Fitting RC8 R forks to the 390….. Works Great !!

[Old3]

Ordered up a pair of rc8 forks too. I'm thinking of using just the right 8 leg. I have a 320 rotor on the way, leave the brake side alone, speedo pick up, etc., Stock axle with a bushing on the right, fit the fender via adapter bracket and see how it flies. I'm 200 bare, so the .95 combined with the stock left might still be soft. I'm street riding though, so I'll find a good setting or modify to suit if it all plays out.

Thanks for the help, and I'll post up how my project works out too.

 

[psych0hans]

Ordered up a pair of rc8 forks too. I'm thinking of using just the right 8 leg. I have a 320 rotor on the way, leave the brake side alone, speedo pick up, etc., Stock axle with a bushing on the right, fit the fender via adapter bracket and see how it flies. I'm 200 bare, so the .95 combined with the stock left might still be soft. I'm street riding though, so I'll find a good setting or modify to suit if it all plays out.

Thanks for the help, and I'll post up how my project works out too.

Thej you will have a progressive Spring in one leg and a straight rate spring in the other.

 

[Old3]

Yep. The effective rate will be an average of the two.

 

[Old3]

RC8 forks are here, ever so slightly shorter by a few mm. I'll just run the left leg up a bit to compensate for now. Looks like a simple bushing on the axle and an aluminum bracket to mount the fender and it'll be rolling.

In in hand cycling the legs, the 390 actually binds up and releases very poorly. The RC8 leg is stiffer, but smooth thru the stroke. Both in compression and rebound I have little doubt the RC8 legs will be more plush and controlled.

Feeling the stock action, now I'm tempted to just go all the way and mount both legs. I'll see in the coming days which way I'll start out.

 

[Fasteddy]

...
...Also, has anyone tried to use the rear shock from an RC8?

This question so intrigued me that I immediately started investigating it by looking at pics of the RC8 shock and finding specs.

I even met up with a friend to measure his RC8 in person, So, jump ahead to today / test fitting (note this is with Werkes pipe) and the answer is YES it will fit. It is 8mm shorter then stock but I am not too worried about that as I don't plan on racing, the boss on the top of the RC8 shock needs to be machined down about 4mm so it will clear and some shims / washers will be needed to keep it located to the left side. I am working on getting it to a friends machine shop to mill the boss but I think it will be worth the $126 from ebay!

 

[reenmachine]

This question so intrigued me that I immediately started investigating it by looking at pics of the RC8 shock and finding specs.

I even met up with a friend to measure his RC8 in person, So, jump ahead to today / test fitting (note this is with Werkes pipe) and the answer is YES it will fit. It is 8mm shorter then stock but I am not too worried about that as I don't plan on racing, the boss on the top of the RC8 shock needs to be machined down about 4mm so it will clear and some shims / washers will be needed to keep it located to the left side. I am working on getting it to a friends machine shop to mill the boss but I think it will be worth the $126 from ebay!

Huh. They're all over eBay for around $120 like you found. That would be amazing if with a few mods it worked out.

Once you have some photos and results please start a thread!

 

[Fasteddy]

There was a nice orange tie wrap in the way of top mount, filing to fit....

 

[psych0hans]

There was a nice orange tie wrap in the way of top mount, filing to fit....

You could possibly fab up a bracket to make up for the difference in height and even give you a decent height increase.

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[psych0hans]

I managed to get the spacers made to install the stock RC390 axle to the RC8 forks. If anyone needs the dimensions, I'll post them here later. Next step is to get the Brake rotor mounted up and install the brakes.

 

[psych0hans]

For the life of me, I can't seem to get the brake caliper to align with the disc. I don't know what I'm doing wrong, as I'm using the RC8 forks and the same Ducati 320mm disc with a 10mm offset, but I just can't get the rotor to align with the caliper. Please help. @jokerio

 

[psych0hans]

It's official, I'm an idiot... I realised, much too late, that the forks were being fitted the wrong way and made the switch immediately, wasting half the day as a result... It's currently well on it's way to being a perfect fit, just need to fab one small shim. Will update with results.

 

[Old3]

Psycho, any idea where the big caliper center falls in relation to the stock wheel, rotor, caliper?

Ive done the right hand RC8R leg, it works great. I have the left side and a proper 100mm caliper but ill be using the stock wheel with the HP 320 rotor if/when i get around to that side. Honestly it works so well now its not really an issue. With the ABS delete, Brembo pads and the Ohlins shock the bike is frigging excellent.

i will pull it apart at some point and eyeball it myself, just wondering if you have a fixed measurment with stock stuff in relation to the brake pads.

Thanks.

 

[psych0hans]

Psycho, any idea where the big caliper center falls in relation to the stock wheel, rotor, caliper?

Ive done the right hand RC8R leg, it works great. I have the left side and a proper 100mm caliper but ill be using the stock wheel with the HP 320 rotor if/when i get around to that side. Honestly it works so well now its not really an issue. With the ABS delete, Brembo pads and the Ohlins shock the bike is frigging excellent.

I'm currently stuck at that point. If I centeṛ the disc in the caliper then the wheel is off center and if I center the wheel then the disc rubs against the caliper on one side. I've mounted the disc the conventional way, as it wasn't working out as Jokerio explained. Might have to grind it down a bit to size.

 

[Old3]

Have any pics? Cant you just space the rotor over or is it too far out already?

i will be pulling mine apart to drop in the tapered steering bearings i keep forgetting about so i will deal with it then. Hope you can get yours sorted! (Save me the trouble! Lol!)

 

[psych0hans]

No pics, sorry... The disc is already too far out to the right and the wheel is off center to the left. I'll need to shave off some of the back of the disc to reduce the offset and try to center the wheel using spacers. That's the only solution I can think off. Don't know why Jokerio's instructions aren't working out. Maybe he used some different spacers?

 

[Old3]

Wait a minute, the stock rotor is on the left.... I know your doing dual discs but are you talking about a right side rotir being too far right, too close to the fork leg? Away from center?

 

[psych0hans]

This is when I'm facing the bike. Rotor is still in the original location, so when I'm facing the bike it's on my right. I'll take pics once it's installed. Also Jokerio was kind enough to offer to email me some pics of his install on the bike, so that should help tremendously. I'll update you with complete details ASAP.

 

[jokerio]

Sorry for the major delay, but as promised, my notes on the RC8/RC390 fork conversion. I'm no machinist or engineer so excuse my amateur attempt at drawing the measurements…. This is what I have…..
Keep in mind, I'm also using a single (320mm) front rotor from a Yamaha FZR1000 mounted backwards !

 

[Old3]

Sorry for the major delay, but as promised, my notes on the RC8/RC390 fork conversion. I'm no machinist or engineer so excuse my amateur attempt at drawing the measurements…. This is what I have…..
Keep in mind, I'm also using a single (320mm) front rotor from a Yamaha FZR1000 mounted backwards !

Is that rotor 320mm by chance? It fits a standard 100mm Brembo caliper and the RC wheel just flipped around?

Thank you!

 

[psych0hans]

It has to be a 320mm rotor as the RC8 forks are spaced out to accept 320mm rotors. Also, it's a 10mm offset rotor mounted backwards. Also 1mm was shaved off the mounting face for the rotor to laugh with the calliper. The only issue is I haven't been able to install the ABS ring as there just isn't enough clearance. I'll take pics today and post them here.