parts I printed today. I haven't sanded the edges or removed the tape or anything. Just wanted to see if it fits, and I'm impressed with the opportunities a 3d-printer brings to the table:


IMG_20200301_181733 by Lars Krogh-Stea, on Flickr


IMG_20200301_181846 by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

48737553807_0a319a6834_o by Lars Krogh-Stea, on Flickr


2019-09-18_10-45-33 by Lars Krogh-Stea, on Flickr






I'm not that satisfied with the headlight.. It looks too small, and the profile is too deep wich makes it stick out too far. I still have the first headlight i bought lying around. At the time i thought it was too big, but now I think it maybe looks better. Any thoughts?






IMG_20170328_111354 by Lars Krogh-Stea, on Flickr


IMG_20170328_111151 by Lars Krogh-Stea, on Flickr

[steve murdoch]

I think the larger one suits the proportions of the bike and it looks better too.
What ever colour paint or even if you go with the bare metal look, consider doing the headlight the same. I like the continuation along the top of the bike..

[roeme]

I'd go with your "first" headlight.

To me, the small "choppery" buckets (I think mainly used on the L's?) and deep buckets give a dated look, so I like the "european" (?) buckets best. They're not too deep, while having a nice diameter. I even found some new aftermarket ones which are almost indistinguishable from OEM. I don't have any specific pictures, here are some from my rebuild (click for fullsize):

[LarsKroghStea]

Thank you for your opinions

I will go for the large headlight and probably make a little dent at the bottom of the dome so I can position it a little lower.

It's also a great idea to give it the same finish as the rest of the bike. I will keep the "worn/bare metal"-look and add that to the headlight.

I like the worn racing look, and will try to transfer that to the headlight

IMG_20170630_144318 by Lars Krogh-Stea, on Flickr

2019-08-02_10-14-25 by Lars Krogh-Stea, on Flickr

[Buffalo Bill]

Looks very good, original. The number on there, no but it would be acceptable if it designated the model year.

[LarsKroghStea]

Got the fuel problems sorted today Firstly, there was a slight kink in the fuelhose. Secondly, and more important, the fuel cap venting mekanism wasn't letting air in and out of the tank. Fascinating how fast the vacuum stops the flow of gas. Now it runs as smooth as it did with the small plastic tank I used for the test run. The petcock is still too tall (can't get the tank to sit low enough and line up with the seat), so I'll have to change it out one day. I'll save this for task for later.

[LarsKroghStea]

Also got the first sidecover done (not with the final paint..). I've had those perforated stainless steel sheets laying around forever and finally got around to use them. I wanted to be able to remove them easily and for that reason I've kept the original mountingpoints on the frame.


First I fired up the lathe and made a "push-button" for the bottom mountingpoint:

Then I made a cardboard template and cut the perforated steel into a loose fit:
Påska by Lars Krogh-Stea, on Flickr


Påska by Lars Krogh-Stea, on Flickr


I'll line the edge with an edge protection profile like this:
96520-K1367-Kantenschutzprofile-Edge-protection-profiles-Form-C by Lars Krogh-Stea, on Flickr


I used the same profile to line the backingplate for the licenceplate:
Påska by Lars Krogh-Stea, on Flickr


I shaped two pices of the same perforated steel to the back of the sidecover and pop riveted them in place, also drillet and riveted the "pushbutton" fastener:
Påska by Lars Krogh-Stea, on Flickr


Did a quick "paint-job" and mounted the cover. The fit is prettyr tight and there is very little room for vibration. I'll go over the edges and fine trim them when i get the edgeprotection profiles:
Påska by Lars Krogh-Stea, on Flickr


Next weekend it's time to fit he speedomoter, and then I'll get to drive it home. That will hopefully speed up the process significantly

[LarsKroghStea]

And here's the back side of the cover. The two "pockets don't look pretty, but the holes line up with the cover and they're hard to see through the small holes:

Påska by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

Today I measured the "speedo A/D converter" and redesigned the housing to not be so bulky. I saved a lot of space by flattening the inside of the housing so it only builds 1mm from the forkleg. Top pictures are the old ones, bottom two is the file I sent to my friend for printing:


Speedogearhus_huset v3_4 by Lars Krogh-Stea, on Flickr
Speedogearhus_huset v3_3 by Lars Krogh-Stea, on Flickr
Speedogearhus_huset_kort v3_5 by Lars Krogh-Stea, on Flickr
Speedogearhus_huset_kort v3_2 by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

