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1967 CB450K0 Black Bomber Rebuild - By Royhall
royhall:
--- Quote from: royhall on November 23, 2020, 04:16:45 PM ---Thanks for that Ash. The plot just thickened a bit read below.
CB450 K4 vs K5 alternator rotor swap- beware!
The K5 engine I had on my CB500T framed cafe racer-ish fun bike was having transmission woes, and finally crapped the bed when 4th gear on the countershaft lost a chunk. I sourced a 71 CL450 engine that looks beautiful for it’s age, but has no history whatsoever. All I know is it came from a defunct dealership in Nebraska, and was on the original frame, albeit sporting a knobby rear tire and a bunch of mud caked into every depression.
As I’m going over the engine, I discover the alternator rotor is missing altogether, but the stator is still in place. No problem, I’ll just chuck the K5 magneto in there and send it. I set the valve clearances by the timing marks on the rotor, seal it up, slap it in the frame, and start kicking (I delete the starters on these so I can use a tiny battery- plus kickstarting is straight gangster). It’s popping some and has compression and clean carbs, so why the hell is it spitting the gas back through the carbs and not running?
Long story truncated, I end up taking the head off to check the valves and seats (which are fine), and find that the left cylinder at TDC puts the timing mark on the rotor about 20° PAST the index mark for timing. For some reason I cannot fathom, the magneto rotors between 71 and 72 models are keyed differently. The keyway is the exact same size on the tapered crankshaft extension, so it fits right on, it just doesn’t line up.
Further research showed that they’re vastly different rotors in terms of the starter gearing on the backside as well.
This information will probably be of no use to anyone ever, but if it saves one person the hassle of cutting the cam chain and removing the head, or just junking a perfectly good motor out of ignorance, it’s been worth my time to type it out. My searches post-op have revealed no hits regarding this, so it should be out there in the world.
--- End quote ---
Going back to this earlier post. I have the Bomber all built up and the Pamco ignition set on the start mark ready for strobing. The engine starts and runs okay and after a short warm ticks over at 1k. Now the fun bit, when I strobe the timing to get a precise setting the timing marks are way off ie.15 to 20 degrees. Now if that was a mechanical problem like the exhaust cam set wrongly the engine would not run okay. I fear the above post may correct as I now have a K2 rotor (1972). Does anyone have anymore information on this as I'm reluctant to use the bike with a timing rough setting. As the starter and alternator are now working okay (after a long expensive remedy) this setup will be staying. At worst I may have to borrow a K0 rotor and make a thin aluminium timing disk from it that I cant secure with the centre bolt when timing. What concerns me most is that I checked the cam position against the rotor before fitting the cam chain but surely at 20 degrees out the engine would run like a pig if at all. Tonight I will whip the plugs out and physically find TDC with a wood dowel and see where the rotor mark lands. The cam was set using the old damaged rotor but I didn't see any differences between the two. Any ideas?
AshimotoK0:
I can measure or loan you a Bomber one Roy if necessary.
Just a thought .. is the static marker on the later stator you fitted in the same position as the K0 one? ..bit of a long shot I know.
Also when I am back at work Wednesday I can compare the timing marks on my later DK rotor with a Bomber one.
royhall:
Ash. I think my damaged original one is possibly a later version as well. Will check this all out later today. Do you by any chance have a K0 exhaust cam and a later version to compare where the keyway for the points is. That could also be changed. Cheers.
UPDATE. My old K0 stator doesn't have a pointer on it, that was one of the reasons I had to change it to a later model so I can't compare that.
AshimotoK0:
--- Quote from: royhall on January 18, 2021, 10:15:44 AM ---Ash. I think my damaged original one is possibly a later version as well. Will check this all out later today. Do you by any chance have a K0 exhaust cam and a later version to compare where the keyway for the points is. That could also be changed. Cheers.
UPDATE. My old K0 stator doesn't have a pointer on it, that was one of the reasons I had to change it to a later model so I can't compare that.
--- End quote ---
I will check the cams I have later Roy .. a mixed bag but I am sure I have both narrow and wide lobe versions.
royhall:
This afternoon I have been back through the settings. With the left piston at TDC the LT mark on the rotor is dead on the pointer and the keyway is at 12 o-clock. The dowel in the camshaft is just before 12 o-clock by a few degrees. Took the exhaust cam cover off and at left TDC the marks on the camshaft are spot on. I really knew all that would be correct as the engine runs okay. My other alternator rotor looks to have the keyway and markings in exactly the same positions.
What I would say though is the Pamco magnetic rotor is a real piss fit on the camshaft rod, but not so much that it would cause a 15 degree strobe error. My problem here is I would like to think it's a Pamco problem but no matter what the ignition system I am still strobing it on the HT lead to a fixed point on the crankshaft. When I try to retard the ignition to get to the marks it runs rougher and rougher then backfires and dies. Set it wrong again and it runs okay (but it is just a guess). Not sure where to go from here but I feel the only answer is the real K0 rotor has the markings 15 or so degrees further round? Can I take you up on your offer of borrowing your K0 rotor Ash and I will pay the postage. Hopefully it is different, if that's the case I will make a thin alloy disk with the correct markings that I can secure with the rotor centre bolt just whilst I strobe it. That would be an easy fix.
Just to try to prove the Pamco one way or another I could refit a points plate and condenser and try to strobe it again and see if I get the same result. But I would still be strobing on the same HT lead to the same marks? Baffling.
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