Hello, Red_One. I am reporting on how I am cleaning up Honda's first liquid-cooled straight 4-liter bike, CBR1000F (SC21), through trial and error.
In this 4th issue, I will report on the repair and O/H (overhaul) of the front fork, which is in a state that might be a bit tough to do by DIY.
I have done O/H of front forks twice in the past, but this is the first time for me to see a long-term stored vehicle with rust on both inner and outer tubes. The rust on the stroke part (agitator part) looked relatively small, so I decided not to re-plate the fork this time.
After the completion of the project, we will test-ride the vehicle to see if the fork oil leaks due to rust. We hope you understand that this work was done with the intention of checking if the forks leak oil due to rust after the completion of the test ride.
Start full of anxiety
Front fork area immediately after acquisition
My impression when pulling it around was that it was functioning normally, but when I first saw the front forks in the cowl, it was a hopeless sight.
I was under the impression that it would have to be re-plated due to the rather large rust spreading here and there.
I was under the impression that it would have to be re-plated, but after removing the surrounding parts and running a high-pressure washer on it, I found that there was not so much rust on the agitating parts and I thought that maybe it could be done. I was beginning to think that maybe we could do something about it.
Front fork area after high-pressure cleaning
After removing the fork and loosening the end bolts with an impact wrench, I disassembled it. I pulled out the oil seal and found that the oil inside was quite normal. It does not emit a bad smell and seems to be functional.
Since this model (first generation CBR1000F) is equipped with a unique anti-nose drive mechanism, the surrounding parts were also disassembled. Since brake fluid will inevitably adhere to the outer tube, we would like to paint the outer tube with the gun coat as well as the brake calipers. The detailed work of the gun coat was introduced in a previous article, so I will not go into it this time. Anyway, the paint film is so thin that if the base surface is uneven, the bumps will appear as they are. This time, the outer tube was sandblasted to remove the paint and prepare the substrate at the same time. For the inner tube, we decided to use soda blasting, which has almost no aggressiveness to metal.
Front fork after disassembly
Sand & Wet Blast - Gun Coat Paint
The paint on the outer tube is still strong, although it is peeling in places, so I used the power of sandblasting to sharpen it.
In the meantime, I masked the forks to avoid media from getting into them, and I also pulled out the needle bearing at the base of the anti-nose dive since I was able to get a new one.
After purchasing it, I checked and found that it had been discontinued, so maybe it was one of the last ones in Japan. It may have been the last one in Japan.
(Be careful about parts that are not compatible with other models because the anti-nose dive mechanism is rare.) It seems that it is important to check the availability of parts for bikes of this era before dismantling them.
OEM parts obtained for replacement
The sandblasting was successfully done in the cabinet utilizing a clear case.
After a thorough wash using parts cleaner and other products, I applied a matte black gun coat coating and baked it in a simple oven. When I took it out thinking it was done, I discovered that it was noticeable when touched with a greasy hand.
I reapplied a coat of glossy satin black. The days of modest experience improvement continue.
Before and after 1st coat
As for the inner tube, which was our biggest concern, we soda-blasted it and found that the rust was not on the surface but formed on top of many rust spots, and the plating was not peeling off.
However, point rust also existed on the agitating parts, so we would like to carefully check them after the project is completed.
The top bolt and other small parts inside the fork will be soda blasted and polished before assembly.
Areas of severe rusting
Prevention of recurrence of spot rusting
How can I make the many spots of rust above the agitator area less noticeable?
Can we prevent the rust from reappearing? After much thought, I decided to try polishing with a metal polisher after applying galvanizing paint as a trial. I worked with masking to avoid scratching the agitating parts of the polishing.
Galvanized paint and chrome plating are not similar, galvanized paint is more effective in preventing rust, but will turn matte gray if left untreated.
Is this better than turning the rust black with a rust converter? I tried it, but it looks almost black when polished. I am thinking of trying a plating-like paint for plastic models after assembling it.
Agitating section after the repair is completed
Maintenance of anti-nose dive mechanism
We want to keep the rare anti-nose-dive mechanism in good condition, so rubber parts such as O-rings and piston boots are replaced with new parts.
Needle bearings, which may be difficult to obtain in the future, are press-fitted with bolts and washers.
In addition, the parts that were tightened with Phillips-head screws have been replaced with hexabolts so that they can be tightened precisely to the specified torque.
Cleaned up the anti-nose dive mechanism section
Fork assembly
We are putting the disassembled fork back together, but the inside of the part that is the guide bushing on the fork agitator had been shaved off, so we are replacing it just in case. We will know if it is affected by rust or not at the next O/H.
Replaced guide bushings
When I disassembled the fork this time, I didn't have a seat pipe around, so I was saved, but if I applied too much screw stopper to the fork end port, the screw wouldn't loosen even if I used an impact wrench, so I had to make a special tool. (I got hooked on the YZF-R15.) For those who can check it regularly, I think it's better to apply a light amount of screw stopper.
The outer tube is put in a vise to stand it vertically and assembled back together. When assembling the oil seal, I put a wrap over the top of the inner fork to prevent scratches, then oiled it and slipped it in.
I put the wrap over the top of the inner fork to prevent scratches. I am not sure.
Front fork being assembled
Also, this time we used the OEM oil seal, and I got the impression that it required more force to press-fit than the inexpensive external one, and I could feel the difference.
We reaffirmed the words of our predecessors that it is better to use genuine parts as long as they are available in terms of not causing oil leaks.
When hammering in the seal, there are examples of utilizing PVC pipes that are the same size as the fork, but I had a tool with me so I used that.
Oil seal pusher (fork seal pusher)
Oil is Yamalube's G-10 at my own risk, although it is a Honda vehicle.
If you are concerned about it, please use the oil specified by the manufacturer.
While bleeding air, fill the oil to the height specified in the manual and tighten the top bolt with a new O-ring, and the F fork overhaul work is complete.
Oil level adjuster (oil level adjuster, fork oil level gauge)
Work Summary
The front fork outer is an important part that reminds us of the history of the bike, so many owners who value the age-appropriateness of the bike and the original appearance of the bike would only O/H the inside of the fork.
I was working on the theme of how much I could clean up by DIY this time, so I removed rust by sanding and soda blasting, cleaned, painted by the gun coat, and replaced the parts recommended for replacement.
Since the inner tube is not in perfect condition, we are going to keep an eye on it for a while. This is a unique DIY decision in this area. If you are concerned about it, it would be better to replace the inner tube or have it re-plated.
In the case of upright forks, the work itself is simple, and if you can get the replacement parts, the difficulty level is not so high.
Front forks with O/H completed
The DIY restoration work of the CBR still has a long way to go, and we plan to introduce the freshening up of the rear linkage and suspension in the next issue.
Tools and equipment used
High-pressure cleaner
Soda blasting tool set
Gun coat environment set
Electric impact wrench
Galvanizing paint
Metal polisher
F Fork oil seal pusher (Fork seal pusher)
F Fork oil level adjuster (oil level adjuster, fork oil level gauge)
vise
Purchased Parts
SC21 OEM parts
F front fork seal set, O-ring
F fork guide bushing
Rubber parts related to anti-nose dive
Needle bearing at caliper mounting base
General-purpose copper washer
Front fork oil (YAMALUBE G-10)
