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Old 08-31-2014, 09:40 AM   #1
rc mad OP
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Slight TeDiuM

How many fork upgrades require taking a hole saw and a rats tail file to the front wheel I wonder



I blame the ducati for this you know, if the suspension wasn't so bloody good then perhaps I'd have left the other bike well enough alone, but no, the duke has spoiled me with its plushiness

So, which bike is under the knife today, its my 1998 TDM 850,


It's good for motorway work but the suspension department is shocking, and not in a good sense when it comes to city streets, where it crashes from one pot hole to the next. It's saying something when a ST4S is better in town than a longish travel bike!. Up front we have a set of basic 43mm forks with rebound damping and pre-load adjustment, coupled to 0.64kg springs.

Perusing ebay for a set of 43mm forks to fit and forget found me these absolute beauty's



A set of slightly bent forks from a 2000 Yamaha R6, the uppers are trash but the lowers and internals were good, and after a good think that's all I needed Well apart from a new axle, wheel bearings, spacers. the usual bits

The plan at this point was simple, a forced marriage of tdm uppers and r6 lowers / internals. That should net me proper compression / rebound adjustment along with pre-load and 0.74kg springs. A good starting point I figured. I feel that the stock forks were under-damped on the compression side of things so having some adjustability is a good thing.

So the forks duly arrive and I start the process of ripping things apart to see where I stand, good news is that that I have all the bits I need, bad news is that there may be some coercion needed to make things work.

And at that point a Sunday lunch is calling my name
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Old 08-31-2014, 03:40 PM   #2
Navin
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How do I bookmark this thread to remind myself to never buy a used motorcycle...

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Old Yesterday, 12:06 PM   #3
rc mad OP
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You've just done it

Also, I've been here before












Similar mod to a sv650, stock sv lowers with different uppers and internals, can't remember which bike but it gave me rebound damping and pre-load adjustment, a big step up from the standard forks. Forks were longer than stock but had 10mm less travel. Also shoved a 2000 era r6 shock in the back, had to move the battery tray to fit it in. Changed the handling of that bike for the better.

Also did a couple fo bits to my dakar, before it was written off



yamaha yz forks, wilbers rear shock with custom dog bones, bike was a good inch taller than stock and was a blast in the twisty stuff




The tdm was an absolute steal when I got it, 1998 with just over 6800 miles on it, owned by an army bod.

Where was i, oh yes, Coercion of parts to make them fit

The idea is to make the R6 internals (top) fit where the tdm bits (bottom) used to go and not lose too much fork length in the process, the length of the tdm fork from axle centre to top is 825mm, stock r6 is around 35mm shy of that. The r6 internals do have a bit of give in that department so I'm hoping to end up somewhere between the two figures. It's an experiment so I'll not know for sure until it's all back together.



a quick check fit revealed some minor stuff but thhe main issue is that the tdm and the r6 fork caps have different threads, tdm on the left, r6 on the right.



that meant that this whole thing wasn't going to be a straight forward swap, even the pre-load / rebound adjusters have different threads.



I thought that was the end of it, I did think about rethreading the tdm cap to take the r6 internals but there wasn;t enough material to do so, and the tap required is a m23 x 1 tap, those aren't cheap as they aren't a standard size. Couldn't swap over the rebound damping between the two as they are different setups.

The solution I came up with was quite simple, and involved high strength locktite and a vise





Whadda you know, perfect press fit I know some people my think that's about the worst idea possible, believe me I thought long and hard about doing that as its a little brutal and there was no going back if it didn't work out. I figure that part won't see much if any force trying to pull it apart, 99% of the force is trying to push the centre section through the fork cap. Of course this means i have to go old school and add washers between the spring and the cap to alter the pre-load, I'm fine with that.

In the end I figured I've got nothing to lose if it doesn't work, apart from having to fit an entire new front end of course, which would't be a bad thing I ensured the o-ring was good before I did this as it'll never get replaced now, also did the other side and checked the lengths out to make sure they were good.



I also cleaned up and re-sprayed the lowers too, went with bedliner with a laquer coat to see how it holds up. Also cleaned up all the parts ready for final assembly in the next coupe of days. The fork lowers came out great

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Old Yesterday, 05:09 PM   #4
Navin
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What did you do with the hole saw???


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Old Yesterday, 05:50 PM   #5
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Old Yesterday, 06:27 PM   #6
cleatusj
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My guess would be bore center of wheel for larger diameter axle.
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Old Yesterday, 06:47 PM   #7
Navin
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Quote:
Originally Posted by cleatusj View Post
My guess would be bore center of wheel for larger diameter axle.

That was my first guess and greatest fear!
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Old Yesterday, 07:09 PM   #8
k-moe
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Quote:
Originally Posted by Navin View Post
That was my first guess and greatest fear!


Yer s'posed ta use a 1/4 round bastard file for that sort of fine work.
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