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Old 07-17-2009, 10:58 AM   #1
cgoodwin OP
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DIY HPN KTM USD forks for r80gs

Does anyone know which KTM USD forks can be made to fit a 1983 R80GS???

cgoodwin screwed with this post 07-17-2009 at 02:53 PM
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Old 07-17-2009, 11:17 AM   #2
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Quote:
Originally Posted by Solo Lobo

any really, you can buy plug and play triples from boxer toko that allow the use of WP Extreme conventionals.. (and others)... or contact HPNGuy who has machined custom triples to run the most modern KTM USD forks...

There is a thread here about bolting on DR650 forks... with the downside of loosing a bit of steering lock as the BMW triple have something like 36mm of offset and the largest dirtbike one is 20mm-ish....
Any idea where I can find triples like these, I have fouynd several sets of KTM USD forks but do not really know which ones to get and judging from the caliper mounting differences, I would rather know for sure than spend money on forks I can not use. Distance between forks, caliper mounting, fork diameter....
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Old 07-17-2009, 11:20 AM   #3
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Similar thread but no real answers...

http://www.advrider.com/forums/showthread.php?t=342100
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Old 07-17-2009, 11:20 AM   #4
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Quote:
Originally Posted by cgoodwin
Any idea where I can find triples like these, I have fouynd several sets of KTM USD forks but do not really know which ones to get and judging from the caliper mounting differences, I would rather know for sure than spend money on forks I can not use. Distance between forks, caliper mounting, fork diameter....
I wouldn't buy KTM forks and plan on using the beemer wheel and brakes. You're better off replacing the WHOLE front end. WP USD forks are going to jack up your front end quite a bit. Have you looked at lengthening your swingarm and also hopefully reinforcing your frame for using longer forks?
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Old 07-17-2009, 11:36 AM   #5
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Another thread with many photos of HPN bike porn...

http://www.wilddog.za.net/forum/inde...topic=23723.60
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Old 07-17-2009, 11:39 AM   #6
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Quote:
Originally Posted by Airhead Wrangler
I wouldn't buy KTM forks and plan on using the beemer wheel and brakes. You're better off replacing the WHOLE front end. WP USD forks are going to jack up your front end quite a bit. Have you looked at lengthening your swingarm and also hopefully reinforcing your frame for using longer forks?
Yes, the frame reinforcements are basic and well outlined in the last post I referenced, I have a complkete fab shop and plan on making patterns for the front frame/steering head plates then welding them in as well as the swing arm pivot point reinforcement.

Any idea which fork set is most easily adapted???

I am going to cut a spare mono I have and add 100mm, then have the shaft lengthened similar to what was done here.

http://www.advrider.com/forums/showthread.php?t=467221

and here

http://www.stephenbottcher.net/BMW/R....htm#extension

cgoodwin screwed with this post 07-17-2009 at 11:59 AM
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Old 07-17-2009, 11:45 AM   #7
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Quote:
Originally Posted by cgoodwin
Yes, the frame reinforcements are basic and well outlined in the last post I referenced, I have a complkete fab shop and plan on making patterns for the front frame/steering head plates then welding them in as well as the swing arm pivot point reinforcement.

Any idea which fork set is most easily adapted???

I am going to cut a spare mono I have and add 100mm, then have the shaft lengthened similar to what was done here.
Both touratech and HPN sell kits to fit the WP 4860 forks which are used on the KTM 640 950 990 Adventures as well as many others.
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Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 07-17-2009, 11:50 AM   #8
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Here is a photo of a similar extension from a company in Europe

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Old 07-17-2009, 11:51 AM   #9
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Quote:
Originally Posted by Airhead Wrangler
Both touratech and HPN sell kits to fit the WP 4860 forks which are used on the KTM 640 950 990 Adventures as well as many others.
I can find nothing for the early r80gs in the touratech catalog... Got a link?
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Old 07-17-2009, 11:54 AM   #10
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You also might consider reinforcing the shock mounts, both on the frame and the swingarm.
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R80ST Gets The HPN Treatment
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Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 07-17-2009, 11:56 AM   #11
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Post 6th from the bottom points out that the point of lengthening the monolever is partly to reduce "Shaft Jack". Interesting.

http://www.fjrowners.ws/discus/discu...c=9&page=34971
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Old 07-17-2009, 12:03 PM   #12
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It appears that the BMW R1200C had a monolever that was 90mm or 3.54" longer, similar to the HPN which was 100mm or 3.94 longer, I wonder if I can just find one and swap it out???

From http://www.raditude.com/bmwboxer.htm


Extra-long Monolever instead of the Paralever. Apart from the lower angle of the Telelever fork, the rear-wheel swinging arm extended in length by 90 mm or 3.54" also contributes to the much greater wheelbase of the BMW R1200C. Since a long swinging arm is just as efficient in balancing the reaction of the shaft drive as a short, but more complex double-joint single swinging arm, the BMW Paralever, BMW’s suspension and running gear experts have chosen a longer version of the original single swinging arm, the BMW Monolever, for the R1200C for reasons of function and design. Here, too, smooth and superior suspension is ensured by a central spring strut with a single-sleeve gas-pressure damper mounted on the swinging arm. Yet a further feature is that pre-tension of the coil spring may be adjusted mechanically according to load conditions, spring travel being exactly 100 mm or 3.94".


Looking at images, it appears to be a paralever bike some years, and mono others...????
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Old 07-17-2009, 12:09 PM   #13
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One big thing those FJ forum guys missed: The other reason that driveshaft splines need to be able to slide (apart from swingarm travel) is that whenever a UJ rotates with a bend in it (ie the two segments are rotating non-coaxially) the shaft lengthens and retracts at the joint with every half rotation. This inherent behavior of universal joints intensifies with sharper angles. If the splines don't slide smoothly, you're putting a rapidly pulsating load on your UJ's bearings.


Although I will encourage the destruction of as many R1200Cs as you want, I'd stick to the known good solution for this. Reinventing the wheel like that brings a BUNCH of unknowns into the equation such as swingarm pivot bearing spacing, final drive attachment, driveshaft fit, shock mounting points, etc.
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R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.

Airhead Wrangler screwed with this post 07-17-2009 at 12:15 PM
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Old 07-17-2009, 12:35 PM   #14
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Quote:
Originally Posted by cgoodwin
Does anyone know which KTM USD forks can be made to fit a 1983 R80GS???
Three answers here...

1. Pick the best forks - one with both on-the-fly tuneable comp and rebound and use the complete front end off of a KTM.. pay somone to shorten and tune the forks... loose steering lock using the stock KTM 18mm or 20mm triples..

2. Buy the triples from Boxer toko that go with 1999 and 2000 KTM conventional WP "Extreme" 50mm forks and be able to use the stock wheel, headlight bucket, etc (I think)

3. Contact member HPMGuy to have him make another set of R-Dubb's custom triples that can be machined to run the Extreme's or the modern KTM USD's...
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Quote:
Originally Posted by Stagehand
your bike is suitably dirty. Well done.
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Old 07-17-2009, 12:38 PM   #15
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http://www.advrider.com/forums/showt...r-dubb+triples



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Quote:
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your bike is suitably dirty. Well done.
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