Topic: Oh no - cracks in my fork case!

[krksquared]

I was shocked to see these cracks today on my CB400F. This a common thing? Potentially dangerous?

[pjlogue]

It looks as though the fork lower has been painted by the flaking at the top.  If it was painted, I would make sure that what you are thinking as cracks is actually a crack in the fork casting and not the paint cracking. 

If it is actually a cracked lower fork tube you can probably find a used one on ebay at reasonable cost. 

To actually crack the fork lower  like that I would think there would have to have been a substantial impact like an accident bad enough to bend the fork tube then driving the fork lower onto the bent upper tube.  Are there signs on other parts of the bike of an accident?

-P.

[newday777]

I agree with P. That looks like it has been poorly painted and the paint is cracking. Take the fork apart and use paint stripper (or old brake fluid works to strip paint too) to see what the bare aluminum looks like.
Report back your findings here.

[MauiK3]

+1 cracking paint

[Jerry Rxman Griffin aka MuthaF'er]

I see no leakage to indicate cracking aluminum

[bryanj]

If it was cracked alloy it would have fallen apart

[Don R]

 FYI. they are the same as CB360 forks which sell cheaper.

  If your chrome tubes are good, I have a set in Illinois with air caps on them, one chrome tube is pitted but you could do a swap. Everybody is always so far away.

[krksquared]

I'm working on removing the paint as suggested. Using brake fluid but the paint is resisting my effort. Must be good paint. I can catch my finger nail in the cracks which I guess could happen with paint but we will see. If after full paint removal it isn't obvious, maybe a Zyglo check is in order. As for accident damage, none is apparent. The bike looks otherwise excellent.

Another question occurs to me. If it is cracked and I need to replace it, should I just refinish to original paint or get them polished? The bike looks close to what it looked like when new so I lean to original paint but I'll be durned if they don't look so good when polished 

[scottly]

At the edge of the dust cover it looks like paint flaking away?

[krksquared]

Aha, I see what you mean. I accelerated the paint removal in that area and yes, I think you are right. I'll give the brake fluid some more time as I don't want to use abrasive methods as I fear actual cracks might fill with old paint.

[scottly]

Brake fluid works best at removing paint when you don't want it to.

[newday777]

Aha, I see what you mean. I accelerated the paint removal in that area and yes, I think you are right. I'll give the brake fluid some more time as I don't want to use abrasive methods as I fear actual cracks might fill with old paint.

Put brake fluid on and wrap the fork leg with plastic wrap to keep it liquid.
Lay down the sheet of plastic on the bench, put the fork on the plastic and coat the leg. Wrap it up. Let it set 3-4 days or more.

[krksquared]

It was cracks in the paint. Was worried because the cracks felt real & deep to my fingernail. Now I have to decide to repaint or polish. Here's what the bike looks like. What do you think? Stay original or polish?

[bryanj]

Polish

[denward17]

Polish

+1

[Don R]

 If you polish start with fine sandpaper and then go finer. I've often been tempted to use coarse grit and then was forced to deal with the sand scratches. 
  I had some interleaf flap wheels that had sandcloth alternating with Scotchbrite. They do a decent job without digging in. I think they came from a farm store.

[pjlogue]

When I restored my bike's fork lowers, I used a scotch bright buffing wheel on a bench grinder (fine grit scotchbright) after removing any paint/clear coat.  If you go this route wear a facemask!!!  After light buffing, I switched to a cloth buffing wheel and buffing/polishing compound.  It does a respectable job of restoring fork lowers. You can then either leave it uncoated and polish them from time to time or degrease after polishing and use a clear coat. 

-P.

[M 750K6]

Sad, but I enjoy getting the Polish out and going over the forks and engine covers. They come up lovely, but they seem to tarnish quicker than my old Norton. You can also see flaws in the alloy, if you look closely. So I'd guess the alloy spec was what was required for a paint finish.

[Johnie]

An old Honda guy told me to use 320 then 600 grit all wet. Then went to my polish wheel with white rouge. The result was great. I did not use clearcoat as I wanted to be able to touch them up if necessary. Oxidation was pretty bad on these.

[scottly]

Polishing is a lot of work, and the forks need to be disassembled to do a proper job. Do you really want to take the bike off the road right at the start of riding season?

[newday777]

An old Honda guy told me to use 320 then 600 grit all wet. Then went to my polish wheel with white rouge. The result was great. I did not use clearcoat as I wanted to be able to touch them up if necessary. Oxidation was pretty bad on these.

Nice job John. I have some to do too. I'll try that process.

[Stev-o]

Polish

+1

+1

[CycleRanger]

Doing the work of polishing suuuuuux but the fork lowers are about the easiest thing to polish if you're gonna. 

[krksquared]

Yup I'm thinking polish is the way to go especially after seeing Johnie's pics. And Scottly read my signature. I have 4 other bikes plus my daughters CB300F. 

[Johnie]

Polishing isn't so bad a long as you have a buffer. I use a 6" bench buffer with cotton wheel. You have to take your time and wear gloves as the leg does get warm. It a messy process so wear a mask and eye protection.