Topic: FRONT FORK TUBE SWAP -1974 versus F model tubes

[andy750]

Hi all,
When Chris and I tried to replace the left front fork seal today on a  1974 CB750K4, we discoverd the fork tube under the boot had a large chunk out of it and would need to be replaced. We tried using a K2 fork tube but they have a different lower part. Chris has F model fork tubes, so question to anyone that knows.... is the F model tube the same as the K4 tube? i.e. same length? same fork spring length?? Does anyone know??

Thanks in advance,
Andy in Boston.

[bryanj]

I think F and F1 yes but F2 and F3 no. Best if you replace as a pair as age/mileage will set the springs/damper valves different

[frostypuck]

So, I looked at my pair of forks That I was giving to Andy's cause, I had originally thought were going to be from an F model, but quite obviously, they are from a K. I just didn't remember which bike I pulled them off of. Now, the interesting thing...these forks have exactly the same damage on them that made Andy's fork tube useless.
Just above the seal, an area the size of a dime has been worn away. Probably 1 mm deep. This, likewise was on the left fork that we removed from Andy's bike. Therefore, new seal or not, fluid gets by and leaks out. It's doubtful that these tube can be saved.
One more thing to look for on these bikes.
Chris in Boston

[CB750R]

I've repaired small dings in downhill mtn bike forks with an aluminum filled epoxy, sanded down with 1500 grit wet, the repair was good enough to prevent oil blowing past the seals, and worked till I sold the bike.  Another trick I've been told is finishing some JBweld with a laquer to make it super smooth, but I haven't tried that. 

[Terry in Australia]

F2/F3 tubes will work fine, I've got F2 tubes in my CB750K3, cut down (shortened) Honda XL250 dirt bike tubes in my CB750F2 and Suzuki GS750 tubes, dampers etc in my CB750K1!

Don't mess around with epoxy and the like, there are a squillion sets of forks for sale on ebay cheap, so you should never have to resort to that sort of repair, and remember, if it's chewed through a layer of "Hard chrome" already, what hope will you have with soft epoxy? Cheers, Terry.