I haven’t had to work on any CB450K0 Black Bombers for a couple of years now. I only know of one other one in the San Diego area, but the latest one was trucked down from Orange County by the same owner who brought a nearly-mint CL360 within the past year.
This one was one of those eBay auction bikes that you never know how well they were repaired or “restored” until you start digging deep within the bones of them. Complaints were:
*Unknown as to whether it has had the oil pump update done (showing 9k miles on the speedometer)
Honda’s first venture into “Big Bike” territory was the release of the 1965 CB450K0 (nicknamed the Black Bomber). This was their first DOHC (double overhead camshaft) model, which was pretty exotic for the day, but was saddled with a wide-ration 4 speed transmission and carry-over CB77 style suspension and brakes. Lacking a counter-balancer, the big motor shakes on a par with the vibrations you encounter with a late model CL77 Scrambler. I owned a CP450 version of the bike, back in the 1990s and while it was unique in that it was a factory Police bike edition, the overall effect didn’t thrill me. Honda released 25 of them to various law enforcement agencies, hoping to woo them away from their massive Harley-Davidsons. Their experiment failed, unfortunately, as the bike really wasn’t up to standards in most respects for Police duty.
Early model bikes had failures of top end components due to lubrication issues that came from two sources. There was an odd design shape in the roof of the oil pump which caused an oil vortex that created stress on the oil pump screens. The screens failed, allowing screen particles to either be swept up into the oil galleys that fed the top end and/or clogged the bypass valve open causing the oil to be redirected elsewhere. The original pump can be modified or replaced with a later version. When the modification was done on the early models, the mechanics were supposed to place a couple of punch marks on the base of the cylinders to notate that the work was complete.
The second failure was related to the clutch cover gasket, which ruptured on occasion, again bypassing the oil flow away from the top end. Anytime I hear from someone with an early model CB/CL450, I always mention the TSB information to them, of which, generally, they are unaware. Honda beefed up the gasket around the area of the oil pump and no further mods were required.
The owner mentioned that the gasoline in the fuel tank had suddenly gone low without any plausible explanation. The bowl gaskets seemed to be weeping during a visual check, which can indicate a bad gasket and/or incorrect float levels. There was also an additional carburetor mod for the Bombers, however all the update parts are long extinct.
The first order of business was to drain the oil, which lead to the first of many surprises found during the repair process. It took about fifteen minutes to get the oil plug out as the hex on the drain bolt was not a 17mm (too tight) or a 19mm (way too loose). I tried an SAE socket… same thing; either too tight or too loose. Finally a 6pt ¾” impact socket was fitted up on a long ratchet, which was treated to a few hammer blows. The plug loosened up enough to unscrew it a little at a time by hand. Because the actual plug is so large, when it is pulled off the threads a huge rush of oil comes spraying out in all directions. In this case the quoted 3 qts of motorcycle oil came out along with about another quart or more of gasoline! My automotive drain pan, which carries 4.5 quarts of oil from my Toyota 22RE truck engine with a bit of room at the top, was similarly challenged with the “3 quarts” that was supposed to have been released in this instance. One can imagine what might have happened if a stray spark ignited the fumes inside the cases. BIG, BIG, BOOM!
The tsunami of oil/gas ran out like water as it flushed out minute flecks of metal which sparkled in the solution. There were no big chunks to worry about, but one would be lead to think that there is some wear going on inside at some small level. The engine appeared to have been overhauled, at least the top end, judging from the gaskets and addition of small Allen-head screws holding the cam bearing holders in place. Some of the debris could have been from new piston/rings and cylinder wear as the engine was broken in.
Removing the clutch cover requires taking the right footpeg (2 nuts), the kickstarter arm and then the right side exhaust system. Once the side hardware is out of the way, the next step is to remove the three screws from the oil filter cover. This reveals the end of the oil filter, which has an outer cover that is sealed with a thin o-ring. To remove the filter cap, you have to extract the inner 6mm bolt, then thread in an 8mm bolt to drive the cap out of the inner housing. Once that cap is off, look deeply into the base of the filter housing to locate the tab of the locking washer and then come up with the correct 4 prong special tool to remove the inner nut from the end of the crankshaft. Once the nut is removed the filter body can come off the end of the crankshaft splines for cleaning. The filter needs to be removed anyway to allow the clutch basket and oil pump to be removed as an assembly. There are six bolts holding the clutch pressure plate onto the inner clutch hub. The clutch springs come out when each bolt is removed, then the whole clutch plate pack slides out of the inner/outer clutch hubs.
