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Author Topic: Overcoming Modern fork swap issues!  (Read 54490 times)

Offline mrvass123

  • Posts: 2
Re: Overcoming Modern fork swap issues!
« Reply #50 on: Jan 11, 2019, 19:46:01 »
Hey everyone,
New here and first post in fact so please go easy.
I'm planning a cafe project for my 1984 Kawasaki gt550 and one of the ideas was to do a front end swap. Sound's easy enough but i have a problem. My brother (who is helping me with the project) is saying that the stems are welded in and can't be removed and that we have to find a front end with the exact dimensions for the stem in order to do a straight swap, front end with front end.
My response was simply to do a stem swap... That's the genera Idea but, wait until you read about the parts i'm looking at.
The new front end consisting of some bad ass Brembo calipers and some beautiful inverted forks off a Ducati 696 monster. Can anyone help me with some info on the best way to go about this?
Thanks, great content all round.

Offline Streetfighterkz

  • Posts: 158
Re: Overcoming Modern fork swap issues!
« Reply #51 on: Jan 11, 2019, 20:29:44 »
saying that the stems are welded in and can't be removed...
My response was simply to do a stem swap...
Can anyone help me with some info on the best way to go about this?

The GT550 stem can most definitely removed even if it’s welded in. I removed the stem on my Gpz750 and it was welded. I simply ground down the weld until I could see the seam between the lower triple and stem. Then using an appropriately sized socket, hammered the old stem out.

The trick is getting the old stem in the new triple clamp. You may luck out and the stems’ OD’s are the same. If not you may need turn up a bushing to adapt the old stem to the new tree if the stem is too small (most likely in your particular case).

I have pics of a couple stem swaps I’ve done that I can dig up if needed.

Later, Doug
'78 Kz1000
'76 Kz900 'Stripfighter (work in progress)
'83 Gpz750 (work in progress)
'89 V-Max
'89 Gsxr750 Trackfighter

Offline mrvass123

  • Posts: 2
Re: Overcoming Modern fork swap issues!
« Reply #52 on: Jan 12, 2019, 19:28:35 »
hey, that sounds awesome! i would love to see those if possible. Although, I've had a little change of heart, instead of putting the complete front end off the ducati on the gt550 i would simply just use the parts i need such as the forks and calipers. i'm planning on getting a similar yoke and tree which fits both the kawasaki and the forks etc. what do you think?

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Re: Overcoming Modern fork swap issues!
« Reply #53 on: Jan 12, 2019, 20:30:24 »
....... I've had a little change of heart, instead of putting the complete front end off the ducati on the gt550 i would simply just use the parts i need such as the forks and calipers. i'm planning on getting a similar yoke and tree which fits both the kawasaki and the forks etc. what do you think?

First off I would remove your bike's forks and measure the overall length and the stem dimensions. If the donor (Ducati) fork stem is close enough, it might be possible to use it or have it modified.  If not a new one can be machined and pressed in.  The probability of pressing out teh GT stem and using it in the donor forks is slim.

But before you go too far down that rabbit hole, check the overall length of both sets of forks to be sure that they are close to the same. If your new forks are much shorter then you will be changing rake and trail and ground clearance and if those changes are not well understood you could make the bike unstable or even unsafe.

Next thing to consider is that you will be changing from a skinny 19" (or is 18") front rim to a fatter 17" rim if you use the Ducati wheel and brakes and it will be much wider than the rear so that will look odd.  And it will lower the front end and change rake and trail and clearances. 

A simple way to see what will work is to take a clean picture of your bike form the side and then measure forks and wheel diameter and measure the parts from the Ducati and draw them onto your picture and work out how much it changes things. There are also more accurate tools on line to do the same thing. 


