Topic: CB750 K1 fork tubes

[Dunk]

I am pulling apart my 71 CB750 to do all the maintenance and wear items that may not have been done by the previous owner. As I get it apart, the more I'm thinking I should just take it completely apart and paint or powder coat the frame and more or less restore everything. I'll ride it a lot though, and it will be in the rain from time to time, so don't need everything to be original parts or factory correct, but I want it to be presentable and not a beater.

Anyhow, I got one of the fork tubes out of the triple tree last night and it is fairly rusted and pitted above the lower clamp. I was not able to get the other tube out so I sprayed it with PB and left it to soak in. I didn't clean up the one I got out yet to see exactly how bad it is, but I suspect the one that doesn't want to come out is worse and may need replacing. I suppose I'll find out when I get the other one out and both cleaned up. How bad can these be before they're not safe to use? If they clean up alright should I paint the top part to keep it from rusting? What are my options for new fork tubes for a K1? I believe they are different than K2 and up tubes.

[Magpie]

Based on my experience, that's pretty typical of the top part of the forks. The tubing is thick so unless there was some major pits in the tube I just wire brushed and sanded them smooth and painted them with some Tremclad rust paint. I don't know the difference between K1 and K2 tubes but I'm sure someone will post soon about them.
How is the chrome surface?
Cliff.

[KC_Northstar]

Like Magpie said that's pretty typical for the fork tops.  My K2 looked the same way.  I put a brass wire wheel on my bench
grinder and cleaned them up.  Then I just coated them with some motor oil.  As far as the forks go they are the same from
K0 up to K2 Ser num 2093730.  After that they changed to the K3 and later type and parts are not interchangeable.
I would just clean those up and put new seals in.

KC

[MCRider]

To help removing the rusted up tube, stick a tire iron (or screwdriver  ) in the lower tree clamp and spread it apart a little. Tube should come right out rust and all.

To me the rust is purely a cosmetic issue and will not affect the strength of the tube for our purposes. Clean it up, stabilize the rust with some phosphric acid type product, paiint it with your favorite rust product.

Tog et new tubes chromed all the way up your only supplier is Franks Maintenance. You are right that the K1 forks are different than the K2 and up in that they have several circlip groves and a diffferent system for damping. You'll find other suppliers for tubes but they won't work on a K1.

http://www.frankmain.qpg.com/

[MCRider]

Additionally, if you're going to restore with fork ears and rubber boots, no need to get new tubes as others said before.

[754]

If the lower tree tapped holes go thru, and you want go spread them. Put a shim in the slot, then thread a bolt thru from the back side.. No marks on the triple trees....and no twisty marks on your new chrome tubes if you get them.

[Henning]

Do you have the top triple off? If not, remove it, it will let you wiggle the fork leg around some more and it should come right out. If you have trouble getting the rubber gaiters off, heat them with a heat gun until they soften and then they are a piece of cake to remove.

Bike looks reasonably clean from the first photo. Do you really need a full on restore? It takes a lot of time, money and effort, and you sure ain't going to do much riding while it is spread all over the workshop.

[MCRider]

If the lower tree tapped holes go thru, and you want go spread them. Put a shim in the slot, then thread a bolt thru from the back side.. No marks on the triple trees....and no twisty marks on your new chrome tubes if you get them.

Now there's a good idea! 

[Dunk]

Thanks for the tips and advice.  I think with your tips on spreading and removing the top triple I should be able to get the other fork out. Hopefully they clean up nice. If not obscenely rusted and pitted I'll just clean and paint to protect it and not worry, since it's hidden anyhow. I also have new progressive springs and tapered triple tree bearings I'll be putting in.

Bike looks reasonably clean from the first photo. Do you really need a full on restore? It takes a lot of time, money and effort, and you sure ain't going to do much riding while it is spread all over the workshop.

It is pretty clean and presentable. There is over spray on the paint job though, and not everything was removed to paint. It looks great from a distance but when you get up close you see the imperfections. There are also a few scratches here and there on the frame. Overall it is very presentable. I wasn't planning on doing the whole thing, but with the bike half apart it might make sense to. I'm still debating that. I did order a valve cover gasket and although ym leak is very small I'm thinking now might be the time to pull the engine and replace that... Swing arm will also be coming out for new bushings. At that point I don't think there's much left to the bike, which is why I'm thinking of doing a restoration now.

Here is a pic of the bike all together... What do you guys think? Should I totally disassemble, paint frame and bike, etc..?