So, I went to pick up the last 3D-printed part. It was a little bit skewed, but I don't mind as I'm going to sand and paint the parts anyway. I think the whole setup looks awesome, and I'm a little bit proud to have designed my own 3D-printed parts (I know I'm a little bit biased ). Anyhow, I present to you the analog to digital speedometer converter

IMG_20200416_204315 by Lars Krogh-Stea, on Flickr

IMG_20200416_223222 by Lars Krogh-Stea, on Flickr

IMG_20200416_223337 by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

Thanx


Installed the speedoconverter and tested it yesterday. Worked almost as I hoped. It was a bit shallow and I had to shim the lid a bit to get it working. The worst thing though was that the hexagonal holes that were intended to keep the nuts from spinning wasn't working properly. I think at this small size, the holes and nuts would need to be square to keep the nuts from spinning.
As a signal pickup though, it worked flawlessly, and I'm going to make a revised housing at a later date.


Throwing in a couple of pictures as usual. The first one is from the finished left sidecover (now with rubber edge protection) and one of me and the bike just before I rode it home. About an hour long journey. It still runs as it gets to little fuel, and I blame the petcock. Will test other solutions to this problem, as it must be sorted before I take another trip. First I'll take a short test run with the small white plastic tank to verify that it indeed is the petcock. The third photo is just for fun


IMG_20200418_190938 by Lars Krogh-Stea, on Flickr


Første tur (2) by Lars Krogh-Stea, on Flickr


IMG_20200418_201004 by Lars Krogh-Stea, on Flickr

[LarsKroghStea]

Well.. I've done a couple of comparisons with regards to flow of fuel. I'm starting with three pictures. You can see the combinations of filter+hose/hose/no hose. Time to flow is 30 seconds and measurements are in milliliter. The reason is this; when I tested the bike last fall with the little one liter fueltank (last picture) it took off like a rocket. Ever since that I've not managed to get it to run properly. I'm guessing it runs lean, but I didn't think it would need that much fuel or be that sensitive to variations in fuel hight (I'm guessing). Anyway, here are the flow tests:


Hose and filter (90ml in 30 sec):
IMG_20200419_190656 by Lars Krogh-Stea, on Flickr


Only hose (110 ml in 30 sec):
IMG_20200419_191027 by Lars Krogh-Stea, on Flickr


Only petcock (110 ml in 30 sec, same as with hose. I'm not holding it completely upright)
IMG_20200419_191409 by Lars Krogh-Stea, on Flickr


This is obviously not enough flow. I havent changed anything else since the test run, and I'm running new white paper filter and have new intake boots between plenum and carburettors. All tests are done whith tank lid off, so there's no vacuum that hinders flow. Tanklid on/off only differs 5ml or so.


This is the small test tank I used last year:
IMG_20200420_184926 by Lars Krogh-Stea, on Flickr


As you can see, it flows over 2.5 times as much as with the hose and filter:
IMG_20200420_184910 by Lars Krogh-Stea, on Flickr


I blame the petcock for this. It's a repro Honda cx500 petcock to fit the cx500 tank. AFAIK the xc500 has two carburettors, and maybe thats the reason it copes with lesser flow. Or maybe the repro-petcock is crap.. I have one more petcock. Also repro but different design. I've drilled out the rivets on this one, and will try to modify it for better flow.


What do you guys think? Anyone know how much the petcock wil need to flow per minute to keep up with full throttle?

[Grimly]

Rough rule of thumb is about half a pound of fuel per horsepower per hour and that will provide a comfortable figure to work within.
Or, if you want to get metric on its ass...

https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption

[LarsKroghStea]

Rough rule of thumb is about half a pound of fuel per horsepower per hour and that will provide a comfortable figure to work within.
Or, if you want to get metric on its ass...
https://en.wikipedia.org/wiki/Brake-...el_consumption

Awesome! If my calculations are correct, that amounts to 0,44liter/minute. I managed to fix the biggest petcock, and when I flow tested it, I got 170ml/30sec with fuel filter and 230ml/30sec without filter. It's an easy choice then to ditch the filter. Now that I'm getting 0,46 liter fuel/minute I'm taking it out for a ride tomorrow

Here's a comparison of the petcocks. I didn't realise the difference before I opened them.

IMG_20200421_171648 by Lars Krogh-Stea, on Flickr

IMG_20200421_171922 by Lars Krogh-Stea, on Flickr


I sanded down the gasket and the bakside of the valve, flipped the gasket with the sanded surface in (opposite to the picture) and drilled holes for nuts/bolts. Now it works as intended
IMG_20200421_163650 by Lars Krogh-Stea, on Flickr