Author Topic: KTM USD swap on a CB350f / CB400/4... direct bolt-on!  (Read 2947 times)

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Offline Erwin83

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KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« on: March 04, 2020, 12:39:21 AM »
Just a little tip for people contemplating doing an Upsidedown fork swap in their CB:

A USD fork of a KTM 125/390 Duke or RC (Duke has handle bar mounts, RC has clip-ons) will fit without any hard work, and relatively low cost (I got a complete fork with yokes, handlebar clamps and front wheel axle for 300 euro).
- bottom bearing standard CB350f / CB400/4
- Top bearing ID 30 instead of 26mm
- Best bit: stem length is spot on.
- Even the steering angle stoppers fit.
- CB350f fork is 69cm long (wheel axle to top-cap), when parked on the main stand.
  - KTM fork is 72 cm long, when parked on the jiffy. KTM uses a smaller wheel of course.

Fitting as follows: The Allballs CB stembearing kit comes with 2 spacers, combined they are 7mm thick. Exactly what is needed to clear the KTM bottom yoke and the CB frame.
Top bearing: fit as standard KTM.

Keep in mind:
- I have not yet checked tank clearance.
- This fork set-up has a single brake disc only.
- offset of the fork is approx. 40mm. CB350f is approx. 60mm, so trail is affected. Don't know yet what this will do with handling, but I guess this is similar to most USD fork swaps.

Big thanks to allballs for providing their conversion tool (https://www.allballsracing.com/forkconversion/), and the KTM Duke rider who helped me measure the KTM fork before putting the money down.
CB466f

Offline andy750

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #1 on: March 04, 2020, 03:16:57 AM »
Great info and I will be interested to see how this affects handling. Looking forward to seeing the finished bike.
good luck!
Andy
Current bikes
1. CB750K4: Long distance bike, 17 countries and counting...2001 - Trans-USA-Mexico, 2003 - European Tour, 2004 - SOHC Easy Rider Trip , 2008 - Adirondack Tour 2-up , 2013 - Tail of the Dragon Tour , 2017: 836 kit install and bottom end rebuild. And rebirth: http://forums.sohc4.net/index.php/topic,173213.msg2029836.html#msg2029836
2. CB750/810cc K2  - road racer with JMR worked head 71 hp
3. Yamaha Tenere T700 2022

Where did you go on your bike today? - http://forums.sohc4.net/index.php?topic=45183.2350

Offline SOHC4 Cafe Racer Fan

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #2 on: March 04, 2020, 10:01:13 AM »
Erwin,

Also keep in mind that the KTM likely has a smaller offset between steering head and fork tubes than the 350F/400.  If so, this can make the bike tend to want to fall into corners. 
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline 754

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #3 on: March 04, 2020, 10:31:02 AM »
He mentioned that in his post..
 I am wondering what bearings in the top, how it all fits.
 And the travel is probably a lot longer than stock forks. Are you cutting down the amount of travel, or increasing back travel ?
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #4 on: March 04, 2020, 11:30:38 AM »
The 2013-2016 KTM Duke/RC is quite a sporty Street/City bike. I expect suspension travel to be less or more or less equal.

This fork is absolutely NOT a KTM cross or Supermoto fork.
Those forks will NOT fit like this one.
CB466f

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #5 on: March 04, 2020, 11:33:59 AM »
Erwin,

Also keep in mind that the KTM likely has a smaller offset between steering head and fork tubes than the 350F/400.  If so, this can make the bike tend to want to fall into corners.

Yes, the offset is 40mm, instead of 60 mm stock CB.
How this will affect handling, i don't know yet.
Let's be honest, people doing these swaps care about looks more than anything else. That includes myself, I confess.
CB466f

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #6 on: March 04, 2020, 11:38:35 AM »
I am wondering what bearings in the top, how it all fits.

I am using all balls bearings.
The top bearing can be ordered for this swap:
99-3541-5
It is basically a 48,5mm outer shell and the 30mm ID roller bearing, same as used at the bottom yoke.

It's rather unbelieveable how easy this fits as the steering pin is exactly the right length...
CB466f

Offline 754

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #7 on: March 04, 2020, 12:20:31 PM »
Erwin,

Also keep in mind that the KTM likely has a smaller offset between steering head and fork tubes than the 350F/400.  If so, this can make the bike tend to want to fall into corners.

