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Fender rust...how to eliminate (revisited)
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pdedse Offline
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Fender rust...how to eliminate (revisited)
#1

Back in 2016, previous forum member Honda Lover posted a wonderful "how-to" eliminate fender rust and treat the underside:

http://cb1100forum.com/forum/showthread....ght=Fender

When I did a search within this forum (the .net), I don't find his post.  But the search did bring up others posts that referenced his work.  I've copied and pasted here so that perhaps a search within this forum accesses his work (see below).  

When I changed out tires on my 2017EX, I saw that rust had covered a good deal on the underside.  I've got the time to take this project on and am trying to do what Honda Lover did.

I've got the front fender off, it's easy to do and there was some rust but not too bad.  But I'm having a difficult time understanding one of the first steps to remove the rear fender.  

From the manuel: 
1. Remove batter cover (done)
2. Remove the rubber boot and disconnect the brake/tail light 3P connector

[Image: USYG0ac.jpg]

And it's the rubber boot that I'm not seeing.  

This is what my EX looks like: Is that semi-transparent thing the rubber boot?
[Image: 6FMSs0i.jpg]

But the brake/tail light 3P connector doesn't appear to lead to that, but rather down deep into unreachable recesses: that silver thing in the photo below, to the right of the red cable.
[Image: 4jRniNI.jpg]

Removing the side cover isn't mentioned in the fender removal instructions from the manual, and doing so doesn't really help access.  

Anybody with an EX who has removed rear fender?  Is it the same for '13/'14 models and I'm just missing something?

Thanks.



How  to protect the undercoat on bare metal fenders
Honda Lover: 

If you haven't looked lately, our CB's wheel wells/under the fenders are bare metal and if you've been riding your CB for a few years there is a good chance at least some rust has started to set in. This was a thread discussion some time ago, however, I've listed out a few steps outlining the process for lining our under-fenders with a rubber spray liner that prevents and/or significantly reduces rust build up...
STEP 1. Parts needed for this job are
1. Appropriate tools to remove both fenders. I used a ratchet driver, along with Allen key tip to remove the side panels. Not much in the way of tools required to remove both fenders. Follow your service manual. It is fairly straightforward.
2. Materials list: Undercoating Spray, Rust Remover spray, wire brush, shop rags, painters tape/newspaper for masking, rubber shop gloves, large pieces of clean cardboard for staging areas. Thread locker, WD40 or equivalent, chrome polish and/or wax.
3. I used Rustoleum Rust Dissolver Spray Gel and Rustoleum Undercoating Professional Grade. Both Purchased at Autozone but any good automotive store should stock Rustoleum products. I found both products easy to apply, work with and was very satisfied with the results. 3M makes products like this as well.
[Image: 7b0e9a35c90853cf7e306273d00c831e.jpg]
[Image: 87f988ea580934b7f15e421cb27bcb80.jpg]
4. Remove fender/s from bike. Be sure to set fenders top side down on a smooth/protected surface to avoid scratching the chrome top finish. Advise setting the fenders down on a piece of soft cardboard to prevent abrasion.
[Image: 0066cb93d7c4243508ed748d714287a6.jpg]
5. Using the wire brush firmly brush from side to side on the fenders underside removing any loose rust debris. Use a sand wheel bit with your drill if necessary. Fully rinse with warm water. Leave wet.
6. Apply Rust dissolver liberally to the underside of the fender/wherever rust is present. Ensure to do this in a ventilated area and wear rubber gloves. Be careful not to get the dissolver on painted or finished chrome parts. If you do, be sure to wipe up immediately.
[Image: c69148a164fe4ec2092a5713fdaeb199.jpg]
7. Wait 20-30 minutes for remover to begin to dissolve/lift any Rust. 30 minutes worked well for me but this depends on the amount of Rust on the fenders.
8. After letting the fenders under-body soaking for a while, with the spray dissolver still on the fenders, use the wire brush to firmly scrub with short straight strokes on any visible rust. The Rust should fall away. Use more dissolver spray and repeat the process until ALL Rust is removed. The more Rust you remove here, the better the liner will adhere and the better longevity you will experience as far a Rust protection goes. I was able to remove ALL Rust.
9. Rinse with warm water and dry, BOTH VERY throughly. Ensure all the dissolver is off the finish. Allow the fenders to sit for at least 1 hour to ensure the chemical reaction subsides, giving the undercoating spray the best chance to adhere.
[Image: 1af582c5138154f765bceaad18c79e46.jpg]
[Image: 0a9b1491b211274b63bcf56ded12321c.jpg]
10. After thoroughly dry, use painters tape and newspaper to mask the top/ finished chrome sections of both fenders. Use small pieces of tape crumpled up into balls and lodge into any mounting screw holes to protect screw threads from excess liner spray. Take your time here to ensure 100% of the top/finished chrome surface is sufficiently covered.
11. Use 2 small blocks of wood to support both sides of each fender upright, with top/finished side on soft cardboard.
12. Shake Undercoating spray can for minimum 1 minute from the time you hear the mix ball starting to move. Apply in a well ventilated area and far enough from other items to avoid overspray. Hold can 12" from each fender and apply in even lateral strokes slightly overlapping with each pass. Rustoleum advises 2 coats minimum, however I applied 4. I found allowing 6 minutes between applying coats was best. I also found allowing each fender to dry for at least 4 hours before handling was best. (Rustoleum states 1 hour)
[Image: 903710d772f209024e694bd0565ab46a.jpg]
[Image: 35a48af127618a2a205367a30d8c72fe.jpg]
13. After removing all masking, wipe down the top chrome surface with a basic cleaner to prevent any glue, oils or other substance from bonding to the chrome surface.
14. Reinstall fenders. I always take this opportunity to treat all threads and hardware with WD40. Note, Honda does advise thread locker blue for front fender hardware in certain areas. Follow service manual torque specs as usual.
15. For you neat freaks out there, I applied 2 coats of chrome polish to each fender to restore the finish to showroom new..
[Image: 8c2aa277f2ff365d402b100970c8bdf8.jpg]
[Image: 7ec46bd014e32dfa5fee50776bdb0491.jpg]
[Image: 0966a0dcda436246361bd41af17bb548.jpg]
From looking at your CB, no one will know anything was done however going forward you will have the peace of mind that Rust build up will be kept to a minimum depending on when and where you ride! Feel free to add other items or tips you feel I missed...
[Image: f53cac76f10fc845f1442523669ea322.jpg]


