Front end conversion / engineering ???

[atgreg]

I had a serious flirt with buying a HP2 this week, I decided i couldn't part with the AT, so the old girls got to get tarted up a bit, she really needs a decent front end

I'd like more travel to match the longer custom ohlins shock and some better quality forks than the standard damper rod jobbies and also be adjustable.

Ive got a front end of a 99 KTM Rallye, 50mm whitepower extremes. After doing some measuring the KTM steering stem is a lot bigger than the Honda and there are bearings to match them up. At the least it's going to require a new stem machined up and fitted to the clamps. The KTM clamps also have milled out areas where the bearings sit and the Honda clamps are flat, maybe I'll have to have some spacers made up to fit into the milled areas, also the steering stops are all in the wrong places. Qbviously its not going to be easy, ive thought maybe some custom clamps might be the go, ive been quoted $900 by Franks, yikes,

Another option is to fit some XR600 forks, they are cartridge forks and are adjustable, they are also the same diameter as the AT fork, 43mm so they would slip straight into the AT clamps and I'd only have to sort out spacers and brakes. Im not sure that longer forks in 43mm would be strong enough for the AT's weight, again any thoughts ??

Any thoughts or ideas would be appreciated

greg

[Xander]

cant help but to say: you are my hero dude,,, I say go the whole hog and get the WP extremes fitted only cus that would be sooo cool

[pinoy-al]

I thought alot of changing my forks also. I think the way to go would be the WP. They make one of the best on the market. You will have a lot of things to fiqure out.
1. Make sure the forks are close to the same length. You want the bike to sit level
2. How about getting a stem made so it will accept all your Honda bearings ect.
3. You still will have wheel and brake spacing (as well as fork stops) but the end result should be perfect!!!
I see no advantage of using the 600 forks. You would need to change the fork springs for sure because the bike is lighter.
Go for the WP and let us know what you did and I think I'll do it also!!!!

[atgreg]

I thought alot of changing my forks also. I think the way to go would be the WP. They make one of the best on the market. You will have a lot of things to fiqure out.
1. Make sure the forks are close to the same length. You want the bike to sit level
2. How about getting a stem made so it will accept all your Honda bearings ect.
3. You still will have wheel and brake spacing (as well as fork stops) but the end result should be perfect!!!
I see no advantage of using the 600 forks. You would need to change the fork springs for sure because the bike is lighter.
Go for the WP and let us know what you did and I think I'll do it also!!!!

Obviously the WP's would be the go but it will come down to engineering / $$ etc. Wheel and brake spacing for the Wp's is no prob, I have the complete front end of a 99 660 rallye. It's just going to be a big job to get the clamps to fit the AT steering head. Whatever forks I go it will be a single big 320 - 330mm disc for the brake.

I want longer forks, with more travel, my bike already has a longer custom rear ohlins, I have about 250mm travel at the rear and my bike is quite a bit taller than standard. The longer forks will match very well.

XR600 forks are MUCH better than AT forks, they are proper cartridge jobbies not the prehistoric damper rod forks on the AT. They offer much more scope for set up and have adjustable clickers plus they have 280mm travel. My only concern is whether longer forks in the standard diameter of 43mm will flex to much.

Any longer trailbike fork whether XR or WP will need to be sprung and vlved to suit the AT's weight

[atgreg]

This is the KTM front end I have, they a big barstads

[pinoy-al]

I think I will take back what I said about the WP stuff after hearing that the 600 forks are of the "modern" type with all the hot prop settings.
It would be a lot easier to get seals for also.
43mm is a very big fork tube!! I really can't see much flexing at all even with the @ weight. Worse case do a fork brace, but I don't think you will need to.
I did a lot of this kind of stuff in California before I moved to the Philippines. I like the idea of a Honda part going on a Honda!!!
Good luck. Keep me posted cause I think I can get a XR600 front end here.
By the way, one single brake disc the size you mentioned would be perfect. You may want to think of the word "Brembo".

[atgreg]

I think I will take back what I said about the WP stuff after hearing that the 600 forks are of the "modern" type with all the hot prop settings.
It would be a lot easier to get seals for also.
43mm is a very big fork tube!! I really can't see much flexing at all even with the @ weight. Worse case do a fork brace, but I don't think you will need to.
I did a lot of this kind of stuff in California before I moved to the Philippines. I like the idea of a Honda part going on a Honda!!!
Good luck. Keep me posted cause I think I can get a XR600 front end here.
By the way, one single brake disc the size you mentioned would be perfect. You may want to think of the word "Brembo".