Yes, the offset is 40mm, instead of 60 mm stock CB.
How this will affect handling, i don't know yet.
Let's be honest, people doing these swaps care about looks more than anything else. That includes myself, I confess.
I have a 43 mm ZX fork I want to put on a 750 this year, floating big rotors, 4 piston calipers. Like you I will mount it and try it and see. My forks are junk, I haven't had a bike that handles well in over a decade.. I just want brakes a damping..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #8 on: March 04, 2020, 02:20:54 PM »
Erwin,

Also keep in mind that the KTM likely has a smaller offset between steering head and fork tubes than the 350F/400.  If so, this can make the bike tend to want to fall into corners.

Yes, the offset is 40mm, instead of 60 mm stock CB.
How this will affect handling, i don't know yet.
Let's be honest, people doing these swaps care about looks more than anything else. That includes myself, I confess.
I have a 43 mm ZX fork I want to put on a 750 this year, floating big rotors, 4 piston calipers. Like you I will mount it and try it and see. My forks are junk, I haven't had a bike that handles well in over a decade.. I just want brakes a damping..

Googling around, I found that steering stem length is the biggest challenge with these conversions, as changing that requires pressing in a new pin, which can be expensive. Cognito motor sells conversion pins for instance. $$$ ouch.
Stem length is also a piece of data unavailable of most motorcycles, meaning many of us are left to gambling, and just sourcing the fork (gixxer, zixxer, r6/r1, cagiva mito, i’ve found many examples) and see what happens.


That’s why I am so chuffed to find out that this KTM unit fits directly
CB466f

Offline 754

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #9 on: March 04, 2020, 02:44:15 PM »
As soon as I get my lathe going I can make  my own stem, made a few before. On this ZX I press the original out, then a Honda one out, machine a sleeve to put between the two,  and weld sleeve to the stem , and press it in.
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #10 on: March 05, 2020, 12:37:19 AM »
That is "traditionally" the way to go indeed.
I just don't have a lathe (yet)  ;) and all "pressing" I can do in house is with my vise...

A boy can dream of an even better equipped garage though.
CB466f

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #11 on: March 05, 2020, 12:33:10 PM »
Some more images.
Literally fits like a glove.
CB466f

Offline 754

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #12 on: March 05, 2020, 01:51:48 PM »
Looks beefy , want to see it with wheels on it..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #13 on: March 05, 2020, 02:03:30 PM »
That's going to be the next puzzle.
I bought an aprilia 650 pegaso front wheel. Which has a 300mm brake disc, like the ktm.
Axle is slightly off, and brake disc won't fit the caliper.

So, getting it on both wheels will take some time.
CB466f

Offline 754

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #14 on: March 05, 2020, 02:41:27 PM »
Usually not hard to fix..except.. with radial caliper mounts it gets harder. If you slip the caliper on , does caliper need to go in or out  ?
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline SOHC4 Cafe Racer Fan

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #15 on: March 06, 2020, 06:46:08 PM »
This little 4 is going to look great with the 17" wheels.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #16 on: March 07, 2020, 02:03:09 AM »
This little 4 is going to look great with the 17" wheels.

 8)
I'm going for 18" wired wheels. What you see in the pic is actually a 19".
The game plan now is a front hub of a suz DR.
Front rim 2.15-18, rear rim 2.50-18 on original hub.

CB466f

Offline SOHC4 Cafe Racer Fan

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #17 on: March 08, 2020, 03:56:00 PM »
I must be losing my mind and eyesight!  ;D
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline Erwin83

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Re: KTM USD swap on a CB350f / CB400/4... direct bolt-on!
« Reply #18 on: March 09, 2020, 04:08:16 AM »
I must be losing my mind and eyesight!  ;D

No worries, it's the enormous 300mm brake disc that throws you off, I'm sure.
I don't think I'll be keeping that b.t.w. The DR comes with a 280mm disc, and the KTM caliber has spacers that allow for a slightly smaller disc.
Goal is, again, finding a fitment that doesn't require any real machining work, since I don't have a lathe or CNC, or whatever.

We'll have to see how the DR hub fits though.
CB466f