you should get a degree wheel and a dial guage and see what the cam timings set at...then tell me. i wouldn't worry about the weld infact its there as a backup. the gear is a press fit and everytime you press that gear on/off it becomes looser, so the weld is there to make sure it holds it position. there's a better way at doing this to make them fully adjustable...

the more important clearance here is piston to valve rather then cam timing. although cam timing does effect the clearence. either there wasn't enough clearence, exhaust valve springs were due for changing, a collets let go or it was over reved. you have to allow extra clearence for the exhuast valves as there's less controll over them and the simple fact that the piston is chasing it upto the head.

Stimpy

Does sound like a bit of hassle, I've got another 23 motor in the shed (busted somehow to lol) so will pull that down and sus it first.
Bike does have custom CarbonFibre airbox tho, so carby fitment might not be much of a drama (I can test all that outta the bike i think).

Dannc,
Yep i'll look into that also, that it matters much now i supose lol

its always nice to find out why an engine shits itself, you dont want to make the same mistake twice.

drew70 wrote:Your lucky you got two sessions, my record for busting a 23 motor is three and a half laps

i th0ought it was doing the test ride round the car park

drifterwannab wrote:

drew70 wrote:Your lucky you got two sessions, my record for busting a 23 motor is three and a half laps

i th0ought it was doing the test ride round the car park

That was the first one but doesn't count because it didn't happen on track. It done 3/4 of a season before it let go in the car park

Hey, thought I'd provide an update on this old news. Haven't done much due to funds, but am getting stuck back into it.

The 3 motors I have (2 x blow (piston to valve) 1 x rebuilt CB400) are at the original guy who built the bike/motors before I got it.

He has a good 23 head rebuilt with new valves ready to roll, but has also said one of the busted heads could be fixed and the valve seats etc recut.
I've got a few options, but his recommeded I rebuild my blown engine keeping all but the busted rod/piston (obviously) but using the bottom end complete as it has a balanced lightend crank, new clutch and rebuilt/cut gearbox.
The barrels and spare rod/piston would be salvaged off the other busted engine, and the ready to roll head he has currently used.

Obviously this all involves a a fair bit of cost. (mind you his pricing does seem fair)
The cheaper option is keep the CB400 together, pull the head off, put on the NC23 rebuilt head. The CB400 motor is already rebuilt with new rings and bearings but other wise is completely stock. (there was mention clutch was also new)

The head that is now damaged on this motor had porting done to it, which he will do to the rebuilt head in stock.

I guess my question, realistlicly i there much gain by having a balanced bottom end with lightened crank? Will I see pretty much the same just tossing the head on the rebuilt CB motor, with that head having similar porting and same dialed in cams?

Later I figure I could rebuild my original motor and as a spare once funds allow.

i lunched my 23 engine at cadwell park a few years back, it had a flowed head full gf system and quietening gears removed from the cams, it went like stink but i changed down 2 gears instead of 1 and ended up with a conrod stuck in the starter motor, since then it has had a standard engine fitted and the damaged head is in the shop being repaired, starting racing again next year so will be sorting the engine again

im unsure if the cb and cbr head are compatable.....
i know mine wont interchange...
stimpy

The heads are quite different, but do apparently bolt on.

Whats finally happening, using the already rebuilt CB bottom end, a already rebuilt 23 head that has new valves and springs. Changing one of the side engine covers from the busted 23 motor, and apparently according to the builder this is all good. His putting it together and I'm helping him put it back in the bike so guess we'll see. lol

Later I'll get one of the other 23 heads fixed, used the barrels/cyl's off the 'lightly' busted motor, the case and crank from the original, replace piston and rod and build up a spare basically same as original.

i forgot to mention...my heads wont change over because they are so different...or did i mention that...
stimpy