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Old 08-18-2011, 08:04 PM   #76
motodavid2000 OP
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Ohlins forks, headstock and steering stem

OK - we have been measuring, thinking, re-working and using the lathe. We knew going into this that the Ohlins forks were longer and would therefore affect steering geometry - how much we did not know.

Here is a set of pics that places each of the forks - stock Suzuki, KTM WPs and Ohlins legs side-by-side, using an axle through all 3 fork legs to align the centerlines of the axles of each leg and then measure the fork length difference.




Lining up the top of the Suzuki fork legs at the fork caps and then measuring off the length differentials between the three sets of forks.

The Ohlins and WP are tapered legs at the top - hence some daylight visible at the top of the Ohlins leg with the square attached to it. I am decently square to the longitudinal centerline of the fork legs. Photo angle distorts the perspective a little.




The Ohlins leg looks to be approximately 46 mm longer than the stock Suzuki fork leg when measured from the axle centerline.



The WP leg looks to be "approximately" 38.5 mm longer than the stock Suzuki forks.




We know that the Ohlins forks, with the fork caps set at the top of the KTM triple clamp produces some evil weave and handling issues. Therefore, we decided to work on keeping the fork leg distance / length from the lower triple clamp to the axle centerline as close to stock as possible for the next setup & test.

In order to do this, we had to design a longer steering stem with a bushing to effectively raise the upper triple clamp to accomodate the extra length of the Ohlins forks. This - we think - will have three primary benefits:

1) it will raise the bars - I had thought about using bar risers anyway

2) it will provide additional clearance for ease of ignoition key removal and use

3) it will provide additional clearance for headlight and windscreen vertical adjustments

This move, if we decide to keep it after testing it, will require a re-work of the ignition switch locking mechanism to the headstock. We think spacers can be made to solve this height issue. We do not know about cable length and any possible binding issues until we get the bike back together and see if we have any problems.

My machinist friend drew up a dimensional diagram, we measured yet again and turned a new 6061 stem on the lathe. He also fabricated a new 6061 bushing to our dimensions to effectively raise the upper triple clamp and provide the required height for the Ohlins lork legs.



He used liquid nitrogen to shrink the newly turned stem and dropped the new stem into the lower triple and dropped the bearing on the new stem. Once all the parts returned to ambient temperature, the interference fit for the new stem and the lower bearing with dust cap was perfect.

New aluminum bushing for use between the upper triple clamp and the upper headstock bearing.



Here is the new stem installed in the lower triple clamp with the old KTM stem beside it in its approximate relative position as if it were installed. This is just to provide a rough idea of the extra length on the new stem.



Here are the calipers on the new stem that has an upper and lower end to match the KTM triple clamps perfectly, lengthened for the Ohlins forks, yet diameter turned to match the stock Suzuki 30 mm ID NTN bearings with dust cap.

At the lower bearing & triple clamp with interference fit dimension & yes I whacked my left hand getting one of the old bearing races out of the headstock.........




Upper bearing surface - slip fit only.

Note the dimension - varies at 29.97 to 29.98. Should work well.




First test fitup of newly fabricated KTM steering stem, sized for Suzuki 30mm bearings with upper bushing to accomodate Ohlins forks.



Another view from underneath the upper triple clamp.



No interference between lower headstock surface and lower triple clamp. This verifies that the shoulder for the lower bearing position that we cut into the new steering stem was placed correctly. The position of the lower bearing will not allow the lower headstock to interfere with the rotation of the steering assembly; or allow the lower triple clamp to rub on the headstock anywhere.



Obviously we will have to lower the ignition switch and locking mechanism to engage with the headstock properly. I am hoping to have the forks back on, the new headstock bearings installed & pre-loaded and test ride the bike sometime this weekend. I want to see what the effects are to the bike from the geometry changes and bar position changes.

Thanks for looking - Dave
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Old 08-18-2011, 11:09 PM   #77
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You may find with that setup that with the extra travel of the Ohlins forks, your front wheel will bottom under the guard before the forks bottom. This can instantly stop or slow the front wheel. Same effect as grabbing a handfull of front brake with the front suspension fully compressed.
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Old 08-19-2011, 05:46 AM   #78
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Fork Stroke

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Originally Posted by Phreaky Phil View Post
You may find with that setup that with the extra travel of the Ohlins forks, your front wheel will bottom under the guard before the forks bottom. This can instantly stop or slow the front wheel. Same effect as grabbing a handful of front brake with the front suspension fully compressed.
Yes, you are correct. We are going to stroke the Ohlins forks to bottoming and attempt to determine the full stroke length & then the tire / fender clearance. I would rather not find out the hard way.

Thanks for the comment & input - Dave
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Old 08-20-2011, 06:30 AM   #79
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Quote:
Originally Posted by motodavid2000 View Post
Yes, you are correct. We are going to stroke the Ohlins forks to bottoming and attempt to determine the full stroke length & then the tire / fender clearance. I would rather not find out the hard way.

