Topic: CB750 experts - can I do this?

[750K4]

I have a CB750K0 sandcast head that is missing one of the cam tower castings (holders). I also have a head and towers from a CB750K4, or so it was described by the guy I bought it from. My plan was to use the parts from the K4 head to replace the missing tower on the K0 head.
My engine builder is hesitant to do this, as he feels the K0 and K4 parts are a mismatch and that the cam would fail if run this way. Upon closer inspection, the K4 head I bought for parts appears to have been assembled from parts vs a matched set. Imprints on the K4 towers seem to show that they were both assembled on the same side in two different engines, so they probably are not a matched set.
The parts fiche shows the same part number on the towers right/left, as well as from K0 to K4, so does it matter that they were on different engines?.
Should I:
use whatever fits;
stick to a matched set regardless of year;
find another K0 tower to pair up with the one I have;
find a matched pair of K0 towers:
buy a new pair of cam towers;
something else?

[dusterdude]

you "can" do it ,however i would have the head align honed to ensure trueness

[Clyde]

The later towers from K3 onwards had two additional 5mm screws to locate each rocker arm shaft in the tower. Hence the tower and the shafts are different. I prefer the later type as the shaft is firmly held in the tower, but the older ones still work fine.
You should not mix and match individual components, but there is no reason you could not use a complete matched K4 tower/rocker shaft on a K0 head. Nor do I see any reason why you could not use a K4 tower on one side and a K0 tower on the other side.
The main problem will be the bearing clearance on the cam shaft and that will need to be checked if you use a K0 or K4 tower (essential if they are not matched).
I would assemble the towers and cam on the head without valves/springs/chain. Torque to normal specs but check that the cam turns freely as you tighten.
Then undo the holders and use strips of plastigauge/flexigauge to measure the camshaft bearing clearances. Also look for any alignment problems i.e. the stirp should be the same thickness over the length of the bearing.
If they are within specification there should be no problems. I have found that they are generally pretty good and have had no problems using different towers on engines. I have found unmatched sets sometimes work and sometimes do not
I would stick to a matched set if possible for the reason that they are bored as a set to match the camshaft, but if you do the above check then it should still be OK
Regds
Clyde

[bryanj]

I have many times changed just one tower, usually for new and with new cam (mostly only one oil jet blocks) and see no problem with using second hand towers from two different engines with any good cam.

YOU SHOULD NOT MIX AND MATCH THE BEARING CAPS on the towers.

I have seen, and used, repaired towers where the bearing holes have been bored and fitted with phosphour bronze "split" bearings pegged in

[750K4]

74chopper
I'd use the K4 towers if I knew for sure they were from the same engine. I'm not even sure the bearing caps that are on them came from them originally. They have marks on them showing they were both mounted on the same side of the engine. That's what tipped us off.

clyde
I'll ask my mechanic to bolt it together and check it with plastigauge. I'll post what he finds.

dusterdude and bryanj
I'll double check that the caps haven't been moved around. If so, I'll have to have them align bored.

Anyone have a good matched set of towers they'd like to part with?