Topic: Fork problem on a CB550

[mgilvary]

I bought a set of used forks on eBay to replace the originals on my 75 550, since one of them is bent. The new set came with good seals and filled with oil. After a long day in the hot sun, I swapped my old forks for the new ones. The operation went so smoothly that I commented to my buddy that it was "too easy."

Then I took her for a ride. I hit a bump at about 30mph. The forks compressed... and stayed that way.

I propped up the front tire and the forks remained compressed. I pushed down on the tire and the forks remained compressed. Finally, with the aid of a 2x4 set against the rim, and a nice, big hammer rapping on the other end of the 2x4, the forks popped back into their extended position.

Took the bike for another ride. Hit a speed bump. Forks compressed... and stayed that way.

Can somebody please tell me why my forks are binding in the compressed position?

I opened the bolts to take a look at the springs and found that the PO had put 1 1/2-inch spacers in the tubes, which suggests to me that the springs are in bad shape. However, when I had both sets of forks off the bike, I leaned on each of them to see if the new ones felt any different and they were much stiffer than my old ones. Besides, can a spring be so worn out that the fork binds in the compressed position and won't even extend again when the wheel is propped up off the ground?

Could there be something wrong with the internal parts? Or is the problem just the springs? (Please say it's the springs)

[TwoTired]

I'd bet that the fork tubes are bent.  It's a tube sliding in a tube.  When they slide over a section that is bent, it binds.  Dismantle the forks and roll the upper tubes over a known flat surface.  I use my table saw.  It will be pretty obvious if they flop instead of roll.

I have straightened bent forks.  But, I have a 10 ton press to do it with.  Not all of them can be straightened.

Sorry,

[kghost]

How did you know they were filled with Oil?

The oil in them might be really old. A congealed mess in the forks is going to make them bind up.

Swollen seals will make things bind up too.

Tootired may be correct in that one or both could be bent.

You should really take them apart and look at everything carefully.

[bryanj]

If the tubes are straight it could be a deformed alloy slider. I came across that on an accident CX500 years ago

[Uncle Ernie]

Sorry, but I can't imagine buying used forks.   The fact that the "new" ones had added spacers suggest that he was a very aggressive rider. He probably sold them because they were bent.

[mgilvary]

Two Tired -

It hadn't occurred to me that the tubes could be bent since one of my original tubes was obviously bent and did not bind in this way. Still, your theory seems plausible.

kghost -

I trusted the seller when he said they were filled with oil. Once they collapsed, I started to wonder. But, when I pulled the springs, they were dripping with the stuff. That, of course, doesn't rule out old gunk at the bottom.

bryanj -

The alloy certainly appears to be in good shape on the outside. Do you think there could be internal damage that might do this?

Unlce Ernie -

As for buying used forks, my whole bike is used, so I'm not really worried about it. Admittedly, though, it's starting to make sense why these forks were so cheap.

So, it looks like the next step is to drain, disassemble and examine. So here's my follow-up question:

If one of these "new" forks is bent, or otherwise damaged, theoretically, I could cannibalize my straight orginal fork for parts. However, the two sets of forks are not exactly the same. Overall, they are the same length and have identical caliper/fender mounts. However, the alloy lowers on the "new" set are noticeably longer than the originals -- maybe an inch longer. I don't know what year the "new" ones came from. They were simply listed as CB500/550 forks. Does anybody know what the difference in lower housing length signifies? Does it mean the internals are incompatible? What about the tubes?

[TwoTired]

I'm not 100% certain, but I think the upper tube lengths are different.  There were at least three variations in fork design over the 71-78 CB500/550 models.  The valving internally changed with the introduction of the 550 for example.  They changed the design again in 77.   The fork assemblies will interchange between models.  But, individual components of the forks must be compared on a case by case basis before interchange.

In your case, I suspect you have CB500 forks, particularly if they still have the accordian boots on them as your 75 does.  Were it me, I'd be carefull to keep the sets intact and not mix an early and late model design left & right.  And, I wouldn't be too hopeful of any parts interchangeability between models.

As far as tube binding is concerned, placement of any bends would be key to sticking.
However, from your description, someone has clearly meddled with the insides of your forks.  Who's to say they put it together correctly?  The Shop Maunual shows the need for a HONDA Special tool for dismantling the forks on the CB500.  I haven't taken this design apart yet to verify if there is a common substitute for the tool.

Good luck,

[mgilvary]

Thanks for the insights.

However, from your description, someone has clearly meddled with the insides of your forks.  Who's to say they put it together correctly?

