The first generation CB450K0 “Black Bomber” models continue to rise in “value” as the beginning of Honda’s quest to enter the middle-weight market. American Honda even imported 25 CB450P Police bikes to challenge the prevailing Harley-Davidson models which were prevalent in the 1960s. Sadly, even with a sophisticated DOHC 444cc 180 degree firing twin, the bike lacked power and a competitive 5th gear in the transmission to aid patrol performance, so the whole experiment was halted right away. Your author owned one of those first 25 bikes and was even able to order a new rear rack and solo seat right from Honda in the late 1990s.
When the bikes were first introduced in the US and the UK, testers were less than enthusiastic about the model, apart from the torsion-bar equipped DOHC cylinder head. Rated at 44HP (crankshaft rating), the bikes were barely faster than the 305cc CB77 in top speed, but did have more mid-range torque to move the heavier chassis down the road. Honda chose poorly for the tire selections, which consisted of a hard compound ribbed front tire and a universal tread rear. Suspension selection did not stray far from that of the Super Hawks, either, which was less than precise to say the least.
During the initial roll-out Honda played with a Type 2 (360 degree firing) engine configuration, however the engine produced excessive vibration into the chassis, so that too was scrapped early-on. This was Honda’s largest leap into the expanding market, prior to the CB750 Four and there were some teething problems that plagued the earliest editions. Of significance was a carburetor calibration update to improve drive-ability and later discovery that the oil pump design was flawed causing damage to the pump screen, which then shed particles into the oil stream and/or jammed the oil pump relief valve open, short-circuiting the oil flow to the top end components. Repairing damaged camshafts, cam bearings and rocker arms became an expensive and time-consuming affair. The clutch side cover gasket was also problematical, as unsupported sections broke free and clogged oil passageways, causing similar damage to that of the oil pump issues. The pump bulletin covers CB450E-1000001-CB450E-1021156.
Whenever a CB450 Bomber owner contacts Bill about their new find/acquisition, the first response is “Has the oil pump been checked and the clutch cover gasket been replaced?” Honda mechanics were supposed to put a set of punch marks on the engine case to show that the pump had been modified or replaced. Seldom have those markings been noted to date, so one must assume that the pump was NOT modified or replaced. The service bulletins are available with details about how to modify the pump inlet, as well as the one pertaining to the clutch cover gasket issues. There was also a transmission gear bushing update for selected models, too. Failure to inspect and verify that the modifications were accomplished could lead to catastrophic failure and possible injury to the rider.
In the past two months, two different Bombers have found their way down to Casa De Honda for these safety checks which are somewhat time-consuming, but not technically challenging. After oil drain (a separate challenge due to the very LARGE size of the drain plug, dumping the 3 quarts in a matter of seconds), the right side muffler and footpeg must be removed to access the clutch cover. The outer three screws on the oil filter outer cover are then removed, allowing access to the oil filter, itself. This is a centrifugal style filter, bolted firmly to the end of the crankshaft. The outer filter cover is retained with a 6mm bolt, which is then replaced with an 8mm bolt which pulls the outer cover out of the filter housing. A small tab on the locking washer must be turned back and the nut removed with a 4-pin special socket which engages the nut edges. The last bike’s nut required an air wrench to loosen the nut from the end of the crankshaft.
The filter is in the way of the outer edge of the clutch basket/cover, so must be removed first. The oil pump is driven off of the back of the clutch outer basket via an eccentric machined on the back of the clutch. The clutch basket and pump have to be removed as a unit, so the clutch springs/plates and inner hub must all be removed.
Once the pump is removed from the two studs, it can be inspected for the proper configuration after the rubber-edged, slip-on screen is pulled from the pump body. The pump screens were originally made of brass, but replacements seem to be made from a steel screen material which is more resistant to the pulsations of the pump’s plunger action.
The new clutch cover gasket design changes help to strengthen the gasket material where it is sandwiched between the cover and crankcase. Original gaskets were made from asbestos materials, so removal needs to be done with caution and then proper disposal. Original gaskets tend to bond to the engine case surfaces with tenacity, so plan for an extra 15-30 minutes of scraping and cleaning of the cover and engine case surfaces.
Once the oil pump has either been passed for clearance or modified to match the service bulletin, then you have to reverse the order of disassembly of all removed clutch and pump parts. It is a great time to inspect the clutch plates as you are reinstalling them in the stack. Steel plates can either form rust or become bonded to the adjacent fiber plates. In order to prevent clutch “drag” due to plates grabbing at each other, the steel plates must be cleaned of any surface corrosion/debris and flat.
Remember to re-secure the locking tabs on the pump nut washers. With all the components back in place, install a fresh, correct clutch cover gasket after insuring that all gasket surfaces are cleaned up. After all this work, you don’t want an oil leak due to leftover gasket material adhering to one surface or the other. It is a good time to replace the kickstarter seal now, but seals can be replaced without clutch cover removal.
The early carburetor update for “surging and hesitation” included:
Vacuum piston springs
Jet needles, stamped with #MR4
Jet needle holders
Slow jets, No. 35
Pilot jets, No. 35 (2x of each of the above parts) The update parts were part of a NLA complete kit, so some digging might be necessary to find individual part numbers.
Like any 50 year-old motorcycle, a full tune-up, including compression test, valve adjustment, ignition timing adjustment and carburetor synchronization is necessary to ensure proper reliability and performance of these classic machines. The early CB450s had their share of teething problems, but once those are addressed, the bikes can be trusted companions for years to come.