Honda Twins banner

1 - 19 of 19 Posts

·
Registered
Joined
·
703 Posts
Discussion Starter · #1 ·
Gentlemen (and gentle ladies)- hi, its been a while.

Pulled the 450 out of the garage for a bit of a clean-up and look over during the week, and discovered something slightly concerning. Took a couple of snaps, but it's hard to capture the detail well:

Front end of the 450. Hybrid - K5 bike with chrome toaster tank and wheel and disk off an earlier model, or the scrambler variant.



Cleaning the right fork lower, spotted this:




A sharp edged scratch - or crack - deep enough to catch a thumbnail, and which extends 6-7/8 of the way round the circumference of the tube. The optimist in me hopes it's some kind of scratch - the sensible voice in my head urges caution, says it could well be a crack. Not a lot of info to go on with the pics - but I thought I'd throw it up and see what you more experienced guys think ?

If it's not immediately obvious - is there perhaps anything I can do at home to check further/confirm one way or other, short of taking the leg off and depositing it with somebody with metal crack detection facilities ?

Thanks,
Alan
 

·
Registered
Joined
·
6,495 Posts
Wow, that doesn't look good.
Is the front wheel 18" or 19"??
If it's 19" it's from a CL model. If it's 18" it's from an earlier CB (K1 or K2 in the US).
Since the forks have gators, they're probably CL, assuming a 19" wheel.
Fender probably unique to the forks.
FYI, all 5-speeds use the same stem and bottom clamps, top clamp varies widely with the model, so does tach/speedo mounting.
 

·
Registered
Joined
·
3,257 Posts
Perhaps clean and dry the outside of the tube, then pump the forks a few times while holding the front brake on then dust the scratch with talcum powder looking for some fork oil seepage?

Alternately you could raise the front of the bike and support it with the front wheel off the floor, then loosen the front axle looking for the crack to separate or change in any way.
 

·
Registered
Joined
·
3,537 Posts
It looks like a scratch to me. Has the front end have any other impact damage? Is it leaking fork oil? I have never heard of a fork slider cracking on any bike. If you are really worried bout it, take the slider off and do a dye penetrant inspection. Every front end damage I have ever seen on a motorcycle, the fork tubes bend and then the wheel will collapse against the engine. Then the steering neck bends at the frame. It takes a hell of a hit for that to happen, even then the sliders can sometimes be salvaged.
 

·
Registered
Joined
·
4,458 Posts
Looks like a scratch to me as well. Try taking a sharp razor blade and trace along it to see how deep it goes.
 

·
Registered
Joined
·
703 Posts
Discussion Starter · #6 ·
^ Will do. Odd shape for a scratch though - 3/4 of the way round the tube ?

Was also thinking of taking some wet and dry to a sample area, either see how deep it goes if it's a scratch, or follow it down and confirm if it's a crack. Good idea / bad idea ?
 

·
Registered
Joined
·
703 Posts
Discussion Starter · #7 ·
It looks like a scratch to me. Has the front end have any other impact damage? Is it leaking fork oil? I have never heard of a fork slider cracking on any bike. If you are really worried bout it, take the slider off and do a dye penetrant inspection. Every front end damage I have ever seen on a motorcycle, the fork tubes bend and then the wheel will collapse against the engine. Then the steering neck bends at the frame. It takes a hell of a hit for that to happen, even then the sliders can sometimes be salvaged.
No impact in my time James, but that's only 2 years out of the last 40 plus :) No signs of any impact anywhere else on the lower tube, and no leaks as yet. Odd place for accident damage too: one and only time I ever stuffed a bike in a frontal impact, the inner sliders took the brunt of it and bent as you describe.
 

·
Registered
Joined
·
3,103 Posts
Warm the area with a torch or a heat gun. Oil will wick out if it's cracked.
 
  • Like
Reactions: 80cb400t

·
Registered
Joined
·
3,257 Posts
I've seen lowers shattered, but that was an 89-90ish Suzuki Katana.
 