Thanks for the comment & input - Dave
I did a USD swap on my DL so I have kinda looked at this experiment. I got a push bike rim with the same OD as the standard rim with tire and then just moved it up the forks knowing the amount of travel the forks had. Its a bit backyard but found a close result without to may complications. Might work...
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Old 08-20-2011, 11:18 AM   #80
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why not just bolt on an rm/drzsm usd fork?

adjust spring and valves to new weight
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Old 08-20-2011, 01:36 PM   #81
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RM forks

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Originally Posted by tdrrally View Post
why not just bolt on an rm/drzsm usd fork?

adjust spring and valves to new weight
tdrrally -

You're right of course, but then that wouldn't be much of a project. If I can get the Ohlins to work for me then I will go that route, if not, I will fall back and punt to the original WPs, or go with the RM fork conversion. I am not doing anything on the front end that can't be reversed and started over.

I did test ride the DR650 this afternoon now that I have the front end back together. It is a huge improvement from before - no weaving or scary handling. I rode it a little in my woods and used the front brake very hard from full throttle in 3rd gear - sitting and standing on the pegs. No adverse reactions.

With the moto on the lift, I have 11.75" between the top of the tire and lowest point inside the front fender - bolt head. With knobbies, it would be less. I will take a static sag measurement and see what the clearance is unloaded and then loaded.

I do not yet know what the full stroke length of the fork is, so I will be working to bottom the fork - or get some stroke data from Ohlins to ensure that the forks will bottom before tire contact with the fender fasteners. I will then need to do some mods on the Ohlins for fully loaded touring weight.

Thanks for looking & for your input - Dave
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Old 08-20-2011, 02:36 PM   #82
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I think the DR650 steering geometry is a bit "fussy". On my first DR I experimented with some KX 125 clamps I had laying around. These had less offset than the DR clamps. I was hoping to get a more positive / planted feel with the steering but it introduced a waggle in the bars over 100kmh. It never progressed passed a waggle but it was unnerving. My current DR has a DRZ400 front end. No worries at all with this setup.
Keep up the god work.
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Old 08-20-2011, 02:42 PM   #83
tdrrally
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don't get me wrong
i do enjoy a good project
even more if its done right

keep up the good work
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Old 08-20-2011, 06:13 PM   #84
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Quote:
Originally Posted by motodavid2000 View Post
I did test ride the DR650 this afternoon now that I have the front end back together. It is a huge improvement from before - no weaving or scary handling. I rode it a little in my woods and used the front brake very hard from full throttle in 3rd gear - sitting and standing on the pegs. No adverse reactions. Dave
Sounds like major progress! I hope you get a chance to test ride on a twisty paved road to test out the balance and handling while turning sharp corners. Quick left to right transitions will let you know if the balance and rake & trail are in the ball park.

Most single dual sports I've ridden begin to weave at about 80 or 90 mph. DR's are pretty good in this regard ... but my KTM 640, XR-L, KLR and older XL600 Hondas all had some sort of mild high speed weave. All kinds of things can affect this. I never worried about it as long as handling was correct and bike responded normally to input on a twisty road.

The ultimate test will be to do the same twisty roads with your full travel load on the bike. It took me a day or two to adapt to my DR carrying 100 lbs. of stuff. (Givi, racks, gear, spare tire, tools) I weighed everything. Biggest problem was brakes ... I have stock brakes. With weight you really need more braking IMO. I think you've upgraded you rotor?

When I went from the Givi hard bags to soft bags I reduced weight by nearly 40 lbs.

I'm envious of all the travel you've got up front. Those Ohlins shocks will surly pay dividends once dialed in.
The best way to test to see if the tire is hitting the fender is do that same hard braking test you did ... but hit a few pot holes while hard on the brakes. This is when bottoming typically will happen, especially on a steep downhill run ... but sounds to me like you've got it very close to perfect!


Great Mojave brake and suspension testing downhill. The lead bike is my buddies 68 year old dad, riding his CRF230 ... former enduro rider. You can see he's bottomed the suspension ... once that happens the tire will lock and ... away you go! The old guy made it down fine but he was pissed at me for taking him down that hill.
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Old 08-20-2011, 09:32 PM   #85
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Thumb Shocking!

Looking great David!

I am not familiar with USD forks but can't you just take the fork caps off and remove the springs to let the forks drop to their maximum travel? That is easy on conventional forks to determine max travel. Of course, if the bike won't roll with the springs out because the tire is rubbing on the fender, you will want to make the internal limiter/bump stops longer.

With conventional forks the springs don't even need to be removed if you don't mind some oil dripping off the springs that are sticking out the top. A bit messy that way though.
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Old 08-28-2011, 08:51 AM   #86
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Dave have I been operating under a miss assumption? I have always thought that atmospheric pressure pushed the fuel out of the tank ( Tank Vent ) and with your loop in your fuel line you would only have a very small amount of fuel left in the line after the tank runs dry. Am I missing something?