Pinoy, late model XR600 91- are cartridge forks, earlier ones are damper rod so not worth using. 93 on XR forks have the same axle diameter as the AT - 17mm., earlier ones are 15mm the same as a Transalp Also 87-88 CR500 / CR250 forks are the sameso could be used

here's a rundown on fitting XR forks to a Transalp, fitting them to the At
would be similar but you'd need the later foks for the right axle diameter
http://www.transalp.org/phpbb2/viewtopic.php?t=52

[Jenna]

cant really comment on @ and honda parts swaps as we dropped the idea of using honda and went with yamaha, however the principle is the same...

the YTZ we bought is now 99% fitted out with WR 450 front end and although it was a fairly easy swap as there are a lot of 'common' parts even between two bikes produced 10 years apart.

WR and XTZ yokes although totally different in design share the same headstock dimensions, they also share the bearing od and id which has meant the yokes are in effect a straight swap, the wr runs a 46-48mm USD Kabaya race fork which although is is only 2" longer thanks to the through bolt for the wheel being on the base and not 2" up the fork its given the bike a usable 3-4" raise in front suspension, however!!

.. due to the increased weight the WR springs are not happy and most of the extra travel is lost in fork compression in static load (bit of an own goal!) so sadly the springs will need to be changed which is a shame as they are already WP progressive as standard.

Another issue to consider is breaking and the wheel you fit, i want the dual disk that the xtz has as standard so its not an option to use the WR wheel, this means the o/s fork will need a calliper mount fabricated and welded in ( not a big issue as the n/s fork with a mount will need to be 'modified' too)... Though bolt is being machined as there is no match between the XTZ wheel bearing and the WR through bolt ( uses 2 diferent systems)....

So from all this whats the conclusion... stick with the original make, different manufacture use different sizes and unless you want to get into the realms of machining bearings, making yokes and having a total mish mash of parts it just aint worth it!.. i would suggest you go purely with XR or honda sourced bits if you ever want to get it finished!

[Jenna]

something else you have to consider which has only just been mentioned is if you up grade the front end you MUST do the rear if the forks change the static height.

Spoak to a lot of people about this and they all come to the same conclusion that the only true answer is a new longer shock. You can opt to swap out the dogbones for a shorter pair that will in effect 'pull' the rear wheel under the bike more. Certainly at just £30 they sound very tempting over a £300 shock BUT.. by shortening the dogbones you are also changing the spring rate and doing nasties to the the crank angle of the linkage at full compression which seams to be unanimously agreed on as making the bike unstable on the tarmac under medium/heavy breaking and when the bikes rear suspension bottoms out...

another possible option is to change the shock-link to one that has a higher distance between the lower bearing and the base of the damper, by going this route you can retain the stock damper and linkage. As far as i am aware this was what AQ's were doing on the race bikes. Due to a rapidly dwindling budget (and i like to play) I'm going to see if we can re fabricate the XZT shock-link in steel with all the original dimensions except the those of the damper tower, once fitted we can then determine the correct offset and lastly drill the holes for the damper through-bolt. this should mean that we can set the rear exactly to match the front....

ummm why is nothing ever easy!!!

[atgreg]

G'day Jenna,

yep, going with XR forks would be easier, they share the same steering head bearings as the AT. The WP etremes I have are a better fork so thats what im going to try 1st and we'll see how we go, brakes etc wont be too bad if i can fit up the clamps as I have the wheel and axle to match the forks, I'll just have to get a big supermoto isc and caliper spacer which are available off the shelf from KTM sommer in Germany. Seeing Im going to defineately going to need a new stemmy 1st try will be to machine down the KTM stem to match the Honda stem and see how thick it is after and if it's safe to use.

I already have a 10mm longer rear ohlins shock, gives me about 250mm travel at the rear and my bike is already considerably taller than standard.

Just for some more info and another option, one of the few Atowners in the US has fitted CR500 forks to his bike, apparently the lower bearing / steering steme as the AT but the top bearing and stem is bigger so he just machined the top of the stem down