06-22-2025, 05:44 PM
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peterbaron Offline
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RE: Fender rust...how to eliminate (revisited)
#2

I used wd40 to clean the rust,  then rubbed in a ACF-50 and sprayed a thin layer onto the rear fender. No more rust.

           "Drop a gear and disappear"®
'24 Kawi Z650RS - Hooligan®
'14 CB1100 DLX, s/n 170, 38K kms - FOX® 

'14 CB1100/ABS, 134K kms - sold
'13 CB1100/c-ABS - 56K kms - sold             
            *Grand Chancellor* 


06-22-2025, 06:37 PM
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pdedse Offline
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RE: Fender rust...how to eliminate (revisited)
#3

(06-22-2025, 06:37 PM)peterbaron Wrote: I used wd40 to clean the rust,  then rubbed in a ACF-50 and sprayed a thin layer onto the rear fender. No more rust.

Did you remove the fender to clean the rust, or just "reach under there"?


06-22-2025, 06:40 PM
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peterbaron Offline
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RE: Fender rust...how to eliminate (revisited)
#4

(06-22-2025, 06:40 PM)pdedse Wrote:
(06-22-2025, 06:37 PM)peterbaron Wrote: I used wd40 to clean the rust,  then rubbed in a ACF-50 and sprayed a thin layer onto the rear fender. No more rust.

Did you remove the fender to clean the rust, or just "reach under there"?

Remove and do it right.

           "Drop a gear and disappear"®
'24 Kawi Z650RS - Hooligan®
'14 CB1100 DLX, s/n 170, 38K kms - FOX® 

'14 CB1100/ABS, 134K kms - sold
'13 CB1100/c-ABS - 56K kms - sold             
            *Grand Chancellor* 


06-22-2025, 07:42 PM
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pdedse Offline
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RE: Fender rust...how to eliminate (revisited)
#5

(06-22-2025, 07:42 PM)peterbaron Wrote:
(06-22-2025, 06:40 PM)pdedse Wrote:
(06-22-2025, 06:37 PM)peterbaron Wrote: I used wd40 to clean the rust,  then rubbed in a ACF-50 and sprayed a thin layer onto the rear fender. No more rust.

Did you remove the fender to clean the rust, or just "reach under there"?

Remove and do it right.

yep, that's what I'm tryin' to do.


06-22-2025, 07:47 PM
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peterbaron Offline
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RE: Fender rust...how to eliminate (revisited)
#6

About 6 bolts/nuts or so.
Did twice, on my '13 and '14

           "Drop a gear and disappear"®
'24 Kawi Z650RS - Hooligan®
'14 CB1100 DLX, s/n 170, 38K kms - FOX® 

'14 CB1100/ABS, 134K kms - sold
'13 CB1100/c-ABS - 56K kms - sold             
            *Grand Chancellor* 


06-22-2025, 08:05 PM
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Cormanus Offline
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RE: Fender rust...how to eliminate (revisited)
#7

pdedse, I can't find Honda Lover's post on the new forum. Can't have made it across for some reason.

Sometimes the road not travelled is best left that way. (Jane Goodall)


06-22-2025, 10:50 PM
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pdedse Offline
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RE: Fender rust...how to eliminate (revisited)
#8

(06-22-2025, 08:05 PM)peterbaron Wrote: About 6 bolts/nuts or so.
Did twice, on my '13 and '14

Those I can see well enough, it's the disconnecting of the tail light wiring that I'm unsure of.


06-22-2025, 11:42 PM
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rdprdp01 Online
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RE: Fender rust...how to eliminate (revisited)
#9

(06-22-2025, 10:50 PM)Cormanus Wrote: pdedse, I can't find Honda Lover's post on the new forum. Can't have made it across for some reason.

It is not there. There was something about the Thread which threw an error when we tried to port it. I will recreate it sometime this week. It is an important thread we need to keep. David

2017 Honda CB1100 EX
The most sophisticated, smooth, perfectly engineered motorcycle I've ever owned. A pleasure in every way.


06-23-2025, 01:06 AM
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Cormanus Offline
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RE: Fender rust...how to eliminate (revisited)
#10

pdedse has included Honda Horder's original post in the first post in this thread. So, unless there's lots more in the discussion, we've got the important bit.

Sometimes the road not travelled is best left that way. (Jane Goodall)


06-23-2025, 01:19 AM
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