Just like in the CB750, the too-thick head gaskets we get in today's CB500/550 gasket kits will cause an oil leak at the 2 main head oil feeds in the head-cylinder joint. The 'fix' is to increase the O-rings in the 500/550 joints from 4.9x2.5mm (stock) to 5.2x2.6mm, aka Parker #01-107.
Thanks to one of our members who bought 200 of these (to get two!), I have a whole bunch of these for you who are building a 500/550. So, for a donation of any size to our forums, I'll send you a pair for your 500/550 project. PM me with your address and send a donation, and I'll send them out.
Many thanks, Mr. Powell, may your generous legacy follow you!