Great bike build. Was worth the two year wait to see.

Tom


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The way the fuel will need to go down and then back up is sure to cause a problem. When you've got the weight of 5 gallons of gas pushing down on it, then it should be OK. But by the time you have only 1/2 a tank of gas left, there may not be enough force on it to push it back up into the carb inlet. In effect, you'll be running out of gas when you're half full. Perhaps a 90 degree elbow to bend it in, or shorten the hose. Either way, the hose shouldn't sag lower than the carb inlet.
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Old 08-30-2011, 05:46 PM   #87
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Head Pressure of Fuel

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Originally Posted by TRAVELGUY View Post
Dave have I been operating under a miss assumption? I have always thought that atmospheric pressure pushed the fuel out of the tank ( Tank Vent ) and with your loop in your fuel line you would only have a very small amount of fuel left in the line after the tank runs dry. Am I missing something?

Great bike build. Was worth the two year wait to see.

Tom
Tom -

Good to hear from you. Hope that you are enjoying Costa Rica.

No, you are not under any misconception. From my classes back at Purdue University so many years ago, the head pressure of the fuel is the delta in fluid levels. The issue becomes flow rates to the carb from the tank, combined with dropping fluid (fuel) levels and reduced head pressure.

Without spending time calculating some theoretical point, I am sure that the carb can be "starved" of fuel when a combination of low head pressure (low fuel levels) and high flow rate (fuel draw) causes insufficient fuel delivery to the carb based upon engine needs. I think that this would be experienced at very low fuel levels and higher loads & revs on the engine; perhaps exagerated with high altitude operation.

My general take is that the carb should not be starved of fuel when it is at least 25% or more full of fuel, operating at any reasonable engine load.

My fuel line loop below the carb inlet would cause a loss of a small amount of fuel not being available for the engine, and possibly an air bubble to form. This would be an extreme case, and the engine would / may be starved of fuel before that time with low head pressure and higher engine loads.

I don't think that the engine would starve at idle until the fuel reached the level of the fuel tank petcock intake.

Getting ready to make a few more mods to the windscreen and instrument panel supports. Will post some pics when the work is done.

Also, still resolving fork stroke / tire bottoming probabilities - have not disassembled the forks yet and want to ride it first. If I need to change springs, I will check fork stroke / bottoming stroke and also change springs at the same time.

Take care - Dave
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Old 08-30-2011, 06:47 PM   #88
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Dave thanks for taking the bait. I thought of writing more in my question but wanted to leave enough for your grand explanation. Every time I try to inform the troops I get flamed. BTW with the stock IMS tank and IMS supplied petcock, cap and a loop in fuel line my DR would run to the last once or two in the tank running full throttle down the highway, experienced. I would expect yours to do the same but you do have a different petcock.

Ride safe and have fun!


Quote:
Originally Posted by motodavid2000 View Post
Tom -

Good to hear from you. Hope that you are enjoying Costa Rica.

No, you are not under any misconception. From my classes back at Purdue University so many years ago, the head pressure of the fuel is the delta in fluid levels. The issue becomes flow rates to the carb from the tank, combined with dropping fluid (fuel) levels and reduced head pressure.

Without spending time calculating some theoretical point, I am sure that the carb can be "starved" of fuel when a combination of low head pressure (low fuel levels) and high flow rate (fuel draw) causes insufficient fuel delivery to the carb based upon engine needs. I think that this would be experienced at very low fuel levels and higher loads & revs on the engine; perhaps exagerated with high altitude operation.

My general take is that the carb should not be starved of fuel when it is at least 25% or more full of fuel, operating at any reasonable engine load.

My fuel line loop below the carb inlet would cause a loss of a small amount of fuel not being available for the engine, and possibly an air bubble to form. This would be an extreme case, and the engine would / may be starved of fuel before that time with low head pressure and higher engine loads.

I don't think that the engine would starve at idle until the fuel reached the level of the fuel tank petcock intake.

Getting ready to make a few more mods to the windscreen and instrument panel supports. Will post some pics when the work is done.

Also, still resolving fork stroke / tire bottoming probabilities - have not disassembled the forks yet and want to ride it first. If I need to change springs, I will check fork stroke / bottoming stroke and also change springs at the same time.

Take care - Dave
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Old 08-30-2011, 06:51 PM   #89
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Thanks

Been watchin this thread for a while and just wanted to say thanks for the inspiration and details.
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Old 08-31-2011, 05:23 PM   #90
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Inspiration

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Been watchin this thread for a while and just wanted to say thanks for the inspiration and details.
dirtyrod -

Hey, thanks for looking and following along. Not sure if this build is inspirational or not. It might be inspirational if the contraption actually works as intended and survives long distances, loaded down and "put up wet".

Until then, just keep your fingers crossed -- mine are.....

take care - Dave
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