Ascot Forum

First Generation Ascots => Tech Section => Topic started by: kansloos161 on August 08, 2017, 11:01:26 AM

Title: How To: CBR900RR forks in FT500
Post by: kansloos161 on August 08, 2017, 11:01:26 AM
I've been getting quite a lot of questions regarding the CBR900rr forks that I put in my FT, so I figured it might be more convenient to write up a little how to for everyones info and entertainment.

First of all, Why?
The FT forks are not the best ever, they are not adjustable, you can only fit a wheel with 1 brake disk and frankly I didn't like the overall look of the FT with the standard forks (very long, axle in front of the fork center line etc.)
I wanted to get rid of the old forks and just happened to have a set of CBR900RR forks lying around. They are fully adjustable (get the 96+ ones) a LOT shorter, very thick and badass looking.

Differences:
The FT forks are 37mm thick with 152mm front suspension travel.
The CBR forks are 45mm thick with 120mm front suspension travel.
Length wise I know the CBR forks measure 732mm from the middle of the axle to the top of the forks in complete uncompressed state (loose on the bench). If anyone can provide the same info for the FT I can add it here.
(https://s13.postimg.org/a7g5dg5if/20130819_163317.jpg)

At first I thought the steering stem was exactly the same. It has the same lenght and diameter. It turns out that the threads for the different nuts are at slightly different spots.

The mounting diagram for the two is also a bit different. If you look at the diagrams below you can see the FT has a spacer under the lower ball bearing and a spacer underneath the nut on top of the top bridge, however it lacks a secondary retaining nut underneath the top bridge and it lacks a dust seal underneath the first retaining nut.

Diagram FT500 top bridge
(https://images.cmsnl.com/img/partslists/honda-ft500-ascot-1982-c-usa-handlebartop-bridge_bighu0186f8c05_1c20.gif)
Diagram FT500 Steering stem
(https://images.cmsnl.com/img/partslists/honda-ft500-ascot-1982-c-usa-steering-stem_bighu0186f8c06_51fe.gif)

Diagram CBR900RR top bridge
(https://images.cmsnl.com/img/partslists/honda-cbr900rr-fireblade-1996-t-germany-handle-pipetop-bridge_bigecw0n41f__0500_f8e8.gif)
Diagram CBR900RR steering stem
(https://images.cmsnl.com/img/partslists/honda-cbr900rr-fireblade-1996-t-germany-steering-stem_bigecw0n41f__0600_b2b9.gif)

The ballbearings for both stems have the exact same inner measurements.

Fitting the bastard:
- Remove the old FT forks and throw them in the trash.
- Remove the old FT bearing races in the frame tube
- Remove the old CBR bearings from the steering stem
- Buy new bearings for a FT500 (suggest you buy the conical ones as they are better)
- Fit the new bearing races in the FT frame tube
- Remove/grind the steering limiters from the FT frame tube and the CBR lower tripple tree in order for them to fit.
- Fit the new FT bearings to the CBR stem don't forget the dust seal and the FT spacer (if you buy tapered bearings you will get a 4mm spacer with the bearings. They include this as the tapered bearings are lower than the original ballbearings. I'm looking to remove this to see if that makes the fit even better)
- Put the steering stem in the bike and fit the upper stearing bearing and FT retaining nut.
Here you will start to see the difference in the placement of the steering stem threads. The CBR900RR frame tube is a bit shorter so now the secondary retaining nut doesn't have any thread to go one anymore. However it is important that you fit this secondary nut as it acts as a spacer for the top bridge, this is because the lower retaining nut flange is wider than the hole in the top bridge. If you ommit to fit the secondary nut the top bridge will press on the nut flange destroying it and your precious steering bearing along with it.
- fit the secondary steering nut
- fit the top bridge
- fit the top nut (do not fit the FT spacer)

Impact on steering/riding:
The forks are a lot shorter and stiffer.
Since they are so much shorter the whole bike will lean forward quite a bit more. This means severall things.
- Less ground clearance, both in corners and if you go over a bump
- Side stand is a bit to long, result is very straight up bike while on sidestand and risk of falling over
- middle stand is a bit to long, result is very easy to put on the middle stand.... very easy to get off/fall off too.
- More weight on the front resulting in a tighter feel around the bends
- More frequent ball crushing on the tank
- Might develop a speed wobble at high speeds although I haven't felt that yet.

The FT originally had a pretty lazy stance, with the shorter forks the bike wants to turn and fall into the corners much quicker. I am used to superbikes and like this new handling.
(https://s2.postimg.org/e8hpplm21/20130820_154934.jpg)
(https://s15.postimg.org/oy1llgoaj/20130820_173646.jpg)
Title: Re: How To: CBR900RR forks in FT500
Post by: Lefty on August 11, 2017, 04:55:49 PM
Interesting, I'd like to see what it looks like. I'm thinking of replacing my front end but not sure if I want to go this route, my Ft had a broken off drain plug on the left & I feel pretty sure the P.O. rode it that way forever. I rebuilt both, after sealing the left leg up with some liquid steel type stuff but the left started leaking from the seal pretty soon after the rebuild. So I bought another single seal set from Honda- that lasted about 6 months tops before it started seeping out of the seal. I'm thinking about doing the Hurricane swap, but currently working on another bike, so it'll be a while before I do anything with the FT.
I'm real interested in this swap you're doing, let's see some pics!
Title: Re: How To: CBR900RR forks in FT500
Post by: triguyracer on August 11, 2017, 06:00:35 PM
You can make the stock forks work pretty good by just buying a set of race tech fork springs, the stock setup is really bad some of the worst I have ever rode on ,I powder coated my lowers black and they look good way better to me ,put a stainless steel brake line on with some good brake pads and you will have a good brake , maybe not roadrace good but good enough for some good stopping power and the springs will take away the front end dive under hard braking,want faster handling add a half inch to your rear shock length this will  speed up handling and you will not lose ground clearance,this is a inexpensive way to help with the stock junk setup by a long way,if you go that way and need a stock lower leg pm me as I have a stock one that I will sell cheap 
Title: Re: How To: CBR900RR forks in FT500
Post by: kansloos161 on August 12, 2017, 02:30:16 AM
added some pictures.
Since then the bike has been heavily modified so those pictures do no longer represent how just the change of forks looks like.
My hole topic can be found in the modified to full customs section.