Sunday, September 26, 2010

1974 CB 360

After bending two intake valves due to a loose tappet lock nut, I am finishing up reassembly of the 360 engine, I made some improvements to the bearing setup as well, notably the stainless sleeves on the cam and a change to the shim system used to keep the cam lined up with the rocker arms.  I cleaned up the pistons and inspected for any cracking due to the valve collision, and none was found, nor were the wrist pins or conrods bent or damaged, so I got off fairly lucky.  I reringed the pistons and renewed the base gasket sealer (not running a base gasket) and installed the block.  These bikes are nice because you can to a complete top end rebuild with the motor still in the bike, which saved me at least a few hours of work.

I bought a new copper head gasket for the motor as well, from Lani at copper gaskets unlimited, he fixed me up with a .050" gasket and already had the pattern for the 360 on file, so I was happy.  I sprayed both sides of the gasket liberally with copper gasket spray, waited about an hour and then installed the gasket, everything lined up nicely so I was ready to install the head.
A friend donated some old cb350 intake valves, and since the guides and seats were fine (seats were a little damaged, but not enough to affect the seal), I lapped in the valves using Goodson 280 compound, and reinstalled the valves.  I checked for seal by putting the head on its side and filling the ports with paint thinner, it has a low vapor pressure so it can find the tiniest of leaks to get through, and after a half hour, no drops made it through, so the seals were good.  I did some additional machining to prep the head, and installation went fine.

I had a spare 360 rockerbox laying around (I bought a used one for the rocker arms, as one of my old ones had what looked like a crack forming), so I cut it up to make a holder for the #1 intake valve rocker. This tool can be used to properly degree the cam without removing the rockerbox to adjust the sprocket.  The cam sprocket needs to be slotted so it can be adjusted in relation to the cam, this is necessary if you change the distance of the cam to the crank, as removing the base gasket does.  This modification bumps up engine compression slightly, and being able to properly degree the cam ensures the engine will still run well.  It's not a bad idea even for a stock motor, as the cam chain will stretch and retard the cam timing as it does.  Degreeing the cam is a fairly simple maintenance step to keep the engine running strong.  It's amazing what a noticeable change in performance even 1 degree makes.

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