·
Registered
Joined
·
703 Posts
Discussion Starter · #10 ·
Perhaps clean and dry the outside of the tube, then pump the forks a few times while holding the front brake on then dust the scratch with talcum powder looking for some fork oil seepage?

Alternstely you could raise the front of the bike and support it with the front wheel off the floor, then loosen the front axle looking for the crack to separate or change in any way.
Warm the area with a torch or a heat gun. Oil will wick out if it's cracked.
My knowledge of metallurgy's not great.

Just thinking - even if those tests were to reveal nothing - is there a possibility it's some kind of 'incipient' crack ? ie not yet deep enough to go through the wall of the tube, but with potential to grow and potentially fail catastrophically at some future stage through fatigue or some other mechanism.
 

·
Registered
Joined
·
703 Posts
Discussion Starter · #11 ·
Update:

Took to an inch long section of it with some 240 grade wet and dry, and then shined it up a bit with some 1200 grade to see what was beneath:







Whatever it is doesn't go deep - polishes out easily enough without taking too much aluminium away. If it is cracking, it's not coming from the inside out at least.

Would the fact that it seemingly can be polished out completely that help firm up the scratch theory over the cracking at all ?
 

·
Registered
Joined
·
2,837 Posts
I thought it odd how it went 3/4 the way around too but just now thought about how taking brakes,wheels and fenders off can be interesting and the lowers will spin...
 

·
Registered
Joined
·
3,257 Posts
I think you've proven it was a scratch, good work.
 

·
Registered
Joined
·
703 Posts
Discussion Starter · #14 ·
I think you've proven it was a scratch, good work.
Dunno if I'm out of the woods yet..

I spoke to a machinist - guy who does work with aluminium. Says the fact that it polished smooth with the wet and dry doesn't necessarily mean there is no latent cracking underneath. Recommended I get the hold of a chemical crack detection kit for peace of mind. Better safe than sorry I guess, esp if it ever gets sold on to some unsuspecting individual down the line.


Wow, that doesn't look good.
Is the front wheel 18" or 19"??
If it's 19" it's from a CL model. If it's 18" it's from an earlier CB (K1 or K2 in the US).
Since the forks have gators, they're probably CL, assuming a 19" wheel.
Fender probably unique to the forks.
FYI, all 5-speeds use the same stem and bottom clamps, top clamp varies widely with the model, so does tach/speedo mounting.
It's a 19" wheel Bill - further confirmation if any was needed that she never came out of the factory like that :)

Depending on how the crack test turns out (or even if it's clear) I might take the opportunity to convert her back to disk.

The left fork lower has lugs for a caliper. I'm wondering whether this means I could bolt an 18" disked wheel set-up directly to them, or does the fact that they are currently mated to a 19" mean that they won't be able to take the 18" without major work ?
 

·
Registered
Joined
·
3,133 Posts
If it's so shallow that you can polish it out, it's a scratch. I've never heard of a short hairline crack in aluminum that didn't go all the way through, anyway.
 

·
Registered
Joined
·
756 Posts
I've been following this but not commenting. Call me crazy, but I'd replace that fork lower.
 

·
Premium Member
Joined
·
2,838 Posts
PO cut something off? Scratched while disassembly of fork?

Being that long it would be deep and seeping fluid if a crack. Scratch.
 

·
Registered
Joined
·
3,257 Posts
I was thinking the fork could have been clamped in a vise to hold it while the damper rod bolt was removed. I'm thinking if the vise wasn't tight enough (which is common because nobody wants to gouge up their fork lowers) and the fork could have twisted in the vise while attempting to remove the damper rod bolt causing this scratch.
 

·
Registered
Joined
·
3,133 Posts
Any time I need to clamp something pretty in a vice, I stick a short piece of a 1x4 between it and the jaws on both sides.
 
1 - 19 of 19 Posts
Top