Author Topic: Gsx400r front end swap  (Read 327 times)

Offline Henrico123

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Gsx400r front end swap
« on: January 09, 2021, 01:21:14 PM »
Hi guys! Has anyone done a gsx400r front end swap on their GS? I can get a complete frontend for cheap, but if it is not worth it, then I am not going to bother.

Offline sledge

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Re: Gsx400r front end swap
« Reply #1 on: January 10, 2021, 04:56:59 AM »
If I were you I wouldn't waste time swapping the front end over..............I would swap the whole bike  :laugh:

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #2 on: January 11, 2021, 12:01:54 AM »
That would be defeating the purpose of building the GS cafe racer! :laugh: But I can only get the front end in any case. I have decided to go for it and figure it out along the way.

Offline sledge

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Re: Gsx400r front end swap
« Reply #3 on: January 11, 2021, 11:47:28 AM »
Look at the online parts fiches and check out the headstock bearing sizes, always a good place to start.

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #4 on: January 11, 2021, 12:45:27 PM »
According to allballs racings website, bearings and headstocks seem to be the same, so I might be in luck. Picking up the frontend on Thursday, cant wait.

Offline mr72

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Re: Gsx400r front end swap
« Reply #5 on: January 11, 2021, 01:46:51 PM »
I guess I don't understand why it would be worth it.

... either a) to use a GSX400 fork, b) to try and turn a GS500 into a "cafe racer", or c) why a "cafe racer" needs an upgraded fork?

is there any performance improvement in the GSX400R fork over a GS500 fork? is this improvement even possible to discern on a street driven GS500? if not, then are you really going to take a "cafe racer" to an actual race track for track day events or to race?

A stock GS500 fork with the correct springs and oil for the weight of the rider and intended use, along with a matching rear shock, should be more than enough to optimize performance on public roads.

I am sure I am missing something here, like a lot of something. I'm the guy who tried to turn a GS500 into an adventure bike, so I understand turning what you have into something more like what you want but if you don't have sentimental reasons to keep a this specific GS500 then swapping it for a GS450 or just about any UJM will give you a much better "cafe racer" platform.

I have seen folks swap GS500 forks for others for a number of reasons, most often it was a technical challenge they just wanted to try, sometimes they had the parts laying around and wanted to see what they could come up with, etc. Tinkerers at heart. But those folks don't tend to ask these kinds of questions.

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #6 on: January 12, 2021, 12:42:54 AM »
To answer some of your questions:

- I bought a semi-finished (All be it a bit crappy) GS400e cafe racer off someone for cheap as a project, thus it only makes sense to continue with the cafe theme
- The stock GS400 forks are pretty crappy, not adjustable, and are in pretty bad shape rust wise. Rebuilding them costs way more than what the complete front end will cost.
- The front end comes with the brakes off the GSX400 = twin-rotor, way more stopping power, as the motor is currently receiving some performance mods it will just make me feel a bit safer on the roads although it will still not be a rocket, I still like to know I have enough to stop it.
- I will indeed be doing track days as I stay pretty close to one
- Aesthetically it just looks way cooler in my opinion

I have built and raced quite a few 2-stroke bikes in the past, mostly MX and one TZR road bike (and then I got married), so the world of the GS and four strokes are new to me. The cafe racer will be my daily transport to my workshop and back, as well as a bit of marketing, so it needs to tick all the boxes as far as looks go.

Offline mr72

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Re: Gsx400r front end swap
« Reply #7 on: January 12, 2021, 08:00:48 AM »
I get it. I am not sure about your performance mods on the engine, and I'm not sure you have a "GS400e" ... I don't even know what that is. But I also don't think the replacement fork will be an upgrade and I'll be surprised if it can be swapped and cost less than a replacement set of GS500 fork legs to remedy rust etc., even if you add in the cost of a new set of springs and a cartridge emulator setup. And cheap ebay top caps for preload adjustment if you just HAVE to have adjustability.

The dual front rotors is going to require a different master cylinder, two calipers, a whole different front wheel along with rotors, etc. I recently replaced the broken fork legs on my Bonneville with Thruxton parts which bolted straight into the triples but required a 10mm different rotor, a custom machined part to adapt the rotor, and more custom fab parts to get the fender to mount correctly. It was a major chore, and that was a very slight change.

If you just want to do it, then just do it. But it's going to be a whole lot more work and expense than you think and you are not likely to get a single bit of measurable benefit. Likewise your engine mods are not likely to yield any performance improvement. With a rejet and maybe a slip on muffler, you are going to essentially optimize the GS500 engine with stock parts and tune. To add actual usable power is going to require major surgery that would be far easier to do by swapping a whole different engine, and then why? Why not take the entire bike instead?

I mean, frankly, I don't usually like to agree with Sledge, but I do in this case.

Offline sledge

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Re: Gsx400r front end swap
« Reply #8 on: January 12, 2021, 10:13:35 AM »
There has been at least 3 versions of a GS400E that i can think of, one each from the 70s 80s and 90s.

The last one looked identical to a 500E but had a strap across the seat but I believe it was only available in Japan.