The clutch disks were all unremarkable, aside from the fact that all the steel plates were somewhat glazed and had signs of rust from sitting up for too many years. Generally, when there are no signs of excess wear, cleaning the steel plates with a wire wheel cuts the glaze and removes the rust allowing the plates to connect with each other more fully. The inner clutch hub is held onto the end of the transmission shaft with a snap ring. Once removed, the clutch basket only moves off once the oil pump locking washers and nuts are loosened and set aside. The oil pump is driven off of an eccentric mount on the back of the clutch basket, which provides the in-out pumping action for the pump piston which is attached to the end of the pump actuator arm. When the pump was removed from the two mounting studs, the normally attached pump screen fell off onto the ground! Apparently the gasoline caused the rubber to swell and distort the whole screen assembly. As fate would have it, I happened to have one new CB450 pump screen in a box of odd parts which I have had for many years.
The oil pump, in this case was the updated version, however the gasket was not the updated one, so the whole surgical episode was worth the effort. Time was spent on cleaning the clutch parts, oil filter components, clutch cover nooks and crannies and removal of the old gasket. Most of the engine components looked fairly clean and free of varnish and old deposits, but there were pockets of grunge and gunk hidden in recesses within the crankcase.
Once all the loose bits were cleaned up and reassembled, the new gasket was trimmed slightly around the pump body where there was some interference. Otherwise, the cover went back on easily and the screws were returned to their original positions. The oil drain plug showed signs of filing and grinding, probably to clean up some previous damage during removals in the past. These drain plugs are notorious for getting jammed into the cases, when people decide to “fix” a leak by tightening the plug with a big wrench rather than just replacing the flattened out o-ring which does all the sealing work. Honda finally worked their way out of using such massive drain plugs when the 450 (and later CB500T) models went out of production.
Going over the tune-up procedures, more unpleasant findings were: spark advancer springs stretched out, allowing spark advance to come in way too early; indicators for the valve adjuster shafts were incorrectly positioned on two of the four adjustment shafts; float level setting on the left side was about a millimeter off on the left side (too high); clutch adjuster out of normal slot position and carb cable synchronization was off.
The spark advancer required disassembly, lubrication, squeezing the ends of the springs together in order to increase the tension on the weights. There was no sign of cam lube present on the point cam or the point’s rubbing blocks. Ignition timing was reset and then the eccentric valve lash shafts were turned about 90 degrees to get the rocker arm geometry correct. Once the engine was running, I did a final valve adjust, listening to the tappet sounds until they stopped but the engine didn’t falter and then cinched down the locking nuts.
The floats were checked for signs of “sinking” due to fuel incursion, but both were found to be full-floaters so far. Float levels checked with the float gauge on the float and the petcock turned ON. Fuel stops just as the float gauge hits the carb body.
Once everything checked out, the bike needed to be wheeled near the compressor to air the tires up from 15psi to about 32psi on each end. THEN, it was ready to ride… and ride we did. I have a test loop that is a few miles around and includes a nice long uphill climb to see how the engine pulls a load. The overall impression is not unlike that of a good running CB77, in actuality. Same bouncy shocks at the back, a little more vibration and fortunately brakes that were well bedded-in, as stopping power was quite good.
The ride went fine, but after the bike was parked again a mysterious blob of oil appeared on the top right side engine fine. There was a drop of oil at the tachometer cable junction nut, which might have blown back, but the leak looked more like it was dropping straight down from the right front camshaft holder. Finding the cause and cure will be about the last thing on the list to complete this Bomber project that almost went alight in spontaneous combustion from the inside out. Fortunately, that didn’t happen and a good running CB450K0 will be back on the road very soon.