Topic: CB350F upper triple tree

[eunsan]

I am pretty certain that I saw a discussion about these upper triple trees that are inclined to fracture, but cannot locate it. l also recall that there has been no reproduction of these fragile items. I also cannot find any NOS supply, and perhaps don't want one even if I could located one.

Since this part appears to break on CB350F much more so than on other Hondas, I have assumed that it is caused by a brittle zinc alloy casting, and not a much tougher aluminum as appears to be used in many other Hondas. Can anyone tell me if that is correct?

I am restoring a few earlier Hondas on which breakage is not a problem, and guess that those unpainted upper trees are aluminum.

I have been looking to see if there is a more robust direct interchange from another model, but have not found  anything that appears to be identical on eBay.

I am however, parting out a 1978 CM185t on which the upper tree is overall very similar and the hole spacing appears to be identical with the CB350F. The CM185T fork openings are about 2 mm smaller as is the steering stem opening. The vertical offset is also similar.

I have not yet set the two pieces side-by-side to check the fine points, but the potential appears to be quite good since there is lots of meat to enlarge the CM185t openings.

I am hoping that the 185 tree is an aluminum casting, and therefore a tougher beast than whatever alloy was used on the CB350F.

Before I get too wrapped up with this "thought" can anybody provide me with some guidance?

tks

Gary

[grcamna2]

I have a top triple clamp that has been fine bead blasted and in nice,solid condition for the late CB350 and CB360 twins and it will fit and bolt-up nice as stock except you would need to modify your meter bracket a little to make it wider.I can post a pic if you like.This can be polished as the aluminum will shine or painted,whichever you prefer.

[eunsan]

I have now removed my damaged CB350F upper triple tree and compared it with the one from 1978 CM185T. Close,  but not workable since the front-rear offset is different by about 6 mm.

I looked on eBay to see photos of the later CB350 and CB360 versions. They appear to be cast of the same weak alloy as was used on the CB350F. Some of the eBay listings show breakage at the same location as with the CB350F. Even if I had a perfect CB350F version, I am not wanting to go that route since I already have three broken ones, all in the same location.

Looking at other eBay listings, I note that the 1977-80(?) CB400T used a different design concept in which the aluminum (?) handle bar supports are mounted on a pressed steel base, as shown on the photo below. It would perhaps be not so challenging to modify one of them to suit the CB350F. The lack of "clamping" on the forks hopefully would not be a problem, since that design is used on many other same period Hondas.

The successor mid-70s CB400F triple tree looks quite a bit different, so that is not an option.

Cheers

 

[grcamna2]

The reason they keep breaking in that same (clamping) area is the 'D' washers fall out and the mechanic never saves them,etc. when he re-installs the forks;then he torques-down on those 2) top pinch bolts and w/o the 'D' washers in there it over-stresses the top triple in that area.They need those spacer washers otherwise it will keep cracking in that critical area.