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Offline Henrico123

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Re: Gsx400r front end swap
« Reply #9 on: January 12, 2021, 11:05:18 AM »
It is a 1991 GS400e, was not available for a long time before they replaced it with the GS500E.  As far as the rest goes, I got a complete front end of the GSX400R, wheel, rotors, triples, switches, clip ons,master cylender etc. All but the rest of the bike that is usually connected to the frame, for the South African equivalent of $250, so not too bad in my opinion. Taste differs I suppose, as does opinion, there are loads of guys that have done fork swaps on the forum, so I figure why not try it, even if it is just for looks. Hell, all the pro builders out there doing swaps on Cafe builds must have some reason for doing it.

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #10 on: January 12, 2021, 11:08:30 AM »
As for performance, again, not looking to build a rocket, otherwise I would have just bought a proper super bike, or better yet, put a big bore 2 stroke into the frame,  but getting things done like a port and polish, some minor work on the cams and getting the carbs properly sorted will no doubt improve the stock performance.

Offline Sporty

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Re: Gsx400r front end swap
« Reply #11 on: January 13, 2021, 05:05:57 PM »
What the heck, go for the swap... Trying things and making it your way is true custom... not just what someone else does.

I looked up the GS400E and found the specs on the 91. It looks just about the identical bike to the 500. Pity the stroke is shorter on the 400, otherwise an easy cylinder block and piston swap would net a nice improvement in power.
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Offline Henrico123

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Re: Gsx400r front end swap
« Reply #12 on: January 13, 2021, 09:51:17 PM »
What the heck, go for the swap... Trying things and making it your way is true custom... not just what someone else does.

I looked up the GS400E and found the specs on the 91. It looks just about the identical bike to the 500. Pity the stroke is shorter on the 400, otherwise an easy cylinder block and piston swap would net a nice improvement in power.

It is a pity, its one of the first options I looked at.

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #13 on: January 14, 2021, 04:24:24 AM »
Just got back to my workshop with the new front end, I suspect I might not get much work fone this afternoon, you know, priorities and such, the bike takes preference over all else :D

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #14 on: January 14, 2021, 07:15:23 AM »
So I have the front end test fitted, bearings are the same, stem is slightly longer, so I will have to machine some spacers, but I think it makes a huge difference looks-wise over the stock front end. Once I have fitted it for the final time I will do a write up for anyone wanting to do the same conversion.

Offline The Buddha

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Re: Gsx400r front end swap
« Reply #15 on: January 14, 2021, 04:53:24 PM »
GSX means 4 valve per cyl, I forget what the r means, 4 cyl ?? No Katana's had F but are 4 cyl.
Anyway Is the GSX400r a 4 cyl water cooled ??? What year ? Looks like its part of the GSXR genre from the forks. Bandit 400 was an F wasn't it ? GSX400F in 91 ? Which had the same 39mm fork as the GS but disk on the other side.
A fork leg swap and you have twin disk 320mm rotors (the biggest ever freaking rotors you can fit on that wheel)
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Offline moe_tunes

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Re: Gsx400r front end swap
« Reply #16 on: January 14, 2021, 05:29:21 PM »
I do like the look of the beefier upside down forks on the GS.
Going by the photos those GSX forks look a bit shorter than the stock ones. Have you measured the difference?
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Offline Henrico123

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Re: Gsx400r front end swap
« Reply #17 on: January 15, 2021, 02:20:14 AM »
GSX means 4 valve per cyl, I forget what the r means, 4 cyl ?? No Katana's had F but are 4 cyl.
Anyway Is the GSX400r a 4 cyl water cooled ??? What year ? Looks like its part of the GSXR genre from the forks. Bandit 400 was an F wasn't it ? GSX400F in 91 ? Which had the same 39mm fork as the GS but disk on the other side.
A fork leg swap and you have twin disk 320mm rotors (the biggest ever freaking rotors you can fit on that wheel)
Cool.
Buddha.

These are off a late 90's GSX400R, the SP2 model. It is basically like a smaller version of the slingshot, watercooled, 4 cylinder. I am not sure which countries recieved them, in SA we do have a few around, but they are all grey imports.

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #18 on: January 15, 2021, 02:24:31 AM »
I do like the look of the beefier upside down forks on the GS.
Going by the photos those GSX forks look a bit shorter than the stock ones. Have you measured the difference?

They are only slightly shorter, but not enough to adversely impact handling, it looks way more due to the fact that the bottom neck bearing is not in at the moment, so the rake angle is not correct. Got some spacers made up this morning, so I am going to try to get it fitted properly this afternoon.

Offline Henrico123

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Re: Gsx400r front end swap
« Reply #19 on: January 15, 2021, 02:28:02 AM »
GSX means 4 valve per cyl, I forget what the r means, 4 cyl ?? No Katana's had F but are 4 cyl.
Anyway Is the GSX400r a 4 cyl water cooled ??? What year ? Looks like its part of the GSXR genre from the forks. Bandit 400 was an F wasn't it ? GSX400F in 91 ? Which had the same 39mm fork as the GS but disk on the other side.
A fork leg swap and you have twin disk 320mm rotors (the biggest ever freaking rotors you can fit on that wheel)
Cool.
Buddha.

This is the SP2 model

 

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