Offline crazypj

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Re: Overcoming Modern fork swap issues!
« Reply #54 on: Jan 12, 2019, 23:41:40 »
Just about all USD forks are way shorter than 'old school' 1980 (and earlier) bikes although 2000+ GSXR forks are just about identical length to CB360 / CB400F. The yoke offset is also 20~40mm less so you increase trail dramatically. The trail increase is somewhat compensated by lower front end which restores some of the trail.  I have seen clamp on extensions made to increase overall length of fork leg but to be strong enough they look ugly as they are so oversize (basically a piece of 6061 about 2.5"~3.00" diameter, 5"~6" long  bored to slip over fork top then clamp in place with top reduced diameter to fit 'original' top yoke)
 I recently saw on You Tube a neat way of clamping using a single bolt (Stefan Gotteswinter, chamfer cutter) I think it would be possible to 'hide' the extension adapter but would require a lot of machining. IIRC, Kawasaki GT550 has quite ling forks plus 19" wheel, even 'back in the day' they looked spindly
« Last Edit: Jan 12, 2019, 23:53:32 by crazypj »
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

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Re: Overcoming Modern fork swap issues!
« Reply #55 on: Jan 12, 2019, 23:54:12 »
There are quite a few sets of 37,39 or even 41mm conventional forks that would be a better upgrade.  For example on a GT750 (similar length 35mm forks) I could upgrade to 37 or 39mm forks from say a GS1100 or even a GL1000 and for 41mm I could go to GSX600 forks or even a set of FZR400 (39 IIRC) forks.  Lots of options that can be made to fit with less work and less upsetting to the geometry.

https://www.kiwavmotors.com/en/faq/about-fitment/23-motorcycle-fork-tube-size-chart

or http://www.dotheton.com/forum/index.php?topic=20950.0.  Choose the same make as your bike and look for say 37 or 39mm from a similar year and maybe somewhat more engine displacement and then see what's available.

You could probably bore your triple clamps to take a set of suitable 37mm legs and maybe even a set of 39s and then rebuild or replace the wheel to suit.

Forks can also be "stretched by an inch or so with custom gull wing (dropped) top triple clamps.

Offline crazypj

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Re: Overcoming Modern fork swap issues!
« Reply #56 on: Jan 13, 2019, 02:18:29 »
I picked up several sets of GSX-F (Katana) 41mm.forks 16 or so years ago when no one wanted them so VERY cheap. They were cheap at the time as you could get BSX-R cartridge forks for around,  $150. Suzuki had zero finance, etc (way too many crashed with less than 100miles One had about 5 ft, never made it off lot)  Katana are conventional spring and damper but stiffer by far than the originals (and lighter)  Put two sets on XS 650's and a set on CB360. Dead easy as they have steel bottom yoke (same as Honda) so swapping stems is simple
« Last Edit: Jan 13, 2019, 03:47:08 by crazypj »
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

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Re: Overcoming Modern fork swap issues!
« Reply #57 on: Jan 13, 2019, 02:45:23 »
I have a set here and sometime soon I should put them back on ebay.  Too many forks, not enough projects to put them on. 

Offline Streetfighterkz

  • Posts: 158
Re: Overcoming Modern fork swap issues!
« Reply #58 on: Jan 13, 2019, 12:25:52 »
Here are some pics from swapping a Gpz750 stem into a Zx11 lower triple. The Zx11 stem’s ID was the same as the Gpz’s OD so I cut the Zx11 stem flush and used it as a bushing. Then welded the Gpz stem into the “bushing” as both were steel.




I also swapped a ‘74 H1 stem into a ‘00 Zr7 triple clamp. That was a simpler press out the Zr7 stem, press and weld the H1 stem.

Later, Doug
'78 Kz1000
'76 Kz900 'Stripfighter (work in progress)
'83 Gpz750 (work in progress)
'89 V-Max
'89 Gsxr750 Trackfighter

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Re: Overcoming Modern fork swap issues!
« Reply #59 on: Jan 13, 2019, 13:16:47 »
I have a slightly modified GSXR alloy stem pressed into an RD350 lower triple to reduce weight on our RD350 drag bike. 

On GT750 Suzukis a GSXR lower triple and stem slide straight on with a set of allballs taper rollers.

I have a set of TZ350 triples with a custom alloy stem pressed in.

On another GT750 I plan on machining out the triples from 35mm to 37 -39 to fit later model forks ( amount of metal left and choice of forks dictate the size).

Lots of ways to get thicker fork legs onto an old bike that don't necessarily include USD forks or using the OEM stem.  For example, any competent machinist can machine up a new custom stem or modify an existing one.