I've got an email in to the seller for model/history info, and to find out if he has any knowledge of this problem. 

The Shop Maunual shows the need for a HONDA Special tool for dismantling the forks on the CB500.  I haven't taken this design apart yet to verify if there is a common substitute for the tool.

The shop manual calls for a special tool on the 550 as well, but when I changed my seals a while back, a regular old allen wrench worked fine.

[Uncle Ernie]

"As for buying used forks, my whole bike is used, so I'm not really worried about it."


                                     Well.....      alrighty then!

[mgilvary]

Y'know, I always assumed that new OEM forks were unavailable, but your post prompted me to test that theory. I punched the part no. for a whole fork assembly into the Service Honda website, and it actually showed up. Of course, to buy two new ones would cost $530. I got these used ones on eBay for $18. If I can get them to work, it'll be well worth the trouble.

[oldbiker]

Why don't you try the for sale/wanted forum on this site? You are less likely to get ripped off>

[mgilvary]

I'd never even thought to check out that forum before. Thanks for pointing it out.

[Uncle Ernie]

Stop me if I'm flogging a dead horse; your statement just sounded to me as if I were to say, "My home is used, so used shingles should work on my leaking roof".  When I was young and impressionable, I worked under a couple of the best mechanics I can imagine (even now). They taught me to get the best tools I could possibly afford, they loosened and re-torqued head bolts before setting valves, and never tried to fix bent forks. After experiencing lock-to-lock high soeed wobble for myself, and seeing the result of what may have been the result of such, to be honest- I'm too scared to even think about that. Used carbs, reconditioned wheels, body parts, hell- even used tires, but not forks. I, on the other hand, am NOT even a fair mechanic. Just one mans opinion.

[TwoTired]

Any machine is only as good as the mechanic that repairs it.  Mechanics and technicians are people, none are perfect.  So, the quality of their work is less than perfect as well.  The best ones are those that get close to perfect or have the judgment to know how close to perfect is required to do the job.   Such is the nature of repairs.

Mechanics don't straighten bent forks for two (or three) reasons: 1- severity of the bend has fatigued the metal beyond repair, or 2- for minor bends, the time taken to get it straight exceeds the cost of replacement.  Further, it takes the right equipment they either don't have or don't wish to create and then pay monthly storage space for equipment with infrequent use.  Besides, (3) the customer pays for it anyway.  Further, with todays frequent frivolous lawsuits, liability transfers to the manufacturer of the forks rather than the repairer should any type of accident happen to the bike in the future, regardless of true cause for the accident.  Lawyers cost money.

Your fears not withstanding, saying all bent forks are unrepairable and unsafe is just bogus.

By your own line of thinking, a bike in any kind of accident should be tossed by the wayside because who knows what might be bent, frame, swingarm, etc., and thereby be "unsafe".

Lastly, you can bet that if I found a used slate shingle that matched the color and size of one I need for my roof,  darned right I'd use it.  They only last a few hundred years or so.  I won't be alive when it wears out, most likely.

Another mans opinion...

Have mercy on the poor horsey,
 

[mgilvary]

...your statement just sounded to me as if I were to say, "My home is used, so used shingles should work on my leaking roof".

My reasoning is not that my bike doesn't deserve new forks. What I'm saying is, since I'm riding a 30-year-old bike, I am already riding on used forks. So, I don't see what's so bad about buying a replacement set that's also used.

I appreciate your opinion, and please know that nobody values my life more than I do (which is why I'm not riding the bike in its current state). I'm not going to attempt to straighten a bent fork. I have neither the tools nor the expertise. But I also can't afford to plunk down $500+ on a new set of forks. So, I'll have to find a straight tube and rebuild either the "new" used set, or my originals. Or find yet another set of used ones that are already straight.

[Uncle Ernie]

TT, there's another reason; someone who has the equipement but doesn't know how to use it.  The 5th reason is someone who has the equipement and only THINKS he knows how to use it.  The mechanic I respect the most is one who can look me in the eye and say, "I don't know".
Anyway, I guess it mainly depends on experience and judgement. I wouldn't throw all bikes away. The first time I got hit by a car, the bike ended up in the lobby of an art gallery. The second time, I managed to save the frame by throwing my leg between the bike and the car  but I finally ended up with the bob-job I always wanted.    A friend says you can always fix a bent frame by adding a sidecar 
Never used these face things before- haven't decided if they're fun or obnoxious- could be another poll.
Thanks for some perspective.
Wish I had a slate roof. If you ever need some cheap composite, I've got some good used stuff left. I'd only charge postage  .