It is possible to replace the "A" cam chain in the CBX without disassembling the engine. It is even fairly easy given skill and tooling. But not the way advocated online. This should not surprise you.

The cam chain
There are three different "A" (vertical) cam chains available for the CBX and its production cousins the first-gen DOHC fours. No matter where they come from, there are these three types. First, the original chain has 3mm pins. This chain is nearly impossible to find now, but is is definitely preferred because it is the strongest and the CBX engine really stresses its cam chain. Second, there is a chain that has 2.7mm pins. This is the one marketed by Brent Hyde in New Zealand. Third, there is a chain with 2.5mm pins. This is the chain sold by wholesale parts supplier K&L in Northern California. They also offer a master link for this chain. The master link will work only on this 2.5mm chain.

The tool
The correct way to replace the cam chain without removing the crankshaft is to use one of the several tools made for cam chain disassembly and reassembly. Honda actually offered two different tools, in their tools catalog, for use with the 1970s 450 DOHC twin. Though Honda's Hy-Vo chain did not yet exist and the tool was therefore intended for the older roller type cam chain, it works very well on the Hy-Vo type also.

The method
Whichever tool is used, the basic technique is gradual pressing of one of the pins out of a link. Any link can be chosen, it doesn't matter. Then on reassembly of the chain, the pin is gradually pressed back into the link and its end crimped for security. Note that certain of the tool's tips are used for specific operations. For future reference, I like to dye the link red using Dykem.

Things to know:

• The CBX cam chain is stressed very highly. Almost too much as can be demonstrated by A) the fact that Honda dumbed-down the cams and made them less aggressive after the first year of production, and B) that the well-known warning about accidentally changing the engine's firing order breaks the chain within 25 miles of use. (See Honda dealer mechanic's newsletter, The Wrench, Vol. 2, No. 1, dated January 1979). There are 48 valve springs working on this chain! Don't use an inferior replacement chain if you can help it.

• The wear point in any chain is the pin. The pin determines the chain's strength. No matter what anyone says. Therefore, the original 3mm chain is best. Unfortunately, it is the most difficult to find. For that reason, I have used the Brent Hyde sourced 2.7mm chain on all the engines I have rebuilt. Also, because the wearing part is the pin, this pin pressing in and out should never be done on an in-service chain. Always replace the chain.

• Generically, the Hy-Vo chain is known as "gear chain", "silent chain", "link-plate chain", and "inverted tooth chain". "Hy-Vo" stands for "high velocity" and is a Morse company trade name. The official name comes from the idea that centrifugal force kept the chain taut and self-tensioned. This worked in the cast iron V8. But not nearly as well in powersprts application wherein it is squeezed into submission instead of being allowed to self-tension, with the resulting consequences. The chain's mass works against it in the powersports application, causing it to be fast-wearing and difficult to keep tensioned. And very noisy, more so than the roller chain that preceeded it, when it's not.

More...